SCIENCE SCIENCE FOR FOR SOUTH SOUTH AFRICA AFRICA
ISSN 1729-830X ISSN 1729-830X
VOLUME 4 • NUMBER 2 • 2008 VOLUME 3 • NUMBER 2 • 2007 R29.95 R20
Sout h Africa and
Int ernat ional Year of Pla net Ear t h
M e gac it ie s C limat e c ha nge Minera l re source s Africa n la nd sca p e s
A C AACDAEDMEYM YO FO FS C I EI ENNCCEE OOFF SS O U TT HH AAFFRRI C I CA A SC OU
AEON, the Africa Earth Observatory Network, is a centre for Earth Systems Science at the University of Cape Town that provides a research and educational environment for consilience between earth and life sciences, engineering, resource economics and the human sciences to forge Earth Stewardship as a science. AEON will prepare fertile ground for a new kind of earth exploration, particularly for Africa, that will marshal revolutionary tools and technologies to answer fundamental questions about earth systems and resources and to stimulate more sustainable harvesting of its natural capital and conservation of its heritage. AEON’s mission is the cultivation of a high-level, internationally-connected, scientific research and analytical learning environment promoting a modern interdisciplinary view of our Earth, and of Africa in particular. AEON has established a number of fellowships, through the John Ellerman Foundation, the Eranda Foundation, and Lonmin Plc, to encourage participation in the intellectual adventure that this approach holds, and to engage in research to promote new ways of thinking about and evaluating the relationship between earth and society under the rubric of Earth StEwardShip SciEncE, specifically, but not exclusively, with a focus on Africa. Applications from African nationals and/or permanent citizens in African countries are invited from suitably qualified and well-established researchers with a proven track record of leadership. Applicants will be expected to engage in research with AEON’s members and other academics from various institutions in Africa and beyond, and will crucially be expected to act as mentors, sharing their knowledge, wisdom, research experience, and their vision for science in Africa, with the next generation of African scientists. AEON’s EarthLab has a set of cutting-edge analytical facilities that significantly enhance the ability of scientists in a wide range of disciplines to carry out analyses and investigations that have previously required collaboration with laboratories and scientists outside Africa. Two Multi-collector Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS) instruments, a rare-gas mass spectrometer and an electron microprobe were recently purchased through a grant from the Innovation Fund of the Department of Science and Technology. EarthLAB is operated as a National and African Facility. For more information consult the AEON Website: http://web.uct.ac.za/depts/aeon/ and/or contact Andy Duncan (CEO, AEON, email@example.com) or Maarten de Wit (Director, AEON, firstname.lastname@example.org).
IYPE Out of Africa South African National Committee for the International Year of Planet Earth The world celebrates and the Earth sciences get down to business 6
African landscapes from remote sensing Frank Eckardt Clear views in 3D
Climate: past changes & future uncertainties John S. Compton et al. Reading the rock record helps
VOLUME 4 • NUMBER 2 • 2008
Nurturing soil Greg Botha et al.
It’s payback time
Antony Cooper and Chrisna du Plessis Coping with urbanization 44 50
Healthy foods from Mother Earth Esté Vorster
Viewpoint Mineral resources: wealth at a frightening price
Pioneering dietary guidelines
Maarten de Wit People and planet pay up
Art and map-making Fritha Langerman
Seeing the world in different ways 10
Earth: gigantic recycling machine 56
Maarten de Wit and Steve McCourt How the planet sustains life 14
Africa Alive Corridors John Anderson, Tebogo Mashua, and Maarten de Wit Our continent – our heritage
AfricaArray Ray Durrheim Seismic stations and geoscientists
Regulars Fact files Urban facts (p. 35) • What is soil? (p. 41) • Malnutrition in South Africa (p. 45)
Ocean crossroad at the tip of Africa
Science news Less salt for less sugar; Poor food is bad for birds; Diet sweeteners don’t always help (p. 49) • Saving the world’s water; Drink from safe taps, not bottles (p. 61) • Cellphone radiation; Watch those exhaust fumes; Celebrating wonder-food (p. 62) • Catnapping to improve memory; Remembering the planets (p. 64)
Isabelle Ansorge, Stephanie de Villiers, and Xin Li Where the waters move and meet 19
DNA clocks for dating landforms Woody Cotterill and Sarah Goodier Animals and landscapes evolve together
Groundwater: managing dwindling reserves Lebogang Nhleko and Leslie Strachan Finding and caring for precious water
Your QUESTions answered Why does oceanography matter? What makes oceans salty? – Isabelle Ansorge
The S&T tourist Water in the iSimangaliso Wetland Park – Sylvi Haldorsen
Careers Work in geology – Eugene Grosch
Books Famous Dinosaurs of Africa • and other titles
Diary of events
ASSAf news Scholarly publishing – Wieland Gevers
Letters to QUEST Keeping school science up to date
Geohazards: the risks beneath our feet
Susan Frost-Killian et al.
Back page science • Mathematical puzzle
Quest 4(2) 2008 1
SCIENCE SCIENCE FOR FOR SOUTH SOUTH AFRICA AFRICA
ISSN 1729-830X ISSN 1729-830X
VOLUME 4 • NUMBER 2 • 2008 VOLUME 3 • NUMBER 2 • 2007 R29.95 R20
Sout h Africa and
Int ernat ional Year of Pla net Ear t h
M e gac it ie s C limat e c ha nge Mine ra l r e source s Africa n la nd sca p e s
A C AACDAEDMEYM YO FO FS C I EI ENNCCEE OOFF SS O U TT HH AAFFRRI C I CA A SC OU
A representation of Earth with its vulnerable life-support systems. Image: Fotosearch SCIENCE FOR SOUTH AFRICA
Editor Elisabeth Lickindorf Editorial Board Wieland Gevers (University of Cape Town) (Chair) Graham Baker (South African Journal of Science) Phil Charles (SAAO) Anusuya Chinsamy-Turan (University of Cape Town) George Ellis (University of Cape Town) Jonathan Jansen (Stanford University) Correspondence and The Editor enquiries PO Box 1011, Melville 2109 Tel./fax: (011) 673 3683 e-mail: email@example.com (For more information visit www.questsciencemagazine.co.za) Advertising enquiries Barbara Spence Avenue Advertising PO Box 71308 Bryanston 2021 Tel.: (011) 463 7940 Fax: (011) 463 7939 Cell: 082 881 3454 e-mail: firstname.lastname@example.org Subscription enquiries Elisabeth Lickindorf and back issues Tel./Fax: (011) 673 3683 e-mail: email@example.com or firstname.lastname@example.org Copyright © 2008 Academy of Science of South Africa
Power & vulnerability W ith or without people, powerful planet Earth will survive until the end of its natural life, about 7 billion years from now. But what changes are happening on Earth? how have people helped to create them? how can we preserve the vulnerable ecosystems that provide our survival and quality of life? what is happening in Africa? Contributions to this bumper International Year of Planet Earth issue of come from South Africa’s scientists and scholars who marvel at the miracle of Earth and life, and whose concerns centre on our region. The political will is clear from the message from Minister Mangena (p. 5) supporting the cause of ‘a healthy planet for all’. The Earth’s recycling systems are not for the faint-hearted (p. 10), and understanding how they work is the basis for dealing with their potential to sustain or destroy. Observation and sophisticated technology bring further clarity, generating landscapes based on satellite data (‘how will the Cape Peninsula look if sea levels rise?’) (p. 6), seismic investigations (p. 14), and works of art (p. 54). African landscapes house ancient vestiges of life, and biologists and geologists are together discovering how the Kalahari Plateau’s changing landforms shaped life-forms (such as antelopes and crocodiles), whose DNA now offers new evolutionary timelines (p. 19). Oceans at the tip of Africa detail evolving currents and their effects on climate (p. 16), while rocks of the region offer unique insights into Earth’s past climates, helping humans to prepare for what’s ahead (p. 22). People urbanizing at unprecedented rates (p. 34) make relentless demands on Earth’s limited resources – water for survival (p. 26), soils for food (pp. 40 and 44), and minerals for wealth creation in the name of progress, but at dangerous human and environmental cost (p. 50). Calls to nurture these precious resources are undermined by unsustainable use. Nature’s power is never absent – geohazards fill TV screens with footage of floods, earthquakes, landslides, and collapsing buildings (p. 28). People who are poor always suffer most. Hope comes with Africa Alive Corridors, which defines heritage boundaries for Africa’s treasures – historical, scientific, and cultural – from earliest life on Earth to the present (p. 56). Knowing what’s there and engaging in the life of these ‘corridors’ will help Africans – and others too – to appreciate and nurture the precious continent. Actively preserving Earth for ourselves and others is the lofty aim. But the ecosystem that supports life, as we know it, is vulnerable; and unthinking human processes make it more so. The planet will react with no thought for human wishes, if those who rely on it abuse it. There’s work to be done to prevent turning a comfortable planet into a hostile one. It needs understanding of just how vulnerable our people-friendly ecosystem really is.
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Join QUEST’s knowledge-sharing activities Write letters for our regular Letters column – e-mail or fax your letter to The Editor. (Write QUEST LETTER in the subject line.) ■ Ask science and technology (S&T) questions for specialist members of the Academy of Science to answer in our regular Questions and Answers column – e-mail or fax your questions to The Editor. (Write QUEST QUESTION in the subject line.) ■ Inform readers in our regular Diary of Events column about science and technology events that you may be organizing. (Write QUEST DIARY clearly on your e-mail or fax and provide full and accurate details.) ■ Contribute if you are a specialist with research to report. Ask the Editor for a copy of QUEST’s Call for Contributions (or find it at www.questsciencemagazine.co.za), and make arrangements to tell us your story. To contact the Editor, send an e-mail to: firstname.lastname@example.org or fax your communication to (011) 673 3683. Please give your full name and contact details. ■
IYPE Out of Africa South African National Committee for the International Year of Planet Earth
Above: The shape of Earth – the geoid. People’s perception of the shape of the solid Earth (that is, its shape excluding the oceans and atmosphere) has over time evolved from that of a flat Earth, to a spherical one, then to an oval one. The best present model of its shape is this one of the ‘Potsdam potato’ – highly exaggerated in the vertical scale – derived from satellite observations linked to ground control. Image: GFZ-Potsdam, Germany. Right: Africa’s real size. This equal-area projection allows direct, aerially undistorted comparisons of continents’ sizes. Below: This film strip shows the ‘birth’ of Africa, out of Pangaea, some 200 million years ago, and then, from the present (central frame), its move 200 million years into the future, joining the others again to form one large landmass.
aunched in 2005 by Minister W. Sheya of the United Republic of Tanzania, the International Year of Planet Earth (IYPE) is an African idea. From the start, it aimed to help society make greater and more effective use of the knowledge accumulated by the world’s Earth scientists, and it culminates in the celebration of 2008 by the United Nations as the Year of Planet Earth. Africa is colossal – just over a fifth of Earth’s continental surface (see map). Recognizing its enormous size helps to explain the magnitude of the task lying ahead for the IYPE. Scientists and politicians, for instance, in modelling global climate change, need adequate data from Africa. Yet insufficient information and far too few indigenous science practitioners are two of Africa’s misfortunes, which have to be faced through education, education, education – arguably Africa’s most immediate longterm need. In revealing the history of the lithosphere, biosphere, and anthroposphere (people and where they come from), this continent is without peer. It is the landscape of human origins and culture, and nearly 4 billion years of unparalleled geobiodiversity. Yet its 900 million inhabitants are in the grip of the Sixth Extinction – the present widespread, ongoing, and accelerating mass extinction of plant and animal species – with global warming its potentially culminating blow. By 2015, Africa will very likely have one billion people, most still living in squalor and misery; hungry, sick, without time or energy to dream of study or of a secure future. Over the next 20 years, most Africans will migrate into urban areas, straining infrastructures – in some cases close to breaking-point. Such cities are greedy for resources and consume the environment, covering large tracts of land, generating pollution, changing regional hydrological cycles and local microclimates, and disrupting ecosystem services. The IYPE initiative makes it clear that combating misfortunes across Africa is achievable only when people and nations act in unison. South Africa aims to reach out nationally, and across the continent, to engage with a wider community eager to develop
+ 100 Mya
– 200 Mya
+ 200 Mya
0 Mya – 100 Mya
Quest 4(2) 2008 3
Members of the South African National Committee for IYPE The members of the South African National Committee for the International Year of Planet Earth are: Maarten de Wit (University of Cape Town) (chair), Isabelle Ansorge (University of Cape Town), Urmila Bob (University of KwaZulu-Natal), Greg Botha (Council for Geoscience), Avinash Chuntharpursat (South African Environmental Observation Network), John Compton (University of Cape Town), Antony Cooper (CSIR), Rehana Dada (University of KwaZulu-Natal), M. Ali Dhansay, Ray Durrheim (CSIR and University of the Witwatersrand), Susan Frost-Killian (Council for Geoscience), Lorna Holtman (University of the Western Cape), Lindisizwe Magi (University of Zululand), Mac Makwarela (Department of Science and Technology) (observer), Brian Mantlala (South African National Biodiversity Institute), Steve McCourt (University of KwaZulu-Natal), Jodi Miller (University of Stellenbosch), Jonas Mphephya (South African Weather Service), Val Munsami (Department of Science and Technology) (observer), Lorenzo Raynard (South African Agency for Science and Technology Advancement), Mary Scholes (University of the Witwatersrand). Secretariat (ISL-SA ICSU): Busiswa Molefe.
Special thanks from the Quest team go to Professor Maarten de Wit (Director of AEON-Africa Earth Observatory Network and Professor in the Department of Geological Sciences, University of Cape Town) for coordinating articles for this special IPYE issue and for his generous support and assistance.
Above: An orbiting Galileo satellite, forming part of the European satellite radio navigation system that will make it possible to locate and monitor moving or stationary objects to within one metre of their position. Image: Deutsches Zentrum für Luft- und Raumfahrt and GFZ-Potsdam, Germany.
For information about the IYPE and details of the ten research themes, visit www.yearofplanetearth.org * Eighteen-year-old Laura Byrne (St John’s College, now at the University of Witwatersrand) was one of three students, selected out of 130 from around the world, to present her contribution to the assembly. Her forecast of the state of planet Earth took the form of a novel but ‘stormy’ weather report. The other student winners were Inka Schomer, Maura Pellettieri, Fulufhelo Munyai, and Stephanie Ackermann. ** Professor Sospeter Muhongo, the Director of ICSU ROA, is the chairperson of the Science Programme Committee (SPC) of the International Year of Planet Earth.
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The International Year of Planet Earth (IYPE) is a joint initiative by UNESCO and the International Union of Geological Sciences (IUGS). Its rationale is summed up as ‘Planet Earth in our Hands’. At the last count, IYPE enjoyed the full political support of 191 UN countries (representing 87% of Earth’s human population), and some 70 countries and regions in the world have national committees to plan events throughout the year. The global opening of IYPE took place 12–13 February 2008 at the UNESCO headquarters in Paris, France. Over 1 000 delegates attended, including ministers and ambassadors, as well as leading politicians and scientists from around the world. Among the members of South Africa’s 10-person delegation were the five winners of the South African IYPE student competition held in November 2007*. The South African launch of IYPE takes place at SciFest Africa in Grahamstown (16–18 April 2008), and the Africa launch shortly thereafter, in Arusha, Tanzania (8–9 May). The main IYPE activities (spanning the three years 2007–2009) operate within its science and outreach programmes. The science programme has ten broad, societally relevant and multidisciplinary themes – Deep Earth: From crust to core; Ocean: Abyss of time; Earth and Life: Origins of diversity; Climate Change: The ‘stone tape’; Groundwater: Reservoir for a thirsty planet?; Hazards: Minimizing risk, maximizing awareness; Megacities: Going deeper, building safer; Soils: Earth’s living skin; Earth and Health: Building a safer environment; and Resource Issues: Towards sustainable use. The outreach programme aims to make everyone aware of the work of the Earth sciences. The Regional Office, Africa of the International Council for Science (ICSU ROA) (http:// icsu-africa.org) has been mandated by the IYPE Secretariat to coordinate IYPE activities in Africa, and it promotes and facilitates the implementation of the IPYE’s science agenda on the continent**. From the IYPE’s inception, ICSU ROA has urged African scientists to involve themselves in IYPE activities and to form national committees. The following countries already have such committees in operation: Cameroon, Egypt, Ethiopia, Gambia, Morocco, Mozambique, Namibia, South Africa, and Tanzania. Botswana, Burundi, Cape Verde, Côte d’Ivoire, Ghana, Kenya, Lesotho, Madagascar, Mauritius, Nigeria, Uganda, and Senegal are in the process of finalizing the formation of their national committees. The ten broad research themes of the IYPE dovetail well with four ICSU ROA science plans (Sustainable Energy, Natural and Human-induced Hazards and Disasters, Health and Human Well-being, and Global and Environmental Change). ICSU ROA is assisting the local organizing committee of Tanzania with its IYPE Africa launch in May 2008 (for details, contact Hudson Nkotagu at email@example.com).
partnerships and share scientific news. In this special IYPE issue of QUEST, some of South Africa’s scholars, from many different fields, explore Earth’s curiosities and disturbing facts, and consider ways to reach IYPE goals. At times of crisis – such as those facing the planet today – actions derive from ideas that are currently in circulation1. The challenge is to ensure that the turmoil characterizing our continent and the whole of Earth does not reach uncontrollable proportions, to prevent the need for global disaster management, to revive a spirit of public interest in combating poverty and disease and in supporting vulnerable societies, and to take Earth’s hazards seriously. We, in South Africa, are ready. A gargantuan task lies ahead: we lobby you to join in the activities of IYPE, the Greatest Geo-Show on Earth. ■ Visit www.iype.org.za; www.yearofplanetearth.org; and www.developmentgoals.org. Consult the Atlas of Global Development (HarperCollins, World Bank, 2007) and World Development Indicators 2007 (details at www.worldbank. org/data); I. Stewart and J. Lynch (eds.), Earth: The Power of the Planet (BBC Books, 2007); ICSU Regional Office for Africa, Science Plans available at www.icsu-africa.org; series of scientific articles on IYPE topics, in Nature, vol. 7176 (17 January 2008) available at www.nature.com/nature/supplements/collections/ yearofplanetearth/index.html; D. Edwards, Artscience: Creativity in the Post-Google Generation (Harvard University Press, 2007); J. Sachs, The End of Poverty: Economic Possibilities for our Time (Penguin, 2005); and F. Wilson and M. Ramphele, Uprooting Poverty: The South African Challenge (David Philip, 1989). 1. Canadian journalist, author, and activist, Naomi Klein, for instance, uses Milton Friedman’s doctrine ‘only a crisis – actual or perceived – produces real change’ to explore the power of shock and the actions taken, when crisis occurs, on the basis of ideas that are around at the time. Responses are often political, she argues, and every crisis has an opportunity that someone will exploit. (See Noami Klein, The Shock Doctrine: The Rise of Disaster Capitalism, Penguin, 2007.)
The Earth sciences The Earth sciences form a group of disciplines concerned with the origin and evolution of our planet. Geology is the root science. It developed from attempts to understand the Earth’s rock strata and fossils, then grew into the fundamental discipline of stratigraphy, ‘the science of reading the rock record’. With time, geology has branched out to cover many ways of exploring the Earth’s anatomy, history, composition and internal structure, and surface features (Earth science), and its dynamic properties (Earth systems science). The chief disciplines are geology, mineralogy, stratigraphy, volcanology, geophysics*, geochemistry, geochronology, structural geology, tectonics, economic geology, geobiology, palaeontology, pedology, geography, geomorphology, climatology, hydrology, oceanography, meteorology, glaciology. With further understanding that the planet is not just a static sphere, these topics increasingly overlap as scientists examine the ways in which Earth works as a dynamic system. New cross-disciplinary fields have emerged, such as geodynamics, ecodynamics, palaeoecodynamics, ecological economics, global change, and geomedical studies. With the onset of space exploration, Earth scinces are also overlapping with astronomy, to include the investigation of other planets in our Solar System, and cosmochemistry, which focuses on meteorites and cosmic dust. The combination of Earth and planetary sciences has opened up new fields such as lunar and planetary geology and extraterrestrial impact studies. South Africa contributes globally in all these areas. Because Earth science is both ‘basic’ and ‘applied’, the country’s practitioners in these fields work not only to create new understanding and knowledge of the Earth, but also to apply this knowledge to discover Earth’s mineral resources, mitigate hazards such as earthquakes, floods, and environmental damage, and, increasingly, to forecast such events with the help of powerful computing facilities. These efforts are being consolidated to form yet another new field – that of Earth stewardship science. * Each discipline, in turn, encapsulates a number of sub-disciplines. For example geophysics comprises seismology, geomagnetism, geothermometry, and rock and mineral mechanics.
Message from South Africa for the International Year of Planet Earth Only through science, robust science, the minehead of knowledge, can we appreciate where we came from, where we are, and where we are headed. It is for us all in our different fields to translate that science into daily action, such that its bounty is felt by everyone – today and tomorrow. This is our great opportunity, now, during the International Year of Planet Earth. And it is Africa’s great opportunity to place her unmatched heritage on the world map. This is our greatest opportunity ever to breathe life into that simple creed of freedom, ‘by the people, for the people’. But let us expand on the creed: ‘by the people, for the people and all other species of our time and tomorrow’s time.’ I call all my fellow Africans to action bearing the fruit of science, and to make this Year of Planet Earth a resounding success and to construct a new framework to further the cause of a healthy planet for all.
Minister of Science and Technology Republic of South Africa
Above: The bowels of Earth. Using elastic waves from earthquakes and detonation, geoscientists can now scan into the centre of the planet and assess Earth’s internal temperature variations, as in this image (red = hot; blue = cold; yellow and green represent temperatures in between). Image: Geophysics Department, University of Munich, Germany.
This issue of Quest was specially put together to celebrate South Africa’s contribution to the International Year of Planet Earth, with the support of:
The South African National Programme of the IYPE is supported by the NRF through the South African ICSU Secretariat.
Quest 4(2) 2008 5
African landscapes from remote sensing
An oblique view of the entire African continent – 8 000 km from north to south – without clouds or haze. The broad coastal shelf, great interior plains, and isolated highlands are clearly identifiable. Volcanic mounds and islands populate the ocean east and west of Africa, yet only a few stand out above sea level. Such global-scale views cannot be generated in Google Earth. This image captures important regional topographic differences that result from rifting in east Africa, tectonic collision in Asia, and hotspot activity in the Sahara. The coastal escarpment topography of southern Africa is also clearly identifiable.
Frank Eckardt shows how satellite data are used to visualize the Earth’s surface in vivid 3D detail.
atellite-derived data from Earth orbit have dramatically changed the way we view and perceive our planet’s surface. Earth scientists continue to improve computer tools to interrogate satellite imagery, and ‘virtual globes’ such as Google Earth1 have made the new spatial experience of terrain visualization accessible to the world’s Internet community. Terrain visualization depicts the Earth’s topography in remarkable detail. It also
accentuates landforms and surface features that may be too big or too obscure to be appreciated from ground level. To demonstrate, we obtained actual raw Google Earth data and manipulated it using various image processing techniques. The terrain views presented here are the result, revealing intricate detail of regional-scale escarpments and local-scale tectonic rifting, as well as large-scale continental settings of the southern African landscape.
1. Google Earth is a web-based mapping product available for use on personal computers. Its release in June 2005 caused a more than tenfold increase in media coverage on virtual globes between 2005 and 2006, and has raised the public’s interest in geospatial technologies and applications. Its stated goal is to allow the user to “point and zoom to any place on the planet that you want to explore”. The level of detail varies, but most land is covered in at least 30-m resolution. Google Earth lets the viewer see houses, the colour of motor vehicles, and even the shadows of people and street signs. It draws on digital elevation model (DEM) data to show users the Grand Canyon or Mount Everest, for example, in three dimensions instead of just the two-dimensional views offered by other map programs and sites. Source: Wikipedia.
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The 40-km-diameter Brandberg massive rises 2 000 m above the surrounding plains of the central Namib plateau. This view in particular shows the topographic rim on the flanks of the massive, which indicates the flood basalts that once covered this area but that have been eroded over the past 120 million years.
Useful pictures from space Try to imagine how we perceived our planet before astronauts returned with their breathtaking ‘blue marble’ photograph, taken from lunar orbit, of the Earth suspended against the black backdrop of space. Since those pioneering days, we have collected digital satellite data on the land, oceans, and atmosphere with ever-increasing automation, sophistication, regularity, and spatial resolution2. Today, dozens of satellites in orbit provide a daily tally of data measurable in terabytes. They provide information in near real-time, and can keep pace with dynamic changes – caused by weather patterns – to biological productivity on land and sea, and degradation of the terrestrial surface. Over the past three decades, satellites have been witness to tropical deforestation in Rondonia and Mato Grosso (South America), the relatively rapid and recent drying up of Lake Chad and the Aral Sea (central Africa and Asia, respectively), the break-up of the Larsen B ice-shelf on the Antarctic Peninsula, the decline of the Arctic sea ice, and even the gradual, subtle degradation of the Siberian permafrost. Improved highresolution sensors, and rapid processing and data dissemination technology, have aided relief efforts in Darfur’s ongoing humanitarian crisis, and assisted when the December 2004 Asian tsunami took everyone by surprise. 2.
‘Spatial resolution’ refers to the size of the image pixel. For example, global elevation datasets have gradually improved from 5 km, to 1 km, to 90 m, down to 30 m. Dedicated laser profilers can produce even higherresolution data for such features as glaciers and ice caps.
View of a 300-km section of the central Namibian coastline. It illustrates the important role of dry river valleys in transporting dust from the Namib desert into the Atlantic Ocean. On the right is the Namib Sand Sea and, towards the centre, are the coastal towns of Walvis Bay and Swakopmund (too small to be visible here). The west coast escarpment and the steeply rising Brandberg massive (left) are clearly identifiable. Digital elevation data depict plumes of dust that originate in dry river valleys, where there is an abundance of loose sediment. Dunes and mountainous areas are not sources of dust.
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The Makgadikgadi Basin: a view from the east. The white surface is a dry salt-encrusted lake deposit that covers 6 000 km2 in the Kalahari semi-desert of Botswana. In the foreground is the Boteti River valley. The southern escarpment (above right) is close to 100 m high, but exaggeration of vertical relief makes it appear much taller. Vertical exaggeration of subtle features accentuates landforms that are often invisible to the field observer and to the image analyst. In particular, past shorelines are a good indication of previous highstands (or water levels at their highest); they are important in reconstructing climates, and also helpful in the search for archaeological sites.
The Makgadikgadi Basin: view from the northwest. In the past, this lake basin was filled with water up to 45 m deep, and was one of southern Africa’s largest water bodies. This terrain reconstruction depicts the extent of the former lake in detail. Past lake surfaces would have affected local climate, and knowing where they were assists in detecting contours and shorelines.
Vegetated and degraded fossil dunes close to the Tsodilo Hills in Botswana. These dunes are barely visible at ground level, as they have been flattened and degraded by erosion over time. As a result, they have been covered by vegetation, and have even been subject to some tectonic modification as part of the African Rift Valley.
The Magaliesberg mountains immediately west of Pretoria host Hartebeespoort Dam. Platinum mining and agriculture are pronounced activities (visible in the foreground). Hartebeespoort Dam lies to the west of Pretoria and to the northwest of Johannesburg (cities not visible in this picture). We use an additional midinfrared band to help capture subtler vegetation and soil patterns than can be shown using true colour. These falsecolour images nevertheless show vegetation as green.
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Viewing the details Many Earth observations are generated using visible and near-infrared waveband regions, but further information can be gained from longer waveband portions of the electromagnetic spectrum such as the microwave region3. Producing a microwave pulse and measuring its return time makes it possible to record land- and sea-surface elevations. This technique has helped researchers to keep tab on global sea levels, for example, which we now know to be rising at the rate of about 3 mm a year. Radar instruments have recently also produced a global topographic elevation dataset (SRTM)4 3. We use the broad range of the electromagnetic spectrum to observe the Earth’s surface with more than just visible light. The entire spectrum ranges from high-energy gamma rays and X-rays to lowenergy radio waves. For further details about the electromagnetic spectrum and its use in remote sensing, consult “Views from space: Earth observation”, Quest, vol. 2, no. 2 (pp. 30–31). 4. Shuttle Radar Topography Mission (SRTM) data was generated by a single 11-day space shuttle flight (Endeavour) in February 2000. This produced a near-global topographic data-set (between 60°N and 57°S) of all the continents except Antarctica.
GEOSS: Global initiative to benefit society Our ability to measure is growing with the proliferation of Earth observation capabilities provided by satellites and micro-satellites, as more countries, including South Africa, join the space age. In Brussels, Belgium, on 16 February 2005, 61 countries gave their support to a new worldwide network of Earth observations, the Global Earth Observation System of Systems (GEOSS), that would coordinate data and serve societal needs around the globe in fields including weather forecasting, natural disaster monitoring, health, and the management of water and energy resources. In Cape Town, 28–30 November 2007, ministers and officials from more than 100 governments and international organizations met to plan GEOSS, and, on 30 November, the Cape Town Declaration was adopted during the Cape Town Ministerial Summit. For more on GEOSS, visit www.earthobservations.org (and download the Cape Town Declaration); www.epa.gov/geoss; and read the Wikipedia entry.
with a vertical accuracy of almost 2 m and a spatial resolution of 90 m, and this forms the topographic basis of the images depicted here. These pages showcase the digital fusion of two datasets, such as land surface imagery and digital elevation data, for selected regions of southern Africa. We can visualize surfaces of continents and all their subtleties as never seen before. Although the techniques and datasets are similar to those of Google Earth, we have worked with our own datasets to depict conditions in the past (such as those of the Makgadikgadi Basin in Botswana) and potential environmental changes in the future (such as the flooding of the Cape Peninsula). We can also control such factors as vertical exaggeration and the angle of solar illumination, so as to accentuate subtle surface features, making specific features stand out more clearly for further, detailed examination. The technology – and the quality and usefulness of our information – improves in leaps and bounds. More recent Earth observation advances can now detect subtle changes in the planet’s gravitational field as it responds to mass seasonal fluctuations in the Earth’s hydrological system. This allows researchers to monitor droughts and local thinning of ice caps. In the near future, a new set of sensors called OCO (the Orbiting Carbon Observatory) is to appear aboard satellites, and will monitor local CO2 (carbon dioxide) ‘fingerprints’ to aid the global policing of CO2 pollution. ■ Dr Eckardt is a geomorphologist in the Department of Environmental and Geographical Sciences at the University of Cape Town. He has spent the past 15 years working on various remote sensing applications in the drylands of southern Africa.
Pans and braided dune streams of the southern Kalahari close to the transfrontier park of South Africa and Botswana. Wind and water are active agents in shaping the landscape. The vertical exaggeration by a factor of 20 increases the vertical appearance of landforms 20 times compared with horizontal distances. This view accentuates the topographic heights of dunes and lows of pans, enabling the details to be observed more clearly.
View looking north over the Cape Peninsula, visualized as it would appear if sea levels were to rise by 60 m. This (unlikely) scenario would take place if all the world’s ice caps and glaciers were to melt; it would cause the flooding of Cape Town and of the Cape Flats, and the merging of Table Bay (left of the archipelago in this view) and False Bay (right). (See also p. 24.)
For more information, read Michael D. King (ed.), Our Changing Planet: The View from Space (NASA Goddard Space Flight Center, 2007); consult http://na.unep.net/OnePlanetManyPeople/ for One Planet Many People: Atlas of Our Changing Environment; and visit the NASA Earth Observatory at http://earthobservatory.nasa.gov/. For more on Google Earth, its significance, and its educational value, consult Nature (16 February 2006) for “Think global” (p.763), “The web-wide world” (pp.776–777), and “Mapping disaster zones” (pp.787–788).
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gigantic recycling machine Maarten de Wit and Steve McCourt describe the Earth’s four billion years of recycling that’s necessary to sustain life as we know it.
Some Earth systems and recycling processes System
weather and climate
erosion and sedimentation
continental drift, plate tectonics, volcanism, climate a, b
weather and climate
0 15 75 0 0
magnetic field, cosmic particle shielding c, d
m ’s rth Ea
Figure 1: Pie-shaped section through the Earth, showing its main recycling mechanisms. The planet is a container of complex coupled systems. Convection (depicted as arrows) in the outer, liquid core drives Earth’s magnetic dynamo, creating its magnetic field that shields us from lethal cosmic particles. Details of the convection patterns related to recycling in the mantle remain unclear, and particulars of material and energy fluxes among the systems are still largely unknown. The biosphere3 (not shown here) penetrates about 10 km down into the lithosphere and up into the exosphere2, and derives its recycling energy from both, making ‘life’ the most complex of all Earth’s systems. Today, nearly three-quarters of the planet’s outer solid skin – the ~100-km-thick oceanic lithosphere – lies beneath the oceans and is constantly recycled back into the Earth’s mantle, whence it came in the first place, barely 100 million years ago. At the places (called subduction zones) where this oceanic lithosphere plunges back into the mantle, ‘second-hand’ rocks (granites) are created that make up the buoyant continents. This recycling process provides the mechanism that forces continents to drift across Earth’s surface at rates of centimetres or decimetres per year. Continents also come and go but, on average, they last longer than oceans before being recycled into the mantle. They recycle efficiently only after first being decomposed and eroded through interaction with the overlying exosphere – whose atmosphere, hydrosphere, and cryosphere1, each have complicated interactive recycling circuits operating at far greater speeds.
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long-term cycles = billions of years b medium-term cycles = millions of years c short-term cycles = thousands of years d ultrashort cycles = days to centuries
verything on our Earth is recycled – from bacteria to continents, from mountains to oceans, from rocks to humans. These processes are very efficient in erasing evidence, so the further back in time we probe, the less remains to help us to reconstruct the story of our planet. Rocks of its first 500 million years, for example, have yet to be discovered, and less than 0.5% of the present-day surface of the globe represents the first 1 500 million years of its existence. Every sector of the Earth engages in this dynamic machinery, but its ‘clockwork’ is difficult to comprehend because the multitude of interlinked ‘cogs and springs’ operate at different speeds and react to stresses at different thresholds. The entire system is delicately balanced and self-regulating, and is energized through two very different heat engines: the recycling of
Earth – gigantic recycling machine
The origin of continents and mountain belts Earth’s oldest evidence for plate tectonics is in South Africa. Himalaya-like mountains subduction zone buoyant continental fragment
granites collision suture plate
ocean water rec ycli n lith g of o osp ce her anic e
Pillow basalts & fossils
oceanic pillow lavas
Barberton Greenstone Belt
Kaapvaal Craton 4
suture zone with remnant layer of oceanic rock Limpopo Orogen
Figure 2: Schematic representation of a section of the lithosphere 3.5 billion years ago, showing the amalgamation of an Archaean continent from small continental fragments. These were formed above subduction zones and subsequently welded together during their collisions when oceanic lithosphere was recycled, leaving only small remnants as evidence for their former existence. South Africa is the best place in the world to study these ancient tectonic processes. 5 6
The early Earth Did the young Earth operate as a recycling machine in the same way as it does today? Scientists are still debating this question. It’s difficult to reconstruct what the youthful Earth looked like because so little evidence has been preserved. Archaean rocks older than 2.5 billion years cover some 7% of today’s continental surface, yet they represent nearly 45% of Earth’s history. Rocks older than three billion years are scarcer still (only 0.5% of the planet’s total surface represents the first one-third of its history), and only a few mineral grains date back to about 200 million years after Earth’s formation around 4 560 million years ago. Small rock outcrops in northern Canada are only slightly older than 4 000 million years, and the next oldest, in Greenland, are about 3 800 million years old. These give hints of our planet’s deep past, but their value is limited because all have been ‘cooked and stirred’ under high temperatures and pressures that have erased most traces of their origins. In contrast, the slightly younger rocks of the Barberton Mountain Land in Mpumalanga, South Africa – between 3 000 and 3 700 million years old – are exquisitely preserved. Researchers from around the world come here to ‘read’ and interpret the early chapters of Earth’s history. Volcanic rocks are of special interest, often displaying spectacular bulbous features known as pillow lavas (photographs 1–4 above). The outer rims of the pillows comprise volcanic glass in which unexpectedly, in 2004, microscopic traces of the world’s oldest life forms were discovered in the form of hair-like tubes (photographs 2 and 3 above), similar to those found today in glassy margins of pillow lavas that cover modern ocean floors (Figure 2). These tubular structures are constructed by bacteria that literally ‘eat’ volcanic rock, consuming chemical ingredients from the rock-glass to sustain their metabolisms. The Mpumalanga finds confirm that simple life was common on Earth about 3 500 million years ago, and that most of the planet’s upper oceanic crust teemed with bacteria and viruses. Other microscopic fossils, discovered in the Barberton Mountain Land in various rock types, suggest a significant diversity of bacteria. Thus, already about 1 000 million years after the formation of Earth, primitive life in Mpumalanga was exploring numerous ecological niches and had established the world’s oldest biodiversity hotspots. In a real sense, Mpumalanga represents the cradle of life. Its geological treasures provide tiny glimpses into the early workings of our planet. But the record is fragmentary and there’s much we do not yet understand.
It’s at this interface between the solid Earth and its exosphere that the biosphere3 thrives, deriving its survival from both Earth and Sun. Some geoscientists now think that the biosphere helps to control the system’s ‘thermostat’, enabling the whole-Earth system to work with relative stability for long periods of almost immeasurable time. Leakage (exchange) of chemicals among its
the solid Earth is driven by the heat of its own internal radioactive materials1, while recycling in the exosphere2 – often called Earth’s ‘fluid envelope’ – is driven by energy from the Sun. The number of ‘calories’ delivered to Earth’s surface from each of these sources is very different, and the supply from both is steady but not constant over geological time (see Figure 3).
1. The solid Earth contains sufficient radioactive chemicals bound up in its minerals to heat up its internal systems. This heat, generated through the radioactive decay, is lost mostly through convection and phase-changes during melting and solidification. 2. The exosphere comprises the atmosphere, the hydrosphere, and the cryosphere. The atmosphere is the ~200-km-thick envelope of air surrounding the Earth. The hydrosphere is the whole body of water that exists on or close to the Earth’s surface (including the oceans). The cryosphere (the prefix ‘cryo-’ comes from the Greek kruos meaning ‘frost’) is the totality of ice on Earth. 3. The biosphere is that part of the Earth’s crust and exosphere where living organisms are found, and with which these organisms interact to create ecosystems.
Photographs (left to right) 1 Basaltic pillow lavas, making up 99% of the solid surface of modern oceanic lithosphere, exposed some 3–4 km below sea level. 2 and 3 The world’s oldest fossilized traces of early life in the glassy rinds of pillow lavas, dated at about 3 480 million years old (2). Similar hollow tube in which the bacteria lived, found in pillow lavas of today’s oceans (3). (Both pictures are taken at the same scale.) 4 In the Barberton Mountain Land, pillow basalts, dated between 3 470–3 480 million years, with shapes and structures identical to pillow lavas on the modern ocean floor. 5 Vestige of ancient landscape, Barberton. The flat surface (in the background) is the world’s oldest erosion surface, plained off by ocean waves 2.6 billion years ago. Very recent erosion has exposed older Barberton rocks below it (foreground), extending 1 000 million years further back in time, when Earth was 20% of its present age. 6 South Africa’s oldest rock sequences preserve records of lithosphere-recycling and mountain-building. The finest example is in the linear belt of rocks along the South African–Zimbabwean border, the root of what 2 500 million years ago was a mountain range as high as today’s Himalaya. The metamorphic rocks exposed in the Limpopo region formed about 30 km deep in the Earth’s lithosphere, revealing what lies at similar depths below modern mountain belts (such as the Alps and the Himalaya) and what recycling processes operated in Earth’s early history.
Quest 4(2) 2008 11
Energy budget of Sun and Earth
Figure 3: Within 200 million years of accretion from meteorites and solar dust, which gave birth to the Earth as we know it, the planet differentiated into its fundamental recycling systems. Since then, only the strength of the energy driving these systems has changed significantly. The rate of mantle recycling of the young Earth was faster than today, to cope with the planet’s more intense internal radiogenic heat production. (In response, for example, there were more than a hundred small lithospheric plates compared to the 10 largest plates today, because a world with a larger number of small plates cools more efficiently.) By contrast, the temperature of the early exosphere would have been low enough, under the less energetic Sun, for the oceans to be solid ice, but the early exosphere was richer in greenhouse gases than today, keeping the oceans of the young Earth from freezing over. This figure also shows the present Earth surrounded by a ‘doughnut’-shaped protective ‘cloud’ – in reality, an invisible magnetic shield. Its ‘hole’ hovers above the South Atlantic Ocean and southern Africa, representing weakening in the shield, through which lethal cosmic rays now penetrate our atmosphere deeper than elsewhere in the world; its origin is thought to be related to changing recycling patterns in the planet’s liquid core where Earth’s magnetic field is generated. Researchers monitoring changes in the Earth’s magnetic field over South Africa have found that it has weakened by over 25% during the last 60 years – more than anywhere else on the planet. The reasons for such weakening are not fully understood, but should be of concern as it will increase the flux of cosmic rays into our atmosphere, interfering with satellite communication systems (as is already happening within the magnetic hole), and, eventually, even threatening life itself. Figure 4: Specific events in Earth’s long history can now be well defined with the help of modern radiometric dating techniques. ▲
Millions of years ago
Earth’s Deep Time Chart
Biosphere’s ‘big bang’
Silurian Ordovician Cambrian
Explosive expansion in diversity of MODERN LIFE Multi-cellular life develops
Land bacteria Oldest fossils on Earth
65 Myr 292 Myr
12 Quest 4(2) 2008
(The birth of Earth)
Oldest rocks yet discovered on Earth
Oldest chemical signs of life on Earth
1 500 Myr
Linear time scale
Non-linear time scale
T HE BIG FIVE
G LOB AL EXTINCTIONS
Calculated species loss
4 000 4 500 4 600
[Myr = millions of years]
recycling components (shown with red arrows in Figure 1 p. 10) can upset the balance, however, and once in a while the system goes out of control, catalysing sudden changes in the internal convection and a ‘resetting’ of the recycling rhythms. Following a large volcanic eruption, for instance, the atmosphere can become so polluted by volcanic dust and gases as to produce severe climate change for decades or even thousands of years before the exosphere’s recycling mechanism cleans it up again. How the planet keeps changing Geologists have long studied the Earth’s material cycles and the interchange of mass and energy among different components of Earth’s machinery – how long such cycles last, how they might suddenly speed up and slow down, and how they operate in concert across widely varying scales in space and time, until suddenly a missing beat somewhere causes a cascade of jolts and chaotic responses for a while before the systems settle into new recycling routines. Such sudden disturbances are written in Earth’s rock layers and fossils – as mass extinction events, past biodiversity collapses, and severe climate fluctuations. But we do not yet understand the details, even though reading Earth’s records and dating such past events have become ever more accurate over the last three decades. Modern dating methods use natural radioactive materials present in all Earth’s systems. Technological improvements in radiometric dating now allow extraordinarily accurate dating of tiny amounts of materials (measured in nanograms to picograms)4, which can be checked independently using more than ten different isotope systems5. Rocks and minerals, for example, are now routinely dated to within 0.1% of their true age, with southern Africa’s oldest rocks, near Piggs Peak in Swaziland, being 3 662.8 ± 0.5 million 4. The prefix ‘nano’ (symbol n) denotes a factor of 10–9; ‘pico’ (symbol p) a factor of 10–12. 5. An isotope is any of the set of atomic nuclei constituting a chemical element having the same number of protons (that is, their atomic number is the same), but a different number of neutrons (that is, their atomic weight is different). Isotopes may be produced by various nuclear reactions and can be radioactive.
Earth – gigantic recycling machine Sun
CO2, nitrogen and sulphuric acid
Temperature 474 ˚C Pressure 90 bar
Nitrogen (78%), oxygen (21%), H2O clouds, and a biosphere; variable small amounts of CO2 and CH4 CO2 and nitrogen
0–40 ˚C 1 bar
s ck ilo ld Go
Surface conditions are very different on our planetary neighbours.
Three possible states of planet Earth
1. Greenhouse Earth ...Venus today
2. Icehouse Earth ...Mars today
3. Cosy Earth ...in the ‘Goldilocks Zone’
Figure 5: Schematic representation of Earth and its two nearest planetary neighbours, Venus and Mars. All had a similar adolescent history and possibly sustained bacterial life, but their exospheres evolved into different thermal and chemical states. Only Earth lies in the ‘Goldilocks Zone’ that is comfortable for life. Outside it, closer to the Sun, the atmosphere of Venus evolved into a runaway greenhouse state, with surface temperatures of molten lead and a violent weather system. All prospects of life that might have existed there earlier have vanished. Farther from the Sun, Mars mostly has a cold, frozen surface and windy atmosphere. The evidence suggests that its early climate was pleasanter, with water that possibly sustained life, but if life once existed there, it has either vanished or gone underground. Of the three planets, only Earth retains a coupled recycling system that links mass exchange between the solid Earth and its exosphere. This suggests that recycling on a planetary scale is a prerequisite for sustainable life. Figure 6: Only an Earth that retains a steady carbon and water cycle on a planetary scale can remain in the Goldilocks Zone and thus sustain life. (For more on the carbon cycle, see “The search for the missing carbon sink”, Quest vol. 3, no. 4.)
and temperature conditions deep inside the planet. We do not, however, know with certainty how Earth operates as a complex system – nor the details of its ‘engine rooms’; how long the building blocks last before being broken down, digested, and regurgitated by the recycling machinery; what feedback mechanisms control the operating systems. We need to learn more about Earth’s metabolism and its pacemakers, and what checks and balances have kept it a healthy place for life. How long does Earth need to build continents and how fast are they destroyed? Does the process move smoothly or in sudden jerks? Answers require detailed knowledge of rock circuitry and rates of chemical digestive processes such as weathering and erosion, as well as deep mantle convection, and even the unpredictable overturns
What geoscientists are investigating Tracking Earth’s recycling patterns drives modern geology. Geologists more or less understand the planet’s anatomy, physique, and chemistry. They can make computer-aided design (CAD) scans of the Earth’s interior, and artificially reproduce its building blocks (minerals and rocks) in sophisticated laboratories that simulate the pressure
years old. Such precision allows scientists to address new questions about the rates of global recycling, and it has changed the way we investigate the way the Earth works. Soils can erode away within a century, but how long do rocks take to be sculpted into landscapes? What is the lifespan of a mountain range? Water recycles through the atmosphere in days; but now we know it takes millions of years to recycle through minerals and rocks, and billions of years to recycle through the slowly churning mantle (that is, the zone lying between the Earth’s lithosphere and its core, about 2 900 km thick (see Figure 1). At surface, water stored in ice caps, oceans, and lakes remains there for a relatively short time – geologically speaking. Ice sheets and sea levels, for instance, wax and wane on a thousand-year time-scale, yet evaporation drives water into the atmosphere from which relentless precipitation typically returns it to Earth after just a few days. Falling back onto the continents, it gathers carbon dioxide (CO2) from the atmosphere; this makes it slightly acidic, helping to dissolve rocks and to form soils and concentrated solutions. Some water penetrates deeper still and takes part in chemical reactions to form new water-rich minerals, which, in turn, amalgamate into new rocks and continents. In this way, water may be transferred from its short-term surface recycling processes into the long-term recycling patterns of continents and the mantle, which take hundreds of millions, even billions, of years to complete (see box on p. 10). Carbon is similarly recycled – relatively fast though the biosphere but, once transferred to the continents, it can end up as coal and petroleum, or move farther down into the mantle where it either returns to surface via volcanoes as CO2, or remains locked up in minerals, such as diamonds, stored deep in the Earth for up to three billion years before being released again. All this recycling affects our exosphere’s long-term chemistry. Earth stores excess CO2 in limestone or coal and oil, keeping the exosphere chemistry in check – but when it releases these stored chemicals suddenly, all hell can break loose. Given such complex propensity for change, it is remarkable that our Earth has remained comfortable enough for life to survive since its earliest bacterial beginnings some four billion years ago. This ‘comfort zone’ of Earth is often called the ‘Goldilocks Zone’ (not too hot, not too cold, but just right to sustain life), in contrast with conditions on our immediate neighbouring planets Venus and Mars, with which we have had a closely shared adolescent history (see Figure 5).
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in the liquid iron core that generate our magnetic field and its sudden reversals in polarity. Key to unravelling this complexity are the chemical and magnetic signatures in Earth’s materials – that is, the ‘genetic codes’ (or DNA equivalents) of rocks and minerals. Using sophisticated technology, modern geologists can measure these signatures, track the speed and efficiency of the planet’s complex recycling systems, and trace their histories. Like forensic medics, they monitor Earth’s workings. Some scan Earth using seismic vibrations produced by earthquakes; others measure the time it takes for mantle magmas to puncture the lithosphere and form volcanoes, then determine Earth’s internal temperature variations and provide forecasts of eruptions. To decipher Earth more rigorously, however, we also need to know how its systems operated in its youth. Do they work in the same way today as, for example, in Archaean times, 2 500–4 000 million years ago? We know for certain that Earth has evolved since it first formed nearly 4 600 million years ago, but how much has it changed, and what drives this evolution? When did the first continents form and how and why? How did life start and how did it colonize the continents? Was oceanic lithosphere recycled faster in the past when the internal heat engine of Earth was more potent? How did the chemistry of the exosphere alter from the early days when it had no surplus oxygen, yet teemed with life? How did this life deal with a weaker Sun? What kind of world was it then? Geologists try to answer such questions as they chart the pace of change in Earth’s history by timing the rhythms of rock cycles to unravel their origins. Such knowledge helps to improve scientific predictions of further evolution of Earth’s systems as they take their natural course, and as human activity is beginning to reset the rhythms of the exosphere. This is Earth system science – this is ‘new age’ geology. ■ Maarten de Wit is the Director of the AEON-Africa Earth Observatory Network and Professor in the Department of Geological Sciences at the University of Cape Town. He is interested in how the Earth works and, in particular, how it operated during its early history. He is essentially a field geologist interested in cross-disciplinary studies. Professor McCourt is head of the School of Geological Sciences at the University of KwaZulu-Natal, Durban. He has a special interest in the tectonics of the early Earth. The following books are recommended for further details: A.N. Halliday, The Origin and Earliest History of the Earth (Elsevier and Pergamon, 2003); L. Kump, J. Kasting, and R. Crane, The Earth System (Prentice Hall, 1999); M. Van Kranendonck, H. Smithies, and V. Bennett, Earth’s Oldest Rocks (Elsevier, 2007); P. Ward and D. Brownley, Rare Earth (Springer/Copernicus, 2000); C. Lewis, The Dating Game (Cambridge University Press, 2000); F. Gradstein, J. Ogg, and A. Smith, A Geologic Time Scale (Cambridge University Press, 2004); A. Knoll, Life on a Young Planet (Princeton University Press, 2004); M.R. Johnson, C.R. Anhaeusser, and R.J. Thomas, The Geology of South Africa (Pretoria, Geological Society of South Africa, Johannesburg/ Council for Geoscience, 2006); P. Delius (ed.), Mpumalanga, History and Heritage (University of KwaZulu-Natal Press, 2007); S. Conway Morris, Life’s Solutions (Cambridge University Press, 2003); J. Lovelock, Medicine for an Ailing Planet (Gaia Books, 2005). Visit www.earth-time.org.
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AfricaArray seismic networks.
Africa Array Ray Durrheim describes a network of seismic stations and geoscientists across sub-Saharan Africa
fricaArray1 is a Pan-African geophysical and geological research initiative that was launched in July 2004 and is already starting to yield its first research results. Its network of monitoring stations records earthquakes occurring on the continent and worldwide. The permanent network includes 27 broadband seismic stations spread across sub-Saharan Africa, and is supplemented by temporary deployments of seismographs for specific research projects. The AfricaArray facilities may also, in future, host other Earth observation instruments, such as those used for geodetic and climate studies.
What’s being monitored Large earthquakes shake the ground violently, creating seismic waves that spread through the Earth. Earthquakes can trigger landslides and tsunamis, and cause buildings to collapse (see also pp. 37–39). Broadband seismographs are sensitive instruments that continuously monitor ground motion and can detect minute vibrations caused by a distant earthquake. The seismic waves from the earthquake are refracted and reflected when they encounter changes in rock properties2. The structure of the Earth’s crust and
mantle can be imaged from analyses of the waves produced by many earthquakes at different depths, distances, and directions, as recorded by an array of more-or-less evenly spaced seismographs. The AfricaArray seismographs are typically separated by distances of 500–1 000 km. Seismologists analyse the seismograms to determine the location and size of an earthquake, and they use earthquake catalogues (histories) to determine the seismic hazard of a region. Aims Secure scientific monitoring sites with effective data communication facilities are difficult to establish and maintain. The AfricaArray collaboration aims to: ■ Provide high-level training for African geoscientists: Already, 20 African students – representing Angola, Botswana, the Democratic Republic of Congo (DRC), Namibia, Nigeria, South Africa, Tanzania, and Uganda – are busy with postgraduate research; an annual international field school provides practical training in geophysical techniques. ■ Map the broad-scale geological structure of the African continent: The seismic images of the planet’s crust and mantle provide information
1. AfricaArray seeks to train the next generation of geoscientists to develop the continent’s mineral resources and mitigate the effects of geohazards. Core partners are the University of the Witwatersrand, the Council for Geoscience, and Pennsylvania State University, with participating institutions from other African countries, Europe, and the USA. The data are archived and distributed by IRIS (Incorporated Research Institutions for Seismology), a US-based consortium of universities. 2. Refraction describes the way in which the waves are bent when the seismic velocity of the rocks through which they are travelling changes (owing to changes in composition, pressure, and temperature, for example). Reflection describes the way seismic waves bounce off boundaries where rock properties change suddenly, such as the crust–mantle and core–mantle boundaries. A seismograph simply measures the shaking of the ground. By analysing the seismograms, however, we can deduce which waves were refracted and which were reflected. From this information we can construct an image of the Earth’s interior.
Left: Tomogram of the P-wave seismic velocity in the upper mantle beneath the East African Rift System. The model shows that the velocity beneath the Kenya Rift is 0.5–1.5% lower than normal. Below a depth of about 150 km, the anomaly broadens and dips to the west toward the Tanzania Craton. The anomalously low seismic velocities are attributed to the upwelling of hot rocks from the lower mantle. The geometry of the anomaly is consistent with models that show a low velocity anomaly (the African Superplume) extending upward from the core-mantle boundary beneath southern Africa to the middle of the mantle beneath southern and central Africa. For further information, see Y. Park and A. A. Nyblade, Geophysical Research Letters, vol. 33 (2006), L07311, doi:10.1029/2005GL025605, 2006
that helps geoscientists to understand better the structure and evolution of the Earth, and that assists companies searching for deposits of minerals, oil, and gas. For example, seismic stations currently being established in Angola, Botswana, the DRC, and Zambia will be used to delineate the extent of the ancient block of crust known as the Congo Craton; this knowledge will help to guide diamond exploration. ■ Mitigate geohazards: New seismic hazard maps are being developed for Angola and the DRC. Some AfricaArray stations also form part of the Indian Ocean Tsunami Early Warning System. Earthquakes are often precursors of volcanic eruptions, so seismic monitoring can help with the timely evacuation of people from areas at risk. The Nyiragongo volcano (DRC) and Mount Cameroon are right now being closely monitored. The most recent major eruption of Nyiragongo was in 2002, when lava flowed through the city of Goma, killing 147 people, destroying some 12 000 homes, and displacing hundreds of thousands of people. Earthquakes related to deep-level mining for gold and platinum in South Africa sometimes shake the ground powerfully enough to damage the excavations. Deep mines provide unique opportunities for research, as the approximate location of tremors can be forecast reliably3, making it possible to record many seismic events within a reasonably short period of time. These ‘earthquake laboratories’ attract seismologists from countries that experience natural earthquakes, such as Japan and the USA.
■ Investigate the African Superplume, the largest seismic velocity anomaly in the Earth’s lower mantle: The African Superplume occurs in the lower mantle, 1 500–3 000 km directly below South Africa. It may be associated with the elevated topography of south, central, and east Africa, known, in turn, as the African Superswell. Higher-resolution images of the seismic velocity structure of the mantle are required than are currently available, to explain the origin of the superplume and to understand its link to the superswell. For producing a sufficiently highresolution seismic tomographic image, researchers need an extensive network of seismometers and a long period of observation, to be able to record sufficient earthquakes from different azimuths and distances. ■ NOTE: With regard to the available network, the stations in the Sahara and Morocco (indicated by red triangles on the map on p. 14) are supplementary to the permanent backbone network of AfricaArray, and are operated by the Global Seismic Network (GSN) and the International Federation of Digital Seismograph Networks (FDSN). The data they record are in the public domain and therefore available to AfricaArray researchers.
Professor Durrheim is the new South African research chair of Exploration, Earthquake, and Mining Seismology at the University of the Witwatersrand and holds a joint appointment there and at the CSIR-NRE. Further contributions to this article came from Professor Paul Dirks (University of the Witwatersrand), Dr Gerhard Graham (Council for Geoscience), and Professor Andy Nyblade (Pennsylvania State University). For more information and details, visit the AfricaArray website www.africaarray.psu.edu/ and read L.M. Linzer et al., “Recent research in seismology in South Africa”, South African Journal of Science, vol. 103 (2007), pp.419–426.
3. Forecasts are particularly reliable in deep-mine conditions, as – because the tremors are triggered by the mining activity – seismometers can be installed close to the areas where mining is taking place, and in a closely spaced network around a geologically identified area (zone) of weakness.
Crust (of Earth): The planet’s outermost rocky shell, typically 25–75 km thick in continental regions, comprising rocks that are chemically different from the mantle. Geodesy: The science of measuring the shape or figure of the Earth and its gravitational field. The advent of satellite positioning systems, such as GPS and SPS, has expanded this field of study from topographic and astronomic surveying. Mantle (of Earth): The main bulk of the Earth, extending from the base of the crust to the core/ mantle boundary at a depth of about 3 000 km, composed of dense silicate rocks. Seismic tomography: An imaging method that deduces the 3D structure of the Earth’s interior by using seismic data from an array of seismographs distributed over the planet’s surface. Seismic waves: A general term for waves generated by earthquakes or explosions. There are many types, the principal ones being body waves and surface waves. Body waves travel through the interior of the Earth, whereas surface waves are guided by the surface of the Earth. The two basic types of body wave are the P wave, with compressional particle displacement, and the S wave, with shear particle displacement. Seismic velocity is the speed of travel of seismic waves. The velocity of a seismic wave through a rock (medium) is mainly determined by its composition, but is also affected by pressure and temperature. The P wave is the fastest wave travelling away from a seismic event: it has a velocity typically 6–7.5 km/s in the crust, and 8–14 km/s in the mantle. In any given medium, the P wave travels more quickly than the S wave. Seismic velocity structure is a generalized local, regional, or global model of the Earth that represents its structure in terms of P and/or S wave velocities. Seismic velocity anomaly is a deviation from the average or typical seismic velocity structure of the Earth or of a region within the Earth. Superplume: A large region in the mantle with anomalously low or high seismic velocities attributed to high-temperature upwelling and low-temperature downwelling, respectively. Superswells: The surface expression of upwelling that may be related to superplumes. Tomogram: An image (normally in the form of a slice through) the interior of a body (in this case the Earth), formed using tomography. Tomography*: the science and technological art of creating images of the interior of bodies. * Tomography is also used in medical examinations, to map tumors, for example, using X-ray tomography. The mathematics of tomography was developed by South African-born Allan McLeod Cormack (1924–1998), who, jointly with Godfrey Newbold Hounsfield, won the 1979 Nobel Prize for Physiology or Medicine for this work. He was posthumously awarded South Africa’s Order of Mapungubwe on 10 December 2002.
Quest 4(2) 2008 15
Ocean crossroad at
Isabelle Ansorge, Stephanie de Villiers, and Xin Li describe the ocean circulation around the southern tip of Africa where three oceans meet, and some implications for examining climate change.
Top and middle: Heavy red arrows = intense currents and Agulhas rings; open arrows = background flow; palest blue = continental shelf shallower than 1 km; fronts are shown by broken lines. (Top) Front and currents of the greater Agulhas Current system in the South-West Indian Ocean; purple indicates coastal upwelling along the southwest coast; the broken line just north of 40°S shows the Subtropical Convergence. (Middle) Fronts and currents of the Benguela system in the South-East Atlantic Ocean. The Agulhas rings at the Agulhas Retroflection move northwestward into the South Atlantic, interspersed by cold, clockwise-rotating cyclones (blue). Images: Courtesy of I.J.Ansorge and J.R.E. Lutjeharms
Above: The thermohaline circulation of the world’s oceans – the conveyor belt essential for regulating the even distribution of heat and salt at the surface as well as greater depths. It takes over 1 000 years to complete the circuit.
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o understand what drives global climate change, we need to understand the role of the oceans as they transport heat from the tropics to the poles. Around the southern tip of Africa lies a critical ocean crossroad where subtropical South Indian, South Atlantic, and cooler Southern Ocean water masses1 mingle, exchanging water, salt, heat, biota (that is, animal and plant life), and human-induced (anthropogenic) characteristics. South African oceanographers are exploring the nature and variability of this meeting point, and ways in which the character of the oceans south of the continent might change during this millennium. Where three oceans meet Our region’s oceans have a great variety of circulatory systems. Dominating the eastern seaboard of southern Africa is the greater Agulhas Current: narrow, intense, and fast-flowing, it extends to the ocean floor. Low in nutrients, and therefore in biological productivity, there are suggestions of a tropical and subtropical origin, and the sources feeding into the current remain a subject of scientific controversy.
The circulation on the western side of the southern African subcontinent is very different. Here, the wide, shallow Benguela Current moves water towards the equator. The cold water close to the shore supports a productive ecosystem, rich in nutrients and fish life. Directly south of South Africa, and extending from these subtropical regimes, lies the Southern Ocean. It is characterized by narrow bands (known as zonal fronts)2, extending roughly along lines of latitude from north to south, in which there are rapid temperature changes. The northernmost of these fronts, and the primary border to the Southern Ocean, is called the Subtropical Convergence, a region separating warm salty subtropical waters to the north from cooler, fresher ones in the south. The large temperature gradient (or contrast) between the Southern Ocean and the subtropical water masses acts as a stronger barrier than anywhere else in the world’s oceans, preventing the water of different temperatures from mingling easily. Along and between these fronts, the world’s largest ocean current – the Antarctic Circumpolar Current – carries water from west to east3.
1. A water mass is a body of sea water, defined by its temperature and salinity characteristics, and created by surface processes at specific locations. Water masses can be physically modified as they move along, depending on the rates at which they mix with other water masses. 2. A zonal front (or frontal band) is a narrow region of sharp horizontal gradients of specific properties (such as temperature, salinity, density), which extend through the entire water column to form a barrier. 3. For details about the Antarctic Circumpolar Current, see “Southern Ocean hotspots” in Quest, vol. 4, no. 1 (pp. 6–9).
the tip of Africa
Left (opposite page): The ocean in a Force 10 (48–55 knots) storm at approximately 38°S south of South Africa (or ~500 km from Cape Town), as viewed from the SA Agulhas in 2007. Photograph: Neil Hart Right: Montage of graphic results acquired by oceanographers at the University of Cape Town, who are currently monitoring the inflow of Indian Ocean water masses into the South Atlantic. Bottom right: Satellite imagery showing the northeastward passage of Agulhas rings from south of South Africa into the South Atlantic.
Global climate change The oceanic thermohaline circulation4 – often referred to as the ocean’s ‘conveyor belt’ – is a vital link in the global ocean transport of heat from the tropics to the poles. The physical structure of this ‘belt’, and the extent to which it influences climate, are substantially affected by the character and behaviour of ocean currents and the speed and volume of water transported by its flow amongst ocean basins5. Recent studies have highlighted the relationship between oceans and global warming, and the ability of ocean currents to disperse heat will be critical in determining the ability of their waters to absorb carbon dioxide emitted by human activities in future. The large expanse of ocean between the African and Antarctic continents creates the conditions for one of the world’s greatest open inter-ocean exchanges of water masses. Most of these exchanges occur near the Agulhas Current Retroflection region, by means of large rings of water (>300 km in diameter) that drift into the cooler South Atlantic, carrying the warm, salty
signature of the Indian subtropics. Over time, these rings gradually ‘leak’ their waters, dispersing warmer, Indian Ocean characteristics into the cooler South Atlantic. Scarcity of direct observations has so far limited our understanding of the region’s ocean-current characteristics, the variability of the movement of water from one area to another, and the impact on southern Africa’s biota and climate. While we have evidence of the ring shedding processes, we have only a poor knowledge of the volume of water entering the Atlantic via the Agulhas region, or of the influence that changes in water volume may have in balancing the heat transported from the subtropics to the polar regions. To find out more, South African oceanographers are collecting temperature and salinity6 data along high-resolution monitoring lines between Cape Town and Antarctica7. Sustained observations give oceanographers their only chance to record accurately the physical (temperature, salinity), chemical (carbon dioxide, dissolved oxygen, CFCs), and
Clues from the past While oceanographers determine details of today’s ocean climate south of Africa, palaeo-oceanographers are studying deep seafloor sediments for information about the ocean currents of 20 million years ago, the magnitude of past changes, and, in that context, the significance of changes in today’s ocean and climate systems. Researchers take cylindrical samples of sediment (obtained by the use of a hollow drill), which contain accumulated calcareous shell material, and slice them up into segments that represent different time intervals in history. Inhabiting a wide variety of ecological niches, the microscopic animal species that secreted the shells include planktonic species, which have
4. The thermohaline circulation (THC), literally meaning the circulation of heat and salt, is a term for the global density-driven circulation of the oceans. 5. An ocean basin is the part of the seafloor that is deeper than 2 000 m below the surface. 6. Salinity is a measure of the quantity of dissolved solids (or salts) in sea water. 7. Oceanographers use various data- and sample-gathering tools. A CTD (Conductivity, Temperature, and Depth) is the chief instrument for charting the distribution and variation of temperature, salinity, and density in sea water, which helps towards an understanding of how the oceans affect marine life. Niskin bottles, set up around the CTD, take sea-water samples from different depths below the surface. The water collected goes back to the laboratory, where its chemical characteristics (such as oxygen and carbon dioxide content) are measured. (For further details, see Quest, vol. 4, no. 1, p. 8.)
biological (chlorophyll, zooplankton) characteristics of the water column from the surface to the sea floor.
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Your Q UEST ions answered Q Why does oceanography matter? ▲
distinct preferred depth-habitats within the top 300 m of the ocean, and benthic species that live on or within marine sediments. Such shell evidence helps researchers to reconstruct the physical characteristics of the oceans in the past (that is, to discover whether the region was dominated by a warm-water or a cold-water current)8, and South African palaeo-oceanographers have been working on the chronology of what they believe are climate-related circulation changes within and among major ocean basins south of Africa. The evidence so far suggests that the Agulhas Current may have existed for at least 20 million years; that the position of both the Agulhas Current Retroflection area and the Subtropical Convergence Zone could have fluctuated in concert with global climate for the last couple of hundred thousand years; and that, about 20 000 years ago, during the last glacial period when Earth was much colder than now, the flow of the Agulhas Current could have been reduced, with less water leaking from the Indian Ocean into the Atlantic Ocean. Studying the record of sediment drift through seismic reflection is another way of exploring the evolution of ocean currents, as well as the role of the Agulhas Current in its earlier existence in transporting heat and salt water between ocean basins. Deep ocean currents drive and deposit sediment along the seafloor from one basin to another. Using seismic images that can
probe tens of metres into the seafloor sediment, scientists can examine the way in which the seabed formed over hundreds of years, and data from sedimentary structures in the path of today’s Agulhas Current give an ‘imprint’ of the evolution of its flow9. Such analyses give clues as to how the complex circulation at the oceanic ‘crossroad’ around southern Africa developed over time. The past history of the ocean area south of Africa, as well as more detailed understanding of present-day developments, give modellers valuable material for improving their predictions of changes that might take place in future10. ■ Dr Ansorge, of the Oceanography Department at the University of Cape Town, is examining the circulation and processes in the Southern Ocean and their effects on the productivity of Subantarctic Islands. Dr de Villiers, at the University of Fort Hare, researches the role of the oceans in regulating Earth’s over the last 100 million years. Xin Li, a geophysicist at the Alfred Wegener Institute in Germany, works on sediment transport simulation and ocean modelling. Research conducted by Sebastiaan Swart in the Oceanography Department at the University of Cape Town has contributed to the work reported in this article. For more details, consult J.R.E. Lutjeharms, The Agulhas Current (Springer-Verlag, 2006), and G. Uenzelmann-Neben et al., “Cenozoic oceanic circulation within the South African gateway: indications from seismic stratigraphy”, South African Journal of Geology, vol. 110 (2007), pp.275–294.
8. When planktonic organisms at the top of the water column die, their remains trickle down to the seafloor, providing an indicator of the nature of ocean currents at that particular time. If the ocean was subtropical, then warm-water species dominate the relevant sediment layers; if the ocean was subantarctic, there are more cold-water species. In a changing climate, the differing types of shell material found in the layers give an idea of changes in the nature of the ocean currents at different periods. 9. The characteristics of the sediment structure are sensitive recorders of ocean circulation and climate because the interplay of the currents is widely believed to control the erosion, transport, and deposition of sediment. Within the South African gateway, seismic reflection and refraction data reveal that, during the Early Eocene to Early Oligocene period (50–30 million years ago), there was a strong current at the level of the seafloor, indicating the intrusion of cold Antarctic water masses moving northwards; its presence suggests that Antarctica at that time was covered by far more ice than it is today (see also page 14, footnote 2). 10. Information from the past does not factor in such unprecedented modern-day events and forces as, for example, anthropogenic influences. Scientists around the world are trying to find ways to consider and include these, too, in their predictive models.
Oceanography is the interdisciplinary study of the deep sea and shallow coastal oceans, in which biology, chemistry, geology, physics, and ocean history all play a part. The oceans contain most of the Earth’s water, carbon, and surface heat, and much of its biomass. Together with the atmosphere, continents, and ice-cover, oceans form part of a single larger dynamic planetary system, driven by energy that comes mostly from the Sun, but also from tides raised by the Moon and planets, and heat from the Earth’s interior. Human activity is increasingly affecting the planet’s oceans – indicated thus far by occasional outward signs such as severe tropical cyclones, changes in sea-ice distribution from year to year, more instances of shellfish poisoning, and prolonged red tides. The importance of the oceans to the world’s physical climate, food supplies, and biological stability is becoming ever clearer. It is oceanography’s role in understanding the long-term habitability of Earth that makes it so important.
What makes oceans salty? About 70% of the earth’s surface is covered with water, of which only 3% is not salty. Two-thirds of this small fraction of non-saline ‘fresh’ water is frozen as glaciers and icecaps; the other one-third is found in clouds, precipitation, rivers, ponds, lakes, and underground. The rest, found in the oceans, has an average salinity of 3.5% (35 parts per thousand): in other words, a litre of sea water holds an average of 35 g of dissolved salts. Most of the sea’s salt is sodium chloride (common table salt), but sea-water is a complex solution, containing a variety of smaller amounts of other chemical elements such as potassium, magnesium, sulphur, and calcium. The oceans get their salts in several ways. As rocks on land are weathered, rivers carry their salts and other minerals to the ocean. Salinity also comes from the eruptions of undersea volcanoes and emissions of mineral-rich, super-hot water from deep-sea hot springs called hydrothermal vents. Dissolved mineral ions (electrically charged atoms or groups of atoms) escape from the Earth’s crust through volcanic vents on the seafloor. Salinity also increases by evaporation or by the freezing of sea ice. On the whole, however, the oceans’ salinity remains steady. Although rivers, sea-ice formation, and oceanfloor volcanic and thermal activity add large quantities of dissolved mineral salts to the oceans, many of them (calcium, for instance) are used up in forming the outer shell of various plankton; in addition, salt concentration is reduced when rain falls or ice melts. Salinity is not uniform throughout the world. Polar regions have lower salinity – as a result of sea-ice melting or high rainfall – than do subtropical regions, with their greater temperatures and enhanced evaporation levels. Salinity values at the Red Sea exceed 40 parts per thousand, for instance, compared to those of the Antarctic, which measure less than 33. – Isabelle Ansorge
Serving Africa's needs in understanding ﬁshes and aquatic environments Situated in Grahamstown in the Eastern Cape, SAIAB is an internationally recognized centre for the study of aquatic biodiversity, serving the nation through the generation, dissemination and application of knowledge to understanding and solving problems on the conservation and wise use of African ﬁshes and aquatic biodiversity. Research in the institute is directed at marine and freshwater ﬁsh taxonomy, systematics, genetics, biology, ecology, ethology, conservation, management and environmental issues. SAIAB houses world-famous collections of marine ﬁshes from the Atlantic, Indo-Paciﬁc and Antarctic Oceans, as well as freshwater ﬁshes from Africa and adjacent islands. Its collections are national assets that are held in perpetuity for the beneﬁt of science and future generations. The collections include biological specimens, genetic samples, photographic images, original scientiﬁc illustration artwork, spatial data and publications. It is an information hub for African ﬁsh, ﬁsheries and aquaculture.
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Contact us: Private Bag 1015, Grahamstown, 6140, Tel +27 (0)46 6035800, Fax +27 (0)46 6222403, email firstname.lastname@example.org, web http://www.saiab.ru.ac.za © SAIAB 2007. Illustrations by Elaine Heemstra and Dave Voorveldt. Layout by Magriet Cruywagen
Right: Kazembe–Luapula wetland in Congo-Zambia, associated with lechwe antelopes and tigerfish.
Woody Cotterill and Sarah Goodier describe the way in which biological data are helping to put a time to geological events on the African Plateau.
DNA clocks for dating landforms T
habitats and ecosystems changed. In other words, the very same processes that altered the landscape were also formative events for the origins and history of certain key living species. This shared history is now being explored by biologists and geologists, as they collaborate to compile a hitherto unavailable, broad-ranging, evolutionary history built on the dynamic links between biota and landforms. This history, in turn, can help to date the Kalahari epeirogeny, and specific events that elevated the African plateau in the first place. In reconstructing the narrative of the ways in which Earth and life evolved together in this context, our research has focused on the plateau’s drainage systems and principal wetlands. Unusual drainage The drainage systems of the Kalahari Plateau are unusual. Most rivers on other continents flow into oceans, whereas many of High Africa’s rivers flowed inland to sustain lakes. Only relatively recently have these rivers changed direction, linking up with oceans instead. In contrast to the gentle gradients of rivers entering lakes across High Africa’s plateaus, coastal rivers are steep, aggressively eroding plateau margins and cutting into the valleys. Such incisions diverted gentler rivers formerly contained on plateaus, and captured them in ‘river piracy’ events that greatly expanded the catchment areas of coastal rivers. These changes explain the contrast between the steep profiles of rivers flowing across escarpments of
he Kalahari Plateau is a vast, elevated area (>1000 m above sea level) that distinguishes the topography of southern and central Africa. It extends from the Cape Fold Belt (in South Africa’s Western and Eastern Cape provinces) northwards to the Congo basin. But its origin, and that of the mountain ranges skirting it, is a mystery that geologists have for years been trying to solve. Now, with help from the biological sciences, they are at last starting to succeed. The landforms of what is called ‘High Africa’ include a desert, a basin, and plateau, formed during at least 200 million years of persistent uplift, tilting, and erosion of the subcontinent in a period of time named the Kalahari epeirogeny1. This elevated area’s drainage network came about through changes in its rivers, as well as in its many inland basins, where eroded sediments accumulated in response to the epeirogeny. Calibrating the timing of these changes can help to unravel the origin of these highlands. But traditional geological tools for dating these events are too limited and imprecise for the purpose. Molecular dating of key signatures preserved in the genetic variation of living species, however, can reveal details of when geological events structured the landscapes of the Kalahari Plateau, and how and when drainage systems evolved across High Africa. This is because geological dynamics associated with the uplift of the area not only shaped its landforms, but also the region’s biology and biodiversity as
1. The general term ‘epeirogeny’ (from the Greek e¯peiros, meaning ‘continent’ or ‘mainland’, and gen- meaning ‘be produced or created’) is defined as the uplift of a continent by vertical, broad, relatively slow displacements of the Earth’s crust.
Two maps featuring the Kalahari Plateau. Above middle: Map of the modern basins that drain the Plateau and its margins. Beneath, a map of the former wetland archipelago from which the rivers of today evolved. It comprised shallow basins, each with its associated catchment. Evidence for timing the changes in the landscape and drainage system caused by uplift of the Earth’s crust on the Kalahari Plateau is difficult to obtain using standard geological methods. Insights come from studying species whose evolution followed the habitat changes as river networks developed from this archipelago.
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Top left: View across the Upper Kafue River, Zambia. Below: ‘Snapshot’ of genetic variation revealed in the mutations of the aligned sequences of a DNA marker in lechwe antelopes (only a small part of a sample of 210 individuals is shown here). The patterns in which these mutations have become shared and confined within populations allows phylogeographers3 to calculate when two or more species evolved from a common past. ▲
Above: Map showing modern distributions of lechwe antelopes (Kobus leche) across the wetland archipelago, mirroring formative events that changed drainage systems. The ancestral population occupied floodplains and river basins in the catchment of the Palaeo-Chambeshi drainage system (dotted blue lines), which flowed southwest into northeast Botswana. Its tributaries included wetlands in southeast Congo and northeast Zambia. The timing of speciation among these antelopes in the Middle Pleistocene (~300 thousand years ago) followed the break-up of the Palaeo-Chambeshi river, which then isolated distinct basins (Upemba, Bangweulu, and Kafue basins) from the Upper Zambezi and Cubango-Cuando drainage systems. Beneath: Two territorial male red lechwes sparring on the margin of a floodplain, Moremi, Okavango Delta. Photograph: Jens Kipping
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the Kalahari Plateau, and the gentler highland segments of the Congo, the Orange, and the Zambezi rivers. These three rivers share similar histories: their upland tributaries originally terminated inland, each in its vast basin and wetlands, until piracy later diverted them to the coast. This history of drainage evolution also explains why many rivers in the central Kalahari desert (and also desiccated pans) of today are fossilized vestiges of much larger wetlands, including the palaeo-lakes of Owambo (Etosha, in Namibia) and Makgadikgadi, in Botswana (see maps on p. 19). The key pieces in the puzzle of Kalahari landscape dynamics come from particular aquatic animal species whose evolution has tracked their shifting habitats. With uplift, rivers changed course, affecting such species – isolating some in discrete rivers, and facilitating dispersal amongst others. The trick is to find ways to date these events accurately. Dating the Kalahari geology Traditionally, geologists rely on radiometric dating to decipher the uplift and erosion history of elevated regions. But this method does not provide the high resolution needed to track relatively fast and recent landscaping processes across the Kalahari Plateau. Studies of biodiversity across this area provide the critical missing evidence to time geological events, however, using DNA ‘molecular clocks’2 to indicate when selected species evolved in concert with landscape changes. The first step in this kind of investigation is to quantify the genetic variation of these species. Researchers in a molecular genetics laboratory sequence parts of representative genomes, targeting a stretch of DNA common to all the organisms sampled to serve as a marker. Once they obtain sufficient data from at least 30 individuals, they compare variation in the marker among these living representatives. Statistical analyses quantify the extent to which these DNA sequences vary within a population, compared to variation across two or more populations of the same species. The variation across populations tells the scientist about isolated aspects of each population’s history (literally its segregation from others – geographically
and thereby genetically). What is shared among the populations testifies to gene flow between them. These ‘snapshots’ of genetic variation are windows through which we can read the environmental changes that buffeted these species at different times. Most important for geologists are the signals offered by these genetic signatures that show significant habitat changes in a landscape – in the case of our investigations, changes in the drainage systems in which aquatic organisms have lived in their evolutionary past. With the DNA evidence, we are now able to date these events more accurately. Lechwe antelopes and crocodiles Our complementary studies of lechwe antelope and crocodile populations in the Kalahari Plateau are clear examples of ways in which biology and geology can inform one another. The genomes of lechwe antelopes have preserved records of radical habitat change over the past one million years. Unlike any other antelope, modern lechwes have a curiously patchy distribution across the Kalahari Plateau, which begs the question – how did four distinct populations come to be isolated in their respective wetland habitats? The first part of the answer follows from the fact that lechwes are specialized wetland inhabitants. Their grazing is confined to rich floodplains, and they escape predators by running into water for refuge. On the premise that the ancestor population from which all modern lechwes are descended was widely distributed in the past, their dependency on wetlands provides the second part of the answer. Assuming that the ancestral population split up across today’s isolated patches of habitat, the modern ranges indicate historical changes to the wetlands, causing distinct lechwe species to become isolated and their DNA to evolve separately in Bangweulu, Kafue, Upemba, and the network of vast floodplains that link the Cubango and Upper Zambezi rivers. Each of these basins and shallow valleys is now isolated, but in the past they were linked by rivers that once formed an entire wetland archipelago. The questions to which geologists seek answers are – what were the physical
2. ‘Molecular clock’ refers to the concept that, during evolution, the changes (mutations) in nucleotides of nucleic acids (DNA or RNA) accumulate at a linear rate through time. So, by comparing the DNA of species that diverged a known length of time ago (as determined, for instance, from fossil evidence), one can calculate the average mutation rate, thereby calibrating the ‘molecular clock’. Applications of molecular clock evidence need to be handled with care: they can be controversial if the rate of evolution of DNA is not constant, and/or if this rate is not reliably known.
causes that culminated in such isolation of biota and landform? when did these changes occur? A high proportion of unique genetic mutations in living lechwes accumulated in each population after rivers divided, for example, splitting populations into discrete basins. Our investigations have revealed that most of these mutations occurred after the populations became isolated, and, furthermore, that the segregation events occurred ~300 000 years ago. In researching Nile crocodiles (Crocodylus niloticus), we found that their DNA also reflects evidence of landscape evolution in southcentral Africa. Their more numerous and widespread forebears inhabited the palaeo-lakes and rivers that subsequently dried out to become today’s Makgadikgadi Basin in northeastern Botswana. The crocodiles now living as essentially independent populations in the Cuanda, Cubango, and Upper Zambezi rivers are descended from this ancient population. Crocodile mitochondrial DNA mutates some five times more slowly than that of mammals such as lechwes. On this assumption, the presence of ancient mutations in the DNA of living crocodiles reveals that their predecessors expanded in number and distribution approximately 450 000 years ago (although the uncertainty in reading the genetic material limits our deduction of this expansion to the period between 1.7 million and 120 000 years ago). The timing of the expansion coincides with the existence of a vast palaeo-lake (approximately 80 000 km2 in area, which persisted from about 2 million to 0.5 million years ago). It flooded the Makgadikgadi Basin, sustained by the combined inflows of several rivers including the Upper Zambezi and Kafue. These rivers affected aquatic biodiversity markedly when they were linked by the palaeo-lake, allowing widespread gene flow among species such as these ancient crocodiles. These dates provide geologists with an independent estimate of the tenure of Palaeo-lake Makgadikgadi. They are especially welcome because sediments from the ancient lakes have resisted efforts to employ orthodox geochemical dating techniques. The rivers in the region assumed their present
configuration about 200 000 years ago, by which time independent crocodile populations had become established. These insights into the evolution of crocodiles and lechwes across High Africa shows for the first time approximately when the rivers of the Kalahari Plateau changed their courses in the past, after the period of large lakes in the wetland archipelago. New studies of fishes alongside crocodiles and lechwes provide further indicators of palaeoenvironmental conditions across the Kalahari Plateau. We are just beginning to learn how modern distributions of tigerfish (such as Hydrocynus vittatus), for example, show with greater detail and accuracy how and when river systems changed course. How DNA helps geologists These are just selected examples of how changing landforms, at evolutionary time scales, sifted and moulded a population’s genetic variation. They show how important an archive is offered to geologists by the genomes of species. Molecular clocks that give the rate at which mutations have accumulated in DNA provide a key as to when these changes occurred in a species’ history. They help to calibrate the historical chronicle and to resolve biotic and geological evolution with a level of detail that is otherwise not available. The biological maps constructed by phylogeographers3 reveal patterns of genetic variation in the context of species’ modern and ancestral distributions, and have provided us with a geological history of changes in rivers and lakes. The emerging picture of geologically recent landscape evolution across the Kalahari Plateau, therefore, is centering more and more on detailed biological studies of the evolution of aquatic species across this wetland archipelago. ■ Dr Cotterill and Sarah Goodier are at the Africa Earth Observatory Network and the Departments of Geological Sciences and of Molecular and Cell Biology at the University of Cape Town. Other researchers involved in the work described here include Dr Jacqueline Bishop (Department of Conservation Ecology & Entomology, University of Stellenbosch) and Dr Colleen O’Ryan (Department of Molecular and Cell Biology, University of Cape Town).
3. The relatively new field of phylogeography combines molecular and statistical tools to indicate where and when formative events altered the genetic variation of a studied population – for example, when the division of a continuous river might also have divided an ancestral population of fish into two species.
Top: View of Marromeu wetland in Mozambique. Middle: Nile crocodile (Crocodylus niloticus) hatchlings. Photograph: K. Maciejewski
Above: Tigerfish, Lake Bangweulu in Zambia. For more details consult: F.P.D. Cotterill, “The Upemba lechwe Kobus anselli: an antelope new to science emphasizes the conservation importance of Katanga, Democratic Republic of Congo”, Journal of Zoology, London, vol. 265 (2005), pp.113–132; M.J. de Wit, “The Kalahari epeirogeny and climate change: differentiating cause and effect from core to space”, South African Journal of Geology, vol. 110 (2007), pp.367–392; A.E. Moore, F.P.D. Cotterill, et al., “The Zambezi River”, in A. Gupta (ed.), Major Rivers of the World: Geomorphology and Management (New York, John Wiley, 2007), pp.311–332; S. Wells, “Deep Ancestry: Inside the Genographic Project”, National Geographic Society, Washington, DC (see https:// www3.nationalgeographic.com/genographic/?fs=www3. nationalgeographic.com&fs=www5.nationalgeographic.com
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Climate has varied significantly over periods of thousands to millions of years, and will change over the next century as it responds to human activities. John S. Compton, Brian Mantlana, Roger Smith, and George Philander explain what South Africa’s rich rock record tells us about past changes, and how it helps in planning for the future.
past changes & future uncertainties
Top right: The Southern Ocean between South Africa and Antarctica, a region of high biological productivity, as shown here in the chlorophyll abundance shaded in pale green. Image: NASA ocean colour SeaWiFs website
Above: Earth’s mostly warm and humid climate has been punctuated with cold, glacial ice ages (see graph). The rocks in this image are glacial deposits – tillite – exposed in South Africa’s Karoo, from the 300-million-year-old Late Palaeozoic ice age. Images courtesy of the authors, unless otherwise indicated.
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vidence is mounting that climate change is under way. The summer season at high latitudes is longer (for example, rivers and lakes are frozen for an average of 18 days less in winter than 150 years ago); sea level is rising by some 3 mm each year as oceans warm and mountain glaciers melt; September Arctic sea-ice cover is 50% thinner than it was in the 1960s; and surface ocean waters are becoming more acidic. These changes are part of global warming, linked to rapid increases in the carbon dioxide (CO2) content of the atmosphere from burning fossil fuels and land-use changes, particularly deforestation. Last time CO2 levels were similarly high was over 20 million years ago (Mya). The link with climate is because CO2, water vapour, and methane make up the greenhouse gases that capture and return some of the energy (infrared radiation) emitted by Earth into space. The Intergovernmental Panel on Climate Change predicts a rise in the mean annual global temperature of 1.4–5.8 °C by 2100 in response to the rapid increase in atmospheric CO2. But our ability to predict just how warm it will get, and what the impacts of such warming might be, is limited by climate’s sheer complexity, as well as by uncertainty about the net influence that all Earth’s interacting components will have on it. One
approach is to look to the past for clues about the future. Understanding how the planet responded to earlier climate changes gives us some handle on how it will react to the dramatic recent rise in CO2. Hot and cold Earth’s past climate went from hot to cold and back many times, but, since the planet’s initial hot beginnings, temperatures have never been extreme enough to make it uninhabitable. Throughout deep Earth time, many organisms have gone extinct because of rapid climate change, but new species evolved from the survivors and replaced them. The complex linkages and exchanges among the atmosphere, ocean, rocks, and life tend to counteract gradual disturbances, as well as catastrophic ones such as meteorite impacts and volcanic eruptions. Just as your body perspires when it’s hot and shivers when it’s cold, Earth responds to changes in climate to dampen or minimize their extent and effect. For most of its 4.6-billion-year history, the planet has been a warm and humid, generally pleasant place for life, with relatively few cold periods (ice ages) when large areas were covered in ice sheets up to 4 km thick. Ice ages Earth is in an ice age now that was initiated 30–40 Mya. The volume of ice
Left: Fossil (left) and (right) reconstruction of an extinct mammal-like reptile of the Karoo, a cynodont therapsid of the genus Thrinaxodon. Mass extinction of life has occurred in the past and is often related to changes in climate. Below: Alexander du Toit Mountain, with the Antarctic ice sheet stretching out to the distant horizon. Image: Chris Harris
varies hugely during an ice age, and the current time is one of relatively low ice volume called an interglacial period, with large ice sheets restricted to Antarctica and Greenland. But just 20 000 years ago, the ice volume was much greater than today and ice sheets extended over northern North America and Eurasia. Such maxima in ice volume during an ice age are referred to as glacial periods. The cyclic expansion (glacial) and contraction (interglacial) of ice sheets during an ice age carve out the landscape, cutting grooves into the bedrock and grinding up huge amounts of rock ranging in size from fine rock ‘flour’ to large boulders. When the ice melts, the ground-up rock gets dumped to form poorly sorted sediment called ‘till’, which can, over time, harden into a rock called tillite. Grooved, polished bedrock surfaces and tillite, spectacularly in evidence in South Africa, are what geologists use to identify ancient ice ages.
South African tillites Following these dramatic ‘snowball’ events was a brief, less extensive ice age in the Late Ordovician (450–444 Mya)1. During the next major ice age, in the late Palaeozoic (320–270 Mya), ice extended over much of the supercontinent Gondwana (at that time positioned over the South Pole), and tillite was deposited over much of southern Africa. Referred to as the Dwyka Group of rocks, it corresponds with tillite in South America, India, and Antarctica – a fact that South African geologist Alexander du Toit used in the 1930s to argue for continental drift, long before the theory of plate tectonics was widely accepted in the 1970s. Hothouse world Just how hot it got between ice ages is hard to say, but intervening periods – such as the Mesozoic Era (251–65 Mya) when dinosaurs roamed the Earth – were times of warm, humid climate (like Durban on a summer’s day). Continents were flooded by large shallow interior seaways fringed by densely vegetated swamps, and forests grew at the South Pole. Mesozoic oceans were warm and salty, so they were far more sluggish than today. One of the best-documented warm periods – the Palaeocene/Eocene Thermal Maximum (PETM) – occurred 55 Mya, when global temperatures increased by >5 °C in under 10 000 years. What caused the massive release of greenhouse gases required to produce such rapid warming remains a puzzle,
The Snowball Earth hypothesis proposes that nearly the entire surface of the planet was covered by ice from pole to equator. Evidence comes from deposits in Namibia, where glacial tillite is overlain by limestone. Images: Nature and Harvard University website
Snowball Earth The most extreme climate yet discovered from Earth’s past was in the Late Precambrian (750–600 Mya), when ice may, at different times, have covered the entire globe. Evidence for this Snowball Earth hypothesis comes from rocks exposed in Namibia, where glacial tillite is overlain by limestone. This is unusual because tillite is associated with cold, glaciated environments, and limestone is associated with warm tropical oceans near the equator, so geologists do not expect to find such different environments juxtaposed in the rock record. The explanation is that, during parts of the Late Precambrian, ice sheets extended from the poles to the equator, and much of the ocean was covered in sea ice, transforming Earth into a snowball. With ice over most of the planet, the normal removal of CO2 by the oceans and by weathering of rocks exposed at the surface was effectively shut down. The CO2 emitted
by volcanic eruptions above the ice surface could, therefore, build up in the atmosphere, reaching levels high enough to warm the air until it melted the ice and allowed limestone to form in the ocean. This is why glacial tillites are seen directly overlain by warmwater limestone in Namibia. During these extreme conditions, life is assumed to have survived in small, ice-free areas as well as in the ocean below the sea ice.
A large ice sheet covered Gondwana during the late Palaeozoic ice age 300 Mya (top left), which left behind poorly sorted deposits of glacial till shown in the polished sample, 10 cm across (top right), from South Africa’s Dwyka Group. South African postage stamp (right) celebrating geologist A.L. du Toit, who argued strongly for continental drift (plate tectonics).
1. Some of the best evidence for the Late Ordovician ice age is found in the Western Cape in the Pakhuis Formation tillite exposed along Pakhuis Pass near Clanwilliam, in Michell’s Pass near Ceres, and atop Cape Town’s Table Mountain.
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Top: The North Pole from above showing the extent of large ice sheets and sea ice during the Last Glacial Maximum, 20 000 years ago. Middle: Changes in the coastline around the Cape Peninsula in response to sea-level changes. A 25-m higher sea level than today is shown on the left, and a 125-m lower sea level than today is shown on the right. (See also p. 9.) Above: The record of temperature (black curve, below) and CO2 content (blue curve, top) over the past 420 000 years, from the Vostok ice core, Antarctica. Cold, glacial periods dominate, with relatively brief intervening warm, interglacial periods (red arrows). Present-day CO2 content is 380 parts per million by volume. From L.R. Kump, “Reducing uncertainty about carbon dioxide as a climate driver”, Nature 419 (2002), 188–190, based on J.R. Petit et al., “Climate and atmospheric history of the past 420 000 years from the Vostok ice core, Antarctica”, Nature 399 (1999), 429–436. Images courtesy of the authors, unless otherwise indicated.
but this is actively being researched as it could provide clues about what lies ahead for our new, high-CO2 planet. Icehouse world Since the peak warmth of the hothouse world, Earth has cooled to our present ice age which began 35–40 Mya with sporadic glaciation of Antarctica. By 14 Mya, Antarctica had permanent and large ice sheets and, by 3 Mya, ice sheets began forming in the northern hemisphere. Over the past million years, climate and the amount of ice have fluctuated dramatically on a 100 000-year cycle between glacial periods (when ice sheets expanded over the northern hemisphere) and interglacial periods, such as today’s, with ice sheets limited to Antarctica and Greenland. During the height of the last glacial period 20 000 years ago, the global sea level was 125 m lower than it is now, because of the vast amount of water stored as ice. There were then no ice sheets in South Africa, but lower sea level exposed large areas of the continental shelf. If all the ice on Antarctica and Greenland were to melt, present-day sea level would rise 65 m. Bubbles on ice Amazing insights about our current ice age have come from drilling the thick ice caps and studying variations in the composition of ice cores. Ice traps small bubbles of air. When analysed, these reveal surprisingly large variations in CO2 over the last 400 000 years2 that closely follow the record of temperature
obtained from the chemical composition of the ice (specifically, its oxygen and hydrogen isotope composition). Ice-core records from Antarctica and Greenland show that climate change has followed a saw-tooth pattern on a ~100 000 year cycle. Earth cools gradually to a glacial maximum when ice cover is greatest and CO2 levels are lowest. Such glacial maxima are then terminated by rapid warming and increased CO2 levels. The associated upper and lower bounds of CO2 have been strikingly similar over the last 400 000 years. The timing of the climate changes associated with these CO2 cycles relate to variations in the amount of sunlight received and its distribution over Earth’s surface. For example, the tilt of Earth’s axis of rotation (obliquity) varies from 22.2° to 24.5° over a cycle of 41 000 years, thereby altering the amount of the Sun’s energy received at the poles. On their own, these variations in the Sun’s energy are not great enough to drive such dramatic climate changes; they need amplification by other factors. Two important amplifiers are the albedo – that is, the amount of sunlight reflected back into space especially from clouds, snow, and ice – and the greenhouse gas content of the atmosphere, which is largely controlled by the dynamics of the ocean (see pp. 16–18). Climate change amplifiers To see how these amplifiers work, here’s what happens during the dramatic termination of a glacial maximum when the large ice sheets in the northern hemisphere melt rapidly. A greater tilt of Earth’s axis of rotation increases the sunlight received near the poles: highly reflective sea ice surrounding Antarctica melts back and is replaced by dark blue ocean, which absorbs more of the Sun’s energy and accelerates warming. This sea-ice retreat and warming of water lessen the ocean’s ability to store CO2. Thanks to a combination of, first, changes in the rate at which surface waters mix with deeper waters and, second, less vigorous growth of marine plants, the ocean releases CO2 and, after about 800–1 000 years of warming, atmospheric CO2 begins to rise. This CO2 rise leads to warming on a global scale, which accelerates
2. The age of the ice is determined by counting the annual layers in the recovered ice cores from the top down, much like counting tree rings. With extreme care being taken to avoid contamination, the air trapped in the ice is liberated by crushing thin slices of the ice core under a vacuum. The composition of the gases making up the air samples is then analysed.
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the melt-back of large ice sheets in the northern hemisphere. The cycle continues as retreating ice sheets expose darker, more absorbent icefree land, which captures more of the Sun’s radiation: the result is rapid, runaway melting of the ice sheets. The melting is so rapid that just some 10 000 years suffice to turn a cold, icy glacial climate into a warm, stable interglacial one such as ours today. The warmth normally lasts only about 5 000 years, however, before Earth’s tilt starts to decrease, offering less sunlight at high latitudes and reducing the summer melt-back of snow enough to allow the ice sheets to expand once again. The sheets grow until eventually a glacial maximum is reached and the cycle repeats. The warming that ends a glacial maximum is initiated not by CO2 but by increased sunlight at the poles. It is only about 800–1 000 years after the initial warming that CO2 levels start to rise. But the increase in CO2 and other greenhouse gases, although delayed, is absolutely critical – in combination with changes in albedo3 – to produce the dramatic climate change from a glacial maximum to our warm interglacial world3. Why worry? The importance of CO2 in influencing climate change brings serious concern about the atmosphere’s rapidly rising CO2 content over the past century. It has been argued that this rise in CO2 comes in time to prevent the next cycle into an icy world, and even that agriculture over the past 8 000 years has already affected climate and delayed the onset of the next glacial. The growing human population and its industrial activities, however, have so accelerated as to make climate change over the next 100 years our immediate and primary concern, rather than something representing a natural return to glacial conditions perhaps tens of thousands of years into the future. Two unusual factors make the current situation different. ■ People are raising CO2 emissions and levels during an already relatively warm (interglacial) climate, so the rise in CO2 will now lead, rather than lag,
Sign up for the future! South Africa, and the world as a whole, needs more scientists to study Earth and to prepare its people for rapid change. We need, for example, to know more about the Southern Ocean between South Africa and Antarctica because of its key role in controlling past climate and emissions of CO2, and the likelihood that it will continue to be similarly important in future. If you’re interested in science and want to advance our understanding of the workings of planet Earth, contact us and we will sign you up! For more, visit http://web.uct.ac.za/depts/geolsci/; www.sanbi.org/; www.iziko.org.za/sam/; and www.AfricaClimateScience.org (www.ma-re.uct.ac.za/).
the rise in temperature4. ■ The rate of increase is much faster than in the past, such that CO2 levels in the next 50 years are likely to be double the maximum levels of past interglacial periods. These new, unprecedented factors mean that natural variations over the past 400 000 years may not be the most appropriate indicators as to the future. It is human beings, stated oceanographer Roger Revelle in 1957, who, irreversibly, “are now carrying out a large-scale geophysical experiment of a kind that could not have happened in the past”. Future for South Africa All indications are that our “large-scale geophysical experiment” is under way and the future has arrived, with many documented changes already linked to rising levels of atmospheric CO2. Southern Africa is particularly vulnerable to changes in rainfall patterns because most of it is already hyperarid to semi-arid, receiving only 5–500 mm of rainfall a year. Regional models predict that plant ecosystems, such as the Succulent Karoo and Cape Fynbos, will suffer further species extinctions in response to climate change, compounding the effect of habitat destruction by human developments. Furthermore, South Africa’s food production is closely tied to the amount and timing of rainfall and availability of water for irrigation … among the lessons of the past is the role of erratic climate patterns in the fall of civilizations such as the Maya of Central America. Uncertainties The future could bring surprise changes, unanticipated by climate models5. One unexpected discovery from ice-core records is the instability
3. Albedo refers to the proportion of light or radiation reflected by a surface. Correlation of CO2 and temperature does not necessarily imply cause and effect. The greenhouse gases are not simply following temperature, however, passively tracking the climate cycles as some anti-global- warming advocates argue; rather, the greenhouse gases are powerful amplifiers, providing strong positive feedback that helps to drive climate change. 4. As explained earlier, the ice-core evidence indicates that solar radiation drives the initial natural change in climate (temperature) from cold to warm, and that the change is subsequently amplified by the greenhouse effects of rising CO2 levels. In the present, warmer interglacial conditions, however, the ever rising levels of greenhouse gases keep boosting the temperature, so there is no lag in the process. 5. Climate models are of necessity limited and simplified versions of the real world and therefore might not capture every possible outcome.
of climate, as revealed by evidence of sudden, rapid warming events that spanned only a few decades during the glacial period. Such abrupt fluctuations are believed to result from complex interactions involving the ocean, atmosphere, and ice sheets, but exactly how such changes are produced remains unknown. Warming could cross a threshold, leading the planet through unavoidable knock-on effects into a new climate mode. Some scientists postulate that future conditions could most closely resemble the warm ones of the early Pliocene (3 Mya) when a permanent El Niño existed. But we don’t yet understand well enough what controls Earth’s climate to predict just where our “large-scale geophysical experiment” is leading. ■ Associate Professor Compton, in the Department of Geological Sciences at the University of Cape Town, studies Earth’s past climate changes from readings of the sediment and rock record recovered from offshore the western margin of South Africa. Brian Mantlana, in the Global Change Research Group at the South African National Biodiversity Institute in Cape Town, studies the exchange of greenhouse gases within the savanna ecosystem. Dr Smith, a palaeontologist at Iziko, the South African Museum in Cape Town, focuses on the rock and fossil records of past extinction events of the Karoo Basin. Professor Philander in the Oceanography Department at the University of Cape Town works in the field of past and present global climate, particularly as it relates to the dynamics of the oceans. He is Director of the African Centre for Climate and Earth Stewardship Science (ACCESS). For more details, read J. Compton, The Rocks and Mountains of Cape Town (Cape Town, Double Storey Books, 2004); T. McCarthy and B. Rubidge, The Story of Earth and Life: A southern African perspective on a 4.6-billion-year journey (Cape Town, Struik, 2005); L.R. Kump et al., The Earth System (New Jersey, Prentice Hall, 1999); J. Diamond, Collapse: How civilisations choose to fail or survive (London, Allen Lane, 2005); W.H. Ruddiman, Plows, Plagues, and Petroleum: How humans took control of climate (Princeton, New Jersey, Princeton University Press, 2005); and G. Walker, Snowball Earth: The Story of the Great Global Catastrophe That Spawned Life as We Know It (Crown Publishers, 2003).
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Lebogang Nhleko and Leslie Strachan describe how scientists are helping to keep South Africa’s groundwater resources sustainable.
managing dwindling reserves
outh Africa, as part of subSaharan Africa, is short of water. Increasingly, desertification and erratic weather have worsened the situation, and drought, flooding, and land degradation from erosion and overgrazing add to the problem. Remote rural areas are worst off, and need immediate attention. Changes in rainfall patterns and evapotranspiration1 mean that surface water alone cannot satisfy the nation’s need for clean water. Insufficient surface water supplies – especially for agriculture – are supplemented by groundwater, but it is not used optimally and sustainably. There’s an urgent need, therefore, to calculate what reserves are available, and to search for sustainable groundwater resources. Increasingly,
traditional ways of finding water for boreholes are being revised, and scientific methods are increasingly being used. Deeper fractured zones and geological traps created by the folding and faulting of rock are often good targets, as are dislocations (for example, joints and lineaments) within the Earth’s sub-surface. Geological features2 are being considered more closely, to establish and analyse the relationship between them and successful discovery of groundwater sources. Deep drilling of boreholes reaching depths of more than 100 m is increasing, in the hope of tapping extensive aquifers (that is, underground groundwater-bearing rock masses)3. To ensure that the quantities of water abstracted (that is, taken out
Deep groundwater in the dry Karoo supports life and farming The Karoo Basin occupies half of South Africa, and much of it receives little rain (that is, an average of only about 450 mm per year). During the Jurassic (from about 200–151 million years ago), there was frequent and large-scale magmatism: molten rock invaded preexisting rock, causing millions of fissures in the Karoo sediments, into which magma intruded to form dykes, sills, and ring-type intrusions*. Now that the volcanoes have The dolerite ring-like intrusions of the Karoo gone, the groundwater occupying most basin near Queenstown (3D Aster image) of these old fractures creates a complex are geological features targeted for deep network of aquifers, some of which are groundwater exploration. found at a depth of 300 m. Geoscientists Image: Courtesy of the Council for Geoscience are seeking even deeper water, and testing it for sustainable use. Often, satellite images help in mapping the ring-like dolerite intrusions that are targeted in deep groundwater exploration**. – Luc Chevallier (Council for Geoscience, Bellville, Cape Town) Top right: A wind pump is ‘borehole-targeting’ fractured rock that is associated with dolerite intrusions. Photograph: L. Chevallier Top: Rural land degradation in the Eastern Cape province.
* An intrusion is a body of igneous rock that has crystallized from molten magma below the surface of the Earth. ** This research is a collaborative effort between the Council for Geoscience, Water Research Commission, and Department of Water Affairs and Forestry.
Photograph: L. Chevallier
Above: A water strike – the result of a successful, scientifically sited, deep borehole. Photograph: W. Nomquphu
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1. Evapotranspiration refers to the processes in which water vapour is released into the atmosphere due to heat and plant metabolism. 2. Geological features being examined in the search for groundwater resources include lithology (that is, the physical characteristics of rocks and rock formations) and structures within rocks (such as faults, fractures, fissures, joints, lineaments, folding, foliation, dykes, and sills). The processes being considered include weathering of rock material as well as soil formation.
Q The S&T Tourist
Water in the iSimangaliso Wetland Park of the natural system for other uses) are sustainable, and that future users will continue to benefit, monitoring programmes are in place for whatever groundwater resources are accessed. These programmes are early detectors of groundwater contamination from pollution or leaching, allowing timely remedies to be applied. Where current resources are unsustainable, monitoring can help in finding better ones. Understanding the groundwater system more fully leads to optimal use of this finite natural resource.
This wilderness reserve was the first place in South Africa to become an official UNESCO World Heritage Site. Sylvi Haldorsen explains the importance of groundwater for its extraordinary biodiversity.
Risks Untapped sources, as well as successful siting of boreholes and subsequent groundwater use, are at risk from reckless human activity. Agriculture, industry, and urban developments can contaminate and degrade groundwater. Lack of sewage facilities and of resources in informal settlements have increased the introduction of ‘grey water’ (that is – used household wastewater that has not been contaminated by toilet discharge) into the system. During water restrictions, city dwellers resort to watering their gardens with grey water, and such practices, amongst others, help to degrade groundwater quality. The services of knowledgeable hydrogeologists and environmentalists are crucial to protect the environment and keep the country’s much-needed groundwater clean. But all their efforts will be in vain if society doesn’t participate fully. Public awareness campaigns to inform and teach people about saving water, and to warn them of the dangers of using grey water, have to some extent changed attitudes. But many people – especially in urban centres – still believe that, just because they pay for it, high-quality water will always be available. Everyone needs, in fact, to take responsibility, to ensure access to sustainable water for the next generation. ■
Sustaining freshwater habitats
Lebogang Nhleko, at the Council for Geoscience, Bellville, Cape Town, works on deep groundwater related to dolerite intrusion and on hydrogeological mapping. Leslie Strachan, the Manager of the Water Geoscience Unit at the Council for Geoscience in Pretoria, looks after groundwater resource assessment, contamination, remediation, and protection research. 3. The impact on the environment of such drilling is a subject for ongoing research, and needs to comply with new environmental laws and protocols established to safeguard the environment.
On 1 November 2007, the Greater St Lucia Wetland Park was renamed the iSimangaliso Wetland Park, to avoid confusion with the Caribbean island country of St Lucia, and to reflect its African identity. Its new name includes the isiZulu word for ‘miracle’, and every visitor marvels at the variety and beauty of its ecosystems and natural habitats and the extraordinary diversity of bird, animal, and marine life. During droughts, evaporation from the water body in the St Lucia Estuary causes high salinities, with values greater than those of seawater*. Groundwater that flows into the estuary from prominent sand aquifers along its eastern shoreline forms habitats with reduced salinity for living organisms that are sensitive to salt. When fresh water is scarce, plants and animals can take refuge in the groundwater discharge zone until salinity in the estuary becomes tolerable again. The flow of groundwater can continue during droughts of at least a decade, and helps to maintain the estuary’s resilience. The drought that has persisted since 2001 resulted in closure of the estuary mouth during mid-2002 until it was breached temporarily during March 2007. Groundwater discharging along the shoreline of the Eastern Shores, however, formed streams that flowed across the exposed lake bed around the lake margins into the restricted ponds that were left of the former large estuary. In other places, continuous seepage zones along the shoreline created wet conditions, and groundwater-dependent plants grew in areas normally covered by more saline estuarine water. In Tewate Bay, north of Lake Bangazi, a large and persistent groundwater discharge pond supported a herd of 300 hippopotamuses.
Exotics lower water levels The ecology of iSimangaliso Wetland Park depends on groundwater. The wetlands within the undulating dune topography of the grasslands surrounding Lake St Lucia shrink or expand in response to fluctuations in the groundwater table. During the recent drought, dryland plants slowly migrated into former wetland areas. Plantations of exotic (non-indigenous) pine trees established in the area during the 1960s had significantly reduced the groundwater level. Now that they have been removed from the Eastern Shores and the area has become grassland, the groundwater level has risen higher than it would have done even with a 10% increase in rainfall or a sea-level rise of 40 cm! To recharge this level even more, one of the management policies being implemented is to retain grassland cover over large parts of the Eastern Shores area, rather than to allow woodland and, ultimately, forest to take over. ■ Professor Haldorsen (Norwegian University of Life Sciences, Aas, Norway) is a geologist specializing in groundwater and global change, and has worked in St Lucia since 1999. She is a vicepresident of the International Union of Geological Sciences. Also involved in the research described here are Dr Ricky Taylor (Ezemvelo KZN Wildlife, St Lucia), Dr Greg Botha (Council for Geoscience, Pietermaritzburg), and Dr Lars Været (Sweco Grøner Consultant Company). For visitor information about the iSimangaliso Wetland Park, go to sites such as www.tourism-kzn.org, www.southafrica.info/ess_info/ sa_glance/fauna_flora/stlucia.htm, and www.sa-venues.com/ game-reserves/kzn_lakestlucia.htm. * Salinity is defined as the total quantity of dissolved solids in water, in parts per thousand. The salinity of ocean-water varies, with an average of 35 parts per thousand. (See also p. 18.)
From top: The early stages of drought. The view looks across False Bay, St Lucia, through Hell’s Gates to the Tewate Bay basin. Photograph: G.A. Botha Discharge of groundwater along the Eastern Shores in 2003. Photograph: R.H. Taylor Tewate Bay (19 December 2005), the home of 300 hippos during the drought of 2002–2006. Photographs: R.H. Taylor During the removal of the pine forest on the Eastern Shores, the groundwater level increased almost immediately. Pine trunk remnants are visible in newly formed duneslack wetlands, which in this case became the home of hippos. Photograph: R.H. Taylor
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How safe is the Earth around your home and place of work? Susan Frost-Killian and fellow South African geoscientists explain some of the forces and events that can turn everyday life upside down, and what can be done to minimize the risks.
s we go about our daily business, the solid Earth seems safe enough. But there’s far more going on beneath the surface than meets the eye. Things can change in a devastating flash through floods, earthquakes, and other disasters that displace or kill whole communities of people. The more we understand the natural forces that control familiar landscapes of water, rocks, and soils, the better we can calculate – and minimize – the risks to people and property. The work of geoscientists makes it possible to plan for, and avoid as far as we can, the dangers that the Earth itself can bring. The term ‘geohazard’ refers to any Earth process that poses a risk to human life, including landslides and volcanoes, floods and freak tides, tsunamis, sinkholes, and earthquakes. The main geohazards that South Africans need to know about relate to ‘home-made’ earthquakes in mining areas (through seismic1 activity), massive natural sinkholes, landslides, sudden flooding, and extensive coastal erosion. As people become more aware of the potential dangers, measures are taken to predict and manage adequately not just these events but their socio-economic fallout as well. – Susan Frost-Killian (Council for Geoscience, Pretoria)
the risks beneath our f ee t Earthquakes – induced and natural
Top right: Severe damage to a tunnel in a deep gold mine caused by a magnitude 3.4 seismic event. Photograph: Courtesy of Dave Ortlepp
Above: Collapse of a block of flats in Welkom in 1976 after a mining-related earthquake of magnitude 5.2. Images courtesy of the Council for Geoscience unless otherwise indicated
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An earthquake is a convulsion of the Earth – a sudden release of energy, normally caused by movement along a fault plane2, or by volcanic activity, which generates potentially destructive seismic waves. ‘Induced’ earthquakes South Africa has the deepest mines in the world, with some going down nearly 4 km underground. Excavations created by miners, and the enormous weight of the overlying rock, cause high stresses, which can trigger sudden ‘slip’2 along weak zones, or even cause intact rock to rip and tear, creating (or ‘inducing’)
potentially devastating mining-related earthquakes. The consequences can be catastrophic for mineworkers, as the sudden ruptures create seismic waves, which travel through the Earth at tremendous speeds3, violently shaking the excavations and sometimes ejecting rock fragments. The rates of seismic activity in South Africa’s gold mining districts are higher than elsewhere in the world (even than California and Japan, which are renowned for earthquakes). A typical deep-level mine records about 1 000 seismic events each day. Most are too small in magnitude to cause any harm. Those that damage underground workings, however – called rockbursts4
1. The prefix ‘seism-’, meaning ‘pertaining to earthquakes’, comes from seismos, the Greek word for ‘earthquake’. 2. A ‘fault plane’ is a discrete, planar surface along which there has been appreciable relative displacement of the rock masses on either side. A ‘slip’ is the term used for such relative displacement, to either side of a fault plane, of points that were originally coincident. 3. The typical standard speed of sound in hard rock is 6 km per second; the actual particle motion is substantially less. 4. A rockburst is a seismic event that causes sudden and violent damage to mine workings. This hazard is encountered in some deep mines (below 1 000 m) and may be accompanied by shocks, rockfalls, and air concussion. Mining-induced seismic events normally occur in highly stressed intact rock, so when an excavation is created, the unbalanced stress is great enough to make it collapse. Ways to reduce the potential for rockbursts include systematic stoping (that is, breaking and removing rock in an ore body), reducing open spaces, and using strong supports.
gold mining districts are considered vulnerable to damage and even collapse, posing safety and financial risks. Relatively inexpensive measures can help. It was suggested, for instance, that experienced earthquake engineers be contracted to inspect buildings and review the content and enforcement of building codes.
Above: Damage caused by the 1969 earthquake in Tulbagh.
– Lindsay Linzer (University of the Witwatersrand) and Ray Durrheim (University of the Witwatersrand and CSIR, Johannesburg) Natural earthquakes These shakings of the Earth result from deep-seated forces within the Earth or from volcanoes. Destructive natural earthquakes are rare in southern Africa, but the Ceres Seismicity Cluster (an area of high seismicity between latitudes 33° and 33.5°S, and longitudes 19° and 19.5°E) is an exception. The most destructive earthquake in South African recorded history was a magnitude 6.3 event (on the Richter scale), which occurred on 29 September 1969 in the Ceres–Tulbagh region of the Western Cape, killing 12 people. Aftershock activity had virtually ceased, when a magnitude 5.7 event on 14 April 1970 caused further damage in the towns of Ceres and Wolseley7. On 23 February 2006, in central Mozambique, southern Africa experienced one of its largest earthquakes. The shaking due to the magnitude 7 earthquake was felt as far away as Johannesburg and Durban, but the epicentre was in a sparsely populated region, so there was little damage. The media reported that four people were killed. – Michelle Grobbelaar (Council for Geoscience, Pretoria) ▲ ▲
– cost the South African mining industry about US$1 billion a year5. They are a constant challenge because of the everincreasing depths at which gold and platinum are mined. Each working day, some 300 000 miners descend to drill and blast the rock containing South Africa’s rich metal and mineral deposits. Unsurprisingly, most research in mining seismology focuses on reducing the rockburst risk. Powerful mining-related events that cause damage and injury at ground level are fortunately rare. South Africa’s largest one to date shook the Klerksdorp district on 9 March 2005 and registered 5.3 on the Richter scale6. It damaged buildings and injured 58 people in nearby Stilfontein. Two miners were killed and 3 200 others evacuated. The mine was closed for several months, with serious consequences for mineworkers and Stilfontein residents. Following this incident, the Chief Inspector of Mines commissioned a comprehensive investigation into the risks to miners, mines, and the public, posed by large seismic events in the country’s gold mining districts. It was found that such events can be expected in these areas as long as the current rate of deep mining continues (an earthquake greater than magnitude 5 is expected in the Free State or Klerksdorp mining districts every 20–30 years). It was recommended that evacuation plans and emergency drills be enforced and implemented within the regions’ disaster management plans. Seismic events are likely to be triggered when worked-out mines are allowed to flood, though these events will probably be no greater in magnitude than those occurring during mining. Some buildings in
5. This estimate includes the direct costs of injury, damage to mine workings, and loss of production, as well as the indirect costs of measures taken to combat the threat of rockbursts, such as creating stabilizing pillars, which can also contain precious metal. 6. Depending on the amount of energy released, and the nature and location of an earthquake, seismologists use several methods for estimating its magnitude, one of which is the Richter scale. Named after the American physicist and geologist Charles Francis Richter (1900–1985), it is also known as the ‘local magnitude scale’. It is a logarithmic equation that uses the measurement of the amplitude of seismic waves radiated by an earthquake. An earthquake’s severity can be expressed in terms of both magnitude and intensity – the magnitude indicates the size of the earthquake and is independent of the place where it is measured, while the intensity is a measure of how violently people and buildings are shaken. Intensity generally diminishes with distance from the source, but can be affected by things such as the thickness of the soil layer. 7. The epicentres of earthquakes in the Ceres Seismicity Cluster appear to be contained between the Worcester and Cango/ Baviaanskloof Fault mountain ranges, at the point where the two ranges converge (meet) and terminate. Other similar clusters occur in and around Koffiefontein (around the diamond-bearing kimberlite pipe) and the Matatiele mountain range. On the whole, however, southern Africa has a relatively low level of seismic activity, with earthquakes randomly distributed in space and time.
Top: Structural damage caused by a sinkhole to a house in Thaba Tshwane. Above: A ‘before’ and ‘after’ diagrammatic representation of sinkhole formation (see also footnote 8).
Sinkholes Parts of South Africa’s ground surface are particularly vulnerable to sudden, catastrophic collapse in the form of sinkholes, which can damage buildings and injure or kill people. They’re found in areas underlain by dolomite8, including parts of Mpumulanga, Limpopo, North West, and Northern Cape provinces, and about a quarter of heavily populated Gauteng. Worldwide, sinkholes are generally circular, up to 50 m in diameter, steep sided, and deep. They appear almost 8. Dolomite is a carbonate rock dominated by a particular mineral, which is also called dolomite: CaMg(CO3)2. Rainwater entering the soil mixes with CO2 (carbon dioxide) to produce a weak carbonic acid (H2CO3). The mineral dolomite is particularly susceptible to being dissolved by this acid, which, over millions of years, leads to the formation of progressively larger voids or cavities.
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From top: A palm tree falling as a sinkhole developed in July 2007 in a residential area (Laudium, Pretoria). A sinkhole off the R25 to Bapsfontein, Gauteng (2004), which almost doubled in size from its initial 30-m diameter and 20-m depth in 2003. Photograph: Courtesy of Surina Esterhuyse Tactile examination. Damage to infrastructure caused by problem soils.
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without warning, though cracks in walls or settlement of the ground are often early signs of danger. They have killed at least 38 people over the last 50 years in South Africa and, so far, have cost the country an estimated R1.3 billion, mainly through damage to buildings, roads, and other structures. Some 2 600 million years ago, what is now Gauteng formed part of a large, warm, shallow, inland sea, rich in algae. Photosynthesis of the algae led to the formation of calcium carbonate, which later developed into thick sequences of dolomiterich limestone that, over millions of years, developed into dolomite rock. In more recent geological history, groundwater percolated through joints in the rock, eroding and opening them up to form voids, and, subsequently, large underground caves such as those at Sterkfontein in the Cradle of Humankind. Until the 1960s, people generally were unaware of the voids and caverns a few metres beneath the surface of Gauteng. Then, as urban development took off southwards towards Johannesburg, sinkholes began appearing in Pretoria’s southern suburbs. Geoscientists soon discovered that, if taps were left running, pipes leaked undetected, or water gathered after heavy rainfalls, the water percolated (drained) down through the surface covering of soil and/or the underlying dolomite and its cavities. Where a cavity is close to the surface, the waterlogged soils can collapse into it, forming a sinkhole. Understanding these conditions allows people to plan so as to avoid susceptible areas where possible. Today, before any development begins on dolomite ground, an engineering geologist inspects subsurface conditions by drilling holes into the ground, sometimes to a depth of 60 m. The rate at which the drill rod penetrates the ground reveals possible voids. Highrisk areas are then out of bounds, to minimize risk to future property-owners. Other measures are also put in place to prevent damage – such as raft foundations9, which, if a sinkhole develops, will prevent a structure from toppling into it. Areas at risk are paved to prevent water from flowing into the soil, and pipes have to be inspected regularly for leaks, which are often the ‘trigger’ for sinkhole formation in urban areas. – Greg Heath and Tharina Oosthuizen (Council for Geoscience, Pretoria)
Unstable soils Foundation soils whose volume changes unevenly during wetting or drying cycles, or under the weight of a construction, can severely distort and damage buildings and infrastructure. Four main types of problem soil are common throughout South Africa: ‘expansive clays’ that increase in volume as they take up water; soft wet clays with low load-bearing strength that deform because they lack strength to support structures; dispersive soils that quickly disintegrate and erode; and collapsible soils which, when stressed by a foundation load, settle rapidly the first time they are saturated with water. A particular site may have one or more of these unstable soil types present, creating a variety of problems in a small area according to loading stresses and changes in soil moisture content. They can heave, shrink, or settle slowly due to consolidation, or they can erode rapidly if they are exposed to running water, for example. Problem soils primarily affect the building of new houses, but can also damage roads, pipelines, factories, water reservoirs, bridges, and office blocks. With early detection of potential problems by geotechnical experts, though, correctly engineered solutions can be implemented10. In the early 1990s, CSIR researchers estimated that expansive clays were costing the South African housing industry an additional R1 billion per annum in specialized foundations and R100 million in crack-damage repairs for poorly sited structures7. A decade later, in a review of defective houses built between 2001 and 2003, the National Home Builders Registration Council found that 24% of structural failures in newly built houses could still be attributed to soil movement. Such statistics highlight the need for more – and more diversified – soil investigation and testing to ensure that proper foundations are selected and constructed. – Colin Forbes (Council for Geoscience, Pretoria) Read F.G. Bell & I. de Bruyn, “Sensitive, expansive, dispersive and collapsive soils”, Bulletin of the IAEG (Oct 1997), pp.19–38; and “Problem Soils in South Africa – State of the Art” in The Civil Engineer in South Africa (July 1985), pp.347–407. Next page: For coastal erosion and sea-level research, consult South African Journal of Science, vol. 103 (2007): A.M. Smith et al., “Combined marine storm and Saros spring high tide erosion events along the KwaZulu-Natal coast in March 2007”, pp.274– 276; and A.A. Mather, “Linear and nonlinear sea-level changes at Durban, South Africa”, pp.509–512.
9. Raft foundations are made up of a continuous slab of reinforced concrete below the entire surface of a building. 10. Since 1999, it has been mandatory to conduct basic soil property tests and various specialized field and laboratory techniques to classify sites geotechnically (NHBRC Act 67 of 1999). Foundation design solutions range from regular concrete strip footings 500–700 mm wide, formed in shallow foundation trenches, to concrete slabs with steel-rod reinforcing. In the worst cases, mini-piles of steel or concrete are sunk into the ground to provide support. It is also common to remove soil and recompact it afterwards into thin layers built back up to founding depth; another method is to replace it with inert soil or rockfill.
Coastal erosion South Africa’s 3 000-km coastline is a mix of different types of shore, ranging from jagged rocks to sandy beaches. The rocky shorelines are stable, but the soft-sand ones are particularly vulnerable to sea-level variations11. As little as 18 000 years ago, sea levels were about 100 m lower than today, and, particularly since the establishment of the Intergovernmental Panel on Climate Change in 1988, interest has grown in the rate of sea-level rise induced by climate change. Because computations must be based on as long a record as possible, South African research on sea-level change stayed on the back burner for some time. Durban’s record is reliable from 1970 to the present, so it now offers just over 30 years of information. This pleases researchers whose calculations have best credibility if based on at least three decades of accumulated data (as distinct from those based on 10-year records, which do not accommodate reversals between successive decades). Durban’s records show its sea level rising (in line with global figures) at a rate of 2.7 mm per year. Such a shift on a sloping beach profile can result in the retreat of many metres of shoreline12. South Africa’s beach slopes are relatively steep, but there are particularly vulnerable areas in estuaries and along stretches of flat coastal plains13. Preliminary assessments in some Durban areas show that, by 2100, residential and commercial properties will be affected. In March 2007, storms caused significant erosion along some 400 km of KwaZulu-Natal coastline from St Lucia to Port Shepstone. High-speed winds whipped up waves of up to 14 m, with a significant wave height of 8.5 m14. This wave-generated surge in water levels coincided with the highest
tides in the present 18.6-year tidal cycle. Large amounts of sediment were stripped off the beaches and deposited in deeper water about 22 m below the sea surface – a depth from which little returns to shore. Therefore severe erosion continued in the months after the destructive event, as the system readjusted to the loss of sediment. Dramatic erosion of some 100 m of shoreline Amanzimtoti’s main swimming beaches over three weeks showed the magnitude of the correction, after the commencement of winter storms, which started moving sediment in a northerly direction. Two similar storms, in 1997 and 1984, indicate that devastation on this scale can occur every decade. Such massive erosion events have yet to be factored into planning in the coastal zone. With the additional pressures of climate change and sea-level rise, they have the potential to damage South Africa’s beaches, tourism, private dwellings, and public infrastructure, to disrupt its ports, and to reduce its capacity for global trade. – Andrew Mather (eThekwini Municipality, Durban)
Landslides and collapsing mountains You get landslides when upper hillslopes collapse and the material that’s dislodged moves downslope with catastrophic force, falling, flowing, toppling, sliding, and spreading as it goes. Landslides can be triggered by nature alone, or by human activity. In southern Africa, they are widespread owing to the influences of the region’s dramatically diverse terrain. Slopes are most likely to collapse in areas with high hills and deep valleys, where rain is prolonged and intense, and where there is thick unconsolidated
Top middle: Beach erosion, KwaZulu-Natal coast. Photograph: Courtesy of G.A. Botha
Top right: Along Chapman’s Peak Drive, Cape Town, a system of steel ring catch fences was installed up-slope of the road to intercept falling rocks. Photograph: Courtesy of R. G. Singh Above: Digital elevation model (DEM) showing the collapse of the steep 600-m-high Mount Currie, northeast of Kokstad. Vertical exaggeration x 1.6. Image: Created by and reproduced courtesy of R. G. Singh
sediment. Landslides most often affect urban developments and strategic communication infrastructure, and can devastate natural habitats by denuding slopes of their cover and changing natural water-drainage systems. Devastation has often been a spur to action, however. Landslide fatalities along the scenic Chapman’s Peak drive on the Atlantic coastline in the Western Cape, for instance, prompted extensive structural improvements, removal of loose rock from the steep slopes, and plans to install early warning mechanisms. The catastrophic failure of a mine tailings dam in Merriespruit (a suburb of Virginia in the Free State goldfields) caused by heavy rainfall in February 1994 resulted in mud flow that devastated a residential area and killed 18 people. This event prompted a review of mine health and safety legislation and the introduction of a new code of practice in 1997, which requires tailings dams designed by engineers to have a minimum freeboard15 catering for above-normal rainfall as well as for high-intensity storms. Landslides can move with tremendous momentum, crossing valleys to form natural lakes and affecting drainage. Landslides have, in fact, played a significant part in the evolution of the South African ▲ ▲
11. Warm periods raise global sea levels through glacial melt. The last ‘high stand’ in sea level – that is, the last time sea levels were high – was during the warm interglacial conditions of about 100 000 years ago. 12. Because the beach has a slope, the vertical component of sea-level rise – say, 3 mm – moves up the slope. So, for example, with a slope of 1 in 100, the 3 mm translates vertically into a reduction of 3 × 100 = 30 cm of beach each year. This calculation does not take into account increased wave energy in the increasing depth of the sea, which makes erosion worse. 13. Flat coastal plains are wide areas with almost constant elevation slopes of, say, 1 in 1 000, so for about 50 cm of sea-level rise, 0.5 km would be lost. 14. The ‘significant wave height’ is the average figure of the third-largest recorded wave in the measuring period. It is used by coastal engineers to design coastal structures, as the absolute peak wave may often be a rogue wave, which distorts the data set. 15. ‘Freeboard’ is the distance between the maximum permitted water level in the reservoir behind a dam and the top of the dam wall. With respect to tailings dams, freeboard is defined as the distance between the mean operating level plus the 1:50-year flood level, and the lowest point on the wall crest of the tailings dam.
Top left: Aerial view showing predicted sea-level rise inundation in Durban around the harbour. Photograph: Courtesy of eThekwini Municipality
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• Geological, Geotechnical, Geochemical, Metallogenic and Marine mapping • Minerals Development • Construction Materials and Agricultural Minerals • Water-Resource Assessment and Protection • Environmental Geoscience • Engineering Geology and Physical Geohazards • Palaeontology • Laboratory Services 280 Pretoria Street • Geophysics Silveton • Seismology PRETORIA • Geographic Information Systems (GIS) Private Bag X112 • Information Databases PRETORIA 0001 • National Geoscience Library • Geoscience Museum Tel: +27 (0)12 841-1911 Fax: +27 (0)12 841-1221 • National Core Library
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http://www.geoscience.org.za 32 Quest 4(2) 2008
landscape. The 2-km-long Lake Fundudzi in Limpopo’s Soutpansberg mountain range was formed thousands of years ago by a huge palaeolandslide, which blocked the course of the Mutale River. Upstream of a large rotational palaeo-landslide (about 3 500 years ago) in the Meander Stream valley of the Ukhahlamba–Drakensberg foothills, an anomalous meandering stream floodplain developed, with typically steep tributary valleys. To reduce the risks of landslides to people, assessment of the potential for landslides has over the years become a primary consideration in town planning and zoning for different categories of land-use all over South Africa16. – Rebekah Singh and Greg Botha (Council for Geoscience, Pietermaritzburg), Frederik Stapelberg (Council for Geoscience, Bellville, Cape Town), and Colin Forbes (Council for Geoscience, Pretoria)
Floods and tsunamis Heavy rains, offshore cyclones, and tsunamis17 can cause devastating floods inland and in coastal areas, destroying houses, infrastructure, and crops. Globally, floods are the most damaging type of geohazard in terms of the loss of life and property they cause – their socio-economic effects on communities can be enormous. Floods Semi-arid South Africa has an average annual rainfall of about 460 mm – just over half of the global average – but this can vary dramatically from year to year. In wetter years, cloudbursts or rain that persists over several days can rapidly raise water levels in rivers, sometimes with catastrophic results. In 1981, for example, the Buffels River in Laingsburg (230 km northeast of Cape Town) flooded so badly that 104 people lost their lives. Before 1981, the greatest flooding of the Buffels on record (in 1925) had had a flow of just 742 m3 per second, and there was no hint in the intervening half-century that a flood could ever reach the extraordinary discharge of 5 700 m3 per second recorded in 1981! On a smaller scale, flash floods from heavy downpours are common in urban areas and can cause loss of life. The large areas covered by concrete and tar result in rapid run-off of water into local streams and stormwater drains, causing areas downstream – where rain may or may not have fallen – to be caught unawares by floodwater. Earth sciences can and do play an
important role in understanding and predicting floods. Examination of the geological record of past floods can make it possible to calculate their size and even their timing (whether 10 000 or 2 million years ago), and this important information from the past is used to predict a river system’s future flood pattern. Other helpful information comes from studies of the climate in relation to the river catchment, as well as the geohydrological characteristics of the river system as a whole. Only by understanding the flood patterns can one reduce the associated risks by siting key infrastructural developments carefully, and legislating where people in areas that may be affected are allowed to live. – Peter K. Zawada and Susan Frost-Killian (Council for Geoscience, Pretoria) Tsunamis The Summatran tsunami of 26 December 2004 resulted in approximately 300 000 fatalities. It even caused two fatalities in South Africa, even though it was small by the time it reached this country. Over the past two centuries, at least five tsunamis have impacted on the South African coast. Not all tsunamis are caused by earthquakes. The biggest tsunami wave ever recorded was a 500-m-high monster in Alaska in 1955, caused by a massive rockfall into the sea. Precipitous cliffs around the South African coast could cause a large localised tsunami. The Agulhas slump under the ocean on the South African continental shelf off Cape Agulhas is the largest in the world, and future slumping on this scale would trigger a large tsunami that would affect the southern coast. Impacts from comets and asteroids can also generate tsunamis hundreds of metres high – but astronomers expect no such events for the remainer of the present century. – Dave Roberts (Council for Geoscience, Bellville, Cape Town) ■
16. Landslide susceptibility mapping – initially carried out by the Council for Geoscience office in KwaZulu-Natal, but to be rolled out to other high-risk parts of South Africa – categorizes regions into zones with different degrees of potential instability. The KwaZulu-Natal landslide susceptibility map will become a useful town planning tool for decision-making in regional and urban developments. 17. For more on cyclones and floods, consult Ian Meiklejohn’s “Hurricanes” in Quest, vol. 2 no. 2 (pp. 32–33) and Liesl Dyson’s “Why such floods?” in Quest, vol. 3 no. 2 (p. 44). For details about tsunamis, see Ian Meiklejohn’s “Tsunamis” in Quest, vol. 1 no. 3 (pp. 8–9)
Top left: An oblique aerial view of the Merriespruit failure. Photograph reproduced courtesy of the journal of the South African Institution of Civil Engineering
Top right: Landslide susceptibility map of KwaZulu–Natal. Image: Created by and reproduced courtesy of R. G. Singh
Above top and middle: Flood devastation, Laingsburg, 1981 – only 21 houses were left standing. Photograph: © The Argus Above: Flood devastation in St Francis Bay. Photograph: Tracy de Jager
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Antony Cooper and Chrisna du Plessis examine the challenges of urbanization.
Top: Johannesburg skyline.
Image: A. Cooper
Middle: An informal settlement situated on grasslands in Gauteng. Image: A. Cooper Below: Map showing the spatial development framework for Gauteng Province. The green urban boundary defines the Gauteng megacity. Image: Courtesy of CSIR Built Environment, Planning Support Systems
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Megacities’ are urban agglomerations larger than 10 million people. Such high concentrations of people are a new phenomenon – only Tokyo and New York were megacities in 1950 – and scientists and policy-makers are trying to understand how they function, and how to manage their ecology. Strictly speaking, South Africa does not yet have a megacity. But the three metropolitan areas in Gauteng (Johannesburg, Tshwane, and Ekurhuleni) together cover some 5 765 km2, and the combined population rose from some 7.7 million in 2001 to as much as 8.6 million in 20041. This part of the country reflects all the characteristics of a megacity. Nobody would live in megacities if there were no benefits in doing so – including the size and diversity of economic markets, a rich cultural mix, perceived work opportunities, and specialist services. Furthermore, urban populations are generally assumed to be healthier, more literate, and more prosperous than rural populations. But UN-HABITAT2 reports that the quality of life of slum dwellers in developing countries is as bad as (if not worse than) that of their rural relatives in terms of pollution, crime, overcrowding, and inadequate access to clean water. Megacities suffer from the same problems as other cities, such as traffic congestion and (particularly in the developing world) populations that grow faster than the infrastructure to support them. The size of larger cities
compounds these problems, however, and their effects escalate rapidly, so that relatively small disasters can become major ones because they push the system past critical thresholds. Typical problems Housing and land. The South African government has a large programme, called Breaking New Ground, to build low-cost housing and thereby remove the need for informal settlements. It is still based mainly on a low-density housing model, however, and privatesector housing development is equally sprawling. The large areas that these developments span make it expensive to provide services, and they consume vast tracts of land. In Gauteng, this is often particularly valuable arable land. Furthermore, the demand for housing has been driving dramatic rises in property prices, with the median house price increasing 182% between January 2000 and December 2007 (in contrast with the price of goods in general rising 60% over the same period). Pollution. Air pollution – which also drives climate change – is clearly visible in our cities, particularly in wintertime in the form of ‘brown haze’3. Litter is another obvious form of contamination. Less apparent, perhaps, is the extent to which soil, as well as surface- and groundwater, are polluted in urban environments. Noise pollution is now recognized internationally as a major health threat, and long-term exposure to the persistent sound of traffic accounts for 3% of deaths from heart disease in Europe, for example. In many
1. The source of these figures is the State of the Cities Report 2004 issued by the South African Cities Network, Johannesburg, quoted in South Africa Environment Outlook: A report on the state of the environment (Department of Environmental Affairs and Tourism, 2006). 2. For details, consult the State of the World’s Cities 2006/7 (UN-HABITAT, 2006). 3. For more on brown haze and air pollution, consult the research article by P. Gwaze, G. Helas, H.J. Annegarn, J. Huth, and S.J. Piketh, “Physical, chemical and optical properties of aerosol particles collected over Cape Town during winter haze episodes”, South African Journal of Science (2007), vol. 103, pp. 35–43, and “What’s that brown haze over Cape Town?” in Quest, vol. 3 no. 4 (pp. 17–19).
Q Fact file
infrastructure and growing population. Uncertain electricity supply not only curbs economic growth, but also limits the provision of water and sanitation services, which often rely on electric pump stations. Politics. Megacities frequently lack clear political and administrative definition; where multiple authorities are responsible for different sections, planning and management can become complicated. Johannesburg, Tshwane, and Ekurhuleni, for example, have separate metropolitan authorities even though their areas are adjacent, and, in combination, cover a single large area. A development, such as a shopping centre, in one municipality could affect its neighbours, put pressure on transport systems, and even duplicate services. In addition, through its sheer size, a megacity can dominate a country’s or a province’s economic and political processes at the expense of other, smaller cities and rural areas. Social polarization. As centres of corporate activity, megacities provide opportunities for some residents to become fabulously wealthy and flaunt
Top: Forty-storey blocks of flats, viewed from the Hong Kong Wetland Park in Tin Shui Wai. Image: A. Cooper
cases, pollution comes from recklessly wasteful consumption of resources. Transport. As cities grow, more people need to be transported (particularly between home and work) over ever greater distances. The urban sprawl of low-density town planning exacerbates the problem. Inadequate public transport in Gauteng, for example, has resulted in an overloaded road infrastructure, and the frequency, size, and duration of traffic jams have increased significantly over the past few years4. Environmental degradation. Cities consume the environment – they cover large areas of land with buildings and infrastructure; they are greedy for resources; and they generate pollution and waste. Utilities. South Africa has very good potable water supply in its cities and basic sanitation is being rolled out to ever greater numbers of people5. January 2008 brought a nationwide electricity supply crisis, however, because of inadequate investment in generation capacity (resulting in rolling blackouts) – of particular concern in Johannesburg, with its ageing electrical
■ Half of the world’s human population of over 6.5 billion now live in cities, with 9% living in megacities. ■ The world’s five largest megacities (2007 figures) are Tokyo (35 million people), New York City and Seoul/ Incheon (20 million); Mumbai and Jakarta (nearly 20 million). Next come Delhi, Mexico City, and São Paulo (all over 18 million). In Africa, Cairo’s world ranking is 11th (16 million), Lagos ranks 12th (nearly 10 million), Kinshasa ranks 29th (nearly 8 million), and the Johannesburg-East Rand area alone ranks 41st (about 6.5 million). Source: Wikipedia ■ Between 1950 and 2050, the world’s population is expected to have increased fivefold, from about 2 to 10 billion. ■ Of the global population, the proportion living in urban areas is expected to grow from 47% in 2000 to 60% by 2025. Most urbanization is expected in developing countries, as people move from rural areas. Higher food prices will further impoverish low-income urban dwellers. ■ Africa has the world’s highest rate of urbanization: by 2005, almost 350 million Africans (about 40% of the continent’s total population) lived in urban areas, and the rate is increasing by nearly 4% per year. ■ According to UN-HABITAT, the world’s one billion slum-dwellers are worse-off than their rural counterparts, more likely to die earlier, experience more hunger and disease, attain less education, and have fewer changes of employment. In slums, child malnutrition is worse than in rural areas, and urban children are more likely to die from water-borne and respiratory diseases.
Above left: A traffic jam caused by an accident on the main motorway between Johannesburg and Pretoria – a frequent occurrence on Gauteng’s highways. Image: A. Cooper
4. According to the first South African National Household Travel Survey, conducted in 2003, the greatest transportation problem experienced by households in Gauteng was the lack of readily available public transport. 5. Nationally, since 1994, South Africa has improved access to clean water: in 2001, 9.5 million households (84.5%) had access to piped water, an increase of 2.4 million households since 1996. Over the same period, the number of households with flush or chemical toilets increased from 4.6 million to over 6 million. The proportion of households relying on bucket toilets across the country went down from 5.3% in 1993 to 1.9% in 2003.
Above: Gautrain rail-link, Sandton, Johannesburg, which, when operational, will help to ease congestion on the roads. Image: Courtesy of the Intelligent Transport Society South Africa
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Left: Gauteng megacity highway traffic. Image: Courtesy of Intelligent Transport Society South Africa
Below: A vehicle parking lot in Tshwane, where tarmac has replaced vegetation. Image: A. Cooper
Bottom: Flash floods occur regularly in large cities. Image: C. Du Plessis
Gauteng’s abandoned mines Abandoned mines are a particular geotechnical problem in Gauteng. The risk is that the ground can subside, which limits development and makes it difficult to pursue the IYPE megacity trend of ‘going deeper, building safer’. Former mines are often occupied by informal settlements, because the general public is frequently unaware of the safety hazards. There are other dangers too: ■ arsenic, cyanide, and other hazardous substances still remain in mine dumps and slimes dams ■ radon (an inert, radioactive gas), which can cause lung cancer, emanates naturally from the ground all over the world, but higher concentrations of it are associated with uranium mines – and uranium is a by-product of gold mining on the Witwatersrand ■ people and animals can easily fall into the many unprotected (and often unrecorded) mine shafts.
their wealth, even as many others live in abject poverty6. Focal points of risk. As the events of 11 September 2001 in New York showed, megacities offer real as well as symbolic targets for politically motivated attacks. Mass concentrations of people are particularly appealing to terrorists, as illustrated in the sarin gas attack on the Tokyo subway in 1995, the post-‘9/11’ bombings of public transport systems in London and Madrid, and incidents in other cities around the world. Quality of life. While megacities often give access to the best medical services and great variety of cultural and recreational opportunities, they can also undermine residents’ quality of life – even for the very rich. Of particular concern in Gauteng, for instance, are the congested roads, and the high levels of violent crime. By way of illustration, 54% of all recorded car hijackings in South Africa and 53% of robberies at residential premises between 1 April and 30 September 2007 took place in Gauteng. The pace of life in the ‘rat race’ of the megacity is more stressful than in rural areas, causing serious health problems. Ironically – given the great number of people inhabiting them – megacities are associated with loneliness, as many people lack the community support structures of smaller towns.
The science of city life Megacities are among the ten International Year of Planet Earth themes because of their impact on the Earth, and the potential of the geosciences in improving the understanding, management, and sustainable development of such population centres. Size, design, needs, consumption patterns, economic buying power, and the way cities are used – all these affect water cycles and local microclimates, disrupt soil formation processes, occupy arable land, and cause great quantities of fuels and raw materials to move around the planet. Regional water cycles. The exchange of water between the atmosphere and land alters when trees and other vegetation are cleared to make way for buildings and roads. This interference with the hydrological cycle changes rainfall patterns and raises temperatures around the man-made surfaces that replace the cooling cover of plants. Because roofs, paving, and roads are artificial and non-porous, the land is less able to absorb rain – more stormwater enters drains and watercourses, flooding properties and polluting river systems with waste. Increased run-off in urban areas also lowers groundwater levels, depleting this water source over time;
6. According to the annual survey of the Institute for Justice and Reconciliation released in January 2008, the wealth gap in South Africa is reported to have increased further, from a Gini coefficient of 0.6 in 2006 to one of 0.62 in 2007 (where zero represents perfect equality and 1 represents absolute inequality).
and it reduces local water supplies even as the cities grow. Since megacities cannot rely on their own supplies of surface and groundwater, they import water (via pipelines and aqueducts, for example), thus changing a region’s water cycle. Large amounts of water pumped from Lesotho to Gauteng, for instance, influence urban groundwater dynamics, as all the extra water has eventually to settle somewhere. Geological stability is affected (for instance by increasing the risk of sinkholes in dolomitic areas), and there is greater seepage of toxins and other pollutants into the ground, which contaminates surface water and soil. Local microclimate. Replacing natural vegetation with streets and parking lots creates urban ‘heat islands’. Studies in Kuala Lumpur and Taipei show that reducing ‘green’ areas can make innercity areas up to 10 °C warmer than the surrounding countryside. This burdens a megacity’s energy supply as people revert to air-conditioners – which, in turn, warm the city further through the
Quest 4(2) 2008 37
THE FACULTY OF SCIENCE AT THE UNIVERSITY OF JOHANNESBURG
GATEWAY TO YOUR FUTURE
A STUDENT-FRIENDLY ENVIRONMENT CONDUCIVE TO THE HOLISTIC DEVELOPMENT OF THE STUDENT The Faculty of Science at the University of Johannesburg prides itself on its vibrant, dynamic and diverse scientific community of scholars who are passionate about enhancing the learning experience of our students, enhancing the research profile of the Faculty and enhancing the academic, social, and economic impact of the Facultyâ€™s teaching and research programmes.
A WIDE RANGE OF UNDERGRADUATE AND POSTGRADUATE STUDY PROGRAMMES THAT LEAD TO EXCELLENT EMPLOYMENT POSSIBILITIES We provide outstanding service to our students in respect of learning programmes, learning facilities, in-service training and a learning environment that is conducive to life-long learning. Our students are in great demand in the business sector and contribute significantly to the industry.
INTERNATIONALLY RECOGNIZED PROGRAMMES The Faculty is an active player in a wide network of national and international partnerships and collaborations. One example is a formal agreement with the reputable University of St Andrews in Scotland concerning a joint PhD programme. Students of UJ selected for this programme, will spend one year in St Andrews and will, after successful completion of their 3-year study, be awarded a PhD jointly by UJ and St Andrews. The joint PhD programme will commence within the Department of Chemistry, but will be extended to other disciplines in due course. With regard to undergraduate programmes, we are proud that UJ is the only university in Africa, and only the third outside the UK, that holds accreditation from the British Computer Society for its BSc degree programme in Information Technology which is offered by the Academy for Information Technology.
RESEARCH OPPORTUNITIES AND EQUIPMENT OF HIGH QUALITY Quality research and the effective training of postgraduate students are core academic functions of each department in the Faculty. In 2006 the Faculty had its highest number of research contributions in international scientific journals for 12 years. This achievement attests to the collective commitment of the Faculty to further strengthen its international research stature.
Visit our website at www.uj.ac.za/science or contact us at 011 559 2459 38 Quest 4(2) 2008
Right: Hong Kong’s high-rise buildings are a response to the limited land available on the island; it has to accommodate a population of over 6.9 million people in an area of 1 104 km2 (less than one-fifteenth the size of Gauteng). Image: A. Cooper ▲
heat they displace from indoors to the streets outside. Groups of tall buildings can also disrupt the microclimate, changing air flow and turning streets into wind tunnels. The pedosphere (outermost layer of Earth). Built-up areas occupy just 1% of the Earth’s land surface, but they tend to be situated on fertile soil. In South Africa, up to 16 000 ha of farmland is lost to developers annually, and rapid urbanization puts constant pressure (from formal building projects as well as informal settlements) on nature conservation areas7. Some answers for the future Architects, engineers, and city planners try to improve matters by creating ‘green’ roofs (planting roofs with vegetation); harvesting rainwater; redesigning pavements and water courses to improve the recharging of groundwater supplies and reduce stormwater run-off; and recycling construction material (for instance, by re-using demolition waste in new buildings and roads). It could help for South Africa’s town and city planning to shift focus away from urban sprawl (with its fixation on giving every household its own plot of ground), and rising costs of land in urban areas encourages such directional change. Increasing densities without necessarily following a high-rise model make it cheaper to provide services – particularly to the poor – such as water, sanitation, power, telecommunications, and transport. Also, shorter distances make commercial services more accessible. In the East, governments are already creating the next generation of built-up areas. Compact, sustainable cities, such as Dongtan in China and Masdar City in Abu Dhabi, provide a vision of traditional shaded, pedestrian-friendly streets lined with buildings no more than five stories high, served by good public transport, whose energy comes from the Sun (not from coal mines), and where water, waste, and soil are treated as precious resources. The increasing size and number of megacities internationally can be viewed as a huge problem – or as an
opportunity. No single scenario can be applied everywhere, but pressure is growing to implement sustainable solutions and to make the best of our urban world. ■ Both authors are in the CSIR Built Environment Unit. Antony Cooper’s recent projects relate to crime mapping and analysis, standards, metadata, transport modelling, and modelling armour units around harbours. Chrisna du Plessis specializes in urban sustainability science. Her work ranges from policy on the development of sustainable human settlements to alternative technical solutions for integrated municipal service delivery and settlement design. Download the IYPE megacities brochure from www.yearofplanetearth.org/content/ downloads/Megacities.pdf and visit UNHABITAT at www.unhabitat.org. For more on cities in South Africa and elsewhere, consult The Worldwatch Institute, 2007 State of the World: Our Urban Future (New York, Norton, 2007); South Africa Environment Outlook: A Report on the State of the Environment (Department of Environmental Affairs and Tourism, 2006); A. Coghlan, “Dying for Some Peace and Quiet”, New Scientist (25 August 2007); P. Davis et al., “Reducing Urban Heat Island Effect with Thermal Comfort Housing and Honeycomb Townships”, in Proceedings of SB04 Conference on Sustainable Building SouthEast Asia (Kuala Lumpur, 2005), available at http://forskningsbasen.deff.dk/ddf/rec. external?id=dtu184786; A.R. Turton et al., “Gold, Scorched Earth and Water: The Hydropolitics of Johannesburg”, International Journal of Water Resources Development, vol. 22(2) (2006), pp.313– 335, available at http://researchspace.csir. co.za/dspace/handle/10204/1902. For the First South African National Household Travel Survey 2003 (August 2005) visit www.transport. gov.za/projects/nts/framesPage; for South African crime statistics see South African Police Service, “Crime situation in South Africa April – September 2007” December 2007) at www.saps.gov.za/statistics/reports/ crimestats/2007/crime_stats.htm.
7. Cities impact on the pedosphere in four ways. (1) Physical footprint: tall narrow buildings have a smaller footprint than single-storey constructions; compact cities use less land than sprawling ones. (2) Land clearance: site development and preparing for construction can compact the ground, erode soil, and reduce topsoil. (3) Pollution: the manufacture of building materials and people’s use of the city’s infrastructure change the soil’s chemical composition. (4) Extraction of materials: the Earth’s crust and topsoil are affected when materials are extracted for use in construction. Materials extracted for construction purposes include aggregates (sand and gravel), minerals, and metals, as well as organic materials (such as wood and other agricultural products), especially when grown and harvested in conditions that contribute to soil erosion.
Top: Low-cost housing on former agricultural land in Gauteng contributes to topsoil loss and urban sprawl. Image: A. Cooper Middle: Green roof on a high-rise building in Tokyo, planted with vegetation so as to re-establish local ecosystems. Image: C. Du Plessis
Below: An area in the city of Paris, France, showing high-density development but buildings with no more than just a few storeys. Image: A. Cooper
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Greg Botha and his colleagues explain what’s happening to the planet’s vital surface – the very source of life and growth.
Top: Donga sidewall profile through the St Paul’s donga near Nqutu, KwaZulu-Natal. The buried palaeosols or fossil soil layers preserve evidence of climate change and donga cut-and-fill cycles. Photograph: Greg Botha Above: Generalized soil patterns across South Africa, mapped according to soilprofile classification, help scientists to understand fertility that benefits crop production, for example, and the extent to which different soils can absorb waste materials or recover from land use. Certain soil-type combinations repeat across the Earth, so they can be classified and systematically studied. Each soil group has its peculiarities in terms of sustainability in different conditions. Areas of dark clay soils (9, 10) are moderate-potential soils susceptible to drought and erosion; red, welldrained soils (2, 3, 4, 11, 12) are high-potential agricultural soils; and shallow soils (17, 18, 19) are typical of mountainous areas. Image: M. van der Walt, ARC-ISCW
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he layer of soil – the Earth’s ‘living skin’ – is thinner than we think. That extraordinary ratio 1:12 700 represents its thickness in comparison to that of the rocks beneath. By way of illustration, the layer of paint on the outside of a house, relative to the size of the house, is ten times thicker! A 1-mm film of soil, covering a single hectare, represents more than 10 tonnes of soil. In much of southern Africa, many times this amount is lost to erosion each year, with only a small fraction of that quantity being replenished through natural soil formation during the same period. People’s reliance on energy from diminishing resources of non-renewable fossil fuels is highly publicized. Far less thought goes to our dependence on the energy and sustenance from that other, even more threatened natural resource: soil. Found at the pedosphere – that is, at the meeting point of the atmosphere (air), hydrosphere (water), biosphere (where living organisms are found), and lithosphere (the upper layer of the solid Earth) – soil types differ greatly according to variables that influence their formation, such as climate, their organic and other components, topography (surface features of a landscape), and time. Much of the Earth’s biodiversity is below ground, at the very heart of ecosystems, in the soil environment – a habitat for myriads of terrestrial living organisms – which at the same time forms the medium for growing the crops that sustain us and fibres that cover and protect us. Scientists study soils from different points of view: some focus on soil formation and its beneficial chemical or physical properties; others emphasize ways to exploit these properties for best possible crop production. It is also central to people’s wellbeing, and needs to be a core concern for homeowners, farmers, engineers, and government authorities. As human developments expand, increasing demands on soil resources, communities have to reconsider what they value most - short-term and potentially destructive soil use, or long-term options for nurturing and sustaining the land and its future. – Greg Botha, Jan Schoeman, and Marjan van der Walt (continued on page 42)
Devastating donga erosion There is ample evidence of Early and Middle Stone Age cultures in the region at the time that these cycles occurred, but the hunter-gatherer impact on the landscape was probably minimal. During the past two hundred years, however, inappropriate crop production methods have caused donga erosion to spread rapidly. In some areas, contour drains created to control erosion have in fact caused dongas to form. Much of the soil-cover in the inland drainage basins of rivers such as the Thukela, Mfolozi, and Phongola is naturally susceptible to erosion as a result of periodic changes in climate and vegetation, yet unsustainable land-use practices persist. Rural people continue trying to raise meagre crops from soils in areas that have previously been eroded and buried numerous times before – evidence that any new disturbance could ultimately trigger the next destructive episode. The time has come for everyone to understand the writing on the donga walls, and to heed its dire warning. – Greg Botha
Q Fact file What is soil? Soil, broadly speaking, is the uppermost biochemically weathered part of the ‘regolith’, that is, of the layer of natural, non-cemented, weathered material (including rock fragments, mineral grains, and other superficial deposits) that rests on unaltered, solid bedrock. ‘Soil’ is regolith that often contains organic material, and it is a medium for the growth of plants. It is formed by the destructive breakdown of minerals and microbial decay of organic (animal or vegetable) matter, and by new minerals formed from products of weathering and the addition of compounds such as soluble salts, dust deposits, and the settling of aerosols*. Living soil is one of nature’s recycling systems. It is able to absorb our wastes, including discharge from septic sewage systems, sewage process sludge, and organic industrial effluents. It also acts as a critical filter at the surface of the groundwater table**. For these reasons, management of soil is a concern for all of society. Lessons from history should be heeded today: dynasties founded and enriched by fertile soil soon collapsed once that soil had become degraded through climate change or unsustainable use. * Aerosols are natural or manmade substances that are suspended in air because the small size of their particles make them fall slowly. ** The soil covers the thicker regolith, which is often a groundwater aquifer. In this position, between the atmosphere and the water resource, it helps to protect the groundwater table and, thereby, the Earth’s hydrological system.
Above left: Deep dongas cut a steep hill-slope in the Sinathingi area near Pietermaritzburg, literally dividing the community and creating an ever present hazard. Photograph: Greg Botha Left: Four phases of donga cut-and-fill deposits exposed in a complex donga network near Nqutu, KwaZulu-Natal.
Jagged erosion gullies – ‘dongas’ – scar the upper hill-slopes over much of South Africa’s eastern hinterland, carving up agricultural lands and dividing communities. Many dongas in KwaZuluNatal probably go back 1 000 years when there was little pastoralism, and were possibly triggered by changes in climate and vegetation. But others result from inappropriate agricultural activity – for instance, where people have ploughed soils that are susceptible to erosion. In modern times, common wisdom blames soil erosion for creating dongas, which are often the end product of longer periods of sheet or rill erosion (see footnote 1 on next page). The towering sidewalls of KwaZulu-Natal dongas reveal up to 20 m of stratified sediment with contrasting coloured ‘fossil soil’ layers called ‘palaeosols’. These soil profiles formed at times when hill-slopes were stable, in between repeated cycles of soil erosion and donga ‘cut-and-fill’. The widespread thick deposits illustrate the power of raindrop impact and sheet-flow as mechanisms for transporting sediment. On a slope, a raindrop causes a splash that shoots out, into the air, grains of sediment dislodged from the soil. They fall downslope, repeating the process with every drop that falls, making rainsplash a significant mover of soil. Rainwater that is not absorbed by the soil flows downslope over the land surface in shallow sheets, in between rocks, grass, and other vegetation. When such ‘sheetwash’ is concentrated into the rills of dongas, it is a potent force for erosion. Sand grains in buried soils, now revealed in the strata laid bare in dongas, were deposited on hill-slopes long ago. Using the technique of ‘luminescence dating’, scientists can determine when last these grains saw the light of day. The oldest buried soil layers in central KwaZulu-Natal and Mpumalanga formed around 125 000 years ago, when average temperatures and rainfall were probably higher than they are now. Global change leading to the Last Glacial Maximum (about 18 000 years ago) made the eastern parts of South Africa cooler and drier. Such cyclical climate variations reduced the vegetation cover and led to several episodes of donga cut-and-fill.
Photograph: Greg Botha
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Above: Oblique aerial views of typical donga erosion scenes in central KwaZulu-Natal. Photograph: Greg Botha Above right: Sand dunes. Those in the background have vegetation cover but those in the foreground have lost it.
Water and wind erosion ▲
Soil erosion, by water or wind, is remarkably efficient for forming landscapes. In the semi-arid areas covering over 82% of South Africa, for instance, soils tend to be fragile, and vulnerable to erosion and other kinds of degradation. Losing 1 mm of topsoil a year from ploughed fields can reduce soil fertility and agricultural production, and create dongas. Over millions of years, this rate of erosion can level
entire mountain ranges! Sandy soils, for example, offer little resistance to stormwater runoff across even low-gradient slopes. Some soil types, which are very hard when dry, disperse rapidly when rainfall makes them wet, because they contain clay particles that repel each other in these conditions. Even tough clayey soils with a blocky structure erode easily as individual clods dislodge and wash away. Sheet erosion1 is the loss of a thin surface layer – often crucial rich topsoil containing organic matter – whose insidious reduction over wide areas with thin infertile soils is a more significant threat than deep donga erosion. Wind erosion creates deserts, a grain at a time. The northwestern areas of South Africa, with their low rainfall and low plant biomass production, are most susceptible. Loss of organic matter from thin topsoils slows down long-term soil recovery in these areas. Removing grass and other vegetation from dunes along the coastline and the Kalahari region – through crop agriculture, overgrazing, or roadbuilding, for instance – takes away the covering that so effectively binds these fragile soils, and modifies the forms of the dunes. So maintaining effective plant cover is essential for preserving soil quality in such areas. – Greg Botha, JanSchoeman, and Marjan van der Walt
Air that pollutes the soil
Maps of South Africa showing susceptibility to erosion. The top map shows susceptibility to soil erosion caused by water, with vulnerability increasing (from 1–8) in areas with progressively steeper slopes. The map immediately above shows classes of susceptibility to wind erosion. Sandy soils in arid areas are easily winnowed by strong winds, particularly where the soil surface is disturbed and where large areas have been cleared of vegetation. Images: M. van der Walt, ARC-ISCW
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In the 150 years or so since the industrial revolution began, growth and development have increasingly been driven by machinery that’s powered by fossil fuels, mainly coal – increasing carbon dioxide levels in the atmosphere by more than 35%. Burning pulverized coal, for instance, is one way to produce electricity. The effects on the air – and on the soil – are immense, and increasing with growing urbanization and demand for power.
In South Africa, soil is affected by air in many ways, including deposits of sulphur from vehicle emissions, for example. The gases emitted from burning coal (such as sulphur dioxide and nitrogen oxides) pollute the atmosphere with fine particulate sulphates and nitrates, which, when they fall onto the ground, make soils acidic and less fertile. Water is also affected, and integrated solutions are needed to address these problems. The Mpumalanga Highveld has abundant coal reserves, so most of the country’s coal-fired power stations are situated here. One of them is the Arnot power station. At varying distances from this station, samples of topsoils (0–10 cm from the surface) were taken from the same locations in 1996 and 2006 and analysed for a range of soil chemical properties. It was found that sulphur deposited from the atmosphere had increased significantly, as had soil acidity. Soil can to some extent regulate the services it offers – by retaining sulphur, for instance, it can prevent that sulphur from entering the water systems. The situation is exacerbated by further large pollution sources such as sewage spills and acid mine drainage, however. Evidence from the Vaal region indicate that the soil’s ‘buffering’ capacity is becoming exhausted and that water quality is deteriorating. To understand better how soils get damaged, and to design answers that are economically and environmentally sustainable, we are planning an interdisciplinary project to examine soils, plants, water, and atmospheric chemistry, and the ways in which they affect each other. – Joanne Reid, Theresa Bird, and Mary Scholes
Agriculture Practices that threaten food production Soil forms slowly. It takes several thousands of years to create enough of it for planting crops, and tens of
1. Other forms of erosion include rill erosion, which forms shallow gullies narrow enough to be crossed by an agricultural implement, and gully (or donga) erosion, which creates large, deep gullies.
thousands of years to produce thick soil cover that sustains ecosystems. The degradation and loss of this ancient resource in many areas of southern Africa add urgency to the need for better land use. The sensitivity of soil to degradation is often aggravated by poor recovery potential (resilience) after it has been disturbed2. Rampant erosion in drier parts of South Africa, for example, followed attempts to implement dryland3 agriculture on soils that erode easily. Soil always bears the brunt of practices such as poorly planned veld burning regimes, diversion of surfacewater runoff (after rain) from poorly sited roads or contour drains, and even inappropriate attempts to control bush encroachment or alien invasive plants. In spite of legislated controls, further damage persists to this day, as people plough marginal agricultural soils, and animals such as goats are allowed to over-graze in the veld. Heavy ploughing machinery is another problem. It causes the soil surface to compact, forming a barrier that prevents the roots of crops roots from penetrating in an unrestricted way to depths where they can reach the soil moisture retained there. In some areas, irrigation creates a hard crust on the soil surface; overirrigation causes soils to become waterlogged; and the use of poorquality water makes soils saline and therefore less fertile. Efforts to increase the production of dryland crops by overusing chemical fertilizers is now threatening food production across the region, as soils become acidic, and nutrients accumulate to levels so high that crop yields fall. Industrial pollutants cause further danger and loss of productivity. – Greg Botha Growing crops sustainably Global warming brings the threat of more frequent droughts in future.
Other problems facing many South African crop farmers come from depletion of the soil’s organic content, loss of soil structure, and escalating costs. A move has begun, however, to respond to such threats by changing certain farming methods. Conventionally, farmers till their soil before they plant annual crops such as maize or vegetables. Now there’s a better ‘no-till’ option. After controlling weeds with herbicides, seed is planted in a narrow slot, leaving the residues of the previous crop on the soil surface as mulch, which improves the intake of water. The method not only reduces soil erosion dramatically, but also helps to preserve the soil’s organic matter that is normally depleted by tillage. It saves costs too, by cutting down on energy-intensive ploughing and other tilling methods. Crop scientists, soil scientists, and plant pathologists throughout South Africa are investigating ways to improve these no-till ways to grow crops. Rotating annual crops with pasture is good for retaining organic matter and soil structure, but it’s not always viable. Alternative short-term rotation (or ‘cover’) crops that improve soil organic matter and minimize plant disease are being examined. Improving the management of nutrients, and applying organic as well as inorganic fertilizers, are ways to increase the soil’s fertility more cost-efficiently than before. Precision farming (treating some parts of a field differently to others), using GPSreferenced information, is also being developed as a tool to reduce costs and increase yields. To minimize the soil compaction common in intensive agriculture, equipment is being redesigned to decrease its pressure on the soil over which it travels, and vehicle traffic over cultivated areas when planting, fertilizing, or spraying with pesticides
2. The condition of the soil is a critical indicator of the sustainability of land-use practices across the landscape. In the context of establishing sustainable development guidelines, a 2005 assessment by M.C. Laker highlighted the sensitivity of the region’s soil resources. For details go to www.environment.gov.za/nssd_2005/Web/NSSD%20Process%20Documents%2 0and%20Reports/LITREVIEW_Soil_and_Sustainability_Oct05.pdf. 3. ‘Dryland’ agriculture refers to crop-growing on land that is not watered by irrigation.
Above left: When air pollution settles on the ground, it can reduce the soil’s fertility. Above: The maize in the picture was planted on the same day, and the photograph was taken on the same day during the drought of February 2007. The surface mulch of plant material on the ground beneath the maize on the right ensured that more of the rainfall infiltrated into the soil, and it also reduced water-loss by evaporation from the soil surface. This made the maize on the right stay green for longer than the plants on the left. Photograph: V.G. Roberts
is being limited to the same pathways for each operation. Combining these and other improvements can help South Africa to nurture the soil that nourishes and feeds all who live in the country, now and through the years to come. – Alan Manson and Victor Roberts ■ Dr Botha (Council for Geoscience, KwaZulu-Natal Unit, Pietermaritzburg) is a Quaternary and environmental geologist who studies soils and processes occurring at the Earth’s surface. Based at the ARC–ISCW in Arcadia, Jan Schoeman is Programme Manager for Natural Resource Characterization and Marjan van der Walt is a Researcher in Soil Information Systems. Environmental scientists Joanne Reid, Teresa Bird, and Dr Scholes are at the University of the Witwatersrand’s School of Animal, Plant and Environmental Sciences, and Dr Manson and Victor Roberts are soil scientists working in the field of soil fertility in the KwaZuluNatal Department of Agriculture and Environmental Affairs. For more on the effects of air pollution on soils, consult G. Held et al., “Atmospheric Particulates, Aerosols and Visibility”, in G. Geld et al. (eds.), Air pollution and its Impacts on the South African Highveld (Cleveland, Environmental Scientific Association, 1996). For a superb collation of soil and land-use data, as well as downloadable satellite images, visit the AGIS (Agricultural Geo-Referenced Information System) website at www.agis.agric.za/agisweb/agis.html. ISRIC-World Soil Information is an independent foundation with a global mandate, funded by the Netherlands government and with a strategic association with Wageningen University and Research Centre. Council for Geoscience staff are involved in a wide range of national and international projects and active in policy advisory bodies and professional working groups. The aims include informing and educating (through the World Soil Museum and other means), and, as ICSU World Data Centre for Soils, serving the scientific community as custodian of global soil information. For more, visit www.isric.org/UK/About+ISRIC/Organization/.
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Healthy foods from Mother Earth Esté Vorster explains the science behind South Africa’s food-based dietary guidelines.
ost people know that what they eat affects health, well-being, and risk of disease, and that some illnesses can be treated with diet. But South Africans still don’t have good eating habits or optimal health. All the country’s population groups suffer from widespread micronutrient deficiencies; there are high levels of under-nutrition in rural children in particular1; and we have one of the world’s highest rates of overweight and obesity. Complicating matters further, HIV/AIDS and tuberculosis (TB) create special nutritional needs that are not always met. To help people stay healthy, nutrient recommendations have been compiled to guide diet planning and food choice. Consumers see them on labels of packaged foods, normally as the percentage that a specific serving of the product contributes to the recommended daily/dietary allowance (RDA). But people choose the ‘food’ they want to eat (rather than ‘nutrients’), so a better environment is needed, offering acceptable, affordable, healthy choices – as well as the knowledge and motivation to choose sensibly.
Above: In the schematic or pictorial presentation of the FBDG, those foods that can be eaten more often and in larger quantities take up the most space.
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Food-based dietary guidelines In the late 1990s, the World Health Organization (WHO) and the Food and Agriculture Organization (FAO) designed a process for member countries to develop food-based dietary guidelines (FBDG) for educating people about healthy diets. They advocated simple, positive messages to address a nation’s specific public-health nutrition problems; promote affordable diets using familiar foods; include staple and traditional fare; be sensitive to cultural habits; and rely on local environmentally-friendly foods. South Africa was one of the first countries to design FBDG successfully and include them in national policy so
as to inform the public about good diet. The challenge was to develop FBDG that would simultaneously address under- and over-nutrition. The solution: an ‘ideal or optimal diet’ with core messages that could translate into eating patterns to suit different population groups and budgets. Following the guidelines should help overweight persons to lose weight; undernourished people and children to improve their nutrition and make them less vulnerable to infection; lower the risk of developing noncommunicable diseases (NCDs) such as diabetes, heart disease, stroke, and some cancers; and even help to treat hypertension, hypercholesterolemia, diabetes, TB and HIV/AIDS. The science behind the advice Developing the country’s FBDG was a scientific process, incorporating the professional literature on what South Africans eat, and their main diet-related health problems. Each guideline was defined for maximum impact. For an optimal diet, the FBDG recommend dietary combinations based on different food groups. Traditionally, foods with similar compositions are grouped together, and foods within a particular group can replace each other. Enjoy food variety Enjoy means making mealtimes special, be they appreciated alone or shared with family or friends. ‘Breaking bread’ with others is a shared cultural experience that entertains and relieves
1. The Directorate of Nutrition within South Africa’s National Department of Health has an excellent integrated programme to address malnutrition, but this condition persists and is on the increase. New strategies and actions are needed, so that people can take responsibility for their own diets and health.
Q Fact file Malnutrition in South Africa
stress. We shouldn’t feel guilty about eating (afraid to gain weight) nor ‘eat on the run’. We need a healthy relationship with food! Variety helps to ensure that we take in all essential nutrients in the required amounts. There’s no single perfect food or drink. Even (near-perfect) milk is low in certain essential nutrients, which are stored by babies before birth to help them survive six months of exclusive breastfeeding. Variety needn’t be expensive. It can mean that staple food (such as maize) is regularly supplemented by vegetables (such as marogo and pumpkin) and some protein (milk, beans, peanuts). But preparing the same ingredients differently doesn’t count as variety – potato salad, mash, or chips represent only one food! Be active Activity is good for you. It allows people to eat enough food to provide all essential nutrients without putting on weight, as it’s hard to meet nutrient recommendations when food and calories are restricted. At least 30 minutes of moderate to vigorous activity a day is associated with a 50% decrease in the risk of death from a heart attack. Experts advise inactive people to increase physical activity gradually – identify the barriers to increased activity, and overcome them with help from family and friends.
Plenty of vegetables and fruits About 35% of human cancers are related to diet. There is convincing evidence that protection comes from eating vegetables and fruit regularly – especially cancer of the stomach, esophagus, lungs, and colon. Vegetables also protect against cardiovascular disease, and are important in diabetic and other therapeutic diets. The benefits and protection against NCDs come from the micronutrients in vegetables and fruit (as rich sources of almost all vitamins and minerals, especially vitamin C, folate, and potassium), their low-energy density (low kilojoule value per volume or weight), and their high dietary fibre content. They are also sources of anti-oxidants and other substances that protect human health – many of these are not yet classified as essential nutrients, but there’s growing scientific evidence of their beneficial effects. We cannot, therefore, simply replace vegetables and fruit with ▲ ▲
A starchy base Starchy foods include grains and their products, such as maize porridge, samp, bread, rice, pasta, sorghum, oats, and breakfast cereals. Root vegetables such as potatoes are often also viewed as
starchy, but can form part of one’s vegetable quota. The idea is to plan meals around plant rather than animal products, so as to lower total fat intake. Two more recommendations – first, often have the starchy food in wholegrain form (minimally processed), and, second, don’t add lots of fats and sugars when you prepare it. Wholegrain foods provide carbohydrates for energy, as well as plant protein, vitamins (especially the B-group), minerals, and dietary fibre. High-carbohydrate diets became popular for improving sports performance. High-fibre diets came in during the 1980s, when dietary fibre was recognized as ensuring regular bowel habits and lowering the risk of many chronic diseases2. How much starchy food to eat depends on a person’s energy requirements. A moderately active adult can easily eat six portions a day without gaining weight, provided few extra fats and sugars are added. A portion varies from half to one cup, depending on the type of food. The six portions could, for instance, consist of a breakfast cereal, a medium potato, two slices of wholewheat bread, maize porridge, and a serving of rice or pasta.
■ About 57 000 children born in South Africa each year die before the age of 5 years (2002 estimates). Of the survivors, at least 9% are underweight, 3% are wasted, and 23% are stunted: this alone makes 35% of young children in South Africa either acutely or chronically undernourished. ■ Childhood under-nutrition brings dire long-term consequences, including impaired physical growth associated with cognitive underdevelopment, which makes these children unable to benefit fully from education; brings diminished competence; and inability as adults to create an enabling environment for themselves and their offspring. This is known as the ‘intergenerational poverty-under-nutrition cycle’. Stunted children, furthermore, are at greater risk of obesity and other non-communicable diseases (NCDs) later in life. ■ Almost 30% of South African men and 57% of women are either overweight or obese, which puts them at risk for many NCDs. After HIV/AIDS, cardiovascular disease is now the second-largest cause of death in our population. ■ Ad hoc studies show that many children and adults in all population groups consume insufficient amounts of iron, zinc, calcium, vitamins A and C, and folate.
2. Recent research shows that some medium-length carbohydrates (3–9 units oligosaccharides), some resistant starch, and dietary fibre are not digested in the small bowel, but fermented by the beneficial microorganisms in the large bowel. The products of fermentation are used by the microorganisms to grow; the short-chain fatty acids formed are absorbed and contribute to human health. The butyric acid in particular is thought to protect against colo-rectal cancer. Easily and rapid, digestible starches have high glycaemic indices (GIs), while slowly digestible starches, rich in dietary fibre, have low GIs and are especially suited for diabetic diets.
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vitamin, mineral, and fibre supplements. The global recommendation is at least five portions of fresh foods a day – preferably three vegetable and two fruit portions, each weighing about 80–100 g, which means about half a kilogram daily. The colours of vegetables and fruit indicate their nutrients: dark green leafy vegetables are excellent sources of folate for pregnant mothers (to protect against neural tube effects in babies), while yellow ones provide precursors of vitamin A. All fruit and vegetables supply minerals, water, and fibre. Citrus fruits, guavas, and tomatoes are rich in vitamin C, and berries are rich in anti-oxidants. Most South Africans don’t eat enough fruit and vegetables. The biggest barriers are availability, affordability, and taste preferences (the last mainly in men and children). Eating more of these foods is perhaps the single dietary change that offers the greatest spinoffs for good health.
More legumes Legumes or pulses are amazing – ideal for undernourished people (because of the plant protein and starch content) and also for overweight, obese, hypercholesterolemic, and diabetic people (because of their low-fat, low-energy, slowly digestible starch, and high-fibre content). They’re also
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affordable (great value for money) with exceptionally long shelf-lives. It’s surprising that legumes don’t fom a substantial part of our diets. This could relate to taste preferences and/or to formation of gas after eating them (caused by their fibre and other non-nutritive substances). The good news is that the gas doesn’t last long, and the problem disappears if you eat these foods regularly. Most South Africans would benefit from eating 100–200 g of cooked legumes daily. They’re traditional in many communities – Africans eat beans and samp; Indians eat lentil and dahl dishes; Afrikaners eat bean salads and soups; and the English eat baked beans on toast. Canned beans are convenient, but their high added salt content is a drawback. Foods from animals Red meat, poultry, fish, eggs, milk, and milk products give high-quality protein, as well as vitamins (notably vitamin B12) and minerals (especially iron in meat and calcium in milk). Fish is our main source of the omega-3 fatty acids, essential for brain and cognitive development in children, and as protection against many NCDs. This guideline brings dietary nutritional balance – that is, it includes nutrients that aren’t abundant in plant foods. The daily recommendation is 400–500 ml milk (or equivalent), plus one further serving of an animal-derived food – which could add up to a weekly total of 2–3 servings of fish, or about 4 eggs, or, alternatively, 560 g of meat. Fish, eggs, and meat don’t all need to be eaten every day, as they are equivalents and can
replace each other. Sufficient calcium is a problem for South African girls and women. Too little of it in the diet is associated with early loss of bone density, osteoporosis, hip fractures, and hypertension. Milk and its products are expensive for many people, but legume consumption can help to increase calcium intake. When they can afford it, South Africans tend to eat too much meat. The saturated fat it contains is associated with increased cholesterol levels and risk of heart disease. Some meat (liver and organs containing many cells, and therefore purines) can also raise levels of uric acid. The bad press around red meat shouldn’t discourage people from eating it in moderation. There is good evidence that increasing animal foods in the diet as people become urbanized improves their nutritional status.
Healthy foods from Mother Earth
A balanced diet without animal foods is possible, provided the vegetarian menu is carefully planned (with nuts, for instance) and includes a source of vitamin B12 (such as a fortified spread). Eat fats sparingly As concentrated, low-volume sources of energy, fats and oils have many benefits – when weaning children, for example, and in therapeutic diets for people with HIV/AIDS. Some fatty acids are essential, in that the body needs them and they can be provided only through the diet. But people often eat too much fat because of the good taste it adds, encouraging consumers (as well as the food industry) to add fats to meals. Nutritional research has for a long time studied the detrimental effects of trans- and saturated fats, as well as the benefits of the omega-3 and monounsaturated fatty acids from fish and olives. Today we accept that we should use fat sparingly, that it should not form more than a third of our daily energy needs, and that most of it should come from plant oils, soft margarines, and fish.
Salt: sprinkled not shaken Hypertension or high blood pressure is a problem in all South African populations. It is known as the ‘silent’ epidemic because it is often symptomfree, so many people go undiagnosed and untreated. It is a major risk factor for strokes, heart attacks, kidney disease, and blindness. Salt (sodium chloride) is the main dietary element involved, so it is recommended that salt intake should not exceed 6 g per day – our ‘modern’ diet, however, brings that figure up to a daily 9 g or more. South African table salt is iodized, to prevent goiters and contribute to children’s normal mental development; as little as 5 g of fortified salt each day provides sufficient iodine. The greatest sources of excessive salt in our diet are pre-prepared, packed, and tinned foods, and salty snacks. To promote low-salt products, South African legislation allows them to claim that they are ‘low sodium’ (120 mg per 100 g serving), ‘very low sodium’ (40 mg per 100 g), or ‘sodium free’ (5 mg
Water – the neglected nutrient Water is essential for many body functions, including the regulation of body temperature. A person can die of thirst more quickly than of hunger. South Africa is arid and hot, and not everybody has access to clean safe water, so there are many cases of dehydration or water-related infectious intestinal diseases (the latter are responsible for 20% of deaths in children aged 1–5 years). Adult men need about 2.9 litres of water per day; women need about 2.1 litres; and children need even more, relative to their body weight (but less in total volume because they are smaller). The general recommendation, therefore, is about 2 litres per person per day. If the quality of the water is suspect, you can boil it, or sterilize it by adding 8 drops of household bleach per 3.8 litres of water. You can take it in the form of plain water, tea, coffee, or other tap-water-based drinks. If children are
3. The cardio-protective effect of drinking in adults (aged 35 years and older) is associated with regular moderate intake that translates to no more than 21 units for men and 14 units for women per week (a ‘unit’ is a drink containing not more than 8 ml of absolute alcohol, according to UK definitions).
per 100 g), with the message: “diets low in sodium may reduce the risk of high blood pressure, a disease associated with many risk factors”. You can replace salt in food preparation with extra herbs and spices. Most people can lower their blood pressure by eating more vegetables, fruit, and low-fat dairy products, and less total fat, saturated fat, and alcohol.
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Sample menus to meet South Africa’s food-based dietary guidelines (FBDG) Limited budget ■ One serving soft porridge (maize or sorghum) with 1 cup (250 ml) milk or maas and 1 teaspoon sugar (optional) ■ One fruit (100 g) in season (apple, banana, orange, mango, or other) ■ 250 ml tea with 20–30 ml milk (1 teaspoon sugar, optional)
Generous budget ■ One serving muesli (cereals + nuts + dried fruit) ■ 125 ml yoghurt ■ One cup (80 g chopped fruit, such as berries) ■ One glass (200–250 ml) fresh 100% fruit juice ■ Two slices wholewheat toast with 3 teaspoons margarine or butter ■ One cup (250 ml) tea or coffee with milk (sugar, optional)
■ One serving stiff maize porridge ■ One cup (100 g) vegetable stew (marogo, potatoes, tomatoes, onions, or other) ■ 100 g cooked pumpkin ■ One serving (100 g) vegetable salad (in season, such as carrots, beetroot) ■ One cup (250 ml) tea with milk (sugar, optional)
■ 100 g potatoes (cooked in jacket) ■ 100 g steamed (or tinned in brine) salmon or tuna or fresh fish OR 2 eggs OR 80 g lean steak (fried in 1 teaspoon olive oil) ■ 100 g mixed salad (salad greens, tomato, cucumber, apple, plus 30 g cheese and 2 teaspoons olive oil, vinegar, etc.) ■ 250 ml tea, coffee, or other drink (such as water)
■ Four slices brown bread with 4 teaspoons margarine (OR one cup samp) ■ 100 g cooked dried beans with 2 teaspoons vegetable oil (such as sunflower oil) ■ One cup (250 ml) milk or maas ■ One cup (250 ml) tea with milk (sugar, optional)
■ One cup (100 g) cooked pasta or rice, or garlic bread ■ 100 g mixed stir-fried vegetables ■ 30 g cheese ■ 100 g cooked legume salad (beans, peas, or lentils, with herbs, onion, and lemon juice) ■ 100 g fruit salad with 50 g ice-cream ■ 125–250 ml wine ■ 250 ml tea or coffee with milk (sugar, optional)
■ One fruit or vegetable in season (such as corn on the cob) ■ One cup (250 ml) tea or coffee or other affordable drink (such as water)
■ If preferred, some of the above can be eaten as snacks rather than as part of meals
NOTE: To avoid putting on weight, prepare carbohydrates without using fats or sugars.
taught to like water, it’ll prevent them later on from relying on carbonated drinks to quench thirst. Drink alcohol sensibly Alcohol is part of many cultures, and may even bring benefits, such as
protection against heart disease afforded by moderate drinking of wine3, or the micronutrients in traditional sorghum beer. But alcohol is addictive in some people, and alcohol abuse (especially binge drinking) can damage health, For more of the scientific details, consult H.H. Vorster (ed.), South African Food-Based Dietary Guidelines (special supplement), in South African Journal of Clinical Nutrition, vol. 14(3) (2001), pp.S1–S80; A. Briend (ed.), Food-Based Dietary Guidelines for Infants and Children: the South-African experience (special issue), in Maternal and Child Nutrition, 2007, vol. 3(4) (2007), pp.223– 333; and World Health Organization, Preparation and use of Food-Based Dietary Guidelines. Report of a joint FAO/WHO consultation (Nutrition Programme WHO, Geneva, 1996, WHO/NUT/96.6, pp.1–99).
cause sudden death, harm unborn babies, disrupt families, and lead to violence and crime. The FBDG therefore advises ‘sensible’ drinking. It’s important to know that nobody needs alcohol for protection against heart disease: other dietary measures such as high fruit and vegetable intake, and a low-fat, low-salt, high-fibre diet, will have greater benefits. Use sugar sparingly Sugar is a dietary carbohydrate with the same energy content as starch and about half that of fat. It is criticized for its association with dental caries, and its overuse in products such as carbonated drinks, cookies, sweets, and puddings, which that are linked to obesity (especially in children). The WHO recommends that not more than 10% of total dietary energy should be provided by sugars, which includes table sugar as well as other added sugars such as honey and syrups (but excludes lactose and fructose in milk and fruit). Sugary foods and drinks are best eaten with meals, so that teeth can be brushed afterwards. Sugar helps to make diets palatable, and can form part of a balanced diet if used sparingly. ■ Professor H.H. (Esté) Vorster is Director of Research in the Faculty of Health Sciences at North-West University (Potchefstroom Campus). As President of the Nutrition Society of South Africa, she initiated and took part in the development of FBDG in South Africa and edited the technical support papers. The WHO has appointed her to assist in developing FBDGs in other regions of the world.
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Q Measuring up The measure of our planet How big? One of the first people to try to work out the size of the Earth was English mathematician Richard Norwood (1590–1675). He took two years to measure the distance from the Tower of London to York with a piece of chain, and used the result, together with measurements of the angle of the Sun at the two places, to calculate the length of one degree of the meridian as 110.72 km. Others followed with more measurements but came to different conclusions about whether the Earth was a perfect sphere and in what ways it wasn’t. One team spent more than nine years trying to take accurate measurements in the Andes, near the equator. In fact the Earth’s circumference is greater around the equator (40 075 km) than through the poles (40 008 km). (For an idea of the shape of the solid Earth, see also p. 3.)
What mass? As Sir Isaac Newton pointed out, objects have a gravitational attraction for each other, which depends on their mass and the distance between them. So if an object in space passes Earth, and its path is affected by the gravitational pull of our planet, we have a way of measuring Earth’s mass. The astronomer Edmond Halley (1656–1742) suggested that observing the rare passage of Venus across the Sun from certain points on Earth would yield the distance from Earth to the Sun. Scientists travelled to more than 100 spots around the world – including South Africa – to make their measurements in 1761. These turned out contradictory and inconclusive, but Captain James Cook’s measurements in Tahiti provided the basis for the calculation that the Sun is about 150 million km away from Earth. London scientist, Henry Cavendish, suffered from extraordinary shyness, but was able to get on with all sorts of experiments on his own, including testing the equipment made by a parson called John Michell for measuring gravitational deflection – and thence the mass of the Earth. Bill Bryson explains: “The work was incredibly exacting, involving 17 delicate, interconnected measurements, which together took nearly a year to complete. When at last he had finished his calculations [in 1798], Cavendish announced that the Earth weighed … six billion trillion metric tonnes, to
use the modern measure.” This is close to what today’s sophisticated techniques would also yield. “All of this merely confirmed estimates made by Newton 110 years before Cavendish without any experimental evidence at all,” Bryson adds.
How old? Scottish scientist James Hutton presented proof in 1788 that the Earth was much, much older than the 6 000 years generally believed at the time. He did not put a number to it, though. Seventy years later, Charles Darwin would present his own ideas on evolution, influenced by Hutton’s work, which had also impressed the pioneer geologist Sir Charles Lyell. By the end of the 1880s, physicist Lord Kelvin had refined his own estimate of the Earth’s age to 20 million years. But once the steady, measurable rate of radioactive decay had been discovered in 1902, scientists could work it out more accurately. The most recent accepted calculation, made by geochemist Clair Patterson at the California Institute of Technology in 1956, is 4.6 billion years, based on precise measurements of the lead/ uranium ratios in old rock. Says Bryson: “When at last he had his results [from an Illinois laboratory], Patterson was so excited that he drove straight to his boyhood home in Iowa and had his mother check him into a hospital because he thought he was having a heart attack.” The oldest rocks on Earth are about 3.8 billion years old, so there is almost no trace left on the planet about the very early Solar System. That’s why Patterson used meteorites as his rock samples. The chemical evidence is that life on Earth began somewhere between 3.8 and 4.0 billion years ago, and the oldest fossils and biodiversity have been dated back to about 3.5 billion years ago. Sources: http://science.howstuffworks.com; http://curious.astro.cornell.edu/question. php?number=452; www.enotes.com; Bill Bryson, A Short History of Nearly Everything (Black Swan, 2003); Jack Repcheck, The Man Who Found Time: James Hutton and the Discovery of the Earth’s Antiquity (Pocket Books, 2003).
Keeping track precisely Nowadays, scientists can make all sorts of precise measurements of the Earth. One system developed by the French government agency, Centre National d’Etudes Spatiales (CNES), is called DORIS (Doppler
No more junk food Less salt for less sugar Reduce salt in children’s diets, researchers suggest, if you want to help them to reduce the amount of sugary beverages they drink. Those with higher salt intake consume more sugary drinks. Source: New Scientist, 23 February 2008.
Poor food is bad for birds Low-quality junk food generated by waste from the fishing industry is bad for seabirds, says a report in the Proceedings of the Royal Society. Not only is the additional food not beneficial, as previously thought, but a study of breeding gannets that had fed on fisheries waste showed that most of their chicks did not survive. Source: New Scientist, 16 February 2008.
Diet sweeteners don’t always help Low-kilojoule sweeteners can skew the body’s natural tendency to stop eating when it’s had enough, according to Susan Swithers and Terry Davidson of Purdue University in Indiana, who ran a series of experiments
Orbitography and Radiopositioning Integrated by Satellite). It determines the orbits of satellites equipped with receivers, using ground stations on Earth as reference points. It is used to study the levels of oceans and ice fields and the shape and movements of Earth, including continental drift. Every day, DORIS instruments take 12 000–13 000 measurements. The system has shown that the African and Eurasian plates are moving towards each other at a rate of nearly 2 cm a year. DORIS also monitors the variations of the poles as the Earth wobbles on its axis, and seasonal variations in the planet’s centre of gravity. CNES operates SPOT (Satellite Pour l’Observation de la Terre, French for “Earth observation satellite”), an optical imaging system observing Earth from space. It also operates Jason 1 and 2, satellites that take measurements of ocean currents and sea-surface height variations. Working with Jason is an observation system called Argo (Array for Realtime Geostrophic Oceanography), made up of 3 000 floats around the globe that measure temperature and salinity in the ocean. The cost of this system is shared by more than 30 countries. (Source: www.cnes.fr)
Deepest ■ This year (2008), TauTona gold mine in Carletonville, west of Johannesburg, is due to become the deepest mine in the world, at 3 902 m. (Source: Mining Weekly) ■ The world’s deepest underground train track is said to be in Pyongyang, North Korea, at 110 m. (Source: Wikipedia) ■ The deepest hole ever drilled was started in 1970 and completed in 1989. The Kola borehole in Russia goes down 12 262 m and was undertaken for purposes of geophysical research. (Source: Wikipedia)
Down under down under Australia’s Great Artesian Basin is a groundwater source that underlies 22% of that continent, covering about 1.7 million km2 and containing an estimated 8 700 million megalitres of water. Its aquifers extend to a depth of three kilometres and some of the water may be two million years old. The average water temperature is 30–50 °C (www.science.org.au)
Q News on rats. They gave them unrestricted rat food and water, plus, for some, set amounts of yogurt flavoured with saccharin, and for others, yoghurt flavoured with sugar to the same degree of sweetness. After five weeks, the rats eating sweetener had gained more weight than those eating sugar. When the rats got a high-calorie chocolate treat, two weeks into the experiment, all ate with relish. Those accustomed to yogurt with sugar then reduced the amount of yogurt they ate for their next meal, to compensate for the extra calories consumed. Those accustomed to yogurt with sweetener, however, did not. The researchers think that the cause is a disruption in the brain’s natural connection between sweet taste and calories. After habitual exposure to sweeteners, the brain seems to ‘forget’ this connection, and no longer sends signals to stop the animal eating after it has consumed more calories than usual. Sources: New Scientist, 16 February 2008; and The Economist, 16 February 2008.
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Gold and silver Chrome, platinum, and nickel Copper, lead, and zinc Iron and manganese Tin Uranium
Above: Map of mineral deposits of Africa. Data from the African mineral deposits GIS database (http://www.uct.ac.za/depts/cigces/gondmin.htm). The continent has more than 8 000 known mineral deposits of various kinds. Top left: A handful of diamonds. Left: Site of a new diamond deposit in central DRC. News of finds travels fast, often bringing chaotic and unpredictable behaviour.
Mineral resources Wealth at a frightening price Maarten de Wit assesses the real costs of Africa’s mineral boom.
of bauxite (the main source for aluminium) and 66% of cobalt. But at what price are the continent’s mineral resources being exploited?
South Africa is a global leader in the mining of gold, diamonds, platinum, uranium, coal, iron, and manganese, and scientists believe that there is much more mineral wealth to be found north of the Limpopo. Indeed, apart from South Africa, the continent is already a source of 30% of the global resources
Environmental costs Geology reveals that relatively easy pickings of important strategic mineral deposits are abundant in Africa. The problem is that they often occur in environmentally sensitive areas and biodiversity hotspots. There are vast copper and cobalt reserves, for instance, beneath the wetlands of southeast Democratic Republic of Congo (DRC) and Zambia – a region teeming with unique wildlife. There is also uranium and tin in Rwanda and Burundi’s forests – strongholds of some of the last families of wild gorillas; phosphates in the still pristine Mauritanian deserts; bauxite deposits in the last
nprecedented global demand for natural resources, driven in part by relentless industrialization in China and India, shows no immediate signs of downturn1. Africa’s mineral exploration and exploitation boom has rallied most of the world’s largescale mining and energy companies and financiers to participate in this new scramble for the continent’s finite resources – despite logistical obstacles such as lack of infrastructure, and local political unrest, war, and corruption.
Left (above and below): Open-pit mining excavations. 1. The Annual Mining Indaba in Cape Town in February 2008 attracted a record crowd, with close to 5 000 delegates, including 16 ministers of mining from across Africa and 3 500 of the world’s leading mining investors.
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Q Viewpoint Africa’s mineral riches
South Africa’s position in the world’s mineral reserves and production Commodity Antimony Chromite Coal Copper Fluorspar Gold Iron Lead Manganese Nickel Platinum Titanium Uranium Vanadium
Reserves % 6.4 72.4 6.1 1.4 16.7 40.1 0.9 2.1 80.0 8.4 87.7 18.3 7.2 31.0
Rank 4 1 8 14 2 1 9 7 1 5 1 2 5 1
% 3.2 38.7 4.5 0.7 5.0 11.1 2.8 1.4 13.3 3.1 59.3 19.8 1.6 48.0
Africa comprises as much as 21% of Earth’s total continental surface, and holds great mineral wealth. Southern Africa is exceptionally rich in minerals, and more lie hidden further north, generating a new ‘millennium scramble’ across the continent. The USA, Canada, Australia, and the EU, as well as China and India, are digging for new minerals and energy resources (uranium, oil and gas), in the context of current exceptionally high prices. An ounce (~32 grams) of gold that a decade ago sold for US$200 is now worth four times as much (US$800); platinum, having increased nearly eightfold in price since the end of the last century, now, in early 2008, sells for US$1 800 per ounce. These increases have outstripped the wildest imaginations of global financiers.
Production Rank 7 1 5 16 4 1 7 11 2 9 1 2 11 1
This table indicates South Africa’s mineral reserves and production (as a percentage of the world’s totals and the world ranking of each). In this table, ‘reserve’ indicates the quantity that it is economic to mine in present market conditions; ‘production’ figures depend on the rate at which a country or a company extracts the resource. All the minerals listed above can affect the environment (for example, in terms of by-products, and depending on the mining method used). Arabian-Nubian Shield (0.5–1.0 Ga)
Birimian Shield (1.8–2.3 Ga)
Ga = giga-years ago (giga = 1 000 million)
Zimbabwe Craton (2.5–3.0 Ga)
Above: Locations of three African regions of similar geology but with different ages of mineral deposits. The regions represent three distinct 500-million-year time-slices of African crustal growth between the Archaean (>2 500 million years ago) and the end of the Neoproterozoic (~550 million years ago), during which formation of mineral deposits decreased significantly. This makes old crust more richly endowed with minerals than younger crust, and Africa has enormous areas of old crust.
of Mozambique and Madagascar. In addition, increased demand for energy and the imminently predicted downturn in global oil production (see graph on next page) have opened up for exploration vast new pristine areas in excess of 10 million km2,
2. The Pygmy people of Equatorial Africa are noted for their hunting and forest culture.
vestiges of Guinea’s rainforests; diamonds across Angola’s and the DRC’s savannas, Botswana’s last San hunting grounds, and Gabon and Congo’s tropical rainforests – home to the Pygmies2 and forest elephants; and titanium along unspoiled beaches
Top and middle: Only the best part of the rare hardwoods from central African rainforests is used for decorative purpose, such as panelling for luxury cars, leaving more than 70% of the harvested trees to rot. Other trees are exported mainly to Europe and the Far East. In Gabon, an average of 2 000 such trees are cut down daily for this market. Above: Pigmy dwellings in the southwest of the Central African Republic along its receding forest margins.
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Top: Graph showing Hubbert’s Peak of world oil production and Africa’s development dilemma. According to Hubbert’s now generally accepted theory and predictions of 1956, after ‘Peak Oil’, around the year 2000, the rate of oil production on Earth will enter a terminal decline. Around 2050, global oil production could be back to nearly what it was in the 1950s. Africa’s development has now to take place during the downward slope of the oil production curve, despite the need to increase its energy demand at least 5-fold to raise living standards to the world average and deliver a better life for all its 900 million people. Climate change, global warming, and food and water shortages will exacerbate these challenges. For more details see K.S. Deffeyes, Hubbert’s Peak (Princeton University Press, 2001); International Energy Agency, Key World Energy statistics, 2007 (Paris, OECD) at www.iea.org/ textbase/nppdf/free/key_stats_2007.pdf; and J.P. Holdren, “Science and Technology for sustainable well-being”, Science, vol. 319 (2008), pp.424–434.
Above (middle): Primate meat for sale in central Africa. Resource exploitation and poor wages, particularly in the forestry and mining industries, fuels ‘killing for the pot’ and trade in bushmeat. Primates are openly for sale and widely consumed. A study in northern Congo (Brazzaville) found that 5–7% of the chimpanzee and gorilla populations were being killed each year. A conservationist in Yaounde, Cameroon, estimated that 1 tonne of smoked bushmeat was unloaded at the railway station each day to supply the markets. For more visit www.4apes. com/bushmeat/report/bushmeat.pdf; www.janegoodall.org/africaprograms/objectives/controlling-bushmeat-trade.asp; www. ucpress.edu/books/pages/9403.html. Above: Despite broken bridges and promises, as well as other obstacles, exploitation of Africa’s natural resources is in full swing.
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including central Africa’s deserts, the East African Lakes (for oil and gas), and the Uganda–Sudanese wetlands – the Sudds that ‘filter’ the waters of the White Nile – despite warnings of near-irreversible environmental destruction associated with resource exploitation that has plagued other nations, such as Nigeria. Since decolonization began more than half a century ago, Africa has remained under-explored, and geologists from around the world are now paid handsomely for searching in remote areas to help to stake out new wealth on the continent and convert its landscapes to ‘manscapes’. This is at just the time when GEO-4 (the United Nations Environment Programme’s newest audit, released on 25 October 2007) shows that individuals in the world now need 30% more land to support their demands than our Earth can supply, and that humanity’s ‘footprint’ (or ‘environmental requirement’) is recorded as 21.9 ha per person, even though the Earth’s biological capacity allows, on average, only 15.7 ha per person3. Winners and losers In supplying the world with natural resources, Africa’s new mines and oil fields more often than not create a sorry environmental mess. They frequently degrade conditions beyond repair for rural people – mostly without rehabilitation, because the bulk of the profits go to citydwelling stakeholders and to financial investment centres in the developed world4. The Niger Delta is a familiar example, but similar stories abound on the continent, from small-scale alluvial diamond operations owned by unscrupulous companies in the Central African Republic to large-scale gold prospecting in the eastern DRC5. There are devastating side-effects. New mines and timber factories in central Africa mean sacrificing virgin rainforests – between 1980 and 1995, Africa lost an estimated 66 million ha of tropical forest, at a deforestation rate of nearly 1% per year. Local labourers are easily exploited with inadequate remuneration for tough work, and that, in turn, advances poverty and corruption. Deforestation gives easy access to hitherto inaccessible hunting
grounds, driving the illegal bushmeat trade, spreading new diseases, polluting watersheds, eroding soils, encouraging forced child labour and prostitution, and increasing urban slums. Exploration and mining industries attract investors with best-practice plans, but who all too often renege on their good intentions. This African story remains largely untold and/or falls on deaf ears. Globally, biodiversity is in decline, with extinction rates of species some 100 to 1 000 times greater than in the geological past, as estimated from the fossil records6. More than anywhere else in the world, Africa is at the ‘coal-face’ of this unabated decline, with a further estimated decrease across this continent of 10–16% between the years 2000 and 2050, depending on whether the strategies that are implemented follow principles of sustainable development, or market-driven, business–as-usual ones3. Africa, the ancestral home of primates – gorillas, chimpanzees, lemurs, and humans – is being destroyed, arguably beyond repair. This strategy of plunder highlights a fundamental unwillingness to accept the way in which the world is miscalculating the natural resources wealth of Africa. Those who ignore the permanent loss of its natural capital are guilty – as in colonial times – of disregarding its real value. Accurate valuation needs to set a price for Africa’s wildlife, fresh water, open vistas, cultural heritage, and forest biodiversity, amongst other things. Time for solutions How might the situation be rectified? More than 30 years ago, mathematical biologist Colin Clark exposed why it was (and often still is) viewed as more profitable for investors in dollars and cents, to chop down the forests, kill the animals, sell the proceeds, and live handsomely off the returns for the foreseeable future. This skewed reasoning still prevails, because it is rooted in economics and global trading rules that exclude from their calculations and strategies the costs of social injustice and depletion of Africa’s finite natural habitats. Investor strategies are driven, instead, by financial equations and ‘optimization models’ that encourage ever riskier depth–equity ratios in pursuit of ever greater financial rewards.
3. Detailed information is available in the 2007 report of the United Nations Environment Programme, Global Environment Outlook: environment for development (GEO-4) (available at www.unep.org/geo/geo4). This report assesses the current state of the global atmosphere, land, water, and biodiversity, describes changes since 1987, and identifies priorities for action. For information relating to South Africa, consult South Africa Environment Outlook: A report on the state of the environment, issued in 2006 by the Department of Environmental Affairs and Tourism. 4. For more, refer to “Poisoned Wells”, available at www.harpers.org/archive/2007/04/sb-six-q-for-nicholas-shaxson. 5. See also “Mining firms ‘polluting Africa’ ”, and “Congo arrests after toxic dumping” at 2007-http://newsvote.bbc.co.uk/ mpapps/pagetools/print/news.bbc.co.uk/2/. 6. See Millennium Ecosystem Assessment (MEA), Ecosystems and Human well-being: biodiversity synthesis (World Resources Institute, Washington, DC, 2007 at http://earthtrends.wri.org/searchable_db)
Q Viewpoint Evaluating Africa’s natural resources No robust way is available yet to estimate the long-term health, pollution, and environmental costs associated with, for example, mining copper, gold, and uranium underground, or open-cast (surface) excavation for diamonds, asbestos, mercury, aluminium, and lead. About 40% of global total documented gold production has come from South Africa (that is, close to 50 000 tonnes since about the 1870s), and has been a leading supplier of minerals such as asbestos and lead, copper, and platinum. Yet such mining has also caused terminal occupational diseases, such as silicosis and asbestosis, in over 500 000 former mineworkers – diseases that often develop years after miners leave the mine. The potential estimated bill for the backlog of such diseases in southern Africa is well over a billion US dollars. Furthermore, every tonne of South Africa’s gold production has caused, on average, one miner’s death and about 12 serious injuries*. Because the hidden costs (‘externalities’) of exploiting mineral resources are difficult to assess, they have not been calculated into final commodity prices. Current studies are still inadequate, but according to one estimate, the price of copper should be 20 times higher than it sells for on global markets. Economists’ calculations Economists use two ways to judge the externality costs of exploiting mineral deposits and other natural resources such as timber and fish. The first – traditional natural resource accounting – includes marginal externality costs incrementally, with the effect of making economic equations ever more complex. It introduces the impacts, for example, of improved technology; resource substitution (such as the costs of substituting plastic for a metal in a product); depletion and intergenerational equity (such as equity for future generations); environmental abatement (the cost of cleaning up a mess), and, more recently, anthropogenic global warming. The question asked is how much of a resource should be extracted today and how much left behind. Used in many developed nations, the method is often imposed on African nations by international financiers. But it has excluded high externality costs, such as those associated with climate change, pollution, biodiversity loss, fish stock crashes, poverty, and disease. The second – ecological economics – views Earth as a service provider of, for example, fresh water and fertile soils, and suggests adequate payment for such resources. Earth’s services have an estimated value greater than the 1996 Gross World Product, which was more than US$33 trillion. Such high valuations generate scepticism and debate. But because these hidden costs are not conventionally shown in industry’s audits, society at large – and some African communities more than others – have to pay. Solutions require accurate evaluations of all (not just some) of the resources that societies use, and understanding of how Earth functions as a service provider. The continent’s mineral wealth Mineral deposits are ‘capital’ derived from geological processes converging to concentrate useful minerals into natural stockpiles (or ‘ores’). Some (called ‘reserves’) can be extracted economically under present socioeconomic conditions. To understand their real value (to humans), one can evaluate Nature’s
The real value of African resources ought rather to be determined using principles of ecological economics that treat profits beyond cash-only returns. Setting a fair price for Africa’s riches to ensure sustainable development, well-being, and wise conservation of its heritage is central. Such a solution needs to be implemented now, before the real value of Africa’s natural assets is lost forever. ■ Professor de Wit is the Director of the Africa Earth Observatory Network (AEON) at the University of Cape Town. The work of the following people contributed to this article: Professor Christien Thiart (AEON), Tshifhiwa Mabidi (Anglo American), Susan Frost-Killian (Council for Geoscience, Pretoria), and Dr John Anderson (South African National Biodiversity Institute, Pretoria).
mineral deposits by calculating the cost if human technology had to produce them. Concentrating copper into a reserve, for instance, costs at least an order of magnitude more than the metal’s present market price, which effectively excludes significant side-effect ‘externality’ costs of modern mining. To be socially and ecologically responsible, we recommend that the mineral exploitation industry include such evaluations before embarking on new projects. Value of Earth’s renewable freshwater supply Total volume of Earth’s surface water 1 386 x 106 km3 Fresh water (including ice) as proportion of total 2.5% Proportion of fresh water available for consumption 0.77% Precipitation on land (total terrestrial renewable freshwater supply) 11 x 104 km3 Volume of water used globally for human activities 4 430 km3/year Volume of water consumed by global human activities 2 010 km3/year Replacement cost using current best alternative of desalination (this is 4–8 times the average cost of urban water supply today and 10–20 times more than the price that farmers pay) US$1.50 per m3 Annual value of Earth’s fresh water consumed US$3 x 1012/year globally by human activities (US$3 000 billion/year) Value of Earth’s freshwater supply = 12% of global Gross World Product This table outlines the estimated value of Nature’s natural desalination services as provided by the hydrological cycle in terms of what it would cost to desalinate the water using human technology. Fresh water is unlike other resources in that there is no substitute for it. These estimates represent minimum values. Were the calculation to include replacement cost of water evapo-transpired by trees that have been harvested for wood and fuel, and by grasslands that are used for grazing, the figures would be nine times greater.
* The 1995 Leon Commission Report stated that more than 69 000 mine workers had lost their lives between 1900 and 1994 and a million had been injured. Between 1985 and 1995, 600odd tonnes of gold were produced annually, with an average of 680 deaths a year on all mines. (See the Leon Commission report on the safety and health in the mining industry at www.dme.gov.za/mhs/documents.stm.)
For more, consult R. Ehrlich, “The body as history: on looking at the lungs of miners” (www.news.uct.ac.za/downloads/news.uct.ac.za/lectures/inaug/inaug_ rodney_ehrlich.pdf); R. Morris, “Lawyers divided on outcome of mine claim”, Business Report (10 February 2008) (www.busrep.co.za/index.php?fArticleId=4245318&f SectionId=552&fSetId=662); S. Marks, “The silent scourge? Silicosis, respiratory disease and gold-mining in South Africa” (2002) (http://wiserweb.wits.ac.za/PDF%20Files/ international%20-%20marks.pdf); and J.C.A. Davies, “Worker advocates in the health sciences: where are you now that we need you?” (www.givengain.com/unique/ sasom/upload/tonydavies.pdf).
For more consult the following: I. Blignaut and M.P. de Wit, Sustainable Options. Development Lessons from Environmental Economics (UCT Press, 2004); Chamber of Mines of South Africa, online, Facts & Figures 2006; C.C. Clark, “Clear-cut economics – should we harvest everything now?”, Science, vol. 225 (1973), pp.890–897; R. Constanza et al., “The Value of the World’s Ecosystem Services and Natural Capital”, Nature, vol. 387 (1997), pp.253–260; E.A. Davidson, You Can’t Eat GNP: Economics as if Ecology Mattered (Cambridge, MA, Perseus, 2000); M.J. de Wit, “Valuing copper mined from hydrothermal ore deposits”, Ecological Economics, vol. 55 (2006), pp.437–443 (DOI:10.1016/j.ecolecon.2005.03.032); Enviropaedia 2006–2008 ‘Be the Change’ edition (www. environpaedia.com); J. Lovelock, The Revenge of Gaia (Penguin, 2006); N. Shaxson, Poisoned Wells: The Dirty Politics of African Oil (Palgrave Macmillan, 2007); E.O. Wilson, The Future of Life (Abacus, TimeWarnerBooks, 2002).
‘Consumption’ by Earth Stewardship Science student, UCT, 2004
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Ar t and map -making Fritha Langerman explores ways in which visual systems meet.
eople are paying more and more attention to the ways that art and science converge. In the past, the relationship has seemed one-directional, with science exerting theoretical and technological influence on the manner in which visual thinking developed – for example, the influence of Michel Chevreuil’s colour theories1 on the Impressionist painters, quantum physics on the Futurists and Surrealists, and mass production on Pop Art. It is often argued that science is a language favouring empirical absolutes, wholeness, and rationalism, while art emphasizes intuition, using ambiguity and suggestion to reflect on the complexities of human experience. Whereas much contemporary art aims to obfuscate, disorientate, and render the known world unintelligible, there are more similarities between the two modes of enquiry than might at first appear. Both are concerned with observing, visualizing, imagining, and modelling the known Universe – producing a template by which or against which to interpret the world.
Top left: Paul Edmunds. Sieve (detail), 2005. The artist has subjected an image of the dawn sky to a CMYK (acronym for the colours cyan, magenta, yellow, and key [black]) colour analysis, translated into a 3-D grid of polygons. Using this as a template, hexagonal perforations were then cut through sheets of process colour paper, revealing layers below. The result is a ‘mapped’ analogous representation of the sky, optically complex, yet faithful to the input from the source. Photograph: Courtesy of the artist Top right: Alan Alborough. WYSIWYG (detail), 2005. Photograph: Courtesy of the artist Top: Willem Boshoff. 370-Day Project, 1982–1983. Photograph: John Hodgkiss. Image reproduced courtesy of David Krut Publishing
Above: 370-Day Project (detail). Photograph: John Hodgkiss. Image reproduced courtesy of David Krut Publishing
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Representing Earth These parallel qualities of science and art are perhaps most clearly demonstrated in mapping, which is, in many ways, the positioning of one’s self in relation to what is ‘out there’ in the external environment. To map is to work with analogy, and to make a clear distinction between the world of symbol and that of experience. A map is not the same thing as actual territory, but rather a selective abstract rendering of it. And since mapping is an act of representation, it is as much subject to political and ideological construction as any other visual practice. In the colonial experience and context, for instance, where new geographical areas loomed as worlds of empty space to be possessed and exploited, maps provided indices by which to determine power and exercise social control. Political implications aside, the syntax of a map is not dissimilar to that of an artwork. The modernist grid2 of the early 20th century reduced the visual plane to a system of points, lines, and areas, and concerned itself mainly with formal aspects of size, shape, colour, value,
texture, and pattern. Contemporary practice accepts, however, that context alters the ways in which visual information can be interpreted. So, whereas in map-making the visual language is viewed as providing clarity, an artwork may use such language ironically to do the reverse. Mapping in art Most artists engage in the act of mapping within the creative process. As they plan an image or artwork, a shift occurs when they take an initial idea and subject it to visual simplification, and when they view units of information in relation to one another within a spatial plane. In the work of some artists, the relationship between the units and the more complex whole becomes the underlying content itself, revealing an interest in pattern, formulas, cycles, or systems. Four South African artists in particular – Paul Edmunds, Willem Boshoff, Sandile Zulu, and Alan Alborough – concern themselves with natural processes, elements, and change, and exploring the physical and associative values of materials, reworking and transforming them. Paul Edmunds works with the symmetries of natural structures. For him, pattern reveals internal structures as well as expressing physical processes, organic cycles, and the replication of living organisms. He uses a simple ‘formula’ as a starting point for each work, which develops into its final structure through a series of repetitive acts of labour. The piece Sieve is an example of the visual complexity that results. Willem Boshoff’s singular interest is in taxonomy, etymology, and lexicons. In 370-Day Project, he imposed a ‘Linnaean’ system of classification on his daily routine, dividing the day into acts of sacrifice, duty, and recreation. He evaluated and reported on these activities in a personal code that he inscribed onto 370 tablets, each carved from a different wood that he personally sourced in South Africa. This serialized work, in which small elements make up the whole, is also a map that describes personal experience, the passage of time and, as a dictionary of trees, a natural territory. Sandile Zulu focuses on the elements and formal camouflage, co-opting fire and water as he makes his fugitive, fragile images. In Labyrinth of Genes
1. Michel Eugène Chevreul (1786-1889), a French industrial chemist, published The Principles of Harmony and Contrast of Colours in 1839. In it, he discussed the ways in which complementary contrasting colours persist in after-images and in the shadows that are cast in full sunlight. 2. The formalist concerns of modernism were encapsulated by the grid, which emphasized flatness and repetition. In contrast to perspectival organization of spatial planes, the grid did away with pictorial hierarchies (grounds), and in so doing became a ‘leveller’ of content. All areas of the image plane were seen to have equal value.
Sandile Zulu. Labyrinth of Genes and Elements, 2004. Photograph: John Hodgkiss. Image reproduced courtesy of David Krut Publishing
and Elements, he uses stones as a mask to shield the canvas from the flames – the result is a work that maps the way in which the destructive forces of nature transform a surface. He draws formal parallels to mapping by alluding to contours and using a repetitive grid. Much of Alan Alborough’s work concerns itself with visual puns and wordplay, as well as with visual systems (and the gaps within them). He transforms everyday materials into mysterious devices that appear to have scientific value. The work WYSIWYG (an acronym for ‘What You See Is What You Get’) is typical. It uses an apparatus made of syringes, plastics, batteries, metal, and brine. The materials deteriorate over time, and the residue is captured on the paper beneath. During the process, images emerge on the paper, born of staining and corrosion. Like Zulu’s work, these ‘drawings’ map a process of transformation as well as playing with the ambiguous language
of abstraction. The observable objects and the images they produce on the paper look very different – that is, there is a visual discrepancy between them. The act of translating the material territory (the apparatus) into an abstract image (the marks produced on the paper) is precisely what unites art and mapping – and what connects both with the materials and processes of planet Earth. Just as a map looks different from the territory it represents, and requires a conceptual link to connect the marks on the paper and the geographical terrain it represents, so too, in the process of WYSIWYG, a conceptual relationship is built up between the abstract images and the realities of the physical and temporal world that gave rise to them. ■
Consult the following for further information about each artist. For more on Paul Edmunds, see Art South Africa, vol 5(3) (2007). For more on Willem Boshoff, see Ivan Vladislavi, Willem Boshoff (David Krut Publishing, 2005). For more on Sandile Zulu, see Colin Richards, Sandile Zulu (David Krut Publishing, 2005). For more on Alan Alborough, visit www.alanalborough.co.za.
Fritha Langerman is at the Michaelis School of Fine Art, University of Cape Town. She specializes in printmaking and curatorship, and her research interests include representation and visualization in science and medicine.
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Baberton/Murchison Giyane, Beit Bridge Beaufort Dwyka Ecca Kalahari Meinhardskraal, granite sand river Gneiss, etc. Okiep, Bushmanland, Korannaland, Geelvloer Rustenburg, Lebowa, Rashoop Suurberg, Drakensberg, Lebombo Transvaal, Rooiberg, Griqualand-West Ventersdorp Waterberg, Soutpansberg, Orange River Witwatersrand, Dominion, Pongola
Blyde River Valley
Arid Lowveld Bankenveld Cymbopogon-themeda Veld (Sandy) Dry Cymbopogon-themeda Veld Kalahari Thornveld and shrub Bushveld Lowveld Lowveld Sour Bushveld Mixed Bushveld North-Eastern Mountain Sourveld North-Eastern Sandy Highveld Other Turf Thornveld Piet Retief Sourveld Sour Bushveld Sourish mixed Bushveld Springbok Flats turf thornveld Themeda veld to Cymbopogon-themeda veld transition (Patchy) Transitional Cymbopogon-themeda veld
Londolozi 8 Waterberg Ezemvelo Nature Reserve
Bushveld Igneous complex
Londolozi Archacan granite crust
Bushveld Igneous complex
Witwatersrand Ventersdorp lavas
Australopithecus Australopithecus (Paranthropus) robustus africanus Mrs Ples, Sts 5, Tvl, Mus. Paranthropus, Sk 48, Tvl. Mus 1.7 Ma, Swartkrans 2.6 Ma, Sterkfontein Legend Main image – Topographical Base with the following overlaid: Cradle to Cradle corridor Vredefort Dome Baberton Mountain range World Heritage sites Biosphere Reserves Conservation Areas
n lt rto Be be e Ba ston n ee Gr
Loskop Dam Karoo Supergroup overlapping older strata
Warmbaths Rustenburg Pretoria Johannesburg 5
Location of CCC within South Afica
Cullinan Diamond Pipe
Cradle of Life, Baberton 10 Mountains
The world’s oldest known bacteria (red) embedded in a quartz matrix (green). Baberton Mountains
Number of schools Tourism Index Tswaing Impact Crater
Cradle of Life to Cradle of Humanity Corridor (CCC) 0
Topographic base: courtesy of Peace Parks Foundation
The Sixth Extinction In the last 500 million years since the Cambrian explosion of multicellular organisms in the oceans, scientists have identified five previous global extinction events – when some 80% or more of species died out worldwide. The onset of what is called the Sixth Extinction (or the Holocene extinction event) can be dated from the first colonization, about 70 000 years ago, of Homo sapiens sapiens (that is, anatomically modern humans) originating in Africa. From that time onwards – first as hunter-gatherers, then as agriculturalists and towndwellers, then as industrialists – people have colonized and re-colonized the world. With the Earth’s human population escalating exponentially to its current 6.6 billion came its soaring capacity to alter the environment, bringing with it a large-scale extinction of species and habitat. Estimated measures of this extinction event include: ■ the hunting out of existence of 80–90% of all species of megafauna (larger mammals and flightless birds) outside Africa ■ the destruction of 88% of the original extent of the 25 biodiversity hotspots (places whose relatively rich plant and animal diversity is especially threatened) recognized worldwide.
The Africa Alive Corridors project This initiative aims to help to stem the extinction of biodiversity and natural habitat across Africa; to promote the geological, biological, and cultural heritage of the continent; and, by drawing all Africans into the process, to increase prosperity and human well-being on the continent. The concept was first outlined in 2003 as part of a broader Gondwana Corridors joint project by researchers at the South African National Biodiversity Institute (SANBI) and the Africa Earth Observatory Network (AEON). It has been endorsed by ICSU Africa as a flagship for their contribution to the International Year of Planet Earth (IYPE). The official launch of the project is scheduled for the IYPE Africa launch in Arusha, Tanzania, in May 2008.
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Standing in the Baberton Greenstone Belt looking towards the world’s oldest peneplain across which the Transvaal sea transgressed 2.6 billion years ago.
Population & towns
Cradle of Humanity Vredefort Sterkfontein World Dome Heritage Site 4
Biosensitivity, Erosion, Population and Towns, Number of schools & Tourism Index: darkest colour = highest value
Photos: Alexander Junod (Sept. 2000) (1), Gerry Newlands (1991) (2, 3), Viljoen & Reinold (1999) (4, 5, 6), Varty & Buchanan (1997) (7, 8), Maarten de Wit (9, 10). Compiled by Inge Netterberg & Gaby van Wyk
John Anderson, Tebogo Mashua, and Maarten de Wit explain the mapping out of a continental network of scientific and cultural heritage across Africa.
he Earth’s prodigious diversity of life is in serious trouble, due to the current rapidly escalating global extinction of species and habitats, combined with runaway global warming. Past extinctions (such as the Cretaceous– Tertiary event, some 65 million years ago (Mya), which brought the dinosaur era to an abrupt close) were set in motion by asteroids or megavolcanism. The present one – the Sixth in the past 500 million years – is caused by exploding human numbers and their voracious needs. The ‘Africa Alive Corridors’ project – part of a broader and ultimately global initiative – aims to stem the tide by taking a holistic deep-time view of cause and effect. It has mapped out 21 geographic ‘corridors’ that criss-cross Africa and include all
5. Colliding Continents 5 countries
12. Saharan Paradise Lost 4 countries 20. Carbon Footprint 4 countries
17. Mirror of History 13 countries 14 nodes
The 21 African corridors and their storylines 1. Cradle to Cradle (South Africa): 3.5 billion years ago–present: ‘Celebrating 3.5 billion years of life on Earth’
13. Valley of the Pharoahs 1 country
2. Snowball Earth (Namibia): 1 000–500 Mya: ‘From a lifeless Snowball Earth to the biological big bang’
14. Nubian Nile 2 countries
3. Great Karoo (South Africa): 325–175 Mya: ‘Pangaea through the mother of all extinctions’
19. Sixth Extinction 6 countries
4. African Pole of Rotation (Cameroon): 200 Mya–150 000 BP**: ‘Africa across the Cameroon Hotspot’ 5. Colliding Continents (Morocco to Tunisia): 200 Mya–present: ‘Rifting, drifting, folding along the Atlas Mountains’
15. Songhay’s Timbuktu 12 countries 13 nodes 4. African Pole of Rotation 3 countries 7. Lungs of Africa 5 countries
6. Lemur–Chameleon (Madagascar): 65 Mya–present: ‘Born on a microcontinent’
8. Eastern Rift Valley 4 countries 16 nodes
7. Lungs of Africa (DRC): 10 Mya–present: ‘Womb of our hominid family and of our sister pongids’
9. Western Rift Valley 5 countries 6. Lemur-chamellion 1 country
8. Eastern Rift Valley (Ethiopia to Malawi): 5 Mya–150 000 BP: ‘Our hominid trail from Ardipithecus to Homo’ 9. Western Rift Valley (Uganda to Tanzania): 5 Mya–present: ‘Extreme fish diversity in the Great Lakes’
“For the children of today’s world and the children of tomorrow’s world” – Nelson Mandela
11. Kalahari Khoisan 5 countries 19 nodes
10. Homo sapiens sapiens (South Africa): 140 000–60 000 BP: ‘The first half of our sojourn on Earth’
16. Mapungubwe – Great Zimbabwe 5 countries
2. Snowball Earth 2 countries
1. Cradle to cradle 2 countries
11. Khoisan Kalahari (Namibia to Botswana): 60 000 BP –present: ‘The Khoisan stem of our human phylogeny’
3. Great Karoo 2 countries
10. Homo sapiens sapiens 1 country
12. Saharan Paradise Lost (Tunisia to Chad): 22 000 BP–present: ‘The rock-art gallery traces desertification’
Above: In these 21 corridors, Africa tells the nearly four-billion-year epic story of life on Earth, from its time as an embryo continent (long before it emerged as a discrete entity from the supercontinent Gondwana) to the arrival of humankind. Opposite page: The topography along this corridor, traced on a satellite image of a part of the northeastern corner of South Africa, reflects its uniquely rich geology. The territory includes various aspects of the physical and social landscape.
its countries. Each corridor represents a unique chapter in the story of the continent, with nodes of special interest that highlight its scientific and cultural heritage. All 900 million Africans of every background and persuasion are invited to join together in the ‘co-curation’ of this rich heritage1.
C1 Cradle (of Life) to Cradle (of Humankind) corridor (South Africa) The sinuous strip of territory running from the Barberton Mountains to the Vredefort Dome represents by far the most continuous passage through geological time anywhere on Earth. It traverses the planet’s top-podium geological hotspot in a storyline of Earth, life, and cultural superlatives. Evolution of life. The corridor begins in the world’s oldest, largest, best-preserved stretch of early landscape, the Barberton Greenstone Belt (ranging in age between 3 570 and 3 060 Mya), which yields the oldest known bacteria
Journey into Africa’s autobiography Africa’s epic story is dramatic, complex, and compelling. Its ‘autobiography’ is told by Africa itself, through its rocks, fossil beds, archaeological sites, and the living generations of plants, animals, and humans for whom the continent is home. Scientists and researchers across disciplines translate the story into human language so as to inspire appreciation and love for this mother of all continents. Only through knowledge and awareness of everything that forms part of the story can ways be found to preserve and nurture this part of Earth and all who inhabit it, and to convey its message to the world at large. This article offers glimpses into that story. The Cradle to Cradle Corridor towards the south of the continent forms the overture, then we move north to dip briefly into five later
chapters in the epic. The walk through the 21 corridors of Earth-time in Africa traverses the continent’s – and many of the world’s – prime scientific and cultural hotspots, offering Africans opportunities for scientific exploration, eco- and heritage-tourism, sustainable small businesses specializing in organic farming, conservation, or biodiversity management, and the broadest possible education. In their different ways, all can be active co-curators of Africa’s heritage.
1. The process of encouraging the participation of all Africans starts in close association with the International Council for Science (ICSU) and the organizers of the Africa IYPE launch in May 2008 in Arusha, Tanzania, where further planning is to be workshopped. The aim is to involve the whole continent in promoting the project’s ideal of respecting the dignity of all life on Earth – that of humans and every other species.
13. Valley of the Pharaohs (Egypt to Sudan): 3 100–30 BCE***: ‘Life cycle of the classical Egyptian civilization’ 14. Nubian Nile (Sudan to Ethiopia): 3 000 BCE–present ‘Of civilizations and cultures over 5 millennia’ 15. Songhay’s Timbuktu (Senegal to Nigeria): AD 700–1 600: ‘Key civilizations of the Niger and Senegal River Kingdoms’ 16. Mapungubwe–Great Zimbabwe (Zimbabwe): AD 900–1 700: ‘The rise and fall of a golden empire’ 17. Mirror of History (Western Sahara to Nigeria): AD 1400–2008: ‘Mirror of global history since the Renaissance’ 18. Zambezi River (Zambia to Mozambique): AD 1800–2008: ‘The story of a southern African river and its wetlands’ 19. Sixth Extinction (Somali to Sudan): AD 1940–present: ‘From dumping site to denudation to civil war’ 20. Carbon Footprint (Algeria to Egypt): AD 1900–2008: ‘Oil deposits to carbon footprint across the northern Sahara’ 21. Out of Africa (Pan African): to be constructed. * **
Mya = million years ago BP = before the present (era) (1950 is the base reference year representing the ‘present’) *** BCE = before the Christian era
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Africa Alive corridors far, all continents other than Africa have lost some 80% of their megafauna. Africa has the only intact body of megafauna left on Earth, as shown by the Kruger National Park, which is crossed by this corridor3. Finally, through the history of human migrations in this sector of South Africa – particularly since the major discoveries of gold and coal in the late 19th century – this corridor also boasts a remarkably cosmopolitan social mix of people. Snowball Earth to Sixth Extinction (Africa) Five further corridors are selected here for their wide range in Earth-time and their spread of geological, biological, and cultural heritage. The final one shows the downside of Africa’s inheritance.
(dating back to 3 470 Mya). Towards its close it passes through the world’s richest assemblage of fossil hominid sites, the Sterkfontein ‘Cradle of Humankind’ World Heritage Site. Impact craters. In this corridor lies the world’s oldest, largest known meteorite impact site, Vredefort Dome (2 023 Mya) and one of the youngest, best-preserved impact sites, the Tswaing Crater (220 000 BP). Mineral deposits. The Cradle to Cradle territory crosses the world’s richest gold-bearing deposits, the Witwatersrand Supergroup (formed 3 000–2 714 Mya); houses the world’s greatest body of mineral deposits, the Bushveld Igneous Complex (formed 2 060–2 055 Mya) with about 95% of the world’s platinum group elements (platinum, palladium, iridium); and takes in the Cullinan Kimberlite Pipe (dated to 1 200 Mya), which has yielded the largest diamond ever found (the 3 106-carat Cullinan diamond). Atmospheric oxygen. The corridor traverses the Transvaal Supergroup (formed 2 714–2 050 Mya) and the Waterberg Group (formed 1 900–1 700 Mya), two of the world’s greatest Pre-Cambrian, intracratonic sedimentary basins that give scientists the evidence through which to trace the build-up of oxygen in the atmosphere. The Cradle to Cradle corridor is not only one of Earth’s geological hotspots. It also represents a great diversity of plants, animals, and human beings, and their essential interdependence because of the extreme geo-diversity of the territory2. As a consequence of the Sixth Extinction so
Top: A fast disappearing tropical forest of central Africa, in Gabon. Soon such places may remain only in small protected areas, with dire consequences for their rich biodiversity and for the survival and cultural heritage of humans’ closest living primate relatives. Above: Namibia’s mountains contain evidence of the greatest of all radiations of life (in the world’s oceans) following the ‘freezing over’ of Earth (from 750–600 Mya). Large boulders of rock are encased in a muddy matrix in rock sequences called diamictites. These are overlain directly by thinly layered, cream-coloured carbonate rocks. The diamictites, exposed widely across northern Namibia, are thought to have been deposited near the equator in a glacially influenced, marine, continental-shelf setting, some 600 Mya, towards the rapid end of the ‘Snowball Earth’ period (more correctly known as the Cryogenic Era). The textural details and chemistry of these rocks offer clues as to the rapid global temperature changes of the oceans and atmosphere at that time (see also p. 22–25). Image and source of comment: Ganqing Jiang and Nicholas Christie-Blick
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C2 Snowball Earth (Namibia): 750–500 Mya The 150-million-year Snowball Earth episode (from c. 750–600 Mya) during which the planet was almost entirely covered in ice is witnessed in the parched mountainous terrain of Namibia. Diverse, complex, multicellular life sprang from seemingly nowhere in the interval 525–500 Mya following the meltdown of ice after the polar icecaps had expanded to cover virtually the whole of the planet’s surface. C7 Lungs of Africa (DRC): 10 Mya–present After 4.6 billion years of Earth’s history, at around 8 Mya, in the rain-forests of Africa, a fork occurred in one of the branches of the primate phylogenetic tree: one lineage led to gorillas and the other, eventually, to the emergence of humans – a species able to piece together its deep history and to contemplate its effect on the rest of life. The ‘lungs’ of Africa here represent the expanding and contracting expanse of tropical forest as a photosynthetic ‘bellows’ yielding greater or lesser amounts of oxygen from carbon dioxide and water. C12 Saharan Paradise Lost (Tunisia to Chad): 22 000 BP –present Of the subcontinental rock-art galleries that portray parts of human history, the one spread across the peaks of the Sahara has an especially pertinent story to tell at a time when people across the world have (belatedly) awakened to the disturbing uncertainties of global warming. A 12 000-year chronology of rock paintings and petroglyphs (that is, engravings or carvings on rock), depicting different conditions of the landscape during this time, mirror the drying out of the Sahara from verdant paradise to the world’s most extensive desert. The earliest period (the Bubalus period, from 12 000–9 000 BP), for instance, is characterized by engravings of the elephants, rhinos, and the prehistoric wild ox, Bubalus antiquus, hunted by the people of the region. The third period, the
2. As a country, South Africa has about 24 000 indigenous plant species (close on 10% of the world total), and is recognized as having the most species-rich temperate flora in the world. The country also has 435 vegetation types (far more by area than the USA or Europe). 3. At the start of the new millennium, the species counts in the Kruger National Park were as follows: plants 1 994, birds 507, mammals 149, reptiles 118, amphibians 35, fish 53, insects about 50 000, other invertebrates about 10 000.
Pastoral Period (7 000–3 650 BP), depicts people as dominant over nature, rather than as part of nature, as had earlier been the case. C13 Valley of the Pharaohs (Egypt to Sudan): 3 100–30 BCE Civilization arose in the Middle East with the domestication of plants and animals (agriculture), the concentration of human habitation (cities such as Babylon, Nineveh, and Ur, of the Tigris and Euphrates valleys in what is now Iraq and, most critical and far reaching, the invention of writing as a means of recording information. The earliest writing, a pictographic script used apparently for administrative and economic purposes, was developed by the Sumerians in southern Mesopotamia shortly before 3 000 BCE, which later evolved into the more symbolic Cuneiform. Most fascinating and long-lived of these early civilizations is the one that sprang up along the floodplains of the Nile valley. It is divided into 12 periods, the best known being the Old, Middle, and New Kingdoms (from c. 2 575 to c. 1 075 BCE.] Ironically, it owes much of its success and longevity to the insularity afforded it by the ‘catastrophic’ desertification of the Sahara (C12) – one community’s disaster is another’s opportunity. C19 Sixth Extinction (Somali–Sudan): AD 1940–present By way of an object lesson, a Sixth Extinction corridor runs from the Horn of Africa to the desertscape of western Sudan. The focus here is on virtually every calamity that can befall human beings and nature – spreading desertification, drought, starvation, disease, civil war, dumping of toxic waste, disappearance of natural habitat. This corridor offers a warning to Homo sapiens, harshly proclaiming the ill effects – on people and nature – of human destructiveness. IYPE for Africa The story conveyed by the Africa Alive corridors covers the major steps in the Earth’s story from the earliest bacteria to human civilization, down to the impact of our species on some 50 million others that precariously share our world. Humans are the one species that can choose to influence where this epic story is headed. The International Year of Planet Earth (IYPE) offers a great opportunity to rescript the outlines of the next couple of chapters of our planet’s biography. The corridors outlined here highlight the Earth, and the life and cultural heritage that Africa represents, and provide a platform and stimulus for all to choose to participate in such rescripting. Synergy can play a valuable part in shifting the continent away from the multiple ills that currently bedevil it. The African corridors were conceived to contribute towards the realization (during the
period 2000–2015) of the United Nations’ eight Millennium Development Goals (MDGs)4. If local governments and the African Union accept the corridors as a means to embrace and sustain prime African and global heritage, these geographic areas can become laboratories and focal points for optimal holistic management. Good governance that attracts international finance (as is the case with World Heritage Sites) will go a long way to meeting the UN’s MDGs. The corridors offer an opportunity for different people, nations, and disciplines to unite in pursuit of a common goal. Knowing Africa’s story provides a way in which to ponder the ‘inconvenient’ present and find and implement solutions. ■ The perspective of deep geological time, and understanding more about the constant and interrelated changes of Earth’s lithosphere, biosphere, and atmosphere through 4.6 billion years of history emphasize the fact that people are an integral part of the Earth’s system. ■ The perspective of the evolution of life reveals that human beings are part of the single tree of life that goes back to the earliest unicellular organisms that came into being some four billion years ago. ■ The broad perspective of human-cultural history reveal people as belonging to one great family, sharing the same small band of ancestors somewhere in Africa about 150 000 years ago. These perspectives offer the opportunity for Africans to join with each other and the rest of the world in the task of forging a new and brighter future. ■ Dr Anderson is a palaeobotanist at the South African National Biodiversity Institute (SANBI), with a special interest in global extinction and radiation events. He initiated the Gondwana Alive project, of which Africa Alive Corridors is an offshoot. Ms Mashua is a scientific officer for Gondwana Alive and works at SANBI on threatened ecosystems. Professor de Wit of AEON at the University of Cape Town has been central to both projects from the start.
Top: The Nile meandering across the East Sahara desert, its water’s edge flanked by a narrow strip of green vegetation separating it from the barren yellow sand beyond. This stark contrast symbolizes the importance of access to water for human life and culture. The relatively sudden change from savanna grassland to harsh desert across much of North Africa some 6 000 years ago forced most of its inhabitants to move into the Nile Valley. Above: Women of Africa signatures symbolize their ‘cry’ to stop the madness of destruction along this and other corridors. For more, read M.J. de Wit and J.M. Anderson, “Gondwana Alive Corridors: extending Gondwana research to incorporate stemming the Sixth Extinction”, Gondwana Research, vol. 6(3) (2003), pp.369-408. Keep up to date with the project by visiting www.sanbi.org (the essentials surrounding the project will be on the site by mid-2008).
4. The UN Millennium Development Goals were drawn from the actions and targets contained in the Millennium Declaration, adopted by 189 nations and signed by 147 heads of state and governments during the UN Millennium Summit in New York in September 2000. The eight goals are, by 2015, to: 1 Eradicate extreme poverty and hunger; 2 Achieve universal primary education; 3 Promote gender equality and empower women; 4 Reduce child mortality; 5 Improve maternal health; 6 Combat HIV/AIDS, malaria, and other diseases; 7 Ensure environmental sustainability; 8 Develop a Global Partnership for Development.
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Careers in S&T Q Right: Professor Harald Furnes (University of Bergen, Norway) standing on 3 800-million-year- old rocks in the Isua Greenstone Belt of southwestern Greenland – probably the oldest remnant of oceanic crust on Earth. Below: A 3 000-million-year-old rock sequence in Swaziland covered with striations (groves) that formed when ancient glaciers scraped the surface. In the picture, Eugene Grosch is pointing to the contact plane between two different rock types: it represents an staggeringly long time-gap of history – erased by ice from the rock record – of more than 2 700 million years.
Work in geology A career in the Earth sciences offers great opportunities. Eugene Grosch explains.
Subdivisions of geology Geology covers a wide range of fields. The boundaries of these subdivisions are artificial, and, in practice, various approaches combine in the exploration of Earth’s complexity, and of its materials in their natural state or as created in laboratory experiments. Geochemistry – the study of the distribution of the chemical elements and their isotopes within the Earth. Geochronology – determination of the age of rocks and rates of geological events. Geophysics – determination of the physical properties of minerals, rocks, and the Earth as a whole, including its magnetic field and its internal temperature variations. Igneous petrology – the study of rocks that crystallized (solidified) from molten material (magma) formed from melting processes within the Earth and that often surface in volcanic eruptions. Metamorphic geology – the study of changes in rocks, in response to changes in pressure, temperature, and chemical conditions (for example, during the process of mountain building). Palaeontology – the study and curation of fossils to determine the origin and evolution of life on Earth. Sedimentary geology – the study of ancient sedimentary environments, such as past river basins, coastal shelves, and deep marine processes that might give rise to oil and gas deposits. Structural geology – a subdivision that deals with rock and mineral deformation, the characterization of structure and geometry of rocks, and their fracturing and flow properties; all these aspects relate to the broader field of rock mechanics, earthquakes, and plate tectonics.
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eology deals with the study of Earth’s history, and all its subdisciplines have one thing in common – rocks! Each, like a time machine, can teleport valuable information about chemical and physical processes operating from the planet’s birth to the present day. Studying rocks helps geoscientists to answer questions such as – how and why do mountains build up and erode away again? how do mineral deposits form? what happens inside volcanoes? Geologists travel to remote and sometimes extreme parts of the world and they explore the widest space- and, time-scales on the planet. They use sophisticated analytical instruments that can probe into the very ‘heart’ of rocks to reveal their detailed make-up, and in turn, uncover clues about the Earth’s outer and inner workings. Geologists need to be intellectually flexible and multidisciplinary. The topic of climate change, for instance, lies at the interface of geology, oceanography, atmospheric science, biology, and even astronomy. To help solve critical puzzles related to global warming, geohazards, and earthquake prediction, for example, geologists must communicate with other scientists and industry experts, and help the public understand how scientific knowledge becomes integrated into policy decisions that can serve as models for Africa and the world. South Africa has an exceptionally rich geological heritage – it offers an invaluable testing-ground for scientific
theories and analytical instruments, and a wonderful training-ground for people entering the field. How to study and qualify With good matric grades for physical science, mathematics, and geography, you can study for a degree in geology at a South African university1. The different geoscience departments have research focuses representing their academic strengths, so read up about areas of geology that might interest you before applying to register for a specific qualification, and consider what postgraduate opportunities might lie ahead. It’s good to start with a general geology degree and specialize later. Begin with a B.Sc. (Honours) degree in geoscience, which requires a threeyear undergraduate course majoring in geology followed by an honours year. A double major (for instance, geology plus mathematics, physics, chemistry, or biology) will equip you well for work in industry or research. A further two-year M.Sc. degree can prepare you for more advanced work in industry or doctoral work, and registering as a professional natural scientist (Pr. Nat. Sci.) can lead to managerial positions in geological consulting companies, mining corporations, research groups and/or academic institutions or museums. Skills, interests, and lifestyle A career in the geosciences commonly includes fieldwork (geological mapping and sample collection), laboratory work (analyses), and
1. Institutions offering degrees in geology include the universities of Cape Town, the Free State, Fort Hare, Johannesburg, KwaZulu-Natal, Pretoria, Stellenbosch, Venda, the Western Cape, the Witwatersrand, and Nelson Mandela Metropolitan University and Rhodes University.
Q News Saving the world’s water
Top: Camp at the foot of the Swartberg mountains in the Western Cape for third-year University of Cape Town students engaged in field mapping the geology around the Kango Caves. Lower left: Temporary field station in Western Dronning Maud Land, East Antarctica, on a 2003/2004 Gjelsvikfjella Earth Science Field Expedition, where Grosch conducted part of his master’s degree research. Lower right: Eugene Grosch, currently based at the Africa Earth Observatory Network (AEON) at the University of Cape Town, is working towards his Ph.D. While at AEON, he has travelled to Munich, Germany, for an advanced deep-drilling course; to Paris, France, for a course in geochemistry and isotope geology; and to Norway to conduct analytical experiments.
office work (computer modelling, interpreting data, writing up scientific results). You need to be curious about how things function in the natural world, and enjoy travelling and the outdoors; you must be self-motivated yet be able to work in teams. You also need to think critically, analytically yet creatively – and you need good communication skills.
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Job opportunities Many South African geologists work for the Council for Geoscience as well as the Council for Scientific and Industrial Research (CSIR). But our vibrant mineral and energy industry employs most of them: as mining and production geologists
or as exploration geologists searching for new mineral deposits; overseers of drilling operations; environmental geologists; engineering geologists; marine geologists; petroleum geologists; geophysicists; hydrogeologists; and experts who can manage geohazards and disasters. Many companies also need geotechnicians for their specialized analytical facilities. At present there is a serious shortage of all types of geologists in South Africa and globally. It’s a good time to study the Earth! ■ Eugene Grosch is a doctoral student at the Africa Earth Observatory Network, Department of Geological Sciences, University of Cape Town.
The world’s water shortage is very real. ■ Over a billion people in developing countries have no access to safe drinking water, and more than two billion lack proper sanitation. ■ 15 500 litres of water are needed to produce 1 kg of industrial beef – 10 times more than for 1 kg of wheat. ■ The USA alone uses over 500 billion litres of fresh water daily for cooling electric power plants – about as much as for irrigating crops. ■ By 2030, global energy demand is expected to increase by 57%, with water demand for producing food doubling. ■ In regions including sub-Saharan Africa, where over 95% of crops are rain-fed, only 10–30% of the rainfall available is used productively. Future pressure on fresh water supplies will be driven by climate (with rising temperatures leading to drier soils and less reliable rainfall) as well as by population growth and rapid economic development. Overcoming these problems will depend on how well nations collectively implement solutions on offer. Low-tech high-gain agricultural suggestions include harvesting rainfall, planting roots deeper, and using terraces better. High-tech advances include developing hardier, drought-resistant crops through breeding programmes and genetic manipulation; getting power plants to switch from using pristine fresh water to treated wastewater; recycling; and water purification. Source: Nature, vol. 452 (20 March 2008), p. 253, and News Feature suite of articles on water, pp. 269–292.
Drink from safe taps, not bottles The UK’s Consumer Council for Water has begun persuading restaurants to stop pushing bottled water to customers: it’s extravagant, and it also damages the planet. Just transporting it accounts for 32 kilotonnes of CO2 emissions a year in Britain – a country where tap water is cheap and safe to drink. In the USA, bottling water in 2006 created an estimated 2.5 million tonnes of CO2. South Africa follows the fashion. We consumed 260 million litres of bottled water in 2006. In this country, three litres of water are used to bottle just one litre, and each litre generates 600 times more CO2 emissions than a litre of tap water. According to Rodney February, Fresh Water Manager for WWF South Africa, the country has the world’s third-cleanest tap water. Yet the 2006 turnover of the bottled water industry in South Africa exceeded R2 billion, and the country imports some three million litres of bottled water a year. Worldwide, reveals a WWF study, bottled water costs 500–1 000 times more than tap water, and about 1.5 million tonnes of plastic is used annually to bottle the 89 billion litres used. Why not celebrate this International Year of Planet Earth by drinking safe tap water, rather than the sort that comes in plastic bottles and that contributes to global warming and pollution? Sources: Surika van Schalkwyk, “Water on tap, please”, Mail & Guardian, 29 February–6 March 2008; and www.ccwater.org.uk.
SciFest Africa, South Africa’s national science festival, takes place in Grahamstown in the Eastern Cape from 16-22 April this year. You can be part of an international festival which boasts over 500 events for people of all ages and interests. Join us this year and experience for yourself what 45 000 other SciFestinos have enjoyed! To order your programme call 046 603 1106 or email email@example.com
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that the ultrafine particles are coated with the products of fuel combustion, which cause oxidative damage in the body. Being smaller than PM2.5s, their collective surface area is greater, and they could be transporting more tissue-damaging chemicals into the body. There are 100–1 000 times more ultrafine particles than PM2.5s in car exhaust fumes. It is too early to say if the effects found in mice also apply to people, especially since the particles were concentrated before the mice inhaled them. But the findings are of concern to motor-car manufacturers, who are already struggling to comply with existing standards for PM2.5s. Source: New Scientist, 26 January 2008.
Low-level radiation from cellphones may not necessarily be bad for human health, but a study conducted by Dariusz Leszczynski, at the Finnish Radiation and Nuclear Safety Authority, Helsinki, suggests that “mobile phone radiation could alter the expression of some proteins in living humans.” He exposed 10 female volunteers to radiation simulating an hour-long call. He screened 580 different proteins in their skin cells, and found the numbers of two proteins altered in all volunteers: one increased by 89% and the other decreased by 32%. This is the first study to show molecular effects of phone radiation on people. The role of the affected proteins is not known, nor which genes code for them. A larger study is planned, amongst other things to establish any health effects of these changes. Source: New Scientist, 23 February 2008.
Watch those exhaust fumes People living near busy roads seem to be at increased risk of heart disease. A 2007 study in The New England Journal of Medicine showed, for example, that women in 36 American cities were likelier to develop heart disease if the air they breathed was high in particles with a diameter of 2.5 micrometres or less (that is, PM2.5s), which are present in vehicle exhaust fumes. These smaller particles are worse for human health than the larger PM10s; both are now monitored worldwide. A new study led by André Nel (University of California at Los Angeles) shows that ultrafine particles – almost too small to detect or filter – could be even more dangerous. For five weeks, mice in his mobile laboratory near one of the busiest roads in Los Angeles breathed fumes from passing traffic that were concentrated in three streams: one had clean air filtered of nearly all particles; the second had the ultrafine particles; the third had PM2.5s. In the blood vessels of mice exposed to the ultrafine particles, the researchers found 55% more atherosclerotic plaque than in mice exposed to clean air, and 25% more than in those exposed to PM2.5s. This implies
After maize, wheat, and rice, the potato (Solanum tuberosum) is the world’s fourth-most important food. The United Nations declared 2008 the International Year of the Potato for its potential contribution towards achieving Millennium Development Goals – alleviation of poverty, improving food security, and promoting economic development. The potato has all the vitamins, minerals, proteins, kilojoules, and cellulose necessary for human life; and the same area of land with potatoes grown on it can yield four times the kilojoules delivered by grain. Its track record is impressive. The first reference to it as food comes from Spain in 1573. By 1642, it was a field crop in Holland, and within 100 years it was a peasant food around Europe. When Parmentier introduced it to the Parisian court in 1785, the king said, “France will thank you some day for having found bread for the poor.” It sustained the Industrial Revolution – and it sustained Ireland, until crop failure in 1845–6 left the country’s population decimated. Now the genetics of the potato are being explored as a way to produce more disease-resistant varieties. The potato lives on, newly elevated in status by the United Nations, and a continuing life-saver to many people around the world. Sources: John Reader, Propitious Esculent: The Potato in World History (Heinemann, 2008); The Economist, 1–7 March 2008.
Postgraduate study in strong materials MSc and PhD by research Opportunities exist for postgraduate study at MSc and PhD level with the DST/NRF Centre of Excellence in Strong Materials (CoE-SM). Bursaries of R40 000 pa for MSc, and R65 000 pa for PhD are available. The Centre is hosted by the University of the Witwatersrand, in partnership with the Nelson Mandela Metropolitan University, the Universities of Johannesburg, KwaZulu Natal and Limpopo, Mintek and NECSA. Strong Materials are materials that retain their distinctive scientific and applied properties under extreme conditions and have established or potential commercial applications. Applicants have a wide choice of research areas, including: Hardmetals: Manufacturing, testing and characterisation of tungsten and vanadium carbides. Ceramics: Multi-component, ultrahard-phase continuous composites for cutting tools and wear parts. Diamond, Thin Hard Films and Related Materials: Laser-based methods are used to measure stresses, elastic and structural properties of bulk solids and thin, hard films, and to study defects in materials. Developments and studies using diamond include radiation detectors, beam optics, radiation damage effects and surface properties. New Ultrahard Materials: Computational and experimental investigations of potentially new ultrahard materials including advanced borides, carbides, nitrides and oxides. Strong Metallic Alloys: Development of new alloys, e.g. superalloys for high temperature applications, property studies of metals, phase diagrams and structure property relationships. Carbon Nanotubes and Strong Composites: Carbon nanotubes (among the strongest and stiffest structures ever made) are being studied for potential chemical and mechanical applications.
PleASe CoNTACT: Dr Tanya Capecchi Tel: +27 11 717 6873 Fax: +27 11 717 6830 email: Tanya.Capecchi@wits.ac.za 22 Quest 3(4) 2007
Q Books Extinction and survival Both author and illustrator love dinosaurs and both are passionate about science communication, especially when it’s directed at the younger generation. “Luis Rey’s fabulous artistic renditions of African dinosaurs breathe life into animals that we would otherwise know only from fossilized bones,” explains ChinsamyTuran. “For many children, dinosaurs are the first experience of geological time, biodiversity, classification, predator–prey interactions, and extinctions, and often they don’t even know that they’re delving into scientific realms. We prepared this book because dinosaurs can lead to a lasting love of similar investigations, and, for many young people, they are steppingstones into other areas of science.” There is no doubt that Famous Dinosaurs of Africa will provide an excellent start.
Famous Dinosaurs of Africa. By Anusuya Chinsamy-Turan. Illustrated by Luis V. Rey. (Struik, 2008). ISBN 978 1 77007 588 7 This book, complete with poster, is a wellwritten and splendidly illustrated introduction to African dinosaurs, clearly prepared for younger readers, but a treat for older ones too. We asked the author, a professional palaeobiologist, to explain what is different and special about this publication. Most people, she answered, are unaware of Africa’s dinosaurs – they know about Tyrannosaurus rex, or Triceratops, but often cannot name a single African or South African one. “This book is not simply a picture book – it is crammed with information, including maps indicating exactly where in Africa a dinosaur was found, boxes of quick facts, a pronunciation guide. And it highlights what’s still unknown and unsolved.” In addition to the marvellous reconstructions by Luis Rey that help readers to visualize the dinosaurs, Anusuya Chinsamy-Turan tried as far as possible to show the actual fossilized remains of the dinosaurs that have allowed such reconstructions. “It my earnest wish,” she explained, “that local readers will feel pride in discovering some of our most amazing dinosaurs, appreciate the richness of the diversity of dinosaurs that roamed Africa during the Mesozoic, and understand why they are so special in terms of dinosaur evolutionary history.” In this International Year of Planet Earth, she added, the book showcases an important chapter in the planet’s history, which ended, according to many scientists, with a global catastrophe caused perhaps by a combination of an asteroid colliding with Earth, a series of volcanic outpourings, and dramatic sea-level changes. “Of the 3.8 or so billion years of life on Earth, dinosaurs lived for a phenomenal 160 million years (in contrast to hominids’ mere ~2.5 million years). The fact that dinosaurs are now extinct (except for birds, their descendants) highlights the fragility of Earth and the ecosystems that support life.”
killed mammoths, they seem not to have killed enough to have caused extinction, either. The story of the mammoths, suggest the authors, illustrates the complexity of such extinctions. That of the woolly mammoth is very likely the lethal end-product of vegetational change and hunting as a combination. Progressive shrinking into small, isolated populations stressed the mammoths and made them vulnerable. And although the proportion killed by humans would have been relatively small, it may just have tipped the balance between survival and extinction. Such patterns are echoed today. The authors point out, for example, that previously large populations of the mammoth’s surviving relatives, the living elephants, have also been squeezed and divided into thousands of threatened enclaves (as a result of modern habitat loss caused by human development), and are further threatened by poachers. This eminently readable and beautifully illustrated book depicts the rise and fall of the mammoths. It covers their origins, the remains and fossils that have been found, their natural history, their presence in prehistoric human art and culture, and their disappearance. And at this time of relentless extinctions as the 21st century gets under way, it offers a case study worthy of attention.
Mammoths: Giants of the Ice Age. By Adrian Lister and Paul Bahn. (Struik, 1994, revised edition 2007). ISBN 978 1 77007 547 4 This revised edition of a book that first appeared a decade ago tells the story of another animal, now extinct, that flourished across a vast territory encompassing Europe, Asia, and North America, and covering millions of square kilometres. By 5 000 years ago, living mammoths had disappeared from the planet, except for a small population on a remote Siberian island that lasted only a further thousand years. The two theories accounting for their extinction offer an object lesson for remaining large mammals living today, the authors suggest. The first theory is the possible impact of hunting by humans. The second relates to the climate change, after the last Ice Age drew to a close around 11 500 years ago, that turned grass-dominated steppes, which had supported the woolly mammoth and other species, into warmer landscapes of boggy tundra and coniferous forest. The new habitats – no longer suitable for grazers adapted to a diet of grasses and other herbaceous plants – led to the demise of many herbivores that depended on particular plant foods. Carnivorous mammals also died out when their prey species disappeared. Although loss of habitat stressed the remaining mammoth populations, this had happened in previous warm periods without leading to extinction. Although there is evidence that humans
In Celebration of Fynbos. By Petra Vandecasteele. Photography by Paul Godard. (Struik, 2008). ISBN 978 1 77007 490 3. A gorgeous photographic showcase of 50 plants, this volume celebrates the variety and richness of the fynbos (‘fine bush’) of the Cape Floristic Region, and focuses on their use in gardening, healing, cooking, and decorating, as well as associated traditions. It’s a coffee-table book with plenty of interesting and practical information. Did you know, for instance, that buchu (Agathosma betulina) is a natural insect repellent when rubbed onto bedding or skin, and that it can help you get over a hangover if you drink it as a tea? Or that you can treat stings and abscesses by applying a poultice of fresh Pelargonium cucullatum leaves? Or that the strong smell of wild garlic (Tulbaghia violacea) chases moles away from a garden, and keeps fleas, ticks, and mosquitoes at bay? Or that the seeds of the Overberg pincushion (Leucospermum oleifolium) make tasty ingredients for salads and breads? This is a publication to look at, read, use, and enjoy.
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Diary of events Q Shows, talks, & courses ■ Iziko Planetarium, Cape Town For children – "Magic Milo and the Astronaut" Planetarium show for junior stargazers aged 5–12 years, Mon–Fri at 12:00 & 13:00; Sat & Sun at 12:00; plus special shows at 10:00 on 3, 8, & 10 July followed by a Paper Theatre Workshop. The “Twinkle Show” is a playful introduction to astronomy especially for the under 10s. Starting 19 July, it runs every Sat and Sun at noon.
For teenagers and adults – “The Sky Tonight” A live lecture on the current night sky every Sat & Sun at 13:00. “Celestial Clouds” celebrates astro-photography, with images of the Milky Way, neighbouring galaxies, and glowing clouds of gas with dark dust lanes until 31 July, Mon–Fri at 14:00; Tues at 20:00 (& sky talk); Sat & Sun at 14:30. Professor Tony Fairall’s four-part ‘Starfinder’ course (7, 14, 21, and 28 May at 20:00–22:00) introduces astronomy and the constellations, constellation coordinates, the celestial sphere, and the heavenly bodies of our Solar System. Tickets at the Museum’s main entrance. For information phone (021) 481 3900 or visit www.iziko.org.za. ■ MTN Sciencentre, Century City, Cape Town 14 May at 18:00 “The funny side of science” Illustrated talk in which Professor Mike Bruton examines unusual characters in science and technology and the subjects they researched. 15 May at 18:00 “The brain of the matter: What really determines human exercise performance” Second Annual Bruton Lecture, delivered by Professor Tim Noakes. 23 July at 19:00 “Doping in sport: Who isn’t using it?” Talk by Professor Tim Noakes in the context of the upcoming Olympic Games. For information and bookings call
(021) 529 8100 or visit www.mtnsciencentre.org.za. ■ Botanical Society of South Africa (Bankenveld Branch), Walter Sisulu National Botanical Garden, Gauteng 26 April (08:45) “Snakes” Slide show and demonstration with live snakes by Gavin Wilson, and tips on treating snake bites and handling emergencies. Meet at the Nestlé Environmental Education Centre. Booking essential. Phone Karen at (011) 958 0529 (mornings only) or e-mail firstname.lastname@example.org. ■ Maropeng, Cradle of Humankind Until 30 April "Living and Extinct Life Forms: Introducing the Plants and Vegetations of our Past” Special exhibition of fossil plants from the Sterkfontein Valley and countrywide. 17 May "Saturn: The riddle of the ring and the mysterious moons” Vincent Nettmann discusses Saturn, the ring-encircled planet orbited by 60 moons (talk & dinner). 28 June "Our winter skies” Stargazing presentation & dinner. 19 July "Fly me to the Moon: Man’s greatest journey” Retrace Neil Armstrong’s historical lunar landing on 20 July 1969 with Vincent Nettmann (stargazing presentation & dinner). For information and bookings phone Maropeng at (014) 577 9000 or e-mail email@example.com. Visit www.maropeng.co.za for directions. ■ South African Institute for Aquatic Biodiversity (SAIAB), Grahamstown 16–26 June SAIAB Winter School Aquatic Biodiversity course for registered honours and master’s students (preference to students from historically disadvantaged institutions). Contact Vanessa Rouhani, tel. (046) 603 5814 or e-mail firstname.lastname@example.org or visit ww.saiab.ru.ac.za. 27 June–5 July SAIAB Bright Sparks Tour to the Western Cape for schoolchildren. Contact Mrs Nozi Hambaze, tel. (046) 603 5818 or e-mail email@example.com or firstname.lastname@example.org.
Conferences 12–16 January 2009 "Iphakade: Climate Changes and African Earth Systems – past, present and future” Fifth European Geosciences Union Alexander von Humboldt International Conference for Earth system researchers, with the goal of understanding the processes that have shaped Africa as a habitable part of the planet and how these may change in future. Venue: University of Cape Town. Contact Ms Pavs Pillay, e-mail email@example.com. 27 June–5 July South African Marine Science Symposium (SAMSS) For information
contact Carmen Visser, tel. (021) 402 3536, cell 083 268 3804, fax. (021) 402 3675, e-mail firstname.lastname@example.org. 3–7 August 2008 “Interfaces” Joint conference of the Fynbos Forum and Arid Zone Ecology Forum, for researchers, planners, managers, landowners, and other stakeholders in the environmental and conservation sector. Venue: Burgersentrum, Oudtshoorn. For information e-mail Wendy Paisley at email@example.com.
Celebrate ■ National Science Week (NSW08) 10–17 May An initiative of the Department of Science and Technology, which aims to excite South Africa’s youth with science at an early age and encourage them to develop an interest in studying mathematics and science. National information from Erna Rossouw, SAASTA, tel. (012) 392 9300, fax. (012) 320 7803, e-mail firstname.lastname@example.org or visit www.saasta.ac.za. In the Eastern Cape, join the NSW08 Eastern Cape Outreach Programme (NSW08ECOP). Contact Mr Siza Masiza, Department of Education, tel. (043) 743 4599 or 0823426355, or e-mail email@example.com. ■ International Year of Planet Earth (IYPE) For information visit http://yearofplanetearth.org/ index.html. There will be a South African IYPE student competition to select 10 learners (12–18 years old) to attend the IYPE Africa launch in Tanzania. For details visit www.iype.org.za. For Nature’s celebratory articles in its new geosciences journal visit www.nature.com/nature/supplements/ collections/yearofplanetearth/.
Diarize ■ 2008 International Year of the Frog; International Year of Coral Reefs; UN International Year of the Potato ■ June Antarctica month ■ 27 June–5 July National Arts Festival, Grahamstown (go to the SAIAB exhibition and view Aidon Westcott’s mixed-media fish-themed artworks) (For information visit www.nafest.co.za) ■ 6 July–16 July National Schools Festival, Grahamstown (For information visit http://schoolfest. foundation.org.za) ■ 27–29 July Bundu Expo, Tshwane Events Centre, Pretoria ■ August Marine Biosciences month ■ 11–15 August Sasol Techno X (For information visit www.sasoltechnox.co.za) ■ September African Origins month; and International Year of Planet Earth month in South Africa (with events and competitions countrywide)
News Q Catnapping to improve memory Falling asleep – as distinct from sleeping itself – refreshes the brain and might also improve recall. Olaf Lahl and his team at the University of Düsseldorf, Germany, asked students to memorize a list of words, then tested how well they remembered it after an hour of playing solitaire. Those students who had been allowed a 5-minute catnap at the very start recalled significantly more than those who had remained constantly awake. Lahl thinks this is because many of sleep’s functional aspects are accomplished at its very beginning. Others suggest that the brain replays recent events just before sleep, marshalling thoughts in a way that’s crucial
64 Quest 4(2) 2008
for recall. Lahl agrees, however, that long periods of sleep may carry different benefits than does a catnap. Source: New Scientist, 23 February 2008.
Remembering the planets A 10-year-old Montana schoolgirl, Maryn Smith, has won a National Geographic competition to create a mnemonic for the names of the 11 planets now recognized in the Solar System: “My Very Exciting Magic Carpet Just Sailed Under Nine Palace Elephants”. It has been noted, however, that there are just eight proper planets in the Solar System; the other three are dwarf planets (Ceres, Pluto, and Eris). Source: Nature, 26 March 2008.
Q ASSAf News
Scholarly publishing The modern world has been created largely by the immense collaborative efforts of countless scientists and scholars who have placed the fruits of their work into the ‘scientific’ or ‘scholarly’ literature – an ever-expanding edifice of knowledge available to those who seek, by ‘standing on the shoulders of giants’, to make new discoveries using ones already there. For the system to work, however, the participants must abide by principles that regulate the formal publication of research findings or ideas. Among the important ones are that reported findings and/or conceptual insights must be original (that is, must represent the first report); the method and materials used must be described in sufficient detail to be repeatable by other scientists (depending on the discipline); no inconsistent data should be omitted; no fabricated data presented; where used, statistical/mathematical treatment must be thorough and conclusions reasonable; submissions must not at the same time be under consideration by another journal; existing relevant literature must be appropriately and fairly cited. Editors, editorial boards, and peer reviewers work together to ensure that these requirements are consistently met. Journals need accessible editorial policies; engage appropriate expert peer reviewers; assess reviewers’ reports; decide whether to accept a paper, insist on revisions, or reject it; and do the detective work needed to find any misconduct that might lurk beneath the surface. As reported in ASSAf’s 2006 Report On a Strategic Approach to Research Publishing in South Africa, the country may be a giant of scientific publication in Africa, but it is a dwarf in world terms. Nearly two-thirds of the 7 000 or so papers published by South Africa’s scholars appear in journals that are indexed in the Thomson Scientific (formerly Thomson ISI) system in Philadelphia, USA (about a quarter of these papers appear in the 25 South African journals that are indexed), and the remaining one-third in the 230 South African journals accredited for subsidy purposes by the Department of Education (DoE) but not indexed by Thomson Scientific. At least one South African author’s address appears on only four in every thousand Thomson Scientific-indexed articles, however, and few of the country’s journals have international visibility as only one or two of them have ‘citation rates’ around 1 (that is, roughly the average number of times that any other author refers to an article in that journal in a 2-year period). Many of our
accredited journals have had no citations to any of their articles in Thomson Scientific-indexed ‘international’ journals in the past 15 years. There is clearly room for improvement. The ASSAf Report made several recommendations. South African research publications are important and worth retaining, it said, but systematic upgrading and quality assurance are needed. Furthermore, worldwide ‘open’ internet access to quality South African journals would increase their visibility, use, and impact. The Department of Science and Technology (DST) accepted the recommendations that fell within its remit, and is funding the Academy’s efforts to facilitate their implementation over the next three years. ASSAf has established a Committee on Scholarly Publishing in South Africa and a Scholarly Publishing Unit. The National Scholarly Editors’ Forum was launched in August 2007, and its terms of reference and a national “code of best practice in editorial discretion and peer review” are nearing adoption. The Forum has supported the DST’s mandate to ASSAf to create independent peer-review panels for discipline-grouped journals, which will make recommendations for improved functioning; possible mergers, closures, or expansions; online open access; and DoE accreditation. The Committee is also investigating models for quality national journals through a ‘national platform’ taskteam, which will consider, amongst other things, an integrated approach to effective editorial models; online ‘open access’ publishing (co-existing in many cases with continuing publication in print); citation indexing and information analysis; and the required level and channelling of state subsidy. Since these developmental issues are integral to government’s “10-point Plan” in its attempt to increase the country’s “human capital” (including the number of its competent and productive scientists and scholars), the DST and other authorities are aware of the Academy’s programme as a core component of the overall agenda. Learning to draft and publish papers based on systematic investigations is fundamental in research training, forming a gateway to careers and personal prosperity, and translating into socio-economic progress for the whole nation. – Wieland Gevers, Executive Officer, ASSAf For further details, visit www.assaf.org.za
Letters to Keeping school science up to date
would like to use this opportunity to thank you for a wonderful magazine. During these challenging times of ever-changing subject content, has been a life-saver. I have used your articles extensively, not only for personal research but also to broaden my students’ general knowledge to prepare them for Olympiads and quizzes. Here is the way I used your inserts (on carbon and superconductivity), for example. I divided the class into groups, and gave them the insert to read. They then had to represent the information on a mind map. Each group got the opportunity to discuss three ideas or facts that grabbed their attention. I also used the article, “The State of our Environment” (vol. 3, no. 4) as the basis for a debate on sustainable development. Your magazine keeps me in the forefront of science, exactly where a science teacher needs to be! Corlia Wepener, H.O.D Science, Metropolitan Raucall, Brixton
n behalf of the Science Department at Raucall, a Dinaledi school, I would like to thank you for last year’s issues of . I am convinced that they helped us in achieving a 100% pass rate in the 2007 matric exam, as all 99 of our learners who took science as a subject passed. Our facilities are average, but our teachers are determined, and our approach is based on hard work. We expect a lot from learners, and encourage them to believe that they are able to achieve. We use practical hands-on methods to help the students to get to know the work. Please continue to support our school with , as we are a dedicated maths and science school and all our learners take both these subjects. As the principal of the school, I am keen to ensure that we are up to date with the latest research and knowledge in science. Carel Freysen, Principal, Metropolitan Raucall, Brixton Address your letters to the Editor and fax them to (011) 673 3683 or e-mail them to firstname.lastname@example.org (Please keep letters as short as possible. We reserve the right to edit for length and clarity.)
Quest 4(2) 2008 65
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66 Quest 4(2) 2008
Q Q UEST crossword You’ll find most of the answers in our pages, so it helps to read the magazine before doing the puzzle.
You + Science = Planet Earth : A better place to live! At Stellenbosch University’s Faculty of AgriSciences you will learn how to apply your knowledge of science to the benefit of both people and the earth.
At the heart of a nuclear power station (7)
You hope to find gold or corals here (5)
Dinosaurs roamed at this time (8)
They can be igneous, metamorphic, or sedimentary (5)
The tide at times of the month when there is least difference between high and low water (4)
Elevated land like a table with steep sides (4)
Our degrees take three or four years to complete. After a bachelor’s degree, you can broaden your career opportunities through postgraduate study.
The only known brown element; good conductor of electricity (6)
The UN celebrates this International Year in 2008 (6)
Term for the shape of the solid Earth (5)
Unit of geological time corresponding to a series in rocks (5)
Area of open uncultivated land; also what you do with a ship (4)
Home for life on Earth (9)
A zone just right for life (10)
Deep chasm (5)
--- Carbon Observatory; new set of pollution sensors that will appear onboard satellites (8)
Carbonized vegetable matter (4)
Seismic event that damages underground mines (9)
Silver-white metallic element that is resistant to corrosion; ingredient of some steels (6)
Vast treeless plain in the Arctic region (6)
Find your way with this (3)
Amount of light reflected off a surface (6)
(Answers on p. 68.)
Yellow metal (4)
Essential component of diamond, graphite, and life (6)
Hot, fluid material under the Earth's crust (5)
Yellow non-metallic element, considered a major pollutant (7)
The most extensively used of all metals (4)
Animal and plant life (5)
Another name for sodium chloride (4)
Ridge of sand created by wind (4)
Soft grey metal that forms toxic compounds (4)
How do you like the crossword puzzle? Was this one too difficult? Too easy? Just right? Would you like more difficult puzzles as well (with prizes)? Or other kinds? Fax the Editor at (011) 673 3683 or e-mail your comments to email@example.com (mark your message CROSSWORD COMMENT).
South Africa needs well-trained agricultural and forestry experts at all levels to supply our growing population with food and fibre, to ensure that food and food sources are unpolluted and safe, and that the environment is used and managed in ways that preserve it for posterity. There are wide-ranging and challenging job opportunities in agriculture and forestry, from the most practical to the most high-tech – outdoors, in laboratoria, or in business.
Agricultural and forestry education Admission requirements ● A National Senior Certificate (NSC) as certified by Umalusi with an achievement of at least 4 in four designated university entrance subjects. ● An achievement of at least 50%, calculated in a ratio of 40:60, for the SU Access Tests and the average (excluding Life Orientation) obtained for the NSC. ● Mathematics 4, Physical Sciences 4 OR Physical Sciences 3 and Life Sciences 4.
Exciting careers to consider after finishing your degree at Stellenbosch University ● Conservation ecologist ● Winemaker ● Forester ● Eco-tourism operator ● Entomologist ● Viticulturist ● Entrepreneur ● Community developer ● Animal or plant geneticist ● Horticulturist ● Wood processing specialist ● Quality controller
● Agricultural economist ● Researcher ● Environmental impact assessor ● Plant pathologist ● Extension officer ● Food scientist ● Animal scientist ● Soil scientist ● Consultant ● Water research manager ● Game ranch manager
Closing date for applications: 30 October 2008 Contact our Faculty Secretary (Leon Jordaan) at (021) 808 4833, fax (021) 808 3822, or e-mail firstname.lastname@example.org for more information and visit http://www.sun.ac.za/agric
Back page science Q ■ “The earth is not a mere fragment of dead history, stratum upon stratum like the leaves of a book, to be studied by geologists and antiquaries chiefly, but living poetry like the leaves of a tree, which precede flowers and fruit – not a fossil earth, but a living earth; compared with whose great central life all animal and vegetable life is merely parasitic.” – Henry David Thoreau (1817–1862), US philosopher, author and naturalist ■ “On-the-ground monitoring is unglamorous work, seldom rewarded by funding agencies or the science community. But we neglect it at our peril. Sometimes discovery comes slowly, not with a flash of revelation but creepingly, as larger patterns emerge painfully from years of data.” Euan Nisbet, Nature, vol. 450, 6 Dec 2007
Where melty meets hard ■ The Mohorovicˇic´ Discontinuity, named after the Croatian seismologist who discovered it in 1909, is quite a mouthful, so it’s also known as the Moho. It’s the boundary between the Earth’s crust and its mantle, and a place where seismic waves accelerate because of the lower density of the crust. The Moho lies at an average depth of about 8 kilometres beneath the ocean basins and 32 kilometres beneath continental surfaces. (http://geology.com/) ■ Changes to ice sheets are an indication of climate change, but may also indicate other processes. In 1991, an ice stream – a flow of ice within an ice sheet – was seen for the first time in northeast Greenland. Scientists have now found that, at the base of this area, the Earth’s crust is relatively thin and so magma is closer to the surface of the Earth, warming it up. This could have created the ice stream. The hot spot may result from a volcano or it may be the result of the way heat is distributed by the rocks under the ice. (www. sciencedaily.com/releases/2007/) ■ In Death Valley National Park in California is a dry lake bed called Racetrack Playa, where big rocks slide along, creating furrows behind them, in a way that nobody has quite been able to explain. The playa is a flat area covered with sediment, normally dry and cracked, which becomes slippery when wet. It’s thought that gusts of wind could set the rocks in motion during periods when the lake bed is wet. Nobody has seen the rocks moving, so the theory hasn’t been confirmed. (http://geology.com/articles/racetrack-playasliding-rocks.shtml)
Time for a rethink Every new year, the website edge.org asks scientists and other thinkers a question. This time it was: “Science is based on evidence. What happens when the data change? How have scientific findings or arguments changed your mind?” The Guardian (1 January 2008) summarized some of the responses. ■ Psychologist and language expert Stephen Pinker: “I’ve had to question the overall assumption that human evolution pretty much stopped by the time of the agricultural revolution …. New [laboratory] results have suggested that thousands of genes, perhaps as much as 10% of the human genome, have been under strong recent selection, and the selection may even have accelerated during the past several thousand years.” ■ Philosopher Helen Cronin: “I used to think that patterns of sex differences resulted mainly from average differences between men and women in innate talents, tastes and temperaments .... Females are much of a muchness, clustering round the mean. But, among males, the variance – the difference between the most and the least, the best and the worst – can be vast. So males are almost bound to be over-represented both at the bottom and at the top.”
We miss those pests “Elephants can eat entire trees in much the same way we eat cupcakes,” says ecologist Todd Palmer, of the University of Florida. But one tree in Kenya is protected by ants that are attracted to the sap it exudes. If an elephant tries to eat the tree, the ants let off a scent, which warns the tree to put up its defences. They also swarm onto the elephant if they have to. Palmer set up an experiment to test what might happen to the ants and trees if there were no elephants around. Over 10 years, some of the trees were protected from elephants by fences. What happened was that the trees didn’t flourish, and they stopped producing the ant-attracting sap. Instead, they were invaded by other insects which harmed them. (National Public Radio, 10 January 2008; www.npr.org/templates/story/)
Past their sell-by date Ceramic jars called amphorae are often the only remnants of an ancient shipwreck when the ship’s timber has gone. Now scientists say they can use DNA analysis to determine what those old shipping containers contained – which
could improve our understanding of agriculture and trade in days gone by. The researchers took scrapings from inside jars from a 4th-century BC shipwreck near a Greek island, and found DNA suggesting that one contained olive oil flavoured with oregano and another probably contained a preservative plant called mastic. (www.world-science. net/exclusives/)
The art of little things The Micropolitan Museum celebrates natural things that can be seen only under a microscope. Some of the exhibitions in the freshwater collection, for example, are the Water-flea Circus, Desmid Dome, Diatom Depot, Rotifer Room, Bacteria Basement, Ciliate Centre, Protist Department, Hall of Arthropods, and Archive of Algae. Visit www.microscopy-uk.org.uk/micropolitan/. ■ A Californian entomologist is using insects to create works of art. Steven Kutcher puts non-toxic paint on the ‘feet’ and abdomens of cockroaches, beetles, and grasshoppers and uses light to control their movement across the canvas. (From Nature, vol. 450, p. 613, or www.bugartbysteven.com) ■ Microscopic creatures known as tardigrades, or water bears, can live in droplets of water on plants. If the water they live in evaporates, they lose water too, and go into a deep sleep. A little water is all it takes for them to spring back to life.
World traveller Why did the chicken cross the Pacific? Who knows, but “genetic testing of a leg bone of a chicken found in south-central Chile found the bird was of Polynesian origin and was alive 600 to 700 years ago, well before Europeans arrived at the end of the 15th century”, reported Agence France Presse (6 June 2007). New Zealand anthropologists studying Polynesian migration found that the chicken’s DNA sequence “was identical to that obtained from a 2 000-year-old chicken bone from Tonga”. Answers to Crossword (page 67) ACROSS: 2 Uranium, 7 Mesozoic, 10 Potato, 11 Geoid, 12 Epoch, 14 Moor, 15 Biosphere, 17 Goldilocks, 19 Abyss, 24 Coal, 25 Nickel, 26 Tundra, 27 Map, 28 Albedo. DOWN: 1 Reefs, 3 Rocks, 4 Neap, 5 Mesa, 6 Copper, 8 Orbiting, 9 Rockburst, 11 Gold, 13 Carbon, 14 Magma, 16 Sulphur, 18 Iron, 20 Biota, 21 Salt, 22 Dune, 23 Lead.
MIND-BOGGLING MATHS PUZZLE FOR Q UEST READERS Q UEST Maths Puzzle no. 6
Win a prize!
What are the dimensions of the smallest right-angled triangle for which the following are true: ■ the lengths of the sides are whole numbers ■ the circumference is the square of a whole number ■ the area is a whole number to the power of three. Here’s a clue: the length of the hypotenuse is 240.
Send us your answer (fax, e-mail, or snail-mail), together with your name and contact details, by 15:00 on Friday 30 May 2008. The first correct entry that we open will be the lucky winner. We’ll send you a cool Truly Scientific calculator! Mark your answer “QUEST Maths Puzzle no. 6” and send it to: QUEST Maths Puzzle, Living Maths, PO Box 478, Green Point 8051. Fax: 0866 710 953. E-mail: email@example.com. For more on Living Maths, phone 083 308 3883 and visit www.livingmaths.com
68 Quest 4(2) 2008
Answer to Q UEST Maths Puzzle no. 5 The two solutions are 212/606 = 0.34983498… and 242/303 = 0.79867986…. We received no correct answers.
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Shaping a better future through science Science and technology are drivers of progress. It is what determines the difference between today and a better tomorrow. The Council for Scientific and Industrial Research (CSIR) in South Africa performs multidisciplinary research and technological innovation with the aim of contributing to industrial development and improving the quality of life of people of this country â€“ and increasingly on the wider continent. Working in areas such as biosciences; natural resources and the environment; defence, peace, safety and security; the built environment; materials science and manufacturing; information and communications technology; space and laser technology, we also pursue new areas of research, such as nanotechnology, that will drive future progress. We employ people who are experts in their fields and passionate about creating a better future through science.
tel +27 12 841 2911 email firstname.lastname@example.org www.csir.co.za www.csir.co.za