SCIENCE FOR SOUTH AFRICA
VOLUME 2 • NUMBER 1 • 2005 R20 incl. VAT
ACADEMY OF SCIENCE OF SOUTH AFRICA
Getting to grips with strong materials
Darrell Comins and members of the DST/NRF Centre of Excellence in Strong Materials Cutting-edge research advances South African industry now and for the future
Contents VOLUME 2 • NUMBER 1 • 2005
Exploring fossils ■ The Karoo – a fossil mecca
Bruce Rubidge Earth’s richest fossil deposits
■ Catastrophism and the history of life
Fact file Techniques for investigating strong materials
Phillip V. Tobias
Cataclysms, extinctions, and change
Dinosaurs: new South African discoveries (Adam Yates) (p.18) • Don't cell-talk while driving; Friends bring longer life; World's oldest dinosaur embryos (p.45) 15
Careers Working with strong materials
Your QUESTions answered
■ Early birds
Space shuttle; Spider camouflage 38
The S&T tourist Palaeo-visits See precious fossils and experience prehistoric worlds
Treasure from the molecules of life
Unite to save Earth’s natural capital Sue Milton, James Aronson, and James Blignaut
Discovering protein structures for biotech
Books The Story of Earth & Life, by Terence McCarthy and Bruce Rubidge • and other titles
Into outer space
Celebrating international Space Week
Letters to QUEST CDs; Compulsory science
Diary of events
Subscription form • Back page science
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SCIENCE FOR SOUTH AFRICA
VOLUME 2 • NUMBER 1 • 2005 R20 incl. VAT
Observing & seeing U
ACADEMY OF SCIENCE OF SOUTH AFRICA
Atomic structure of a novel, now patented, cottunite material against a background of carbon fibre rovings woven into twill weave (see p. 3). Pictures courtesy of the DST/NRF CoE–SM and Mark Klein Productions SCIENCE FOR SOUTH AFRICA
Editor Elisabeth Lickindorf Editorial Board Wieland Gevers (University of Cape Town) (Chair) Graham Baker (South African Journal of Science) Anusuya Chinsamy-Turan (University of Cape Town) George Ellis (University of Cape Town) Jonathan Jansen (University of Pretoria) Colin Johnson (Rhodes University) Correspondence and The Editor enquiries PO Box 1011, Melville 2109 South Africa Tel./fax: (011) 673 3683 e-mail: email@example.com (For more information visit www.assaf.co.za) Business Manager Neville Pritchard AdvertisingandSubscription Neville Pritchard enquiries PO Box 130614 Bryanston 2074 South Africa Tel.: (011) 781 8388 Fax: (011) 673 3683 Cell: 083 408 3286 e-mail: firstname.lastname@example.org Copyright © 2005 Academy of Science of South Africa
nderstanding has to do with examining what’s known and then reaching beyond it. While philosophy deals directly with ideas, the natural sciences by definition start with the material world. Using astonishing ingenuity and technology, researchers explore all manner of things normally hidden from view – either because they’re buried, or because they’re too small, or too old, or too vast, or just too obvious. This issue of QUEST celebrates sciences that explore by observation. South Africa’s special focus on African Origins during September takes a look at our remarkable fossil riches – but these are hidden in rocks, so finding them needs a keen eye, and working out what they reveal about the very distant past needs unshakeable logic. Our authors explain many things about fossils – why Karoo fossils are the entry point to any study, anywhere in the world, of where animals came from (p. 16); the implications of cataclysms that have shaken our Earth and helped to make it what it is (p. 24); the unexpected origin of birds and how they learnt to fly (p. 26). In October, World Space Week brings occasion to marvel at explorations of more distant worlds – journeys to probe into the heart of a comet or examine the surface of Mars, and techniques to find galaxies that existed billions of years ago (p. 34). Deep within matter much closer to home are other secrets, which scientists examine for human use. Some probe the life of cells and the minutiae of protein structures so as to help cure disease and bring economic benefits (p. 30). Others explore crystal structures of materials at the atomic level to understand and then to develop ‘strong’ materials with applications from mining to manufacturing (p. 3). The middle ground of everyday carries the necessities of life, which Nature has always provided. They’re so familiar that they’re hardly noticed and, for the most part, they’re taken for granted – water, food from plants and animals, timber from trees. But there’s danger in failing to observe or nurture them. Economists doing their sums have discovered that “For everyone to live like an average American would need the resources of approximately six Earths” (p. 39). Human success in colonizing the planet comes at a high price. In the pages of this issue, the broad range of scientific observation and technology comes into view as researchers explain what they do to observe, enquire, and uncover the extraordinary workings of the commonplace, of cells and atoms, and of worlds out there among the stars.
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Production Pritchard Productions cc Design and layout Creating Ripples Printing Paradigm All material is strictly copyright and all rights are reserved. Reproduction without permission is forbidden. Every care is taken in compiling the contents of this publication, but we assume no responsibility in effects arising therefrom. The views expressed in this magazine are not necessarily those of the publisher.
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Elisabeth Lickindorf Editor – QUEST: Science for South Africa Join QUEST’s knowledge sharing activities Write letters for our regular Letters column – e-mail or fax your letter to The Editor and win a prize. (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 S&T Questions and Answers column – e-mail or fax your questions to The Editor and win a prize. (Write S&T QUESTION in the subject line.) ■ Inform readers in our regular Diary of Events column about S&T 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.assaf.co.za), and make arrangements to tell us your story. To contact the Editor, send an e-mail to: email@example.com or fax your communication to (011) 673 3683. Please give your full name and contact details. ■
Main picture: Carbon fibre rovings woven into twill weave. Impregnation with epoxy resin hardens it for use in aircraft, bicycles, and motorbike wheels, for example.
Many things from precision instruments to machines and structures of all sizes are made from materials strong enough to do their job. Darrell Comins and members of the team in the DST/NRF Centre of Excellence in Strong Materials tell us what they’re researching to improve the materials that industry needs and to create new and better ones. very day we rely on strong materials to stay strong. The materials for making cars, aeroplanes, power stations, and spacecraft need to stay strong enough not to break apart with wear and tear, and to offer protection in the event of an accident. A building’s roof, walls, and floors need to be strong enough to withstand heavy loads, wind and rain, heat and frost. Tools of all sorts – from knives and forks to precision instruments used in surgery and industrial equipment used for cutting and boring – have to stand up to different degrees of heat, abrasion, and pressure. Manufacturing industries as well as private consumers gain when the quality of strong materials improves because efficiency increases and costs go down. If the newest motor car is made of material that’s stronger but lighter than last year’s model, for instance, it can drive further on less fuel. If the blade of a cutting tool is just as sharp but stronger than its predecessor, it lasts longer before it needs replacing. The better a material does its job, the greater the economic and practical benefits. South Africa’s mineral wealth makes it an excellent place to study and improve strong
Insert: In a filament winding process for making tubes and pipes, the glassfibre roving tape (preimpregnated with thermoplastic resin) is heated. After compression by the top roller, it is wound onto the bottom roller (the mould) to form the pipe. Pictures courtesy of Mark Klein Productions
Centre of Excellence in Strong Materials
The DST/NRF Centre of Excellence in Strong Materials (CoE–SM), under the directorship of Professor Darrell Comins, is hosted by the University of the Witwatersrand in partnership with the University of KwaZulu-Natal, the Nelson Mandela Metropolitan University, the University of Johannesburg, the Council for Mineral Technology (Mintek), and the National Energy Corporation of South Africa (NECSA). The centre has an extensive network of collaborators, both in South Africa and abroad. Strong materials are defined as materials able to maintain their physical and chemical properties under extreme temperature and pressure and adverse chemical conditions. Their practical applications are particularly important in the mining and manufacturing industries, in South Africa and abroad. The CoE–SM focuses on six key areas: hardmetals; ceramics; diamond, thin hard films and related materials; new ultrahard materials; strong metallic alloys; and carbon nanotubes and strong composites. The research conducted in the CoE–SM falls within a critical area in the South African government’s Advanced Manufacturing Technology Strategy of 2003. In helping to improve the properties of materials currently used in industry, the work results in cost reduction and, at the same time, the manufacture of more efficient products. The centre also provides consulting services to industry. Over and above its research goals, the CoE–SM trains postgraduate students, mentors future scientific and technological leaders, and runs an outreach programme to promote interest in materials science among schoolgoers and those who teach them. It provides bursaries for students, funding for infrastructure and equipment, and encourages networking to foster the exchange of ideas and to access expertise in many different fields. For details and updates of research and outreach activities at the DST/NRF Centre of Excellence in Strong Materials e-mail Dr Tanya Capecchi at firstname.lastname@example.org or phone (011) 717 6873. Visit www.strongmaterials.org.za (the web site is currently under construction).
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What the work entails
The process of developing strong materials Creating new strong materials and improving existing ones starts with prediction and/or understanding of fundamentals and ends with application. To understand a material, scientists and engineers examine its composition and structure and what it does under specific conditions (its properties). Then, on the basis of what they’ve found, they can try to modify that material (design/processing) to improve its behaviour (performance) in particular industrial purposes. Materials science and engineering can be visualized as a set of models and interventions that link the four points of the pyramid figure below, as well as a set of technologies and techniques that support the work being done at each point.
Properties Understanding To understand a material, researchers need to characterize and define it. Composition and structure give a material its physical characteristics. Its composition is defined by the chemical element(s) that constitute it (e.g. the elements carbon or iron). The structure of a solid material is defined by the relative positions in the crystal lattice of the atoms of which the material is formed (e.g. the crystalline structure of the element carbon differs in diamond and in graphite). Properties are the attributes of a material in terms of its behaviour under different conditions (e.g. what it does at different temperatures or pressures). Application For materials to be developed for maximum efficiency, they need to be designed and processed to behave in a particular way in specified conditions. Designing improvements to a material (or creating a new one) involves planning ways to manipulate its composition and structure to make it behave as efficiently as possible in a given application and in the particular conditions for which it is being manufactured. Processing includes all the operations involved in manipulating or making particular materials (e.g. forging [i.e. shaping a metal by heating and hammering it], casting [i.e. shaping a material in a mould], sintering [i.e. heating a substance in powdered form below its melting point to make it coalesce into a solid]). Performance describes the behaviour of a material in the practical applications for which it is designed and involves measuring and testing. Understanding the links between composition and structure on the one hand, and properties, processing, and performance on the other underpins all materials development. ▲
materials, as many substances found on our own doorstep can be used to make materials stronger. To strengthen steel, for instance, we can incorporate manganese and vanadium (mined in the Northern Cape and Mpumalanga, respectively), which helps the country not only to export its mineral resources as raw products, but also to add value and create jobs through beneficiation1. Understanding strong materials to be able to improve existing ones and to develop new ones, therefore, can help to grow South Africa’s international reputation as a manufacturing country and can greatly increase the value of its exports. This is why scientists in many disciplines have combined forces with engineers in the DST/NRF Centre of Excellence in Strong Materials. Their work ranges from theory to practice, across the spectrum of strong materials, to define and design materials that will help to boost industrial development far into the future.
There are many strong materials because there are many different jobs for them to do. Some (such as those used for cutting tools) need to be hard; others (such as those used in jet turbines) need to operate efficiently at high temperatures in corrosive environments. Each type of material needs customizing and finetuning for industrial use. Sometimes this involves the continuing refinement and improvement of long-established materials. More recently, with the very latest materials, the process of development starts with theory and basic science, moves on to modelling, analysis, measurement, experiment, and testing, and culminates in industrial application. The life of a product brings scientists together with engineers, manufacturers, and people on the factory floor, and each has a role to play. Although the line separating the scientist from the engineer is becoming blurred, the scientist is the one who most often asks the question ‘why?’ during the process of developing a new material, and the engineer emphasizes the question ‘how?’ The end users of the product, however (such as tool-makers in the factory or mining engineers at the rockface) have the most direct, practical knowledge of what exactly the final product needs to do. The ideal process is one in which all these different players take part. Exploring crystal structures of different materials at an atomic level scientifically creates concepts for improved or new materials. These are refined with the help of computer modelling, which simulates the potential behaviour of the material under different conditions. This kind of fundamental work helps to indicate, for instance, what processes could be applied to create the crystal structures that, in turn, will most likely give rise to the material’s desired properties and behaviour. Different properties are important for different applications. Some materials have properties that help with function; others have useful structural and thermal properties (such as alumina, which withstands chemical corrosion and high temperatures). Once a material with the suitable structure and properties has been designed and processed, it is made ready for an application test, in experimental, controlled conditions that do their best to simulate its performance in the field. It is subjected to stresses and other circumstances to test its behaviour in the kind of extreme conditions in which it might later be expected to operate. Materials used for drilling in deep mines, for instance – where the pressures and temperatures are high and rock is brittle – need to be tested in the laboratory under all those conditions before it is ready to go to prototype. If the prototype is seen to work, a pilot is prepared, ready for testing in the field. Many disciplines and specializations come into play during this development process. As
1 Beneficiation: the skilled conversion of cheap raw materials into high-value finished (or partially finished) products. South Africa mines chromium, for instance, and can export it as a raw material; alternatively, the country can export higher-value rods, sheets, or ingots of chromium steel.
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theoretical or fundamental research into strong materials leads to applied science and then engineering, physicists work with chemists to understand the materials being studied; the materials themselves are processed; properties are analysed and tested using a variety of techniques (see Fact File, page 13); and then, once successful, partnerships with industry turn the materials into useful products with the potential for largescale manufacture and commercial use. The CoE–SM works to this end with a wide range of strong materials
New ultrahard materials
Working with the structures of new ultrahard materials
The structure of a material determines its properties, so examining structure is the starting point for understanding. Diamond, for instance, has a simple crystal structure and the synthetic material cubic boron nitride (cBN) – which, unlike diamond, is not found in nature – has the same structure and is almost as hard. (Each carbon atom in diamond is linked tetrahedrally to four others with covalent bonds, making this structure extremely strong and hard to deform.) It is now thought that lightweight atoms like boron (B), carbon (C), or nitrogen (N) can be incorporated in the diamond lattice,
Diamond has the reputation for being the best hard material known – it cuts glass easily, is an excellent thermal conductor, is attractive to look at, and is very valuable. Yet it has shortcomings: as an abrasive it cannot cut steel efficiently, its shape cannot be easily changed, and it wears rapidly at high temperatures. Other common hard materials are ferrous alloys – most machine bearings are made from some form of steel – but these wear and are very heavy, so they are inefficient in terms of energy consumption for use in automotive and aircraft applications. What if materials could be made with properties that compete with metals and even have properties superior to those of diamond? The possibility of replacing metal components with lightweight ceramics and of obtaining materials that can cut steel and be stable at high temperatures is a current challenge for fundamental science and the advance of modern technology. In the last decade, many new materials have been developed artificially through high pressure and high temperature synthesis, and the search for new synthetics has been taken up by the advanced new hard materials focus area of the CoE–SM. In the past ten years, theoretical developments in the fundamental area of quantum mechanics have progressed to the point where we can make acceptably reliable predictions of the properties of assemblages of atoms and molecules. At the same time, rapid developments in
computer technology have made it possible to examine very large atomic systems and to use models to investigate and predict the properties of materials with novel compositions. These advances have given us the opportunity to start from first principles and develop a material theoretically by computing its possibilities – here in South Africa. Then, because we have been creating appropriate experimental conditions in the high pressure laboratory at the University of the Witwatersrand, the material can be synthesized and characterized, and compared with the earlier predictions for the properties that we are looking for. We use diamond anvils to subject the material to extreme conditions of pressure and temperatures, for instance, and we use Raman spectroscopy to characterize it (see box). After that – if it shows promise for industrial application – further properties can be developed and the new material can be manufactured for the marketplace.
Left: Boron icosahedra, each of which consists of 12 boron atoms that are bonded together to give an icosahedron (a regular convex polyhedron with 20 faces, 30 edges, and 12 corners). When linked, they form the basis of new advanced boride hard materials. Very lightweight materials, for example, are formed from boron (B) combined with carbon (C) and oxygen (O) (with compositions such as B4C and B6O being especially important), which makes them attractive candidates for body armour. The crystal lattices of such borides comprise assemblages of fundamental building blocks based upon boron icosahedra. Below: Ab initio computer modelling is able to view the charge (electron) density of new metal nitride structures such as B6O (shown here). Boron icosahedra (regions in light blue) are connected by oxygen atoms (regions in red/yellow). The ability of ab initio modelling to calculate the charge density is important because possible regions of low charge density in a structure become evident, implying, in turn, that other atoms (magnesium and silicon have been investigated here) may be suitable for inclusion and thus for connecting the boron icosahedra.
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now the hardest known oxide that has been synthesized, and hard phases of ZrO2 and HfO2 can be moulded and will be used in medical prosthetics. Another venture in the search for new ultrahard materials involves examining the structure of very small, nano phases or nano-particles of a material. Nano structures of carbon (in the form of fullerenes or nanotubes) are recent discoveries and the possibility that some other materials, for example a metal oxide such as TiO2, can exist at the nano level – as a nanoparticle – has now been confirmed. Computational modelling of such a structure has revealed scientific insight as to how nanoparticles of TiO2 could exhibit stronger properties than their bulk crystalline (largerscale) counterparts. A typical computational snapshot of a 4-nm nano-particle (comprising almost 3 000 atoms) of TiO2 when placed under extreme conditions of pressure shows a very dense stable region around the outer perimeter of the nano-particle, leading to an overall strengthening of the system as a whole. These are just some of the new materials being studied in the advanced hard materials focus area of the CoE–SM. Other materials with strong properties, involving 3 and 4 atomic constituents, are indicating enormous potential for future technology. ▲ ▲
giving rise to B-C-N diamond-like complexes with great hardness but quite different chemical properties from those of diamond. New nitrides – of which cBN has the simplest structure – are emerging as a family of synthetic materials with potentially hard properties. Almost a decade ago, the suggestion was made that C3N4 could have properties superior to diamond’s. The properties of this remarkable material offer a fundamental challenge to science and there is intense effort to understand and synthesize it. Already C-N-based materials have seen application as magnetic reading devices in computer processing units. Silicon nitride has been synthesized and is able to adopt different structures. When its crystal lattice has a spinel structure, this material has applications as mechanical bearings and engine components. The spinel structure has also led to a wide range of other potentially important hard materials. For example, replacing some of the N atoms with oxygen (O), or the silicon (Si) with aluminium (Al), leads to a family of new lightweight materials – the SiAlONs – with hard characteristics and different chemical properties. The possibility of replacing Si with C has been predicted to produce even harder materials than Si3N4. We remember that it is the difference in chemical properties that leads to a variety of applications – such as the ability to cut through different materials. Owing to chemical considerations, Si cannot readily bond to more than six surrounding (or nearest-neighbour) atoms, as is the case with the Si3N4 spinel structure. For this reason metals play an important role – hard forms of metal nitrides are rapidly emerging. The fundamental properties of Zr3N4 and Hf3N4 as well as MoN and CoN have recently been examined. All these materials are likely to be important for future industrial application. Oxides – of which silica or zirconia are now well known – form another series of important new ultrahard materials. Silica (SiO2) as quartz undergoes a series of physical transformations into a variety of different crystal structures, but one important structure – stishovite – has been shown to be one of the hardest. Structures based upon SiO2 form the heat-resistant tiles used on the lower surface of spacecraft such as the NASA space shuttle (see page 37). Stishovite is the hardest lightweight oxide known to date but is quite difficult to stabilize. As with the nitrides, metal oxides have proved to have important structures for ultrahard applications. Cubic zirconia as ZrO2 is known for its use in jewellery and as an abrasive, but its other phases could be even harder than zirconia. One of these has an elaborate orthorhombic structure with Zr coordinated to as many as nine O atoms. This phase – called a cottunite phase (see cover picture) – is also obtained with metals like titanium (Ti) or hafnium (Hf); cottunite TiO2 is
Above left: A diamond anvil is used to exert very high pressures (often reaching well beyond 40 gigapascals) for the laboratory synthesis of new hard materials. The material being investigated is placed between two diamonds situated at the lower part of the anvil. A very large force is applied to the thrust plate, which, in turn, applies an extremely high pressure through the piston onto the experimental material. Left: Argon ion lasers produce light in the blue-green part of the visible spectrum, and are widely used in materials analysis. Pictures courtesy of Mark Klein Productions
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relationships among the various physical and mechanical properties, the effect of compacting conditions on shrinkage during sintering, the mechanisms of wear on hardmetals compared with that on similarly hard ceramics, the effect of various surface coatings on the wear resistance of hardmetals, how they deform at high temperatures, and how to optimise the performance of cutting tools protected by a coating of a hard material deposited from a chemical vapour. Other projects centre on the inclusion of either vanadium (V) or ruthenium (Ru) in the hardmetals themselves to produce WC-VC-Co or WC-Co-Ru alloys. We are investigating the corrosion resistance, sintering properties, and thermal properties of alloys of different composition. Since South Africa produces most of the world’s ruthenium, it is particularly useful for the country to investigate new applications and markets for this metal, specially as it has only a limited number of applications at present. Its corrosion resistance gives it potential for introduction into hardmetals for mining applications where wear combines with corrosion in wet conditions. Our group has been the first to investigate these possibilities.
Above: Section of a tricone drill bit with cemented carbide inserts that is used in mining iron ore. Right: Cemented carbide inserts are used on a variety of mining tools, including this ‘continuous miner’.
Diamond, thin hard films, and related materials
Pictures courtesy of Mark Klein Productions
Hardmetals ‘Hardmetals’ is the name commonly given to cemented carbides, most of which consist of tungsten carbide (WC) particles cemented together in a cobalt (Co) matrix. They are widely used as drill bit inserts, cutting tools, wear parts in the mining and machining industries, and highpressure components. The lifespan of the hardmetal components critically depends on properties such as strength, composition, toughness, and resistance to corrosion, so work on hardmetals combines the science behind each material (needed for understanding its character and properties) with engineering (which deals with its applications for industrial benefit). In the long term, work with hardmetals has two main aims. The first is to improve the performance of existing hardmetals by understanding better the relationships between properties, microstructure, composition, and production conditions. The second is to develop new hardmetals and hard coatings containing South African primary resources, so as to create new knowledge as well as new potential markets for them. The CoE–SM conducts fundamental and applied research on the properties of commercial hardmetals. The work focuses on deriving
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Research on diamond and related superhard materials such as cBN is relevant for developing specialized tools used in the mining industry and in manufacturing, as well as for scientific applications. Diamond used for industrial purposes is mostly synthetic and in the form of small grits. South Africa is the leader in industrial diamond synthesis – it has the world’s largest diamond synthesis plant and produces 40% of the world’s synthetic diamonds. Thin hard and superhard films and coatings used in the automobile, aerospace, optics, and microelectronics industries protect the bulk substrate from corrosion and chemical reactions, and provide resistance to wear or abrasion. A good example is the titanium nitride hard coating on steel drill bits that gives a characteristic golden colour. We are studying the strength of diamond under different conditions. Diamond is brittle at room temperature and can crack. If it is indented at high enough temperatures with a pointed tool, however, it deforms plastically under the induced stress. By using Raman spectroscopy to measure the 2- and 3-dimensional stress patterns surrounding an indentation, we have shown that they agree with patterns calculated from the theoretical understanding of diamond properties. This gives confidence to theoretical studies. We are also studying polycrystalline diamond cutting-tools in which the diamond layer is attached to a tungsten carbide base and maintained under compression in the manufacture of the tool. Raman spectroscopy (see page 13)
to the body in its response to X-rays, which is a further advantage. ■ Diamond detectors for high-energy physics experiments (e.g. at CERN in Switzerland) are being developed. They are more resistant to radiation when recording elementary particles than other detectors. ■ Diamond monochromators for picking a specific X-ray wavelength out of a beam of intense synchrotron radiation are being worked on (in collaboration with the European Synchrotron Radiation Facility). Synchrotrons are now used extensively in engineering and materials studies as well as in the pure sciences and even medical research. Only diamond of sufficient purity will be capable of performing this function for the next generation of these machines. ■ High-level computational methods are being applied to the atomic and electronic structures associated with crystal defect properties and defect-related processes in diamond. Such techniques are important for understanding the cohesive and electronic properties of the material. ■ The atoms that occur on diamond surfaces after they are shaped and polished for use are also being investigated, giving useful information for electronic applications, where surface atoms can make a big difference.
Strong metallic alloys As Earth’s precious natural resources dwindle, we need to mine deeper and in ever more remote, dangerous, and inhospitable areas to keep up with the demand for raw materials. We also need to use resources more efficiently to avoid waste. In this effort, strong materials are vitally important. New alloys
The aim of the strong metallic alloys focus area in the CoE–SM is the development of new strong alloys for commercial applications, focusing on materials that are important to the economy of South Africa. A prime example is platinum (Pt), as more of the metal is mined in this country than anywhere else in the world, but most of it is exported for use in auto-catalysts and jewellery. So we have been among the drivers of a major thrust to find alternative uses for the noble metal platinum. Platinum has excellent resistance against corrosion, is very formable, and has a high melting point – properties that could make it ideal as part of an alloy for use at high temperatures in corrosive environments, such as in jet and land-based turbine applications. Developing an alloy is like making a variety of cakes – different ingredients are combined in different amounts
Top left: Steering mirrors adjust the fine beam alignment of the laser beam into the Raman spectrometer. Lower left: Using Raman spectroscopy to conduct a stress analysis of the diamond layer of a polycrystalline diamond drill bit. Below: The inlet of a jet turbine engine. Static components in such engines need high melting points and good chemical resistance. Pictures courtesy of Mark Klein Productions
shows that, at sufficiently high temperatures, the compressive stress is removed, thus providing information about the temperature limits for tool operation and the mechanism of stress reduction. A wide range of materials has been or is being studied in bulk or thin film form at room or at high temperatures. These include nickel-based superalloys (used in high-temperature applications such as aircraft turbine blades), vanadium carbides and carbo-nitrides (which are hard materials), boron-doped Si used in micro-electromechanical systems, iron pyrite, and hard thin films of titanium nitride, boron nitride, and tungsten carbides. Gold films have been studied at high pressures. These studies provide crucial information about the mechanical properties of important materials, and also yield data that are useful in the field of computational modelling. In research involving radiation and its detection (using various nuclear-based techniques), the advantage of using diamond is its resistance to damage by even intense ionizing beams. This makes it an excellent material for radiation detectors. Practical examples of such applications being worked on at the CoE–SM, in collaboration with local industry and research groups abroad, include the following. ■ Research is being conducted on the use of small diamond dosimeters for mapping the radiation field around the human body during mammography screening. The fact that diamond absorbs X-rays in a similar way to living tissue makes it behave in a similar way
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to make different kinds, suitable for use in conditions that may vary in many ways. To develop platinum-based alloys, other metals need to be added to the platinum, for example Al for strengthening and perhaps nickel (Ni) to reduce the price. The Al additions are useful because another compound or ‘phase’ is formed, based on Pt3Al, which makes it stronger, much as adding pebbles helps to strengthen concrete. (Here, the Pt3Al acts in much the same way that the pebbles do and the Pt-rich matrix acts like the concrete.) These mixtures have to be decided upon, made, studied, and optimized, and many rigorous tests are needed to determine the mechanical and chemical properties of the alloys. Brittle phases (which could form in the mixtures and decrease the strength of the alloy) should be avoided. The microstructure of the alloys (that is, the amounts and distribution of the phases, which can be observed only at high magnifications) can be manipulated by heat treatment – heating to various temperatures and cooling at different rates. To speed up the process, a computer program can calculate the phases likely to be present. Since this work is new and there is very little other work done on platinum alloys (some of it by our collaborators in Germany and Japan), the CoE–SM is building a database for the computer program to speed up subsequent work.
Top: To make it possible to use nanotubes, they need to be modified to give them the properties required for different uses. The pictures illustrate various ways of modifying the tubes with chemical reagents. The reagents can be attached to a tube in different ways, or wrapped around it, or placed inside it.
Another project addresses improvements in the continuous casting of steel. Here, the steel is cast and then, as it cools, the slab has to be bent prior to cutting. There can be problems of cracking at the bend. So we are ascertaining the deleterious (or harmful) phases and their distributions to help in reducing the bad effects and hence the cracking. A problem that causes huge financial losses each year is metal corrosion, but it is still far from being understood in detail. To study it, we have constructed a special micro-Raman cell in which corrosive liquids can pass over a metal sample under different electrochemical conditions. By their Raman spectra, we identify the series of compounds formed. These studies are giving new, detailed information about corrosion processes. Pitting corrosion can occur at particular points on a metal surface, for instance, so we are examining the regions within and surrounding a pit with the scanning stage of our Raman microscope, to understand better the complex processes leading to pit formation.
Carbon nanotubes and composites
Above left: Autoclave processing of lightweight carbon fibre components for aircraft from pre-impregnated materials. Left: Cracks caused by residual stress corrosion on the inner surface of a pipe, which was used in a platinum refinery to carry corrosive, highly concentrated sulphuric acid. Pictures courtesy of Mark Klein Productions
their strength. Researchers in our focus area are examining the possibilities and methods for synthesizing these materials. Making nanotubes is easy – but the high-energy conditions still make it difficult to control their diameters, length and chirality2, or the quantities made. We can try to modify the nanotubes chemically so that they will dissolve in solvents, react with polymers, and
Carbon nanotubes are viewed as one of the hot new materials of the 21st century. They are regarded as folded graphite layers and the very small tubes thus formed have amazing properties. Discovered only 14 years ago, these are the strongest materials known (relative to their size) and, while little commercialisation has occurred to date, there is great interest in
Picture courtesy of A. Hirsch from “Functionalisation of single walled carbon nanotubes”, Angewandte Chemie (International edition), vol. 41 (2002), p.1853.
2 Chirality: ‘Configuration’. In the context of carbon nanotubes, imagine a carpet being rolled up at different angles to one edge. The different ways of rolling the graphene sheets allow different structures to be formed.
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conditions, this technique also allows us to determine tube strength. We are also carrying out work to incorporate the nanotubes in composite materials, which promise to have superior strength over those used today in the manufacture of various engineering structures that require light weight and high mechanical strength. The Wits School of Mechanical, Industrial and Aeronautical Engineering provides the expertise to study the strength of carbon nanotubepolymer mixtures, while studies on catalysts are carried out with help from partners abroad.
Above: High-speed machining of hardened steel with a cubic boron nitride cutting tool. Right: The cubic boron bitride cutting tool insert used on the highspeed machining tool illustrated above. Pictures courtesy of Mark Klein Productions
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interact with catalysts. Postgraduate students in our focus area spend their time making catalysts to use in nanotube synthesis, or advancing wellknown arc-discharge and vapour-deposition methods to synthesize the tubes. We hope that these methods will bring understanding that will help control the process of synthesizing these materials – and, in turn, make it possible to produce them to standard in commercial quantities. Once made, these materials will be developed as catalyst supports and for use in composites. Single-walled carbon nanotubes (SWCNTs) are among the most interesting of the advanced materials we study. They have the highest mechanical strength of any material. They consist of carbon atoms arranged in a hexagonal pattern known as a graphene sheet. When rolled up into a cylinder of typical diameter of a few nanometres, various structures can be formed, which can be either metallic or semiconducting. We are developing characterization methods to establish the identity of the nanotubes. Raman spectroscopy, for example, is used to determine tube diameter and the electronic properties of the nanotubes. Under appropriate
The research carried out in the ceramics focus area of the CoE–SM includes processing, characterizing, and testing ceramics (that is, materials made from inorganic chemicals, excluding metals and alloys). Our central theme at present is on multi-component ultrahardphase-containing composites, suitable for cutting-tool and wear-part applications, and aimed at the world cutting-tool markets as well as at South African mining and manufacturing industries. Therefore hardness, strength, and ease of processing at atmospheric, rather than ultra-high, pressure are the areas receiving particular attention. Making composite materials containing ultrahard materials such as diamond and cubic boron nitride typically involves ultra-high pressures, with a consequent high cost attached. Using the understanding developed over many years in industry, it has been possible to devise techniques for sintering composites containing these ultrahard materials at low pressures without losing the ultrahard phases of diamond and cBN. This drastic change in sintering conditions can achieve savings of up to 50% in the cost of production, as well as access to larger and much more complex shapes of the final objects. The ability to sinter complex shapes is a prerequisite for entering many areas of the wear parts market. This technology has not been pursued systematically anywhere else in the world. Ceramics activities began at the University of the Witwatersrand in 1998 as a result of a request by industry, specifically Element Six. Initially, research was aimed at developing a basic capacity in ceramic materials processing, characterization, and the development of structure-to-properties-to-behaviour relationships for some basic ceramic systems. Research students were recruited as well as a postdoctoral fellow from the Republic of China. Significant funding came from industry in the form of bursaries and research contracts, as well as for major equipment, such as a hot press for attaining 2 200°C and powder-processing machinery. To evaluate the materials being generated, a tribological laboratory and a highspeed lathe have been set up. Now research has
Left: Breaking down coarse powders to a much finer structure typically requires a ball milling operation. This photograph shows the charging of a planetary ball mill with milling media. Picture courtesy of Mark Klein Productions
advanced to basic understanding of interest to industrial sponsors, as well as to the creation of still stronger materials. ■ Members of the CoE–SM who contributed to this article are its director, Professor Darrell Comins (School of Physics, University of the Witwatersrand); his colleagues at the University of the Witwatersrand, Professors Neil Coville (School of Chemistry), Trevor Derry (School of Physics), Silvana Luyckx (School of Process and Materials Engineering), Ted Lowther (School of Physics), Tom Nam (Health Physics), Herman Potgieter (School of Process and Materials Engineering), Jack Sigalas (School of Process and Materials Engineering), Mike Witcomb (Electron Microscopy Unit), Dr Simon Connell (School of Physics), and Ian Campbell (School of Mechanical, Industrial and Aeronautical Engineering); Professor Lesley Cornish (Mintek); Dr Andrew Venter (NECSA); and Shane Durbach (University of Johannesburg).
For more on strong materials in general, read K. Eric Drexler, Engines of Creation (London: Anchor Books, 1987) and the 1950s classic by William Alexander and Arthur Street, Metals in the Service of Man (Harmondsworth: Penguin). For more on ‘hardness’, consult J.E. Lowther, “Superhard oxides”, Materials Research Bulletin, vol. 28 (2003), p.189; V. Brazhkin et al., “What does ‘harder than diamond’ mean?” Nature Materials, vol. 3 (2004), pp.576–577; and T. Irifune et al., “Materials: ultrahard polycrystalline diamond from graphite”, Nature, vol. 421 (2003), pp.599–600. For platinum alloys read P.J. Hill et al., “New developments in high-temperature platinum alloys”, Journal of Metals, vol. 53 (October 2001), pp.19–20; L.A. Cornish et al., “Development of platinum group metal based superalloys for high temperature use”, Materials Research Bulletin, vol. 28 (2003), pp.632-638; and T. Biggs et al., “Platinum alloys for shape memory applications”, Platinum Metals Review, vol. 47 (2003), pp.142–156. For natural and synthetic diamonds, read these two books edited by J.E. Field, The Properties of Diamond (London: Academic Press, 1979) and The Properties of Natural and Synthetic Diamond (London: Academic Press, 1992). For more on ceramics read Derek Thompson, “Ceramics: tough cookery”, Nature, vol. 389 (1997), pp.675–677. For nanotechnology visit http://sunsite.nus.edu.sg/MEMEX/nanolink.html and for details about nanotubes, consult Peter J.F. Harris, Carbon Nanotubes and Related Structures (Cambridge University Press, 2002); M.S. Dresselhaus et al., Science of Fullerenes and Carbon Nanotubes: their properties and applications (Academic Press, 1996); and M. Endo et al., Carbon Nanotubes (Pergamon, 1997). You’ll find more on composites by visiting www.netcomposites.com, www.jeccomposites.com, and www.composites.wits.ac.za. There is more on Raman spectroscopy at www.chemsoc.org/exemplarchem/entries/2004/Birmingham_jones/raman.html.
Q Fact file
Raman and Brillouin scattering
Performing Brillouin scattering measurements at high temperature on strong materials, using the green line of an argon ion laser. Picture courtesy of Mark Klein Productions
smaller than in Raman scattering. In studying strong materials, we use the Raman effect to identify the nature of the material, its state of crystalline perfection or
disorder, changes of phase, the presence of inclusions (impurities), and the effects of temperature, pressure, and strain. Measurements are made with a Raman spectrograph that separates the various frequencies in the scattered light from the sample and displays them as a spectrum. A Raman microscope with a computer-controlled scanning stage studies 2- and 3-D regions of a small sample. Miniature low and high temperature stages can be examined with the microscope; for large samples we use a furnace or a lowtemperature vessel called a cryostat. Through Brillouin scattering studies we determine the elastic properties of materials in bulk form as well as thin films and coatings. The characteristic quantities (known as the elastic stiffnesses) depend on variables such as pressure and temperature, microstructure, composition, and strain, and are sensitive to certain solid-state phase transitions. The equipment that resolves the different features in the spectrum of the scattered light uses an ▲ ▲
Raman and Brillouin light scattering are two powerful laser-based methods to study the properties of materials. Laser light interacts with the vibrating atoms of the material being investigated. A very small fraction of the light that is scattered and emerges from the sample is thereby changed in frequency and wavelength. This provides information about the nature of the vibrations that result from the atoms within the unit cells of the crystals moving with respect to one another in various ways; in this case we refer to Raman scattering. The unit cells also move together in a coupled manner behaving like sound waves in the material. In very stiff materials that resist deformation, such as diamond, these waves (also called elastic waves) have high velocities while the reverse is true in the case of elastically soft materials. The stiffness is a measure of the mechanical strength and also of the hardness. Light scattering in this case is known as Brillouin scattering and the frequency shifts of the scattered light are much
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Fact file Q
advanced interferometer. This works on the interference of light waves to separate their different frequencies. Extremely small frequency differences can be measured in this way. We carry out two forms of Brillouin scattering, that in which the measured elastic waves move through the body of the material and that in which surface waves are investigated. The latter are useful in studying opaque materials where the light cannot penetrate the sample. Using a hightemperature optical furnace or a gem anvil cell, the elastic properties are studied at high temperature and pressures.
Diffraction Diffraction refers to constructive interference phenomena that result when waves of particles are scattered from regularly spaced obstacles to be in-phase. Waves (including electromagnetic waves such as light, radio, and X-rays) can undergo diffraction when the geometrical condition, ≤ 2d, is satisfied between the wavelength () of the waves and the spacing (d ) between the obstacles being observed. This phenomenon is exploited with waves of neutrons, X-rays, or electrons to provide information about the atomic level of matter where the interatomic distances, in the order of 1010 m, are matched by the wavelength of the probing waves. Diffraction of neutrons, X-rays, and electrons thus makes it possible to visualize the microstructure of materials, providing valuable information about physical, chemical, metallurgical, geological, and engineering properties and phenomena. With X-rays and electrons the interactions with matter are with the electrons of the atoms, whereas the neutrons interact with the atomic nuclei of the material. These particle beams therefore provide highly complementary probes of matter. As they are uncharged, neutrons can penetrate more deeply into most materials (typically 1 000 times more deeply than X-rays). This allows us to investigate the interior of materials and components non-destructively. The microstructure of materials is deduced from diffraction patterns that comprise peaks at different diffraction angles (related to the spacings between atoms) with varying intensities (related to the atoms present and their distributions). The technique can be applied to any crystalline material including metals, alloys, ceramics, metal–matrix composites, some polymer composites, and as thin layers. Materials can be investigated by single crystal or polycrystalline (powder) diffraction techniques, each with its own characteristic advantages. Neutron diffraction Neutrons are fundamental particles that exist in the nuclei of atoms. High flux neutron beams are produced in nuclear reactors, such as the SAFARI-1 research reactor at NECSA, from the radioactive decay of 235U atoms. These highenergy neutrons are slowed down by passing them through a moderator, such as light or heavy
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View of the core of the SAFARI-1 research reactor at NECSA, in which neutrons are produced for various peaceful applications of nuclear techniques, such as neutron diffraction and neutron radiography/tomography. Picture courtesy of Mark Klein Productions
water, to change their wavelengths into the 1010 m range for use in diffraction applications. X-ray diffraction X-rays are produced in laboratory-based instruments when rapidly moving electrons strike a target material. Each target material gives off characteristic X-ray wavelengths that are selected for their compliance with the material property being investigated. X-rays are also good for investigating the near-surface residual stresses in materials and components. Neutron and X-ray radiography/tomography With radiography, the interior composition of enveloped components can be imaged. Neutrons provide superior sensitivity to hydrogen-containing materials (water, rubber, and organic polymers). Complementary information comes from X-rays that are more sensitive to high atomic number materials. The two methods complement each other in non-destructive evaluation of fabricated components and materials to identify defects such as cracks and voids and in quality assurance assessments. With tomography, 3-D reconstruction of samples and components is possible that enables non-destructive assessment and reverse engineering applications. Particularly important for investigating strong materials are: analyses of the chemical phase composition; residual stress field determination/mapping at discrete positions in these strong materials; and 3-D tomographic reconstruction (similar to CT scanning).
Electron microscopy Two major types of electron microscopes are vital for much of strong materials work. Electrons are used because they have a shorter wavelength than light and thus give higher resolution images as well as allowing much higher magnifications to be attained than from the cheaper and easier to use light (or, optical) microscopes. To use electrons, a vacuum must be maintained inside the microscope where the specimen and detectors are located because electrons, being such small
particles, are easily deflected by dust and gas molecules. Thus, electron microscopes are much more complex than light microscopes. The scanning electron microscope (SEM) is the most common one. It scans an electron beam across the surface of a specimen and then various detectors collect the products (electrons and Xrays) of the interaction of the incident beam with the specimen. The samples are bulk material and the specimen preparation is fairly easy. Much use is made of the secondary electrons because these come right from the surface region, a few atom layers deep, and once they are collected and displayed (lots of complex electronics!), a 3-D image of the surface topography of the specimen is obtained. This is really useful, because a much higher magnification and a greater depth of focus can be obtained than with light microscopy. SEM, therefore, can give 3-D images of very uneven surfaces, such as fractures, corroded surfaces, and even (these are often seen!) insects. Another SEM mode collects the back-scattered electrons that come from a greater depth within the sample, and these are useful because the contrast they produce in the image depends on the average atomic number, that is, the elements present in the sample. These images show the different phases within the material (regions having different compositions). In addition, X-rays are also emitted from the specimen, which can be collected and analysed to give information about the chemical composition of the entire sample, or on a smaller scale, of the different phases. The most common method used is called energy dispersive X-ray analysis (or EDX). A transmission electron microscope (TEM) needs much more careful specimen preparation since the sample must be very thin to allow the electron beam to pass through it to form an image of its internal structure on a screen or camera. There are two major modes of operation: imaging and diffraction. Imaging provides from very low (tens of times) up to high (millions of times) magnification of the sample's internal structure, allowing images to be seen of imperfections, very small phases that the SEM cannot image, atom planes, and even – in really expensive microscopes – the atoms themselves.
Mechanical, thermal and electrical characterization Mechanical characterization typically involves stressing the material mechanically to obtain the required properties. Impact testing, for example, involves measuring the energy absorbed by test samples during impact events. Thermal and electrical characterization involves tests to obtain properties such as thermal and electrical conductivity, or coefficients of thermal expansion.
Theoretical modelling Computational modelling techniques often allow the final properties of composite materials to be predicted from the properties of the constituent materials without the need to manufacture test samples. These techniques are also used for stress and strain (structural strength) analysis. ■
Q Careers in S&T Strong materials help to make the most of South Africa’s mineral resources, with career opportunities wherever such materials are investigated or used in manufacturing and industry.
outh Africa has traditionally been a producer of primary materials such as gold, diamonds, coal, and platinum. Now the economy needs to expand to satisfy the needs and aspirations of all South Africans, so it’s important to build manufacturing strength too. Manufacturing needs people who understand and work with strong materials. In mining, they are crucial for drilling and extracting ore, for example; Iscor has grown by developing advanced steels; Element Six has a large ceramics programme. Research bodies such as Mintek, NECSA, and the CSIR are developing new applications for resources that South Africa has in abundance, for the more uses we can find for them, the greater becomes their economic value. Even the pebble-bed modular reactor needs strong materials that, for safety, must be developed to withstand radiation. Strong materials work offers career prospects at all levels – research, engineering, and project management, as well as in manufacturing itself.
engineering training in an aircraft or aircraft-part manufacturing factory. After that, the bulk of engineering work could be technical head-office-based, with site visits. With good matric maths and science and a degree in mechanical engineering, you could become a composite materials engineer. You would need to enjoy working with machinery and equipment. The career would normally involve designing, specification, site visits, consulting, and factory supervision. Doing well means having good people skills as well as good engineering skills. ■ QUEST thanks the DST/NRF Centre of Excellence in Strong Materials for supplying information for this Careers page. For wide-ranging and useful information consult the Department of Science and Technology’s Careers in Science, Engineering and Technology, 2005 edition (Pretoria: Beyond 2000 Publishers in association with the DST).
Research Researchers work both in academe (see “Getting to grips with strong materials” in this issue) and in industry. At universities or in research institutes, they conduct fundamental and applied science, often combining the two as they work with industry now and for the future. Industry itself has research and development divisions, where products are designed and manufactured for national and international markets. Scientists in a multidisciplinary academic research centre, such as the DST/NRF Centre of Excellence in Strong Materials, come from various disciplines. They start with good matric grades at higher level in mathematics, science, English, and at least one other language. (This is because understanding the science and doing the mathematics lead to results that must then be communicated efficiently in reports, papers in scientific journals, and in conference or oral presentations to colleagues and prospective sponsors.) Then comes an undergraduate degree in physics, chemistry, or metallurgical or mechanical engineering, followed by postgraduate study to doctoral level in one of the focus areas Industrial research for product development often focuses on practical applications in an industry serving specific markets. What products or equipment might people need? What can we create to satisfy that need and offer good value for money? What is the economic potential of the new product or equipment in the country or for export? These are some of the questions addressed in product development. In this application of strong materials research, a master’s degree is an excellent starting point.
Engineering and project management A four-year engineering degree with special courses in strong materials offers excellent opportunities for project work and management in a chosen field. An aeronautical engineering degree, for instance, qualifies you to become an aircraft structural engineer. This work suits people who enjoy and excel in mathematics and science at school. It involves designing, specifying, and analysing lightweight structures for aircraft. It begins with three years of practical
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Right: Elliot and Clarens formation of the uppermost Karoo (near Elliot). Photograph: John Hancox
Bruce Rubidge describes the extent and uniqueness of South Africa’s fossil heritage, a mecca for palaeontologists that is unmatched anywhere in the world.
he name ‘Karoo’ comes from the Khoikhoi word meaning ‘arid’, ‘dry’, or ‘barren’ ground. Today’s flat semi-desert with its koppie outcrops, however, was once hot, humid, and extensive marshland, similar to the Okavango Delta of our own time. The fossils preserved in Happy 60th birthday, BPI! On 26 October 2005, the Bernard Price Institute for Palaeontological Research (BPI) at the University of the Witwatersrand turns 60. It was founded thanks to the infectious enthusiasm of one of South Africa’s greatest scientists combined with the foresight of a generous Johannesburg philanthropist. In 1945, Robert Broom (employed at the Transvaal Museum) was a medical doctor with an intense interest in fossil mammal-like reptiles. He delivered a lecture at Wits, stressing the need to collect and preserve Karoo fossils because the country was losing much of its priceless palaeontological heritage to erosion every year. He blamed what he saw as an unwilling, unenlightened, and mean attitude on the part of state bureaucrats who, by failing to provide sufficient money to ensure that this heritage was properly cared for, were neglecting their duty to the nation. In the audience was Bernard Price, managing director of the Victoria Falls Power Company. He offered to donate £2 000 a year provided that the fossil material collected was curated by Wits. This led to the establishment, later that year, of the BPI, which today has international standing as a research institute and as South Africa’s only centre of palaeontological training. Its fossil collections make it also the custodian of a large part of the country’s palaeontological heritage, visited by scientists from across the globe. The BPI’s strengths lie most particularly in the fields in which it has worked since its inception: the 200–300-million-year-old fossils from the Karoo and the younger, less than fourmillion-year history of human ancestry. Since 1958, the institute has also produced Palaeontologica africana, the only scientific journal in Africa dedicated to research relating to the continent’s palaeontological heritage. The BPI has made major scientific contributions in the fields of Karoo vertebrate palaeontology (including the discovery and description of the most primitive anomodont mammal-like reptile, the earliest sauropod dinosaur, the earliest tortoise from the southern hemisphere, and the oldest dinosaur eggs); Karoo palaeobotany; micropalaeontology; PlioPleistocene palaeontology (including the first discovery of archaic Homo sapiens from the Cave of Hearths and the first discovery of Australopithecus africanus at Makapansgat); and the palaeontology of the Orapa crater lake deposit in Botswana.
the Karoo rocks tell a remarkable story of changing landscapes and of the animals and plants that lived and died there over the millennia. These rich fossil-bearing rocks cover twothirds of the surface area of South Africa. At first glance they appear inhospitable, but their epic tale covers more than 100 million years. It recounts the ancestry of plants, tortoises, dinosaurs, the distant origins of mammals and, ultimately, of humans as the climate shifted from glacial polar conditions to subtropical desert. No other country in the world has such a complete, largely uninterrupted terrestrial rock record that covers the Carboniferous, Permian, Triassic, and Jurassic periods.
The rocks and their secrets The Karoo Supergroup1 comprises a succession of rocks several kilometres thick that extend over most of South Africa from Laingsburg in the southwest to Vereeniging in the northeast. When these rocks were deposited, from 300 to 180 million years ago (Myr), southern Africa was part of the huge supercontinent we call Gondwana2 and was positioned between the southern tip of South America and east Antarctica. The area covered today by the Karoo Supergroup was then a lowland. The northern border of the Karoo basin was a highland area known as the Cargonian Highlands; its southern border was the extremely high Cape Mountain Belt, whose last remnants today form the Swartberg Range. Because the Karoo rocks were deposited over such an extended period, they record changes in
1 Supergroup: As the Earth’s crust responds to forces beneath the surface – such as submergence below sea level or volcanic uplift – layers of rock and sediment accumulate and erode, and the landscape changes. The name ‘supergroup’ is given to all those rocks deposited during the same period of subsidence (or ‘settling down’) due to a single event. They are normally named according to the region where they are particularly well exposed: hence the Karoo Supergroup, whose layers of different rock types underlie the Karoo region. 2 Pangaea, Gondwana, and Laurasia: About 300 Myr, all of the Earth’s landmasses were a single supercontinent, which we call Pangaea, and which extended almost from the South to the North Pole. It then broke apart, initially forming two large fragments, Gondwana (south) and Laurasia (north). About 180 Myr, these began to fragment further and drifted apart to produce the continents of today.
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ANTARCTICA Cynognathus and Mesosaurus
Geological periods of the Karoo rocks Age Period Group (Myr) 354 Carboniferous Dwyka 290 Permian Ecca
Beaufort Beaufort Stormberg Stormberg
Formation Environment in SA
Molteno Elliot Elliot Clarens
Ice and glaciers Sea surrounded by deltas Rivers Rivers Braided rivers Arid meandering rivers Arid meandering rivers Desert
End Permian (3rd)
End Triassic (4th)
142 Myr = millions of years ago
South Africa’s fossil riches
the environment from glaciers (in the case of the Dwyka, when southern Africa was positioned over the polar region around 300 Myr) to deltas supporting the rich flora that ultimately created the extensive coal deposits mined today in South Africa’s Free State, Gauteng, and KwaZulu-Natal provinces. Over time, the basin became smaller and the environment more arid; rivers deposited sand and silt that then became the rocks of the Beaufort Group and Molteno and Elliot formations of the Stormberg Group.
Below: The first known skull of Melanorosaurus, a herbivorous dinosaur from the late Triassic, found in the Free State, South Africa. Photograph: Adam Yates
Sixty years ago, palaeontology was a Cinderella science in southern Africa and the region’s great palaeontological potential had not yet been recognized. Now it is well known as the only area that has: ■ the oldest evidence of life on Earth ■ the oldest multi-cellular animals ■ the most primitive land-living plants ■ the most distant ancestors of dinosaurs ■ the most complete record of the ancestry of mammals ■ a remarkable record of human origins and of human achievements. South Africa has over one-third of the entire fossil record of human evolution in Africa and spans more than three million years. Cave sites in the provinces of Gauteng, North West, and Limpopo hold evidence of the wide diversity of hominid species and an archaeological record including some of the world’s oldest stone tools and the earliest signs of the controlled use of fire. It is impossible to examine the development of life on Earth without referring extensively to the South African fossil record. Recognizing this, government identified Palaeontology and Palaeoanthropology as one of five key research themes in its National Research and Development Strategy (August 2002).
Top left: Geological map of the Karoo basin showing the different rock formations. Middle left: This diagram shows how today's continents, separated by oceans, were once joined together in the supercontinent we call Gondwana. This accounts for the distribution of fossils of land-dwelling reptiles (such as Lystrosaurus, found in Africa, India, and Antarctica; Cynognathus in Africa and South America; and the estuarine reptile Mesosaurus in Africa and South America). They could have spread so far apart only by land before Gondwana split. Image: Terence McCarthy and Bruce Rubidge Above left: Skull and skeletons of two specimens of the anapsid reptile Owenetta lying alongside each other. Image courtesy of BPI Palaeontology Top right: This reconstruction of a Karoo scene during the Early Jurassic shows the small meat-eating dinosaurs (about the size and weight of the modern secretary bird) Coelophysis (Syntarsus) attacking Massospondylus, an early Jurassic dinosaur from the Drakensberg foothills (which grew to 4 m in length). Image courtesy of Billy de Klerk, Albany Museum; artist: Gill Maylam
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Dinosaurs: New South African discoveries ■ The world’s oldest sauropod dinosaur. Sauropods are the familiar giant, long-necked, plant-eating dinosaurs such as Brachiosaurus and Diplodocus. Their early history is poorly understood, as the first good specimens did not appear in the fossil record till the Middle Jurassic (about 170 Myr), by which time they were already highly specialized giants. Now, in 2003, we have discovered Antetonitrus ingenipes, a comparatively small, very primitive sauropod from the Late Triassic (about 210 Myr) of South Africa, which is answering many questions about the early evolution of the group. ■ The world’s oldest dinosaur eggs and embryos. Research in the past year on dinosaur eggs (which were found by James Kitching in the early 1970s) has revealed that they contain perfectly preserved embryonic skeletons. These embryonic dinosaur skeletons – the oldest in the world – reveal much about how early dinosaurs grew (see page 45). ■ The first complete skull of a Triassic dinosaur from South Africa. This new find is exciting because it appears to be from an animal close to the ancestry of the sauropods, if not actually a sauropod itself. ■ A new large theropod dinosaur. South Africa’s Early Jurassic rocks (aged about 185 million years) have long been known to contain the remains of a small (less than 2 metres long) theropod (meat-eating) dinosaur called Coelophysis. Just recently, in 2004, the bones of a much larger theropod (approximately 6 metres long) have been found in the same rocks. This new dinosaur, which has not yet been named, shows strong similarities to the bizarre, crested, theropod Dilophosaurus from the Early Jurassic of North America. – Adam Yates
The BPI’s Dr Adam Yates specializes in early sauropod dinosaurs (the group that includes all the really large longnecked dinosaurs). He recognized, in 2003, that the earliest member of this group is from South Africa. He named this dinosaur Antetonitrus to emphasize the fact that it occurs ‘before the thunder lizards’.
Above: An archaeological excavation at Rose Cottage Cave in the Free State.
ancestors of all tortoises come from the Karoo. It has also provided some of the oldest evidence of dinosaurs in the form of footprints from the Maclear district of the Eastern Cape province. Antetonitrus, the most distant ancestor of the gigantic long-necked dinosaurs, has recently been described from the Ladybrand district of the Free State; and the oldest dinosaur eggs (preserved with embryos inside) come from the Golden Gate National Park.
Photograph: Lyn Wadley
Right: Procynosuchus, an advanced therapsid from the Karoo.
From mammal-like reptiles to mammals
Reconstruction (right) and fossil skull (below) of a gorgonopsian. With their large sabre-like teeth, these were ferocious predators of the Permian (typically 2–3 m long). They were victims of the mass extinction that occurred at the end of this period. ▲
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Within the layers of rock, palaeontologists have found a great diversity of fossils of vertebrate animals (that is, those having a spinal column). Examined in the context of the long time-span covered by the deposition of the rocks, these fossils yield the evidence for understanding the evolution of the modern ‘reptilian’ lineages, which include tortoises, lizards, crocodiles, dinosaurs, birds, and mammals. All the lineages (except birds) are represented in the rocks of the Karoo, and many of them began their existence in the South Africa portion of Gondwana before migrating to other parts of the supercontinent. So, for instance, fossils of Africa’s oldest tortoise (Australochelys) as well as the
The lineage for which South Africa is internationally renowned is that of the therapsids (informally called ‘mammal-like reptiles’). In a later age, this line gave rise to mammals but, in Permian times, before mammals appeared on Earth, therapsids dominated among land-living vertebrates. In as early as 1932, Robert Broom recognized the significance of our fossils: “The mammal-like reptiles from South Africa may be safely regarded as the most important fossil animals ever discovered, and their importance lies chiefly in the fact that there is little or no doubt that among them we have the ancestors of mammals, and the remote ancestors of man.” Current research supports his bold statement. In the past, the oldest and most primitive therapsids were thought to come from Russia, with the South African forms arriving here by overland migration. In the last decade, however, Wits palaeontologists from the Bernard Price Institute for Palaeontological Research (BPI) have discovered a new and even more primitive therapsid fauna in the rocks of the Beaufort Group near Prince Albert, leading them to conclude that some therapsid families originated in this country and not in the northern hemisphere. At the other end of the time scale, from the mid-Triassic period (240 Myr), John Hancox has discovered near Sterkstroom an advanced type of dicynodont therapsid (Shansiodon) in rock of the upper Beaufort Group. The discovery of this type of animal, previously known only from China, proves the earlier links between countries that today are
Uses of fossils Fossils are useful for ■ determining past biodiversity trends (to help us handle the current biodiversity crisis) ■ determining the rate of deposition of sediments, so that we can understand past environments (how quickly they change, the effect of past climates) and perhaps to predict how climatic conditions may change in the future ■ uncovering evolutionary relationships and the origins and evolution of modern species ■ mineral exploration, by helping • to correlate rock layers from one place to another (within a country as well as globally) • to reconstruct knowledge of past continents and how they broke apart • to interpret past environments, especially those lending themselves to the concentration of certain economic mineral deposits (such as coal and petroleum) • to create basin development models for understanding where economic minerals might be concentrated.
widely separated. James Kitching’s discovery in the 1970s of the first fossil mammal from the Elliot formation in South Africa shows that the country not only has some of the oldest therapsids known, but the earliest mammals too. If you travel across the Karoo rocks from Prince Albert (the place of the oldest rocks of the Beaufort Group), via Beaufort West to Graaff-Reinet and onto the highlands of the eastern Free State – and if you know what to look for – you can trace in the rocks the evolving ancestry of mammals from reptiles. Ours is the only country where this is possible.
John Nyaphuli (above) with the specimen he discovered near Prince Albert, South Africa, of Tapinocaninus, a new type of dinocephalian. Dinocephalians were the earliest large land-living vertebrates from the southern hemisphere. This specimen preserves the most complete skeleton of a dinocephalian and has enabled us to create a reconstruction of the animal (above left). Reconstruction by Marvin Carstens, BPI Palaeontology
Below: The Taung Child, the first Australopithecus, has features intermediate between those of apes and humans. Picture courtesy of the University of the Witwatersrand
It’s the completeness of its Permian-Jurassic sequence that makes the Karoo Supergroup globally significant. South Africa presents to the world some of the oldest therapsids and the earliest mammals, with examples of the evolutionary in-between stages. The rocks of the Karoo basin preserve one of the most remarkable and extended sequences of terrestrial tetrapod (four-footed animal) development over this period, and the most complete documentation of the evolutionary development of early mammals in the world. Though similar geological successions exist in India, China, and Russia, none of them is complete. So every palaeontologist working in
any country on similar fossils of similar age uses the Karoo fossil record as a point of reference. That’s why it’s so important for the country to maintain its fossil collections and to make them accessible to the world’s researchers. Since fossils of the same species of land-living animals are found on continents that today are widely separated, the Karoo remains can help scientists to correlate rock sequences from one continent to the next. This information, in turn, improves our understanding of the breakup of Gondwana, the subsequent movement of continents, and – of great importance for the mining industry – the whereabouts of economic minerals such as coal and uranium. Newly discovered volcanic ashes in the Karoo, moreover, offer new possibilities of dating our fossils, which is a great step forward. Currently, we get our dates3 from abroad – from countries such as Russia and China. Now we have the prospect of being able to put accurate dates to our own rocks and therefore to our own fossil discoveries, to determine not only rates of evolution, length of time of extinction events, and postextinction recovery periods, but also the rate at which sediment was deposited and the basin’s geological history. This research is still in its infancy, but it offers important international
3 Dating fossils. Fossils are dated in various ways. One way is to date the fossil according to the age of the rock in which it is found (methods of dating rocks vary in terms of the age and type of rock). Where direct dating of the surrounding rock is not possible, researchers date by association: that is, they compare the fossil in question with fossils of co-existing faunas whose date is known.
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One science, many disciplines and nations
Above: In this outcrop (near Barberton), the granodiorite (grey) is the oldest rock in southern Africa and was formed 3 644 Myr. It is cut by younger granites (pink). Photograph: Carl Anhaeusser Below: The rocks of the Karoo were deposited almost continuously from 300 to 180 Myr. Their fossils offer a nearly complete record of the different types of land-living vertebrates living during this long period. They also give information about two great extinction events (indicated by black arrows) and a possible third (around 260 Myr), currently being investigated.
The evolutionary completeness of Karoo rocks Main Karoo
Photograph: Adam Yates
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220 230 240 251
MILLION YEARS AGO (Myr)
270 280 290
Right: A bone from the tip of the snout of a new species of predatory dinosaur from the Early Jurassic (Eastern Cape, South Africa).
Palaeontology is ‘the branch of science that deals with extinct and fossil animals and plants’ (from the Greek word palaios meaning ‘ancient’). To pursue it successfully, however, many disciplines – and scholars from around the world – need to work together for fossil finds to yield meaning and to be fully interpreted. The work of any palaeontologist combines Earth and life sciences. Studying a fossil means describing it fully to ascertain what it is, to name it, and to compare it with related forms. These activities involve the disciplines of biology and anatomy. Classifying the animal or plant involves taxonomy. Comparing it with other forms and assessing its place in the evolutionary sequence involves biology and phylogenetic studies. Geology is also crucial. Determining a fossil’s position accurately in the rock sequence and rock record requires sedimentology and stratigraphy. Ascertaining the age of an animal is done by geochronologists. All this information is needed to determine the environment in which that animal lived. Support disciplines also assist: chemistry, for example, helps in the study of isotopes in the teeth to determine the diet of an animal; the worlds of physics and medical hospitals provide CT (computerized tomography) scanning; engineering helps in the building of 3-D models. By putting together the available data for many fossils, scientists can seek out past biodiversity trends and determine extinction events. Accurate information about where fossils are found helps in the study of basin development (how such areas filled with sediment, for instance); information about where fossils occur in the fossil record in different countries helps in determining the break-up history of continents. Our South African fossils regularly travel abroad, as they are studied and compared with similar fossils all over the world (for example, in Russia, Germany, Canada, the USA, Britain, and Australia).
research opportunities for uncovering more of the Karoo story in the fields of palaeontology, geology, and evolution. Because South Africa occupied a central position on the Gondwanan portion of Pangaea (see note 2, page 16), its extensive record means that any researcher anywhere in the world studying the development of Gondwana and the entire Pangaean world needs to refer to the unique fossil record from the Karoo as it continues to unravel.
Biodiversity and extinction events Most people are aware of the impact from outer space that led to the extinction of dinosaurs and other forms of life 65 Myr at the end of the Cretaceous period. Few people know, however, that the last 500 million years brought at least five major extinction events, which altered the course of the evolution of life on Earth. The greatest occurred at the end of the Permian period, 251 Myr, and obliterated more than 90% of species living both on land and in the sea. The Karoo contains many clues as to what happened. It has the best record of the effects of this extinction on land and, of the more than 50 different kinds of land-living vertebrates that lived in the area contained in today’s South Africa at the end of the Permian period, only four forms survived. This extinction event extended over possibly 100 000 years, suggests Roger Smith (of Iziko Museums in Cape Town). Its cause remains a mystery, but it is the focus of several international studies. Together with scientists from the Smithsonian Institution in Washington, DC, for instance, the BPI’s Marion Bamford is examining the impacts of this extinction on fossil plants and insects. In the current biodiversity crisis posed by our own, ongoing sixth extinction4, scientists are increasingly investigating past trends in biodiversity for ideas about sustainable development and help for the future. As the world’s palaeontologists question the causes and effects of past extinction events and try to understand the subsequent recovery of biodiversity, the rocks of the Karoo will be providing many of the answers. ■
Top: Thrinaxodon, the first therapsid fossil discovered in Antarctica by James Kitching. Above: A complete skeleton of a curled-up Thrinaxodon from South Africa. Photographs: James Kitching
Professor Bruce Rubidge has been director of the Bernard Price Institute for Palaeontological Research since 1990. Born and raised in Graaff-Reinet, he is passionate about the Karoo. His research interests are the fossil tetrapods, particularly mammal-like reptiles; the geology, stratigraphy, palaeoenvironments, and development of the Karoo basin; and the correlation of the fossils and rocks of the Karoo with other Gondwanan countries. He is organizing the lecture series, “The Story of Life: A new perspective on South Africa’s 3.5 billion year fossil record”, at the University of the Witwatersrand, on 8 October 2005. (See Diary of Events, p. 47). For more information, consult M.A. Cluver, Fossil Reptiles of the South African Karoo. (Cape Town: South African Museum, 1991); C. MacRae, Life Etched in Stone: Fossils of South Africa. (Johannesburg: Geological Society of South Africa, 1999); and 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). Scientific papers worth reading include G.J. Retallack, R.M.H. Smith, & P.D. Ward, “Vertebrate extinction across the Permian-Triassic boundary in the Karoo Basin, South Africa” Geological Society of America Bulletin, vol. 115 (2003), pp.1133–1152; and B.S. Rubidge, “Re-uniting lost continents – Fossil reptiles from the ancient Karoo and their wanderlust”, South African Journal of Geology, vol. 108 (2005), pp. 135–172.
Above: Dicroidium was the characteristic seed fern of the Triassic that diversified when Glossopteris flora became extinct at the end of the Permian period (actual size).
Visit the BPI web site at www.wits.ac.za/geosciences/bpi
Photograph: John Hancox
South African scientists helped to put the country’s fossil record and scholarship on the world map. These award-winning pioneers have all been associated with the BPI. Robert Broom (1866–1951). This Scottishborn medical doctor came to South Africa in 1897 to study the evolutionary origin of mammals using the fossil therapsids from the Karoo. Later in life, he changed the study of human evolution by showing (with Raymond Dart) that australopithecines were the earliest hominids. In 1936 at Sterkfontein he found the adult australopithecine skull of Plesianthropus transvaalensis (‘Mrs Ples’); in 1938 he identified the robust type of australopithecine, Paranthropus robustus at Kromdraai nearby; in 1947 he found limb bones at Kromdraai and part of a skeleton at Sterkfontein, which vindicated Dart’s claim that australopithecines walked upright. At last the scientific world could accept these fossil forms as ancestors of humans. Raymond Dart (1893–1988). He changed the direction of human palaeontology in 1925 by identifying the infant australopithecine skull from Taung as Australopithecus africanus and by pursuing the controversial idea of the australopithecines as a stage in human evolution till, finally, it was fully accepted in 1985. While at the BPI, he pioneered the study of taphonomy (that is, the analysis of bone assemblages) in South Africa. He also developed his theory – now superseded – of what he termed the ‘osteodontokeratic’ culture of the australopithecines, postulating that many of the bones found in association with fossils of the ape-man Australopithecus were in fact tools. James Kitching (1922–2003). He worked at the BPI from 1945–1996, was responsible for finding 90% of the Institute’s extensive fossil vertebrate collections (including many new species), and discovered the first fossil of Australopithecus in the Makapans Valley. Famous the world over for his uncanny ability to find fossils, he was the first person to discover a therapsid in Antarctica, thus establishing the earlier Gondwanan link between southern Africa and Antarctica. Sidney Haughton (1888–1982). First director (honorary) of the BPI, he researched and described many new species of Karoo fossils. His publications covered geology and palaeontology and included a seminal paper on the fauna and stratigraphy of the Stormberg Series and the major books The Stratigraphic History of Africa South of the Sahara and Geological History of Southern Africa. Edna Plumstead (1903–1989). A worldclass palaeontologist, she was invited to study the first plant fossils collected in Antarctica by members of the American Trans-Antarctic expeditions of 1955–1958. She demonstrated that identical plant fossils occured in Antarctica, South America, South Africa, India, and Australia, and in this way convinced a still-sceptical scientific community that the ancient continent of Gondwana had indeed once existed.
4 Sixth extinction: The term is used to describe the destruction of biodiversity at this very moment, most probably as a result of human intervention, which is causing widespread extinction of many forms of life.
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Phillip V. Tobias considers the role of cataclysmic events in the story of life on Earth. hinking of the past and its message for the future evokes the ways in which the Darwinian picture of evolution has been modified in the 145 years since the publication of the Origin of Species (1859). Early editions of this work stressed continuous change, but, in later editions, Charles Darwin proposed, instead, an episodic pattern of evolution, with periods of stability followed from time to time by fairly sudden bursts of new species. This flowering of speciation seemed to coincide with environmental changes, such as ice ages, rifting, or desiccation. Newly named ‘punctuated equilibria’, the idea of this pattern became popular in the last quarter-century.
Top: Charles Darwin (1809–1882) Above: Early Homo of Africa of 2 Myr: the reconstruction of a male (left) and female (right) skull of Homo habilis. Image: Courtesy of Francis Clark Howell.
‘Catastrophism’ is defined as “the theory that certain geological and biological phenomena were caused by sudden and violent disturbances of nature rather than by continuous and uniform processes”. The British philosopher, William Whewell, coined the term in his 1832 review of Charles Lyell’s Principles of Geology, in which he also coined the term ‘uniformitarianism’, referring to Lyell’s belief that the same physical laws had operated as causes in the past as were operating today. Other 19th-century geologists were
Some cataclysmic events Various catastrophic events have changed life on Earth. Here are a few examples. From within the Earth ■ The fragmentation of Gondwana (Late Triassic times, c. 200–180 Myr); ■ The formation of the Great Rift Valley (from Mozambique to the Red Sea, the Gulf of Aqaba, and the Jordan Valley); ■ Volcanic eruptions (e.g. Krakatoa in 1883, Langai [still active, 3 300 m], and Ngorongoro [with a crater 23 km in diameter, it is the second biggest after Mount McKinley in Alaska]). Of extraterrestrial origin ■ The asteroid or meteorite impact at Yucatán, the Chicxulub impact, about 65 Myr, led to the extinction of most of the dinosaurs (the impact crater’s estimated diameter is c. 180 km); ■ The Vredefort impact structure in the Free State is the biggest on Earth so far identified (its reconstructed diameter of 250–300 km or more was made by a projectile estimated at 10–15 km in diameter) and also the oldest (dated c. 2.1 billion years ago).
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‘catastrophists’, who believed that events of the past had been different from those of the present, both in degree and in quality. For example, vulcanicity of yesteryear was held to be much severer in degree than that observable today. One version of catastrophism (such as that of Georges Cuvier1 and especially Jean Agassiz2) held that, after each catastrophe, new forms of life appeared on Earth to replace those extinguished by the preceding catastrophe. Another variety of catastrophism, subsequently called ‘progressionism’, proposed that the succeeding newly created forms of life made up a progressive series, each phase more advanced than the last. Nineteenth-century efforts to reconcile past cataclysmic events with Judaeo-Christian beliefs presented creation and the biblical flood as telling examples of catastrophes. In this way, catastrophism became associated in people’s minds with an attempted scientific verification of biblical events and was seen as a major deterrent to the acceptance of Darwinism. It is wise, therefore, to detach the term ‘catastrophism’ from its 19th-century theological baggage and replace it by ‘neo-catastrophism’. More and more evidence has been uncovered to indicate that the history of life has been punctuated by often quite violent derailments onto new and different tracks. In trying to understand it, therefore, I use the word ‘catastrophe’ to mean “the occurrence of unexpected, large-scale, one-off events”.
Causes and consequences The Vredefort impact (see box) coincided with two major events: the oxygenation of Earth’s atmosphere, and the first appearance of eukaryotes3 (that is, cellular organisms). Was this coincidence or causality? According to William Schopf, an authority on the earliest forms of life on Earth, “Prior to about 2 000 million years ago [Myr], the amount of oxygen in the earth’s atmosphere must have been kept at a low, more or less anaerobic level.” Since all complete eukaryotes are aerobes (that is, organisms needing oxygen), the correlation in time of appreciable oxygenation of the atmosphere and the earliest record of eukaryotes leads me to suggest that both events
1 Baron Georges Cuvier (1769–1832): French zoologist and statesman, founder of the sciences of comparative anatomy and palaeontology. 2 Jean Louis Rodolphe Agassiz (1807–1873): Swiss natural historian and geologist; he settled in the USA after 1846. 3 Eukaryotes: all living organisms with cells, containing in each cell a nucleus and in which the genetic material is carried on chromosomes. All organisms except bacteria and blue-green algae are eukaryotes.
could have been an amazing, catastrophic outcome of the Vredefort impact. If Vredefort generated – directly or indirectly – the earliest eukaryotes, this gigantic impact brought about a most dramatic event, for from them came the biodiversity whose more recent components include humankind. There have been at least four other great extinctions in the history of life on Earth: their causes are unknown. If extraterrestrial events were responsible, their impressions could be under the sea. The model of Vredefort and Chicxulub should encourage the search for other examples. Perhaps impacts of projectiles from space have played a greater role in the history of life on Earth than Darwin or any other evolutionists ever dared to imagine.
Life on Earth Catastrophes and even mega-catastrophes – whatever their origin – have to be countenanced as factors in the history of life on Earth. Each is unique. Can we predict them? It appears difficult. But it could be even more difficult to predict their effects. The picture is further complicated by the appearance of the new, creeping growth on the planet’s surface called ‘urbanism’. Although towns and cities appeared on Earth a mere 15 000 years ago, as in Mesopotamia and the Nile Valley, they now provide a home, and a new ecology, to half of the members of what is commonly regarded as the dominant species on Earth, Homo sapiens. Direct hits by projectiles from space could produce very different effects today from those that resulted when all the world’s land surface was rural. Apart from catastrophes from the geosphere (within Earth) and the cosmosphere (from outer space), it is possible also to recognize catastrophism from the biosphere (such as pandemics), from the sociosphere (urban overcrowding, high stress levels), and from what I suggest be called the technosphere (environmental pollution). Some may be mega-catastrophes and some micro-catastrophes (such as the extinction or subdivision of only a single species.). From an evolutionary perspective, however, not all impacts on living things are necessarily disastrous. Even the Chicxulub impact (though apparently calamitous to the unfortunate dinosaurs) gave a marvellous opportunity to those most opportunistic of animals, the mammals! Milder environmental impacts might, in the long run, have been most effective in the evolution of humanity and its ambience. About 2.6–2.5 Myr, for example, marked climatic changes in Africa were associated with uplift of its southern and eastern parts. Much of this continent (comprising almost a quarter of the Earth’s habitable land surface) became cooler and drier. At that time, or shortly afterwards, eight major changes appear in the palaeontological and archaeological record:
■ the retreat of Africa’s great wet forest and the opening and spread of the savanna ■ animal extinctions, including that of the bestknown of the small-brained, bipedal hominids, Australopithecus africanus ■ the first appearance of certain species and even genera (early hogs, baboons) in the African fossil record ■ the earliest stone tools found in the archaeological record ■ the first appearance of Homo, of the species Homo habilis or of a recently proposed species, Homo rudolfensis ■ the development of the first truly human kind of foot in early Homo ■ the first signs of the enlargement of the hominid brain, as compared with the smaller brains of African great apes and australopithecines ■ the earliest appearance of the speech areas of the part of the brain called the cerebrum (namely, Broca’s and Wernicke’s areas), as I have discovered, in the endocranial casts of Homo habilis. Were these all coincidences? It seems more likely that they were interlinked, and causally related to the cataclysmic changes in Africa’s climate, from a warmer and wetter climate during the time of Australopithecus africanus to a cooler, drier one at the time of early Homo. For decades, the evolution of living things has been approached by Darwinism, especially natural selection, coupled with accidental change. It is essential, now, that the role of non-selective cataclysms be taken into account. While Darwinism is still fundamental, without neo-catastrophism our picture of changing life is incomplete. ■ Phillip Tobias is an emeritus professor of anatomy and human biology at the University of the Witwatersrand, which he has served for some 60 years, and is best known as a researcher on human evolution. He has been in charge of excavations at the Sterkfontein Caves in Gauteng since 1965, from which some 700 specimens of the small-brained, upright Australopithecus ape-man have been recovered. An earlier, unpublished version of this article was presented by the author to the 62nd Annual Meeting of the Meteoritical Society at the University of the Witwatersrand in July 1999.
Above left: The Vredefort impact structure, the latest World Heritage Site to be listed in South Africa. Image: Courtesy of Uwe Reimold.
Above: Early stone tools, from Sterkfontein, of the Oldowan culture (bottom row) and Acheulean. Photograph: Courtesy of Kathleen Kuman and Ron Clarke.
Consult the following for further information: J.M. Anderson (ed.), Towards Gondwana Alive (Pretoria: Gondwana Alive Society, 1999); J.W. Schopf (ed.), Major Events in the History of Life (Boston: Jones and Bartlett, 1992); P.V. Tobias et al., (eds.), Humanity from African Naissance to Coming Millennia (Johannesburg: Witwatersrand University Press, 2001); P.V. Tobias, “A century of surprises in human evolution” in C.N. Matthews et al., (eds.), When Worlds Converge (Chicago, La Salle: Open Court, 2002), pp.108–135; and P.V. Tobias, “Africa: the cradle of humanity”, in H. Baijnath and Y. Singh (eds.), Rebirth of Science in Africa (Pretoria: Umdaus Press, 2002), pp.1–12.
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Where do birds come from and how did they learn to fly? Anusuya Chinsamy-Turan examines the latest evidence.
Above: A reconstruction of Microraptor gui. Image courtesy of Zhonghe Zhou.
Below: Microraptor gui, the fourwinged dinosaur from Liaoning. Image courtesy of Zhonghe Zhou.
oday there are about 10 000 different species of birds. Astoundingly, this incredible spectacle of diversity in birds represents just one branch of all birds that ever lived on Earth. Scientists have been puzzling for years about the origin and development of this highly evolved group. Some 100 million years ago (Myr), at a time when Earth’s landscapes were dominated by dinosaurs, many types of birds existed that we no longer see today, including flightless, diving, and flying birds. Curiously, no fossils of modern birds (the so-called Neornithes) are known from those times, even though molecular data suggest that ancestors of modern birds may have existed
as long ago as in the Late Cretaceous (about 60–70 Myr). Recent research has come up with some unexpected explanations.
The origin of birds The first indication of birds in the Late Jurassic (some 150 Myr) came in 1860 with the discovery of a single feather in the Solenhofen lithographic limestones of Bavaria in Germany. The following year, in the same locality, a beautifully preserved articulated skeleton1 was found of an animal with a long bony tail, toothed jaws, and with bird-like wings and distinct feather impressions. It seemed to be an animal transitional between reptiles and birds and was named Archaeopteryx lithographica. (‘Archaeopteryx’ means ‘ancient wing’ and the word ‘lithographica’ comes from the fact that the fine-grained limestones from which the fossil was recovered were mined for the manufacture of printing blocks.) Today, more than 140 years since its discovery, Archaeopteryx is still regarded as the earliest known bird and is represented by the original feather and seven skeletons, all recovered from the same area and each preserving feather impressions. But what is the origin of birds? Many hypotheses have been proposed. Even before the first skeleton of Archaeopteryx was discovered, similarities between meat-eating dinosaurs and modern birds made English biologist Thomas Huxley (1825–1895) suggest that they were closely related. Other vertebrates
1 Articulated skeleton: a set of bones joined just as they were in the living animal. That is, the bones were found not to have been separated from each other.
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Left: Caudipteryx, the 91-cm-tall feathered dinosaur from Liaoning, has a plume of feathers (shown by the arrow) on its tail and more feathers on its forelimbs. Photograph: Courtesy of Zhonghe Zhou.
Below: Sinosauropteryx was the first of the ‘feathered’ dinosaurs, discovered in 1995 in the Liaoning locality in northeastern China. The arrow indicates the ‘feather-like’ structures along the top part of the skeleton (the body length is 70 cm). Photograph: Courtesy of Willem Hillenius.
(such as crocodilomorphs and basal archosaurs) were also considered as possible bird ancestors. In the 1970s, John Ostrom revisited Huxley’s idea and, on the basis of strong anatomical evidence, proposed that birds had descended from bipedal, meat-eating dinosaurs. This hypothesis was later tested and supported by independent cladistic analyses2, which illustrate the relationship between dinosaurs and all birds (including Archaeopteryx). They show that birds descend from meat-eating dinosaurs (the theropods3), and, technically, can themselves be regarded as dinosaurs. This is the explanation most favoured by palaeontologists today.
Recent findings of feathered dinosaurs from Liaoning in northeastern China support the idea of the dinosaurian origin of birds. Discovered in 1995, Sinosauropteryx, the first of these feathered dinosaurs, caught the interest of scientists and the public alike, because never before had scientists described a dinosaur with ‘feather-like’ structures all along the top part of its body. After careful study, these structures were considered to be ‘proto-feathers’ (that is, precursors of modern bird feathers). The Liaoning deposits are a treasure trove of feathered dinosaurs. Protoarchaeopteryx was the
second one to be described. It had short true feathers on its body and longer feathers on its tail. Soon, Caudipteryx was discovered: it was clearly a terrestrial dinosaur – its arms were much too small to be useful in flight and a number of adaptations in its skeleton showed that it had been agile on the ground. But feathers (like those of modern birds) are clearly present on its arms and it also had a plume of tail feathers. Cladistic analyses support its definition as a feathered nonavian dinosaur (that is, a feathered dinosaur that was not a bird). The most unusual specimen of a feathered dinosaur, and the one that caused a buzz in palaeontological circles, is Microraptor gui. What caused the stir was not just that this dinosaur had typical asymmetrical feathers like modern birds, but, rather, that both its fore and hind limbs were feathered. In as early as 1915, American biologist William Beebe had proposed that flight in birds evolved through a four-wing stage but, until this discovery, there were no fossils to support such a hypothesis. How did Microraptor use its four wings? And how did the hindwing function? These compelling questions have yet to be answered.
2 Cladistic analysis: a method for classifying animals and plants on the basis of shared characteristics that are assumed to indicate common ancestry. 3 Theropod: any bipedal carnivorous saurischian dinosaur of the suborder Theropoda, having strong hind legs and grasping hands. They lived in Triassic to Cretaceous times. (The word derives from the Greek ther meaning ‘beast’ and pous podos meaning ‘foot’.)
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More recent finds of dinosaurs with feathered hind limbs have brought suggestions that perhaps this four-wing characteristic is peculiar to certain derived dinosaurs and unrelated to the evolution of flight in birds. The feathered dinosaurs might suggest that feathers and featherlike structures arose before birds, and that their primary function may have been for insulation or display and not for flight.
Flight The question ‘How did flight evolve?’ has been hotly debated for decades. The two main proposals are the ‘arboreal or trees downwards hypothesis’ and the ‘cursorial or ground upwards hypothesis’. The ‘arboreal hypothesis’ proposes that the ancestor of birds lived in trees and evolved adaptations for gliding from branch to branch, eventually developing the capacity for true flight. The ‘cursorial hypothesis’ proposes that flight started in a cursorial (running) dinosaur that increasingly used its forelimbs for balance and to catch its prey. ‘Fringe-like’ adaptations helped to increase its leaps and jumps and, ultimately, it developed sufficient ‘lift’ for flight. Before the discovery of feathered dinosaurs, the idea of the dinosaurian origin of birds originally supported the ‘cursorial hypothesis’ for the origin of flight. It now seems likely, however, that flight could have evolved from the trees downwards, and that the dinosaurian hypothesis for the origin of birds is not in fact inconsistent with the ‘arboreal or trees downward’ hypothesis for the origin of flight.
Biology of early birds Although we have a reasonable idea of the forms (or morphology), diversity, and phylogeny of early (or ‘basal’) birds, we understand little about their biology. But within the microscopic structure of fossil bone lie important clues. Since 1994, my colleagues and I have been studying the bone microstructure of various early birds to learn more. We found that they had a characteristic type of bone microstructure showing periodic interruptions in the rate at which bone formed. This type of bone tissue is similar to the condition that occurs in several non-avian theropod dinosaurs, but different from that of modern birds, which grow rapidly to adult size without any such interruptions. Our investigation suggests that early birds grew more slowly than modern ones. It also implies that the rapid, sustained growth rates of modern birds did not evolve from their dinosaurian ancestors but developed later on, in their own evolutionary trajectory. Our argument for slower growth rates in basal birds is further supported by the fact that several differently sized individuals of Confusciornis have been discovered, the smallest being about 50–60% of the size of the largest, and by the fact that the seven skeletons of Archaeopteryx are also quite
Lineages unrelated to birds
TETANURAE THEROPODA SAURISCHIA
different in size from one another (the smallest is about half the size of the largest). More specifically, we have proposed that the growth of basal (early) birds seems to have been in two phases: a rapid initial phase and then a slowed second phase. In the enantiornithine birds (that is, widely distributed flying birds), it appears that the second phase of growth was protracted, and no indication of the earlier rapid phase of growth is preserved in the bone tissue. Analysis of Gobipteryx, the embryonic enantiornithine fossil bird from the Gobi desert in Mongolia, suggests, however, that bone formed rapidly in the early stages of development. Thus, this earlier, rapidly formed bone was obviously resorbed (that is, absorbed back into the body) during later development. Our explanation is that, in the enantiornithines, postnatal growth was slower because energy was directed instead to their superprecocial (early ability to fly) lifestyle, as reflected in the well ossified flight apparatus in the embryos.
Today’s diversity At the end of the Cretaceous, when the dinosaurs famously died out, many other animals also became extinct, including the various representatives of the early radiation (that is, diversity) of birds. We know this, because, after the Cretaceous-Tertiary extinction event, none of the fossil birds abundantly found in the earlier, Mesozoic period are known. There is a fragmentary fossil record of Tertiary birds, but they appear to be unrelated to the diverse array of Mesozoic forms. Modest bird diversity came about after the end of the Cretaceous (in the Paleocene and Eocene), but only much later, around 20 Myr (in the Miocene) does the fossil record show a major radiation of birds, many of the descendants of which we see around us today. ■ Professor Chinsamy-Turan is a palaeobotanist in the Zoology Department, University of Cape Town, and winner of the 2005 Shoprite Checkers/SABC 2 Woman of the Year award.
Above: This cladogram, or branching tree, shows the phylogenetic relationship (or, the evolutionary sequence of development) of all birds to dinosaurs, and illustrates the reason that it is accurate to refer to birds as ‘maniraptoran, tetanuran, theropod dinosaurs’. It shows that birds, or Aves (which all have a reversed first toe and fewer than 26 tail vertebrates), are a subset of the maniraptoran dinosaurs (which have a half-moon-shaped wrist bone). These, in turn, are a subset of the Tenanurae (with their distinctly three-fingered hand) – themselves a subset of the Theropoda (with their three functional toes and hollow bones), which are a subset of the saurischian dinosaurs (with their threepronged pelvic girdle). For more information consult L.M. Chiappe and L.M. Witmer, Mesozoic Birds – Above the Heads of Dinosaurs (University of California Press, 2002); L.M. Chiappe and G.J. Dyke, “The Mesozoic radiation of birds”, Annual Review of Ecology and Systematics, vol. 33 (2002), pp.91–124; K. Padian and L.M. Chiappe, “The origin of birds and their flight,” Scientific American, (February 1998), pp.28–37; and R.O. Prum, “Dinosaurs take to the air”, Nature, vol. 421 (2003), pp.323–324. Read the chapter on the biology of basal birds in A. Chinsamy, The Microstructure of Dinosaur Bones – Deciphering Biology through Fine-Scale Techniques (Johns Hopkins University Press, 2005); read about the clues that pertain to the biology of animals within the microscopic structure of fossil bone in A. Chinsamy and P. Dodson, “Inside a dinosaur bone”, American Scientist, vol. 83 (1995), pp.174–180; read about the two-phase growth in basal birds in A. Chinsamy and A. Elzanowski, “Evolution of growth patterns in birds”, Nature, vol. 412 (2001), pp.402–403.
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Right: The active site of a nitrile hydratase molecule showing the binding of cobalt (grey) to three sulphur (yellow) atoms from cysteine amino acids. Nitrogen atoms are shown in blue and oxygen in red. Picture: Serah Wangari Kimani using PyMol
There’s huge commercial potential within the molecules of life, but scientists first have to understand the structures of proteins at the deepest atomic level. Unlocking these secrets, says Trevor Sewell, gives South African biotechnology a key to the treasure chest of global economic success.
irst-generation’ biotechnology has flourished proudly in South Africa. Using organisms in a targeted way, it has enabled the country to set up and grow one of the world’s largest brewing companies, a globally renowned wine industry, and important programmes in plant and animal breeding. ‘Second-generation’ biotechnology went a step further by breeding useful characteristics into microorganisms. Now the pressure is on to realize the benefits of ‘thirdgeneration’ biotechnology, which engineers molecules and cells to create products such as industrial enzymes, therapeutic agents, pesticides, and vaccines. Exploiting these third-generation possibilities depends on understanding
Generously funded in its initial stages by the Carnegie Corporation of New York, the Programme in Structural Biology arose through the collaboration of academics at the Universities of Cape Town, Western Cape, Stellenbosch, and the Witwatersrand. Currently, its 10 master’s, one doctoral, and one postdoctoral student are working on projects related both to drug design and industrial enzymes.
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how proteins are structured. The new Programme in Structural Biology, initiated jointly by the University of Cape Town (UCT) and the University of the Western Cape (UWC), plans to make certain that South Africa has the expertise to be competitive in this rich and rapidly growing field.
Why examine protein structures? In the last ten years, the ready availability of genetic information has revolutionised biological science. Quickly and affordably, geneticists can obtain the sequences of entire genomes. These sequences provide a catalogue of the proteins that make up individual organisms, as well as details of the proteins’ composition and how they relate to one another. Scientists in the field of bioinformatics analyse this wealth of information and make it accessible using powerful computers and communication networks. Now scientists are seeing that all this information gives only part of the answer. Although gene sequences make sense to the cell, we humans
barely understand them. For more insight into how cells actually work, we have to study the proteins within them – no easy task. The information contained in genes is used to create proteins. Proteins do most of the ‘work’ of the biological cell: they catalyse reactions, transport molecules around, detect and respond to the environment in which the cell is situated, and control the way genetic material is expressed in the formation of cells (see box). They make cells into exquisite, wellorganized, and efficient machines. Enzymes are proteins that act as chemical ‘reactors’, converting one substance into another. This makes them interesting to people for two reasons. First, we can use them to make new chemicals of our own – this gives rise to protein engineering and industrial enzymology. Second, we can use our knowledge of them to design molecules that interfere with the lifegiving processes of harmful pathogens and insect pests – this leads to the creation of drugs and pesticides.
The making (‘expression’) of a protein gene (DNA) Made of DNA, the gene contains information (coded as a sequence of chemical elements called ‘bases’) needed for a particular protein to be made or ‘expressed’. That information is then ‘transcribed’ (or, converted) into a form that can be carried by messenger RNA to the ribosome.
A multimolecular complex made of protein and RNA, the ribosome acts as a ‘machine’ for making proteins, and: ■ positions an adapter molecule called transfer RNA in such a way that it docks with the messenger RNA on one side and locates the amino acid appropriately on the other side ■ builds the protein up, amino acid by amino acid, by forming peptide bonds.
manufacture a chemical compound that inhibits it in some way – by slowing down the activity of the molecule or even stopping it altogether. Peter Colman and his team in Australia used this approach when they designed the first ‘rational’ anti-influenza drug, Relenza, about a decade ago. Influenza viruses produce an enzyme, neuraminidase, that weakens the host cells of an infected person or animal so that the virus can gain entry. Once they had worked out the protein structure of neuraminidase, Colman and his colleagues were able to create Relenza, which specifically targets the active site of neuraminidase and in this way renders the virus harmless. Designing industrial enzymes means solving the inverse problem of how to encourage rather than inhibit enzyme
protein A protein is a biological macromolecule made up of a specific sequence of amino acids linked by peptide bonds1. Proteins vary considerably in length and amino acid composition. Most of them fold spontaneously into a 3-D form that is characteristic of the amino acid sequence. Though many thousands of protein folds are known, it is not yet possible to predict the shape of a protein unless the structure of a protein with a very similar sequence is already known.
Many pathogens and pests in Africa are unique. In addition, the biodiversity of our continent creates great possibilities for new discoveries. It’s the responsibility of Africans to overcome the problems posed by our pathogens and pests, and also to exploit the opportunities that our biodiversity offers. So far, we have been slow to take up these challenges. To help South Africa improve in these fields, the UCT and UWC groups have focused on the study of protein structures.
What’s involved? Exploring the inner space of protein structures – the foundation of thirdgeneration biotechnology – is as complex and difficult as it is fascinating. Nature uses up to 20 amino acids to make proteins. Each has a different side chain1 with its own special chemical properties. The amino acids that together make up a protein are linked in long chains, and every different type of protein has its own specific sequence of amino acids. These long chains generally fold in
such a way that a specific sequence produces a corresponding 3-D (threedimensional) formation. This folded formation is what gives the proteins their interesting properties. Studying protein folds and their consequences is one of the jobs of structural biologists. Understanding the 3-D structure provides unique insights into how proteins work, how they interact with one another and with other biomolecules, and how these interactions produce higher-order complexes and, ultimately, cells. Knowledge of protein structure satisfies our curiosity. But it’s also shaping our technology in two important and different ways. First, it helps us to design molecules that can be used as drugs and pesticides, and, second, it helps us to tailor Nature’s enzymes to produce valuable industrial chemicals. Once we know the shape of the active site2 of an important molecule of a pathogen that causes disease, for instance, we can, in principle,
1 Side chain: Each amino acid consists of a carbon atom to which are bonded an amino group (NH2 ) and a carboxy group (COOH) (as well as a central hydrocarbon group and a variable group). In making a protein, the carboxy group of one amino acid joins the amino group of the next. That joining is called a peptide bond. The term ‘polypeptide’ is used where there are many such bonds: all proteins are polypeptides. Joining onto the carbon is another group of atoms called a side chain. There are 20 different side chains in Nature, each with different properties that form part of the particular amino acid. When the amino acid takes its place in a protein, it is the side chains that do the protein’s work. 2 Active site: the special area on a protein where the chemical reaction of the enzyme takes place.
Computer generated ‘cartoon’ showing the 3-D structure of nitrile hydratase and the overall fold of the molecule. The spirals represent alpha helical regions stabilized by hydrogen bonds. Broad arrows represent strands that are linked by hydrogen bonds in a pattern called beta sheets. These fundamental building blocks of protein structure were discovered over 50 years ago by Nobel laureate Linus Pauling. Picture: Serah Wangari Kimani using PyMol
Part of the map of the electron density of nitrile hydratase (see next page). The red ‘chickenwire’ contours are chosen at a single electron density level so as to determine the location of the backbone polypeptide and amino acid side chains. Interpreting the map involves locating the atoms within these contours. Sophisticated computer programs allow experienced users to position the atoms (here shown linked by yellow, green, red, and blue lines) within the density. This map is a very good one, since the volume enclosed by the contours is continuous, allowing for unambiguous positioning of the atoms.
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activity. Many important chemicals – used in various processes, such as drug, plastic, or paint manufacture, for instance – are difficult to make using traditional synthetic chemistry. But in Nature there exist chemicals similar in structure and function that are produced by a series of reactions catalysed by enzymes. The enzymes have been honed by the process of natural selection to operate with exquisite selectivity on natural substrates (that is, on the molecules upon which enzymes act) within the cell environment. The challenge is to understand how these enzymes work and then modify them to operate on industrially important substrates in the more difficult industrial environment. Knowing the enzyme structure is the first important step in this process.
Top left: Crystals of nitrile hydratase obtained at room temperature in a solution containing polyethylene glycol (PEG), magnesium chloride, and MES (pH 6.5). Typical dimensions of crystals selected for diffraction studies were approximately 0.2 mm 0.1 mm 0.1 mm. Lower left: X-ray diffraction pattern from nitrile hydratase crystals. Many hundreds of such patterns are combined and the intensity of the spots measured. Such spot patterns cannot be interpreted directly but must be converted into a map of the electron density of the molecule that was crystallized. Pictures: Trevor Sewell Top right: Protein crystallographer Muhammed Sayed and master’s student James Onyemata prepare to load crystals for data collection. Lower right: The Protein Crystallography Unit at UWC contains state-of-the art diffraction equipment made up of a high-powered X-ray generator and an image-plate detector that records the diffraction data. Another device, the X-Stream, cools the crystal to cryogenic temperatures, preventing radiation damage to the crystals (which would greatly reduce the quality of the data). Pictures: Cameron Ewart-Smith
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Journey into the interior The Mitsubishi Rayon Company in Japan manufactures large quantities of acrylamide, a chemical used in the production of an important polymer, from the readily available ‘intermediate’ organic chemical, acrylonitrile. As many as 100 000 tons of acrylamide a year are needed globally to make polyacrylamide, which is used mainly for treating municipal and industrial wastewater. A UWC team in the Department of Biotechnology, led by Donald Cowan, has been studying a nitrile hydratase, an enzyme that converts nitriles (such as acrylonitrile) to their corresponding amides (such as acrylamide). These studies aim to produce enzymes that will make other amides from the corresponding nitriles and –
equally important – enzymes that can withstand the rigours of an artificial industrial environment, which is far more hostile than the protein-friendly conditions in the cell. (A living cell has its own salvage processes, for instance, whereas, in an industrial environment, an enzyme must operate in isolation, without the helpful cellular infrastructure that Nature provides.) As with any hunt for the treasure of economically useful knowledge, the research process is complex and takes place in stages, each depending on the successful completion of the last, and each posing its own problems.
The first challenge is to discover a naturally occurring organism that contains a potentially useful enzyme. To find a suitable one, Cowan looked especially at bacteria that could survive in extreme conditions, such as those in polar ice or volcanic pools. In the end, he selected Bacillus sp. RAPc8, a promising bacterium containing an enzyme with nitrile hydratase activity and found in a geothermal pool in New Zealand. The next problem is that interesting proteins are made in small amounts in their organisms of origin and, because their behaviour can be temperamental, are often difficult to work with. For industrial use, we need a material that’s pure and a supply that’s abundant. So, borrowing technology from molecular biologists, structural biologists clone the gene for the protein of interest into an ‘expression plasmid’3. Then, using the plasmid, they transform cells of a more ‘laboratory-friendly’ bacterium – a specially engineered variety of the bug found in our gut, Eschericia coli – to make them capable of producing the protein. These transformed cells can then become ‘factories’ to make sufficient quantities of the protein of interest; these, in turn, can be further purified. Postdoctoral researcher, Rory Cameron, accomplished this step in our journey. Duly encouraged, the team’s immediate goal now was to produce a visual image of the atomic structure of nitrile hydratase – something that, at the beginning of 2004, had never yet been accomplished anywhere in Africa. It seemed a daunting task4. We decided to use a technique called X-ray crystallography, in which an intense beam of X-rays is focused on a crystal of nitrile hydratase, resulting in a pattern of diffracted beams that can be recorded on a special electronic device called an image plate. First, though, we had to grow crystals of the enzyme that would be suitable for X-ray crystallography – that is, crystals of the right shape and size to diffract to a high enough resolution for the atoms to be visible on a computer screen. This was the job of Tsepo Tsekoa. It took him thousands of experiments to obtain crystals suitable for the next step – obtaining X-ray diffraction patterns. The X-ray beam used for protein crystallography is created by focusing
3 Expression plasmid: a circular piece of DNA containing the gene for the protein of interest as well as the minimum number of additional components necessary for E. coli to make the protein. Normally these plasmids also make (or ‘express’) a protein that confers antibiotic resistance so that only bacteria containing (or ‘transformed’ by) the plasmid survive in the presence of the antibiotic. 4 Mastering the various technologies to determine protein structures at the atomic level was a late-20th-century triumph, resulting in the award of at least 10 Nobel Prizes and laying the foundation for 21st-century biological science.
Q Measuring up Listen carefully electrons onto a rotating, water-cooled copper block and then focusing the resulting X-rays with a glass capillary. The crystals (cooled to 160°C to preserve them from the damaging effects of the high-energy radiation) are then placed in the beam and, as the crystal is slowly rotated, a series of several hundred diffraction spot patterns is recorded. The data, which comprise the intensities and positions of the spots, can be read directly off the image plate into the computer. The next step is to convert the many thousands of intensity readings into a 3-D image of the crystal’s atomic structure that scientists can understand and interpret. This is no trivial exercise, because, although the readings give us amplitude (that is, the intensity or brightness of the spots), the equipment has not yet been invented that would give us all the information we need concerning the phases of the diffracted beams. Some cunning techniques invented in the last century make it possible to overcome these limitations. In our case, structural biologist Muhammed Sayed solved the problem by searching the world’s databases for a molecule that was similar to our nitrile hydratase and whose structure was already known, which he could use as a template. He was lucky. He found what he was looking for, which meant he could apply a technique called ‘molecular replacement’ to obtain a first estimate of the missing phases. With the phases determined, the next stage was to create a computergenerated 3-D electron density map5, represented on the computer screen by a 3-D mesh of contour lines – which looks like chicken wire – linking points of the same electron density. Because the electron density is centred on the atoms in the molecule, you can locate the positions of each of these atoms. Seeing our map was an extraordinary and wonderful experience for everyone in the programme. We knew at once that we had generated a picture whose resolution was high enough for us to be able to interpret. This was a triumphant, major landmark of the project. The huge task that followed, of locating the many thousands of atoms in the protein, fell to post-doctoral researcher Ozlem Tastan-Bishop. What’s visible on the map depends on the resolution. Our map, with its resolution of 0.25 nanometres, meant that we could clearly distinguish
individual side chains. This fact, combined with knowledge of the geometry of proteins and the laws of chemistry, made it possible for us to interpret the map using a combination of computer programs, insight, and some very hard work. An atomic model was built to interpret the map. The model needed to be verified against the original data and also against our knowledge of protein structure based on a database of many thousands of known protein structures. It passed the tests: now we could be confident that our insights from exploring the structure of nitrile hydratase were correct – and potentially useful.
What next? The purpose of solving the structure was to develop an industrial enzyme, so we had to answer specific questions. What is the structure in the vicinity of the active site? How does this structure affect the specificity? What factors influence the stability of the enzyme? How susceptible is the enzyme to environmental conditions like pH? We found, for instance, that our nitrile hydratase has a very unusual active site6. But to find out exactly how it works we’ll have to understand it better – which, in turn, will help us to improve it and to discover ways to make it even more useful. So although the enzyme is already being used industrially, researchers in Japan and South Africa continue to investigate the details of the mechanism by which this structure converts nitriles to amides. In this way, the Western Cape’s successful determination of protein structures is paving the way for new and exciting science, with potentially handsome rewards. ■ Trevor Sewell is extraordinary professor of protein crystallography in UWC’s Department of Biotechnology and director of the Electron Microscope Unit at UCT. He is the project leader of the joint Programme in Structural Biology and he co-ordinated the structural research on the nitrile hydratase. For more, read Gale Rhodes, Crystallography Made Crystal Clear (Academic Press, 2nd ed., 2000) and visit Professor Rhodes’s superb web site: www. usm.maine.edu/~rhodes. Other books worth consulting are Carl Branden and John Tooze, Introduction to Protein Structure (Garland Science Publishing, 2nd ed., 1999) and David P. Clark and Lonnie D. Russell, Molecular Biology Made Simple and Fun (Cache River Press, 1997). For more on transfer RNA visit www.rcsb.org/ pdb/mole cules/pdb15_1.html. For more on the ribosome visit www.rcsb.org/pdb/ molecules/pdb10_1.html
5 The 3-D map is generated by using a computer to apply a mathematical process called Fourier transformation. 6 In the case of our nitrile hydratase, we found that part of the active site comprises a cobalt ion, held in position by a crown-like arrangement of the sulphurs of three cysteine side chains.
Because noise covers a wide range of intensity (loudness), its measurement is based on a logarithmic scale. Decibels (dB) express a relationship between two levels of sound. Librarians get agitated if noise exceeds 30 dB SPL and rockets launch at 180 dB SPL (SPL stands for sound pressure level). The unit is named after the inventor of the telephone, Alexander Graham Bell. “Decibels have caused untold confusion among audio people,” says Florida State University’s web site, “and most of this is due to the failure to realize that decibels are not quantities of anything and can represent only power ratios.”
Scanning storms Sciencedaily.com reports that a new radar instrument, Rapid-Scan Doppler on Wheels (DOW), can assess the threat of tornados much faster than was previously possible. It scans a storm every 5 to 10 seconds, using multiple beams. This is important because tornados change so quickly.
How do you measure ... ... quality of life? Sciencedaily.com says the ‘seventh generation standard’ holds that a decision should be judged by its effect on people six generations later. That’s difficult to predict in modern times. But the United Nations’ Human Development Index (HDI) provides a way of comparing the quality of people’s lives in terms of life expectancy at birth, the adult literacy rate, the education enrolment ratio, and gross domestic product per capita. In 2004, the country with the highest HDI ranking was Norway.
... change in acceleration? The unit of change in acceleration is a jerk, equal to 0.3048 m/s3.
... the insulating properties of cloth (using the metric system)? A tog is 10 times the temperature difference (in °C) between the two sides of a piece of cloth, if the flow of heat through the cloth is 1 watt per square metre. A tog is equal to exactly 0.1 m2 K/W.
... the height of your audio, video, or computer equipment? The unit of distance is a U, which is equal to 44.45 mm. For example, a 3U component is 133.35 mm high, and a 20U rack or shelf can house a stack of components 889 mm high.
UK National Measurement Laboratory definitions of basic units Second – the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. Metre – the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second. Kilogram – equal to the mass of the international prototype of the kilogram (made of platinum-iridium and kept at the International Bureau of Weights and Measures in France). Ampere – that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2 107 newton per metre of length. Kelvin – unit of thermodynamic temperature; the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. Mole – the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kg of carbon-12. Candela – the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
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The theme of this year’s World Space Week is ‘Discovery and Imagination’. Recent outer space explorations have involved space travel, observation, and amazing supercomputer simulations.
Celebrating space 1999: The United Nations designated 4–10 October as World Space Week, marking two special events: the launch of the first man-made Earth satellite, Sputnik 1 (4 October 1957), and the signing of the Treaty on Principles Governing the Activities of States in the Exploration and Peaceful Uses of Outer Space, including the Moon and Other Celestial Bodies (10 October 1967). 2005: South Africa’s position in the southern hemisphere has involved it in many international observations. In November we celebrate the official opening of the Southern African Large Telescope (SALT) at Sutherland, in the Northern Cape (see the special inauguration feature in the next issue of QUEST).
Deep Impact scores a hit The washing-machine-sized Deep Impact space probe smashed into comet Tempel 1 on 4 July 2005 at a speed of 36 800 km per hour. The data it sent back about the debris and the crater formed by the impact are giving scientists remarkable new information about the interior of comets. It is believed that these bodies, made of dust and ice and just a few kilometres across, are relics of the primordial material that made up the Solar System, 4.5 billion years ago. The mission went according to plan. In January NASA launched the spacecraft, made up of a fly-by probe about 3.2 m long, 1.7 m wide, and
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2.3 m high, and a 370-kg impactor. The impactor was released into the comet’s path and switched to autonomous flight for the last two hours before impact. The dusty debris thrown from the impact crater formed a far bigger cloud than expected, which suggests that the comet’s surface dust was extremely fine – something like talcum powder. Cameras on the impactor and the fly-by spacecraft recorded the collision, as did observatories on Earth and four orbiting telescopes. In the months ahead, astronomers will have far greater understanding than ever before about the comet’s composition and history. For initial reports read Richard A. Kerr, “Deep Impact makes a lasting impression on Comet Tempel 1”, Science, vol. 309 (2005), pp.226–227; Mark Peplow, “Deep Impact: sifting through the debris”, Nature, vol. 436 (2005), pp.158–159; and David L. Chandler, “Deep Impact strikes home”, New Scientist (9 July 2005), p.13.
Mars Orbiter takes off On 12 August 2005, NASA’s US$500million Mars Reconnaissance Orbiter (MRO) began a 7-month journey to the red planet. Its mission is to determine whether or not longstanding bodies of water ever existed on Mars. The robotic Mars Exploration
With the Atlantic Ocean as a backdrop, NASA’s Mars Reconnaissance Orbiter (MRO) takes off from Cape Canaveral Air Force Station on 12 August 2005. Photograph: Courtesy of NASA
Rovers – still moving around the surface of the planet 19 months after landing – have indicated that water once flowed there, but scientists don’t know if there was enough of it to nurture life. The MRO is two storeys high, twice as wide, and weighs over two tonnes. On reaching Mars, it will spend eight months refining its orbit before starting observations in November 2006. It will orbit at an average altitude of about 320 km, which is 25% closer than the two NASA spacecraft circling the planet at present, so the high-resolution images it transmits will cover an area 10 times larger than previous surveys. Its
communication antenna – the largest ever sent to Mars – will beam back more data than all previous missions put together. The satellite will scan the geology of Mars and look for landing sites for future missions. This is the start of a series of planned visits to the planet that could culminate in a manned launch around 2030. For more, read Tony Reichhardt, “Mars orbiter ready to scout for future landing sites as NASA looks ahead”, Nature, vol. 436 (2005), p.613; and “Monster for Mars”, New Scientist, (30 July 2005), p.5. For details of these and other NASA explorations visit www.nasa.gov and browse.
Exploring galaxies Observation and computation work hand in hand to examine galaxies and what they reveal about themselves and the Universe. The Advanced Camera for Surveys on board NASA’s Hubble Space Telescope, for instance, has spied galaxies near and far. In January 2005, it took the sharpest-ever image of the Whirlpool Galaxy, showing the grand design (that is, with two curving arms) of a spiral galaxy – the arms are factories for making stars, while older stars reside in its yellowish central core. Located 31 million light years away in the constellation Canes Venatici (the
Hunting Dogs), Whirlpool’s closeness to Earth allows astronomers to study its classic structure and its starforming processes. Deep in the Universe, Hubble has found a menagerie of galaxies, big and small, and mostly very far away. Only when their light was captured by Hubble did hundreds of these faint galaxies become known to astronomers. The smaller ones are so distant that their light took billions of years to reach us, so we’re seeing them when they were much younger than larger galaxies that are closer to us. Now supercomputer simulations have blended the giant snapshot of cosmic history provided by modern galaxy surveys into a picture revealing the underlying physical processes of the way galaxies are formed and evolve. An international team of computational astrophysicists, the Virgo Consortium, has successfully modelled the growth of as many as 20 million galaxies to try to understand the evolution of the Universe. ■
Main picture: The Whirlpool Galaxy, showing bright pink star-forming regions and the brilliant blue star clusters that emerge along the outer edge. Courtesy of NASA, ESA, S. Beckwith (STScI), and The Hubble Heritage Team (STScI/AURA)
Top left: This image from NASA’s Hubble Space Telescope shows a corridor of galaxies stretching billions of light years distant in space, corresponding to looking billions of years back in time. It covers a small patch of sky (smaller than the area of a full Moon) but reveals a variety of galaxy types. Courtesy of NASA, ESA, and The Hubble Heritage Team (STScI/AURA); with acknowledgements to J. Blakeslee (JHU) and R. Thompson (University of Arizona)
Top right: An artist’s impression of the MRO in orbit over the martian poles. Image: Courtesy of NASA/JPL
Above left: The moment of Deep Impact’s collision with comet Tempel 1 and the forming of the crater. Image: Courtesy of NASA/JPL/UMD; artwork by Pat Rawlings
Above right: Artist’s rendition of the Deep Impact fly-by spacecraft releasing the impactor, 24 hours before collision. Left to right: comet Tempel 1, the impactor, and the fly-by spacecraft (which includes a solar panel [right]; a high-gain antenna [top], a debris shield [left, background], and scientific instruments for high- and medium-resolution imaging, infrared spectroscopy, and optical navigation [yellow box and cylinder, lower left]). Image: Courtesy of NASA/JPL
For details read “Digitalizing the Universe”, Nature, vol. 435 (2005), pp.572–573 and V. Springel et al., “Simulations of the formation, evolution and clustering of galaxies and quasars”, in the same issue, pp.629–636.
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Q The S&T tourist
The Johannesburg Zoo The Johannesburg Zoo celebrates its centenary in 2004. Like other zoos around the country, it’s a great place to visit at any time of year.
he Johannesburg Zoo has come a long way in a hundred years. In 1904 it was home to a lion, a baboon, a leopard, two monkeys, two sable antelope, a golden eagle, a genet, two porcupines, and a giraffe. Today it has 2 000 animals and 380 species. Hermann Eckstein’s involvement in developing the new mining town of Johannesburg included having three million trees planted in the area we call Saxonwold. After he had died, his firm, H. Eckstein & Co., gave the people of Johannesburg 200 acres of land in 1904 as a place of recreation in perpetuity. At the suggestion of Sir Percy FitzPatrick, a partner in the firm, the land now comprising Zoo Lake and the Johannesburg Zoo was called the Hermann Eckstein Park. By 1910, the Zoo was one of Johannesburg’s favourite places for a day’s outing, with children’s playgrounds, gardens, a bandstand, and a tramway that stopped at the zoo gates. A stone elephant and rhino house was built in 1913, followed by a hippo house and pool a few years later. In 1937 the Zoo bought an Asian elephant and a Bactrian camel, which were trained for rides. Donkey and pony cart rides started in the late 1920s and, with llama and zebra rides, were a great attraction until the 1960s. Some of the old stone buildings of the 1920s and 1930s are still used, though not as animal houses. The elephant house was converted into an auditorium in the 1980s and is hired out for conferences and functions. Johannesburg Zoo was one of the earliest zoos to adopt the principle of ‘cages without bars’ in as early as 1921. Instead it used a moated camp system with vegetation and artificial rocks to give a natural look. The lion enclosure (sponsored by AngloGold and opened in 2000) followed this tradition, and was the first of its kind in the world, using islands and moats to separate the groups of animals. The new ape house, opened on 24 September 2004 by Mayor Amos Masondo, offers another open habitat. The Zoo houses all the great apes –
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gorilla, chimpanzee, and orang-utan. Their new home has increased from 75 m2 to 2 000 m2 and has trees, natural vegetation, streams, and a stimulating environment that includes an artificial termite heap in which the animals use sticks to ‘fish’ for food like honey or jam. The enlarged ape house also helps in the rescue and rehabilitation of chimpanzees that have been abused – during laboratory experiments, in circuses, or in the pet trade, for example. Once such chimps are brought back to health, they go to one of several chimp sanctuaries in Africa. There they are introduced to other chimps and socialized into family groups. Most rehabilitated chimps are kept in sanctuaries rather than reintroduced into the wild, as much of their home territory is in a state of war. Besides recreation and conservation, the Zoo concerns itself with research and education. It also provides information about animal diseases and gives medical care to animals in its fully equipped hospital. The Biofacts Museum has a large collection of preserved animal material such as skulls, skins, eggs, and feathers. These can be hired or in some cases, such as feathers, bought. ■
Dominant male chimpanzee enjoying his new natural environment.
Female chimpanzee checks out the new ape house.
Tours & programmes The Zoo brings environmental subjects to life for everyone – families, schoolgoers, clubs and interest groups, and senior citizens. Phone (011) 646 2000 for information and bookings. ■ Zoo School – wildlife and conservation lessons for grades 1–12: weekdays all year (tel. Deona, ext. 263 for the topics) ■ Behind-the-scenes tours – go where zookeepers go and see close up how the animals are fed and cared for medically (tel. Deona, ext. 263) ■ Zoo-to-you – the Zoo will visit you and your school with slithery animals and cute fluffy animals (tel. Lawrence Tshokgohle, ext. 259) ■ Honey Badger Club – 7–13-year-olds meet monthly for demonstrations and interaction with animals (tel. Martin-John van Rooyen, ext. 262) ■ Sunset tours – see diurnal and nocturnal beasts ‘change shifts’ (bring a picnic) ■ Zoo ferry tours – a guided tour on a private tractor-drawn ferry ■ Moonlight tours – enjoy night creatures by torchlight, then refreshments around a blazing bonfire ■ Senior citizens’ tours – meet the animals close up from your tractor-drawn ferry ■ Be MAD – 14–19-year-olds enjoy a day each month making the lives of animals more fun and stimulating (tel. Louise Gordon, ext. 254) ■ Sleep-overs – camp overnight among the animals ■ Holiday programmes – use school holidays to learn about the world of wildlife (tel. Martin-John, ext. 262) ■ Edutainment – visit the new education centre filled with skulls, bones, skins, and stuffed animals; consult the reference library; try the virtual touch-screen. For general information phone (011) 646 2000, (011) 486 0244, or visit www.jhbzoo.org.za
Q Your Q UEST ions answered
Beating the heat on the shuttle Question What caused the problem with the tiles on NASA’s space shuttle Discovery and what’s the solution ? Answer Each tile is baked to withstand the intense heat of re-entry into Earth’s atmosphere. But in the present 20-year-old shuttle design, they are packed together a bit like tiles on the wall of a bathroom. This leaves room for problems. First, the filler material can get damaged, leaving regions between the tiles through which heat can penetrate (as happened with Discovery). Second, the material from which the tiles themselves are made may not be able to withstand the heat and related stresses generated during re-entry. I believe that the next generation of space vehicles will have to use new materials – for example, new carbides or oxides – that are lightweight and that can form a continuous coating rather than tiles. Some of the new materials that we are studying at the DST/NRF Centre of Excellence in Strong Materials can withstand temperature of nearly 3 000°C – well above that needed for the shuttle. Ted Lowther, Professor of Computational Physics, School of Physics, University of the Witwatersrand and DST/NRF Centre of Excellence in Strong Materials
Answer The tiles on the shuttle are made of ceramic fibrous material and have quite good refractory and excellent thermal insulating properties. However, as Ted says, the problem lies with the tiled structure. The gaps that necessitated the repair in space during the Discovery’s latest shuttle trip are gaps between tiles, which were apparently filled with another refractory material during construction. It was this filler material that was coming off. Eliminating such gaps would require laying down a continuous layer. But how do you lay down such a layer and at
The US space shuttle Discovery was launched in July 2005 and returned safely from its visit to the international space station in August. But during take-off, a largish chunk of insulating foam came off the fuel tank. (This aroused concern because a similar problem had damaged the shuttle Columbia in 2003, causing it to burn up on re-entry into Earth’s atmosphere.) Furthermore, bits of tile filler started to stick out from Discovery’s undersurface, disturbing the flow of air and potentially increasing the heat of re-entry. So the astronauts took an unprecedented space walk to fix the problem (illustrated here). Image credit: NASA
the same time bake it to a temperature high enough to sinter the fibres partially to each other to provide the necessary strength? Maybe a graded material is needed, starting from the shuttle skin and gradually moving onto the refractory thermal insulating material. Not easy. There’s another problem with a continuous layer: a tear through it might remove a bigger chunk than if one were using a tiled structure. The fibres used are reportedly silicon-based, probably made out of silicon dioxide, perhaps with added opacifiers. This material seems to be okay as far as withstanding the temperature of re-entry is concerned, because the NASA engineers talk of patching up with silicate-based glass. Moving to more refractory ceramic fibres could be advantageous. It’s not clear to me why they haven’t done so yet. Jack Sigalas, Element Six Professor of Ceramic Science, School of Process and Materials Engineering, University of the Witwatersrand and DST/NRF Centre of Excellence in Strong Materials.
Spiders in camouflage Question After reading “Wonderful spiders” (QUEST, vol. 1, no. 4), I noticed an amazing spider inside a white rose in my garden. The spider had just a tinge of pink in places, exactly like the rose. But stranger still, as far as I can tell, the rose gets tinges of pink only when it’s been particularly dry. How does the spider find the rose? Answer The spider is a flower crab spider, which belongs to the Thomisus, a genus of the family Thomisidae known to be able to change colour. Colour changes are an advantage in that they can camouflage spiders from both prey and predators. In South Africa, three species of spider are known to be able to change colour: Thomisus blandus, T. daradioides, and T. stenningi. Thomisids ‘balloon’ and are carried by their silk threads through the air, which explains how they reached the rose. The process of changing colour can be explained as follows. The white colour is due to a layer of cells located under the hypodermis, which are filled with guanin crystals that reflect the light through the translucent hypoderm. Between the hypodermal and guanin cell layers there is a space for the peripheral blood vessels. Under the influence of reflected yellow light, liquid containing a yellow carotenoid pigment is transferred from the intestine to the hypoderm. Adult females, which are white, can now
change their colour to yellow. This process takes between 1 and 20 days. They can reverse the process when placed on a white flower. Within 5 or 6 days, as the fluid is withdrawn, the spider becomes white again. Colour changes first appear in the legs and then spread to the carapace and gradually tint the abdomen. Another type of pigment is of a lipochrome nature. It is found in the hypodermic cells and is responsible for the pink colour present in bands or spots on the legs, abdomen, and carapace. This pigment is more permanent and accumulates in increasing quantities with age. Dr Ansie Dippenaar-Schoeman, Specialist Scientist, ARC–Plant Protection Research Institute Send your questions to The Editor (write S&T QUESTION in the subject line) by e-mail to email@example.com OR by fax to (011) 673 3683. Please keep them as short as possible, and include your name and contact details. (We reserve the right to shorten or edit for clarity.) We will send you R50 for every question that we publish with answers from our experts.
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The S&T tourist Q
The fossil heritage of South Africa is precious and fragile, so the best place to view it is in museums around the country. Celebrate national African Origins month in September by visiting a fossil exhibition.
useums are the ‘safe deposits’ of South Africa’s precious fossils, preserving and protecting them from loss or damage. Only one out of every million animals becomes preserved in this way, so each fossil is valuable – once lost, it is gone forever. Finding fossils is difficult; working with them is complicated, and needs the care and expertise of professional palaeontologists.
Work at the fossil site Finding a fossil needs keen powers of observation and deep concentration. For a palaeontologist, it can mean walking many kilometres and many days without finding anything. Fossils can normally be recognized from a familiar shape in the rock – of the bone or animal – or a change in texture or colour. Close inspection shows the features of bones or plants or animals. Next comes preliminary identification. The person finding the fossil assesses what part of the animal or plant is preserved. Only a section may be visible at first, so it’s important to have a good idea of what else might be there, so as not to damage whatever still remains buried. Recording the exact geographic locality where the fossil is found is crucial for studying its meaning. The researcher records accurate GPS co-ordinates (or grid reference) for each discovery, however small, as well as the farm and district locality, the geology of the area, the exact position of the fossil in the geological sequence, the precise orientation of the fossil, how it is preserved, and its relationship to surrounding rocks and fossils. Extracting the fossil from the rock needs qualified and dedicated preparators. They remove the bone from the rock – a slow and timeconsuming process, involving mechanical means and sometimes chemicals. Later, for determining details hidden within a fossil, such as a skull, for instance, CT scanning can also be used.
The scientific record Once extracted, each fossil is housed in a museum to keep it safe and to ensure its ongoing availability. Museum staff catalogue and archive detailed information about every fossil in its collection. The fossil’s catalogue number on the museum’s computer database gives bona fide scholars – wherever they may be – access to the data. Researchers must also describe their fossil finds for the scientific record. If a new species is found, the description is published in a recognized scientific journal to make other scholars aware of it. Named according to the international biological code of nomenclature, the original fossil is then preserved in a museum for future generations as a reference specimen of that new species. As the international repositories for important reference specimens, museums are the research sites or ‘laboratories’ for a country’s natural history, so they all need suitably trained conservators and curators. ■
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Exhibit at the Albany Museum, Grahamstown: a reonstruction of the Karoo landscape about 245 million years ago. The Albany Museum celebrates its 150th anniversary with the opening of its new palaeontology gallery on 9 September 2005. It is named the “Fossil Heritage of the Eastern Cape” but covers the broader fossil story revealed in South Africa’s sedimentary rocks. To book educational visits for school groups phone Mrs Marijke Cosser at (046) 622 2312. For Sasol SciFest outreach programmes visit www.scifest.org.za and for other details go to www.ru.ac.za/Albany-museum (currently being updated). To enjoy fossil exhibitions and get to know the world that ancient animals inhabited, here are some of the many South African places to visit.
Johannesburg’s fossil museum The James Kitching Gallery (Bernard Price Institute, University of the Witwatersrand) is Johannesburg’s only palaeontological museum. The exhibits include ancestors of modern plants; amphibians; tortoises; dinosaurs, crocodiles, and lizards; therapsids and mammals; and humans. Displays include original fossils as well as life-sized reconstructions of prehistoric reptiles that once inhabited South Africa. This museum contains many fossils that are new to science and the only specimens known. Open Mon–Fri. For special guided tours for groups and for educational programmes in geology and palaeontology to schools, phone the educational officer, Dr Ian McKay, at (011) 717 6665. For more, visit www.wits.ac.za/geosciences/bpi
The Cradle of Humankind Declared a World Heritage Site in 1999, the Cradle of Humankind in Gauteng is a scientific storehouse of information about animal, human, and cultural evolution. In total, there are 13 excavated fossil sites within this area of open landscape, where thousands of fossils have been found, including ‘Mrs Ples’ and ‘Littlefoot’ in the Sterkfontein Caves. Open all year round except Christmas Day. Tours of the caves start at 09:00 and last about 90 minutes. For details phone (011) 668 3200 or visit www.discover-yourself.co.za
Some other places For more about fossils and African Origins, visit institutions such as the IzikoSA Museum (Cape Town), the Transvaal Museum (in Pretoria), the Natal Museum (Pietermaritzburg), and watch developments in the Makapansgat Valley in Limpopo, the Langebaanweg fossil site, and the Nieu Bethesda river bed in the Eastern Cape.
Unite to save Sue Milton, James Aronson, and James Blignaut show how ecologists and economists can work together to preserve the world’s natural riches. s everyone who is prudent with personal finances knows: it’s safer in the long term to live off your income than to live off your capital till there’s nothing of it left. Similarly, societies need to be prudent with Earth’s natural resources to sustain increasing human populations. But the way we exploit land for food, fibre, and minerals causes lasting damage. So ecologists and economists have got together to consider how best to look after what nature provides and at the same time make sure that there are enough goods and services to meet the needs of all the world’s people, poor and rich, now and for the future.1 For everyone to live like an average American would need the resources of approximately six Earths. The impact of growing global populations, expectations, and economies on the planet’s finite resources is, therefore, fostering tension between developed countries (the ‘haves’) and developing ones (the ‘have nots’). One option is to repair the damage done to nature. This is costly and can be complicated, and the benefits remain undervalued in developing countries. The spin-offs, however, make it worthwhile for governments and local communities everywhere to invest more in ‘natural capital’. International conventions and advocacy – and growing global awareness of the fact that there are useful natural resources in the geopolitical south – have sparked new interest in ecological restoration.
The eco-value of natural capital
‘Conventional’ economics distinguishes three production factors: land, labour, and capital (here, meaning man-made fixed capital such as infrastructure). In ‘ecological’ economics these correspond to natural, cultural (or social), and cultivated and manufactured capital. ■ Natural capital comprises Earth’s nonrenewable resources (such as natural gas, petroleum, uranium, diamonds, fossils) and renewable ones, made up of natural and mostly unmanaged ecosystems, which maintain themselves at little or no cost to people. ■ Cultural (or social) capital refers to the knowledge and traditions people use to make decisions, exploit resources, make products, and value our world. ■ Cultivated capital (crops) and manufactured capital (such as buildings, cars, or materials) both derive from natural capital, although this fact is often overlooked. Unlike natural capital, they need an external source of energy and labour to produce and/or to maintain them. The 2005 international Millennium Ecosystem Assessment report makes it clear that human well-being depends on four types of ecosystem service flowing from natural capital. ■ Supporting services (needed by all the others) include soil formation, nutrient and water cycling, and primary production. ■ Provisioning services yield food, water, firewood, timber, fibre, and genetic material, for example. In developing countries, many daily necessities come directly from the wild – grazing for livestock, bushmeat, fruit, honey, medicinal plants, building poles, and thatch, for instance. Other common products now cultivated or manufactured were once harvested from the wild (including maize, coffee, resin, rubber, and quinine). ■ Regulating services include moderating the climate, controlling dust and floods, and regulating gases in the atmosphere. ■ Cultural services supply the raw material of human cultures – recreational benefits, images, ideas, the information within myths and traditions, and scientific as well as spiritual understanding of the world.
bridge this gulf and to inspire the disciplines to combine forces for the common good (see boxes). The term links the idea of goods and services that nature generates (‘natural’) with that of a stock of assets (‘capital’) from which useful goods and services flow. It
1 At a workshop in September 2004 on Restoring Natural Capital, in Prince Albert in the Karoo, 37 ecologists and economists from all the southern continents discussed the value of natural capital, and the costs and benefits of its restoration. After a follow-up symposium to discuss global strategies in Missouri, USA, in October 2005, Island Press will publish the outcome of both meetings in book form.
embraces biodiversity and conservation, the concern of ecologists, and also monetary and social yields, the concern of economists. Renewable natural capital gives people basic essentials as well as quality of life, so there are practical, cultural, aesthetic, scientific, and moral reasons as well as economic ones for restoring damaged ecosystems. This is especially true now that, as the 2005 international Millennium Ecosystem Assessment report indicates, the global stock of natural capital has already dropped too low to support the economic aspirations of developing countries, which do not enjoy the same level of resourcing as their Western counterparts.
A shrinking resource We’re losing our natural capital because we don’t recognize its true value or the costs we incur by depleting it. Ecosystems, and biodiversity specifically, support all life on Earth, and we need a critical mass (we do not know exactly how much) to carry on providing the life-supporting goods and services that nature provides free of charge, simply by being nature. According to researchers Oonsie Biggs (Wisconsin, USA) and the CSIR’s Bob Scholes, South Africa’s biodiversity stock (as measured by land surface transformation) has dropped by 20% in the past century and continues to decline relentlessly, while the economy has grown by several orders of magnitude in the same period. The question is: how long can this trade-off continue? Agriculture must be productive to support growing human populations. But cash crops are not self-sustaining and demand massive direct or indirect subsidies, so they are costly. One remedy is to replace tracts of monoculture with mosaic landscapes of cultivated land and natural capital, which can retain some of the benefits of untransformed landscapes – such as refuges for wildlife and dust control during fallow times. Production cannot intensify everywhere, especially in the long term. In arid areas, it is neither feasible nor economical to convert natural rangeland – with its variety of drought-adapted plants – to cultivated pasture. The poor soils of the Western Cape mountains cannot sustain crops and
The common myth is that there’s a clash of interests between economists and ecologists. Both share the prefix eco- (from the Greek oikos meaning ‘home’) and study the functioning of our home, planet Earth. Economists attend to the interaction between the supply and demand of scarce resources; ecologists deal with the abundance and distribution of all forms of life on Earth. Crucial for both are the causes and effects of resource scarcity. Yet many economists seem blind to biodiversity issues and ecologists seem deaf to financial and social realities. The notion of ‘natural capital’ tries to
Ecological economics: some basics
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Q Viewpoint Some ‘natural capital’ calculations Where natural capital is lost or reduced, responses vary, depending on a society’s values and needs, the scale of damage, the consequences for humans, national and international policy, and affordability. Options include ignoring the problem, allocating damaged land for another use, and restoring the land ecologically for maximum natural capital value. The costs and benefits of each option can be calculated – the challenge is to build broad timescales and ethical issues into the accounting procedure. ■ A cost–benefit analysis is normally used to compare the costs of restoration with the expected benefits (e.g. increased water flow, water purification, carbon sequestration, tourism, and employment). ■ Alternatively, Natural Resource Accounts can be constructed to calculate the value of current land use compared with the value of an alternative land use (e.g. a restored site). Conventionally, time enters the calculation in the form of a ‘time preference rate’ (i.e. the rate at which the value of money changes over time). The ethically prudent management decision is the one that renders the highest return or value for money. It is therefore important to understand the ecosystem process and what constitutes costs and benefits, what alternatives exist, and what role time plays before embarking on any calculation of the monetary values of each. ▲
livestock, but fynbos vegetation attracts tourists and has genetic, educational, and recreational value. Urban development, however, has substituted another kind of market value to replace large areas of fynbos; where land conversion for urban use occurs indiscriminately, loss of natural capital accelerates. Extracting minerals, oil, rock, sand, and other non-renewable resources can also destroy natural capital. Surface mining, for instance, clears thousands of hectares of natural vegetation. Mining oil or gas damages the environment through vehicle traffic, oil spills, and frequent fires. In South Africa, the National Environmental Management Act (Act 107 of 1998) obliges individuals or companies to return value to land after environmentally destructive activities, and thereby involves business in the land restoration process. Another way in which developing countries lose natural capital is by overexploiting resources such as timber, grazing, and flora and through the effects of ‘invasive aliens’ (or, animals and plants from other continents that colonize natural systems because, in their new environment, they have no natural predators to control them). Damaged land yields fewer services: it holds less soil or water, supports less livestock, and supplies less fuel, medicine, or thatch. Urban people ignore such natural capital depreciation – but rural people pay a high price as they spend more time and
effort to find scarce firewood or indigenous medicinal plants, build homes with lowerquality material, and lose poorly nourished livestock. They bear the social cost as young people move to cities to find work, leaving the elderly and the children behind with fewer and fewer resources.
Costs of substitution Losing natural capital in exchange for cultivated or manufactured capital can be short-sighted. For example, substituting agriculturally productive plantations for Brazilian forests can have untold hidden costs if it’s found that the plantations cannot regulate the climate and store carbon as the forests do. Some natural goods and services cannot be replaced. Black rhinoceroses, for instance, which can sell for more than R500 000 each, were nearly exterminated in South Africa through being hunted for the sale of their expensive horns. Thanks to conservation efforts they survived, together with areas of habitat, and now contribute to the national economy in a different way: by attracting tourists and through the sale of live animals.
Ecology pays Only rarely, however, can all lost species be returned to areas inhabited or used by people. Restored landscapes are sustainable only if they are appreciated, so winning support for ecological restoration means making sure that local people benefit.
For everyone to live like an average American would need the resources of approximately six Earths.
Ranch-level restoration of natural springs, ponds, pans, and linear wetlands in Patagonia and South Africa creates corridors of habitat for riparian plant and animal species and also improves the land’s economic value and productivity by helping it to retain and filter the water. In Madagascar, hedges and avenues of fruiting trees enable forest animals to move through croplands between habitat patches – and local farmers are supportive because the trees shelter crops from wind and offer shade and fruit to people. In such cases, ecologists and farmers together select tree species compatible with both conservation and farming. South Africa’s Karoo has changed during the past 300 years of human use, where vultures, hyenas, and lions have disappeared together with the migratory game they hunted. Restoring species-poor rangeland that has degraded through erosion can involve processes that made this arid
shrubland resilient to drought in the first place. Since plants need time to set seed after rain, for instance, one option is for farmers to use very large management units and low animal densities; another is to subdivide ranches and ‘rest’ different sections by rotation; yet another is periodically to reduce grazing intensity after rain. Large-scale ecological restoration conducted by governments, NGOs, and private businesses can help natural capital to appreciate in value and can be justified socially, ecologically, and economically. One success story is South Africa’s Working for Water programme, which employs some 20 000 people a year to clear alien plants. Another calculation shows that employing 4 000 people in the Eastern Cape to replant 10 000 hectares of subtropical thicket will reduce loss of soil, water, and biodiversity. It could also, within 20 years, provide building materials, plants used in rituals, fuelwood, fencing, wild fruit and vegetables, traditional medicines, sticks, tools, and fodder worth some US$159 per household each year. Landscapes so badly degraded that they can be identified as such from outer space could, if restored, attract tourists, sell carbon credits, and support local people. We have calculated, for instance, that restoring, managing, and marketing biodiversity-based resources in the communal areas of Bushbuckridge (as is being done in the adjacent Kruger National Park or private game reserves) could boost their total sustainable flow of goods each year from R1 400 per hectare to between R3 500 and R5 500 per hectare. Ecological restoration is slow. It needs knowledge, planning, persistence, and social justice in the distribution of resources. It also means overturning the myth that economic growth can be unlimited on this finite planet. ■ Professor Milton is in the Department of Conservation Ecology at the University of Stellenbosch; Dr Aronson is with the Restoration Ecology Group, CEFE/CNRS, in Montpellier, France; and Professor Blignaut is in the Department of Economics at the University of Pretoria. For more on natural capital and incentives for ecological restoration see J. Alcamo et al., Ecosystems and Human Well- Being: a framework for assessment. Millennium Ecosystems Assessment. (Washington, D.C., and Covelo, CA.: Island Press, 2003); Gretchen C. Daily, Nature’s Services – societal dependence on natural ecosystems (Washington, D.C.: Island Press, 1997); R. De Groot et al., “Importance and threat as determining factors for criticality of natural capital”, Ecological Economics, vol. 44 (2003), pp.187–204; Geoffrey Heal, “Valuing ecosystem services”, Ecosystems, vol. 3 (2000), pp.24–30; William R. Jordan III, The Sunflower Forest – ecological restoration and the new communion with Nature (University of California Press, 1999); Sue J. Milton et al., “Economic incentives for restoring natural capital: trends in southern African rangelands”, Frontiers in Ecology & Environment, vol. 1 (2003), pp.247–254. Visit the Society for Ecological Restoration International’s Primer of Ecological Restoration at www.ser.org/Primer.
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Books Q The Story of Earth & Life: A southern African perspective on a 4.6-billion-year journey. By Terence McCarthy and Bruce Rubidge and staff of the School of Geosciences, University of the Witwatersrand, Johannesburg (Cape Town: Struik, 2005). ISBN 1 77007 148 2
Above: The resistant sandstones of the Waterberg and Soutpansberg Groups offer spectacular scenery in the Limpopo and North West provinces. They were deposited on a vast alluvial plain about 1 800 million years ago. Photograph: Morris Viljoen Below left: A cut-away section through the Earth, showing its component parts.
ere, at last, is a readable, reliable, lavishly illustrated account of the underground riches of southern Africa – the minerals deposited over geological ages and the fragile fossil record that’s preserved more extensively in South Africa than anywhere else on our planet. Are you interested in the region’s mining wealth? This book explains how some of the world’s largest deposits of diamonds, gold, platinum, chrome, manganese, iron ore, uranium, coal, titanium, vanadium, and fluorspar came to be concentrated here. Do you want to Continental know more about life crust on Earth and the evolution of plants, 35 km animals, and humans? Mohorovicic It provides the latest Discontinuity (Moho) research findings. This volume is epic in scope. According to author Terence (‘Spike’) McCarthy, it explains the way the Earth works – basically the story of plate tectonics – and why mountain ranges, volcanoes, and Crust earthquakes, for example, are where they are. Beginning with the Big Inner Core Bang, the formation of the (solid) Milky Way galaxy and our solar system, it goes on to track the formation of Outer Core (liquid) Earth’s first continent, the origins of our region’s Gutenberg rock formations, and the Discontinuity minerals buried there. It explains the evolution of
Oceanic crust Lithosphere
7 km 100 km
upper mantle asthenosphere (low velocity zone)
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the Earth’s atmosphere from its toxic start to its present, oxygen-rich lifesupporting condition, it traces global climate change over the past 55 million years, and it explores mass extinction events that influenced the development of life. It follows life’s increasingly complex forms, through mammals and dinosaurs to the emergence of Homo, it assesses the impact of humans on Earth, and it examines some of the unsettling lessons that the geological record provides for our future. “We’re on a crusade with this book,” says McCarthy and, given threats of global warming and the rapid extinction of species in our own time, the subjects it covers prove increasingly topical. One Saturday in 2001, he and Bruce Rubidge arranged a series of 18 lectures by experts in a range of disciplines from the University of the Witwatersrand to explain South Africa’s unique geology and palaeontology in understandable terms. The Great Hall was packed all day, with people sitting in the aisles. Such interest decided McCarthy and Rubidge to turn the material into a book that would appeal to the general reader and also act as an introductory textbook. “It took many hours of hard slog,” recalls Rubidge, “but the story is such an exciting one, and that kept us going. South Africa is remarkable for the geosciences. Because of the relatively dry climate, we have spectacular rock outcrops, which are well exposed, and a wide diversity of rocks deposited throughout geological
Q Books New books Reminiscences of a Bone Picker 1925–1965. By Phillip Tobias (Picador Africa, 2005). ISBN 1 770100 15 6 Known for his pioneering work at South Africa’s hominid fossil sites, Phillip Tobias is a world authority on human evolution; his formidable skill and reputation as a speaker and teacher have helped to foster public interest in this fascinating subject. In this first volume of his autobiography, Tobias describes his troubled childhood in Durban and Bloemfontein and his early days as a student at the University of the Witwatersrand, where he remained to teach from 1945 till he retired in 1993. He recalls his interactions with scientists including Raymond Dart, Robert Broom, Wilfrid LeGros Clark, and Theodosius Dobzhansky, as well as his work in overturning some prevailing myths about the San of Botswana and in conducting the first human biological study of the Tonga people of Zambia, who were living in the area to be flooded by Lake Kariba. The anecdotes, experiences, and philosophies in this book reveal Tobias as a scientist who loves science, people, teaching, books, theatre, music, travel – as well as tea and cricket. (Available in October 2005.)
Top: The large igneous intrusion known as the Phalaborwa Complex formed 2 049 million years ago in Limpopo Province and has been mined for copper, phosphate, and vermiculite. This open pit mine, 760 m deep, is one of South Africa’s largest man-made holes. Photograph: Terence McCarthy Above: Lava flowing from the Kitazungurwla volcano in Central Africa during the 1986 eruption. Photograph: Judith Kinnaird
time.” The Barberton mountainland, for instance, has some of the world’s oldest rocks, and in them are preserved the oldest known ocean floor and traces of the oldest known bacterial life forms. “The fossil wealth and long rock record of southern Africa is unique for any one region,” he adds, “and it’s a ‘good news’ story we want to tell people about.” The authors also want the book to be used the length and breadth of southern Africa and, adds McCarthy, “to get it onto the radar screens of the 44-birding-wildlife-tree-campingoutdoor people. We have some great scenery here and our book gives the background to the rocks that create the scenery. Knowing about the rocks adds a whole new dimension to the outdoor experience. So we’d like our book to go into the travelling library of the outdoorsy people along with the other tree, bird, mammal, grass, spoor, and insect books. It must be used to destruction!” The book’s story line is broadly chronological. The text boxes are there to “explain the nuts and bolts
stuff”, says McCarthy, and extensive figure captions and numerous figures and diagrams make for convenient reading. Full-colour photographs and illustrations bring the facts and interpretations to life, and the excellent index and glossary make it easy to find what you are looking for. “From the outset we wanted the book to be inexpensive, because we wanted people to buy it. But as Struik added more and more colour,” McCarthy recalls, “the price spiralled. So we found a sponsor (Kumba Resources), whose generosity has made it possible to sell the book for under R200 (333 pages, in full colour).” “This is the first time that such a broad-ranging book relating to the geosciences of South Africa has been compiled for the layman,” explains Rubidge, making the full story of our geological and palaeontological past available outside scientific journals. This volume represents excellent value for money. It will help all who visit or live in South Africa to get to know, appreciate, and value the heritage that’s hidden below ground. ■
The Microstructure of Dinosaur Bone: deciphering biology with fine-scale techniques. By Anusuya Chinsamy-Turan (Johns Hopkins University Press, 2005). ISBN 0 8018 8120 X This is the first book dedicated to the subject of dinosaur bone microstructure, a recently developed technique for studying dinosaurs and other ancient animals. Introducing her study with a general overview of living bone structure and composition, Anusuya Chinsamy-Turan (of the University of Cape Town) explains how bone structure changes at death and during fossilization. She shows why the microscopic structure of fossil bone remains intact after millions of years of fossilization, provides a photographic atlas of the kinds of bone tissue found in dinosaurs, and examines their biological significance. The book offers insights into growth patterns of dinosaurs and the biology of Mesozoic birds; it concludes by discussing what bone microstructure can and cannot disclose about dinosaur physiology.
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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. 1
8 10 11
14 15 17
Don’t cell-talk while driving Even a hands-free cell phone device makes you four times more likely to have an accident when you’re driving a car and having a cell phone conversation at the same time. This was shown recently in an Australian study. Now researchers Takashi Hamada and colleagues at the National Institute of Advanced Industrial Science and Technology in Tokyo, Japan, think they know why. The strength of a telephone signal keeps changing when a vehicle is moving and, during a call, the phone often switches from one base station to another. These conditions cause small losses of sound quality, which force the driver’s brain to work harder to hear and understand the person they’re listening to. So less attention is paid to what’s happening on the road. The researchers compared measurements of the sound signal of cell phones in parked cars and in cars travelling at 65 km per hour. In the moving cars, silent periods, each lasting about 300 milliseconds, interrupted the signal about six times a minute. There was also a time-lag of some 300 milliseconds and, for 5% of the time, distortion in the frequency range. To test the brain’s responses in these circumstances, the researchers played volunteers a recording of a story in similar sound conditions. Whenever the volunteers struggled to hear the distorted sections of the recording, the part of the brain perceiving sound became more active. Moral? Put your cell phone away when you’re driving. From a report in New Scientist (30 July 2005).
Friends bring longer life 31 JEMIMA
1 A line on a weather map connecting places with the same atmospheric pressure (6) 6 Light-scattering technique used for investigating solid materials (5) 8 Sweet sticky fluid made by bees from nectar collected from flowers (5) 10 A two-footed animal (5) 11 Alluvial triangular area at a river’s mouth with diverging outlets (5) 12 Collective word for the animals of a particular region or period (5) 13 Basis of the decimal system (3) 14 Michael --- (1791–1867); the English physicist and chemist who discovered electromagnetic induction (7) 17 Light silvery-white metallic element that gives strength when alloyed and is used widely in domestic utensils, aircraft construction, etc. (9) 19 Archaeopteryx lithographica is regarded as the earliest known what? (4) 24 Organisms that require oxygen (7) 26 The epoch preceding the Pliocene; a period of great earth movements during which the Alps and Himalayas were being formed (7) 28 The chemical symbol for ruthenium (2) 29 A non-metallic element that is combined with carbon and oxygen to make very lightweight materials (5) 30 Nature uses twenty of these acids to make proteins (5) 31 The inventor of the telephone (4)
2 A malleable alloy of iron and carbon capable of being tempered to different degrees of hardness (5) 3 South African word for a ridge of mountains or hills (4) 4 Mammal-type reptile (9) 5 The ancient supercontinent which split up into continents of today (8) 7 Pertaining to or characteristic of birds (5) 9 A long narrow strip of land projecting into the sea; eject saliva from mouth (4) 10 The first indication of birds in the late Jurassic period came from the discovery of a single fossil feather in which European state? (7) 15 The period preceding the Cretaceous (8) 16 A building material provided by natural capital (6) 18 Three production factors in conventional economics are: land, ---, and capital (6) 20 Abbreviation for a common type of electron microscope (1 1 1) 21 A prefix indicating the first, earliest, or original (as in --feathers, found in Liaoning) (5) 22 Reddish dye made from a tropical shrub, used especially on the hair (5) 23 A prefix derived from the Greek word meaning ‘great’ (4) 25 A heaving of the sea with waves that do not break; US for ‘wonderful’ (5) 27 Metallic element with the symbol Fe (4)
Do you like crossword puzzles? Was this one too difficult? Too easy? Just right? Would you also, in addition, like a QUEST competition crossword (with a prize) that is more difficult? Fax The Editor at (011) 673 3683 or e-mail your comments to firstname.lastname@example.org and let us know. (Mark your message CROSSWORD COMMENT.)
Make good friends if you want a longer life, suggests an Australian study led by Lynne Giles of Flinders University in Adelaide, South Australia. It’s been known for some time that good social networks help older people to live longer, but this study is the first to distinguish between the effect of friends and relatives. The researchers surveyed about 1 500 people over the age of 70. Those who, at the beginning of the study, reported close face-to-face or telephone contact with five friends or more were 22% less likely to die in the next decade than those who reported having few or distant friends only. In contrast, there was no such special benefit from close ties with children or other relatives. One reason might be that friends are specially successful in helping people to cope with stress and difficulty, and in encouraging healthy behaviour, such as going to a doctor when medical symptoms arise. Another reason might be that relationships with friends can be less stressful for older people than, in some cases, their relationships with relatives and children. From a report in New Scientist (25 June 2005) and the Journal of Epidemiological and Community Health, vol. 59, p.538 From a report in New Scientist (30 July 2005).
World’s oldest dinosaur embryos Nearly 30 years ago, James Kitching of the Bernard Price Institute (BPI) at the University of the Witwatersrand found a cluster of seven dinosaur eggs with two exposed embryos at Golden Gate in the northeastern Free State, South Africa. Now researchers from Canada’s University of Toronto, the Smithsonian Institution in the US, and the BPI have published the results of a painstaking project to prepare for further study the tiny, delicate embryonic bones from the fossil eggs, in their intricately curled-up position. About 190 million years old, they are the oldest known dinosaur embryos and belong to the prosauropod dinosaur Massospondylus carinatus. One is almost complete, trapped in the act of hatching. Its body proportions are very different from the adult’s, so it’s now possible for the first time to understand the growth trajectory of this animal, and the way in which parts of it (such as the neck) grew more Fossilized dinosaur embryo in its egg. rapidly than others as it matured. Starting as a quadruped, it later took on elements of bipedalism. Absence of well-developed teeth in both embryos and their awkward body shape suggest the hatchlings’ need for parental care. If this is so, these fossils are the oldest known indication of parental care in the world’s fossil record. For the full story read R.R. Reisz, D. Scott, H-D. Sues, D.C. Evans, and M.A. Raath, “Embryos of an Early Jurassic prosauropod dinosaur and their evolutionary significance”, Science, vol. 309 (2005), pp.761–764.
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Letters to M o re on CDs ith reference to the insert, in your splendid magazine, on how CD players work (QUEST, vol. 1, no. 3, p. 6), I thought your readers would be interested to know how the capacity of CDs (and DVDs) is limited by fundamental physical principles. As you correctly point out, the data on all types of CD and DVD are simply binary numbers (called ‘bits’) that can take the value of 1 or 0, depending only on whether or not the laser has ‘burnt’ a small pit on the disk. To store the maximum amount of data on a disk, you need simply to make the pits as small as possible. The laser in a CD-player is focused onto a spot on the disk by a lens, and it is here that the basic physics of optical ‘diffraction’ must be taken into account, as this spot cannot be infinitesimally small. Light is diffracted whenever it passes through any aperture (the same physics, operates when water waves pass through a narrow opening, which you might see in a harbour), and the laser lens is the limiting factor, together with wavelength (or colour) of the laser light itself (CDs use red lasers). As originally designed in the 1980s, this limit was a spot size of about
1.5 micrometres (a micrometre is one thousandth of a millimetre). If you calculate how many spots of that size you can fit onto a CD with an radius of approximately 5 cm, you’ll find that is where the limit of around 700 megabytes (one ‘byte’ = 8 ‘bits’) comes from. So, how has this number been increased by so much (by a factor of about 5) for DVDs? The lasers are about the same size, but the lenses are now better quality, the tracks can be placed closer together (via better electronic servo control of the laser), and shorter wavelength (that is, ‘bluer’) lasers are now possible. These developments were essential to be able to store videos and films as digital data on a CD-sized format. An even greater gain is in the offing, known as ‘Blu-ray’, which uses blue-violet lasers and even closer packing of the tracks to achieve a potential storage of 25 gigabytes per disk layer. This will allow even high-definition films and video to be stored on a single disk. Phil Charles, South African Astronomical Observatory, Cape Town
Compulsory science? Whatever next! know that the country’s youth need to be encouraged to study maths and physics, but I have a problem with the current mindset that sees these subjects as a panacea for all the woes of young South Africans, unemployment, and everything else including crime. Making science and maths compulsory at matric level is absurd, as many people simply don’t have an aptitude for science, and failure and drop-out rates will increase. If it’s thought that our universities are overburdened with BA students, why not limit enrolment numbers? Students who do not have maths and/or science can be guided into other worthwhile fields such
as business science, economics, education, library science, and healthcare (not medicine, but support services). Maybe someone should suggest to the Minister of Education that it could be valuable to offer courses in grades 11 and 12 in basic philosophy and ethics. This would teach our youth to think – and to think morally and justly. I also believe that all university students should have to study at least one year of philosophy and two years of ethics. Why are the humanities sitting back and not promoting their fields of study? Why this inferiority complex? Jay Lin, Centurion
The best letter from a reader published in the next issue will win a Shaeffer pen. Address your letters to The Editor and fax them to (011) 673 3683 or e-mail them to email@example.com (Please keep letters as short as possible. We reserve the right to edit for length and clarity.)
Q ASSAf News Nutrition and human immunity ASSAf is one of the ‘intensive partners’ of the US National Academies in a programme that aims to assist African national science academies in offering evidence-based advice to their governments and nations. Now the ASSAf Council has approved the first topic for its evidence-based, consensus study: “Nutritional influences on human immunity.” The brief is to examine the research evidence that relates to three main issues: (i) nutritional modulation of the normal human immune system as a result of under-nutrition and/or specific deficiencies of both macroand micronutrients; (ii) modulation of human nutritional status in states of infection, both acute and chronic, with special emphasis on infection with Mycobacterium tuberculosis (Mtb) and the human immunodeficiency virus (HIV); (iii) effects of nutritional interventions on
morbidity and mortality in adults and children infected with HIV or suffering from clinical tuberculosis, or both. The topic is controversial in South Africa and has given rise to different viewpoints concerning public policy in addressing the ravages of these diseases; consistent and well-analysed evidence has mostly been replaced by belief, assertion, and anecdote. Some people believe that poverty and under- or malnutrition may be the main cause of acquired human immunodeficiency syndrome (AIDS), with the HIV infection being a non-contributory or trivial supervening circumstance. Others believe nutritional deficiencies to be an appropriate target of primary therapy for HIV infection and AIDS. Most people, however, believe that nutritional support of persons infected with either Mtb or AIDS is a necessary and helpful part of a
therapeutic approach that concentrates on the eradication, or, at least, control of the infected state in each affected person. A further complication is that many products are now sold over the counter claiming to ‘modulate’ the immune system to prevent or ameliorate HIV and/or Mtb infections. They range from ‘nutritional supplements’ to processed ‘drugs’. Such controversial opinions and products threaten to dissipate the national will to address the problem of these out-of-control pandemics. An impartial review of the available evidence is now needed, to assist in resolving controversy and improving health-service planning as well as to promote national cohesion in addressing these devastating infections. The ASSAf report, with recommendations for national policy and practice, will appear in early 2006.
September – African Origins Month The South African Agency for Science and Technology Advancement (SAASTA) is implementing the initiative of the Department of Science and Technology (DST) to engage the public in South Africa’s rich fossil, cultural, and genetic heritage extending back more than three billion years. The theme is African Origins – it all started here! and activities include public lectures and open days at research institutions as well as field trips to fossil parks, World Heritage sites, and museums. For details and updates visit www.saasta.ac.za and consult the media throughout the month. Ezemvelo Nature Reserve (near Bronkhorstspruit)
Q Diary of events
To help to develop appreciation and love of the great outdoors, the reserve has a programme of weekends, each involving an ‘experience’ and a specialist speaker around a special theme. The September and October weekend themes are: 9–11 Sept. Outdoor Photography; 16–18 Sept. and 14–16 Oct. Riverine Ecology; 23–25 Sept. Basic Astronomy; 30 Sept.–2 Oct. Scorpions and Baboon Spiders; 7–9 Oct. Flowers of the Bankenveld; 21–23 Oct. Spiders (speaker – Ansie Dippenaar [see her article in QUEST vol. 1 no. 4, 2005]); 28-30 Oct. Larks, Pipits and Cisticolas. For more information visit www.ezemvelo.co.za
(407 Canal Walk, Century City, Cape Town)
Back by popular demand, X-tra X-Kit maths and science lessons for grade 11 classes run from 27 August–29 October. There are eight different lessons to choose from and X-Kits are included at a 30% discount. For details phone the MTN ScienCentre at (021) 529 8100 or visit www.mtnsciencentre.org.za
African Astronomical History Symposium (South African Astronomical Observatory, Observatory, Cape Town)
8–9 November: the first-ever symposium on African Astronomical History will be held as one of the festivities surrounding the opening of the Southern African Large Telescope (SALT). For details visit www.saao.ac.za/assa/aahs
Plan for 4–10 September – National Mathematics Week 30 September–1 October – Eskom Expo All October – Astronomy Month 4–10 October – World Space Week 31 October–2 November – World Conference on Physics and Sustainable Development November – South African Maths Olympiad For more about science events and activities visit the SAASTA web site at www.saasta.ac.za/events Diary of Events welcomes news of science and technology events or happenings. Send full details as “QUEST DIARY” to The Editor, tel./fax: (011) 673 3683 or e-mail: firstname.lastname@example.org
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Back page science Q Read it and weep We know about Harry Potter, but what else do children like to read? In the UK’s Guardian newspaper (4 May 2005), Tim Dowling comments on the finalists in the children’s category of the Aventis award for popular science books: “... it seems that the magic formula for attracting children is common knowledge. All the books are large in format and slim, with eyecatching graphics and lots of boxed-off text. Each has the look of a mildly disappointing birthday present. My youngest child, who is five, regards all books with suspicion. When presented with six short-listed science books, he burst into tears and stormed out of the room, although he later came back and snatched the one about earthquakes off the pile.” The Aventis prize was judged this year by Bill Bryson, author of A Short History of Nearly Everything (Black Swan), which won the adult category in 2004. As the title suggests, it covers many subjects. Among them, “a regrettable Ohio inventor named Thomas Midgley, Junior.” First Midgley came up with the idea of leaded petrol [now known to pollute the air]. Then, “[w]ith an instinct for the regrettable that was almost uncanny, he invented chlorofluorocarbons, or CFCs” [which attack the ozone layer]. This year, the Aventis prize was won by Critical Mass: How One Thing Leads to Another by Philip Ball (Heinemann). The book looks at individual human decisions and their impact en masse.
It’s a girl thing Harvard president Dr Lawrence H. Summers caused a stir by suggesting that men might have an “intrinsic aptitude” for science that women don’t share. The American Institute of Physics responded with a report by sociologist Dr Rachel Ivie. It says it’s not that US women drop out after graduating in physics or are victims of
discrimination in the workplace; the reason there are fewer women than men in the field is simply that girls don’t make the step from school to university. “Nearly half of students taking high school physics are girls, but fewer than a quarter of the bachelor’s degrees in physics go to women.” (New York Times, 22 February 2005.)
Or is it? What would Summers make of the brute force of Panna Felsen, a 17-year-old schoolgirl from San Diego, California, who beat three robots hands down in an arm-wrestling contest. NASA’s Jet Propulsion Laboratory set up the competition to draw attention to its work on artificial muscles made of electroactive polymers. Incidentally, the lab’s Dr Yoseph Bar-Cohen says he is inspired by ants, which do so much more collectively than they could as individuals. (National Public Radio, 8 March 2005.)
Too studious by half Ellen Vanstone, in the Canadian magazine The Walrus (November 2004), writes: “A new study shows that people shouldn’t believe everything they read about what studies show. ... My study has pointed inexorably to three main truths: 1) A study with encouraging results will always be followed by a study with contradictory results. 2) Despite the fact that many studies are stupid, people believe that sentences beginning with ‘Studies show’ are more credible than their own first-hand experience. 3) Very few studies show anything useful.”
Just image Jen! In a CalTech study of how the brain records visual information, the surprising result was that sometimes individual cells respond to particular things – such as pictures of actress Jennifer Aniston. (From www.nature.com)
■ “Your theory is crazy, but it’s not crazy enough to be true.” Bertolt Brecht (1898–1956), German poet and playwright who initially studied medicine. ■ “Data without generalization is just gossip.” Robert Pirsig (1928– ), author of Zen and the Art of Motorcycle Maintenance. ■ “People will occasionally stumble over the truth, but most of the time they will pick themselves up and continue on.” Winston Churchill (1874–1965), British prime minister. ■ “As long as people are free to ask what they must – free to say what they think – free to think what they will – freedom can never be lost and science can never regress.” Robert Oppenheimer (1904–1967), US physicist and director of the Manhattan Project to develop the first atomic bomb. For more about his life and work, see the comic book Fallout by Jim Ottaviani (www.gt-labs.com).
A competition along the lines of Pop Idol has been running in the UK to find a new “face of science” – someone brilliant at science communication. FameLab contestants have three minutes to impress the judges and audience with their talk about any scientific topic, and they stand to win £2 000 and more opportunities to have their say. (See www.famelab.org.) Answers to Crossword (page 45) ACROSS: 1 Isobar, 6 Raman, 8 Honey, 10 Biped, 11 Delta, 12 Fauna, 13 Ten, 14 Faraday, 17 Aluminium, 19 Bird, 24 Aerobes, 26 Miocene, 28 Ru, 29 Boron, 30 Amino, 31 Bell. DOWN: 2 Steel, 3 Rand, 4 Therapsid, 5 Gondwana, 7 Avian, 9 Spit, 10 Bavaria, 15 Jurassic, 16 Timber, 18 Labour, 20 SEM, 21 Proto, 22 Henna, 23 Mega, 25 Swell, 27 Iron.
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