The KT mass extinction?
What was it? The KT mass extinction event was a large-scale mass extinction of animal and plant species in a relatively short period of time. There is a noticeable boundary indicated in the fossil record [known as the KT boundary], which is marked by a mass extinction topping 17 families per million years [around 15 families per million years above the average]. It occurred roughly 65 million years ago. K is the derived from the German name Kreidezeit, which translates as the Cretaceous Period. T is the abbreviation for the Tertiary Period (an outdated description for the period of time now covered by the Paleogene and Neogene periods). The KT boundary marks the transition between these two periods. Precursor to KT - Species in decline? Many scientists believe around ten million years before the KT boundary, the environment began to get markedly more hostile to life. The lush coastal planes on which dinosaurs depended began to turn arid, as sea levels fell worldwide. Their natural habitat was disappearing. Between ten million and three million years before the KT boundary, the dinosaurs seem to have suffered a huge decline. One interpretation of the fossil record is that forty percent of dinosaur species went extinct before the transition. In an interview with the BBC, David Archibald, Professor of Evolutionary Biology at San Diego State, spoke of the period leading up to the boundary. ARCHIBALD: “Organisms are adapted for a certain type of environment and when those conditions disappear those organisms disappear… we come up to about one to three million years before the end of the Cretaceous and we've got a group that seems to be vulnerable to any kind of extinction events that might be occurring at that time.” Global Warming Could Have Been Contributed To by Organic Sources Increasing concentrations of methane in the Earth's atmosphere would force changes to the earth’s climate on a global scale. Aside from methane coming from seismic sources, the suffocating gas could also originate organically. This organic methane would originate from increased numbers of deep-sea algae deposits and from the digestive processes of plant-eating dinosaurs. Increasing water temperatures could have caused a destructive feedback loop; Algae breeds better in warmer temperatures , and the greater the quantities of algae, the more methane, and consequentially the warmer the environment would become Fossil evidence also suggests that Plankton decreased in number during the Tertiary period. This may help explain the destruction of many marine food webs which relied on them. Adapting To The Change [Or Not..] In the changing climate, animals better able to burrow, or semi aquatic in nature would have had a higher chance of surviving. Harsh conditions would have had a damaging effect on all life, however creatures whose food chains were based on detritus had a reasonable chance of survival.
On this diagram the KT boundary [the last mass extinction event] marks the termination of the dinosaur, pterosaur and mosasaur genetic trees. Food web disruptions – a threat to dinosaurs? In the late Cretaceous, photosynthesizing organisms, including phytoplankton and land plants, formed the foundation of the food chain. Evidence suggests herbivores declined when the flora they depended on for food became scarce; recently evolved flowering plants may have outcompeted many of the nonflowering species that the dinosaurs relied on for food. . Consequentially, predators higher up the food chain such as Tyrannosaurus rex also suffered as prey numbers diminished. At the end of the Cretaceous there seem to have been no purely herbivorous or carnivorous animals. Many more species that were Omnivores, insectivores and carrion-eaters survived the extinction event, perhaps because of a more diverse diet which would act as insurance against declining food sources. Of the creatures that survived the extinction, most fed on insects, worms, and snails. This is significant as this food source fed on dead plant and animal matter. Scientists hypothesize that this detritus based food web fared better than the plant based food chains as there would not have been a significant fall in the amount of detritus [dead organic matter] available for sustenance. It has been hypothesized that with levels of oxygen falling, smaller animals, and animals with more efficient respiratory systems [such as small mammals – which may have required less oxygen than much the larger dinosaurs] would have been better able to adapt to these new conditions. Yum Small mammals preying on dinosaur eggs have been suggested as a contributor of the K-T extinction. However it does not explain why so many other species went extinct around, or the iridium chemical anomalies in the K-T layer, and could therefore be a contributor, not a cause to the ongoing extinction. Repenomamus robustus was an opossum-sized mammal about 1 m long and weighing around 14-15 kg living around 130 million years ago. A Chinese fossil of it was discovered a few years ago with the remains of a juvenile psittacosaur in its stomach area. This is direct evidence that some mammals fed on small
vertebrates, including young dinosaurs.
Artist’s impression of a Repenomamus – with its dinner. Source: http://my.opera.com/nielsol/blog/index.dml/tag/fossils
The origin of Birds A number of groups of Neornithine birds [the precursors to modern avian species] survived the harsh conditions of the KT event as a result of their abilities to dive, swim, or seek shelter in water and marshlands. Many species of birds can build burrows, or nest in tree holes or termite nests, all of which provided shelter from the environmental effects at the KT boundary. Ecological Niches With the decline of the dinosaurs, evolutionary pressures changed. Long-term survival past the difficult conditions at the boundary was easier for the remaining species as they could now fill niches left empty by the extinction of the dinosaurs. In the Darwinian sense, competition decreased for the surviving species, thus making it easier for them to find food and the resources they needed to propagate. Fossil Record Problems – The Signor Lipps Effect Although we have a lot of evidence for the explanations put forward, we are using the fossil record to date the period of the species’ existence. The problem with this is that the fossil record is so incomplete that most extinct species probably died out long after the most recent fossil that has been found. However as the fossil record is the best way of dating we have no other option. We also cannot make any accurate estimations on how long a species may have survived after the last fossil is found. Scientists have also found very few continuous beds of fossilbearing rock which cover an unbroken time range from several million years before the K–T extinction to a few million years after it. Unfortunately, this means there are a lot of temporal gaps we have to fill in with guesswork, due to our dependence on this record.
The KT boundary is the obvious on this rock – marked by the claystone later in the middle - it contains 1000 times more iridium than the upper and lower layers. Some believe that the KT mass extinction was caused by a huge asteroid striking earth. It is rare for an asteroid of a large enough size pass through the earth’s atmosphere intact, but when such events happen, the results are cataclysmic. Scientists believe an object 10 km wide slammed into the earth on the tip of the Yucatan Peninsula, in the Gulf of Mexico. It is thought that upon striking, the comet would have sent a blanket of dust and steam into the atmosphere; this emission of dust and particles would have resulted in environmental changes similar to a nuclear winter, with this new artificial atmosphere of dust blocking out radiation from the sun and causing a planet wide dimming and cooling. The impact blast have caused huge forest fires, immense tsunamis in all directions radiating from the crash site, severe storms due to meteorological disruption, and eliminated all sunlight for a period of 6 months under an ashen sky. The energy it unleashed on impact would have been equivalent to ten billion Hiroshima bombs(Strahan 2004). The result would have been an immediate loss of life from the impact event. The following ‘nuclear winter’ would have caused an even greater loss of life as plants, unable to photosynthesize, died, and the food webs on which they depended collapsed.
The KT Boundary – an impact event?
Artist’s impression of the time immediately after an impact event. A plume of vaporised water punctures the atmosphere into space. Source: http://www.sciencedaily.com/images/2009/04/090427010803.jpg
Where did it impact? - About Chicxulub
Shocked quartz is formed when immense pressures cause a deformation of the internal structure of a quartz crystal. Shoemaker discovered that it often formed in nuclear bomb testing sites. As impact events release comparable amounts of energy, finding shocked quartz in a crater strongly suggests that it was not formed by volcanic activity, as pressures in a volcano are not high enough to cause the deformation. Ample shocked quartz has been found at Chicxulub and the accompanying crash sites(Smit 2003), from this we can deduce that Chicxulub is not a geological formation.
Chicxulub [Nahuatl: “The Tail of the Devil”] Crater is an ancient impact crater buried underneath the Yucatan peninsula, with its center located approximately underneath the town of Chicxulub, Yucatán, Mexico. It is thought to be the impact site of the impactor which is believed to have contributed to the KT extinction.
A sample of Shocked Quartz found at Chixculub Shattered or "brecciated" rock Translated from Italian a breccia is “a stone made by cemented gravel” – which is exactly what they are. Though there are a many varieties of brecciated rock, such as types formed by geological processes, breccias formed by an impact event are quite distinct. They are layers of rock crushed together by compressive weight, exerted by the huge pressure of an impact event. This compressive deformation is similar to the process that creates shocked quartz. In the winter of 2001/2 The Chicxulub Scientific Drilling Project (CSDP), Mexico, dug up an area of impact melt and breccias in the Yax-1 borehole 100 m thick. (Kring et al. n.d.) Further evidence comes from gravitational and magnetic anomalies in the area. Gravitational anomalies on the earth’s surface suggest there are variances the local magnetic field caused by differences in the underlying mass of the earth. Such changes are deemed unnatural, as the geological processes that created the earth generally created a distribution of land uniform enough to result in a gravitational field with very little in the way of variety .One explanation for these anomalies could come from the idea that material has either been excavated or deposited by destructive intervention, such as an impact event.
Topographical image of the Chicxulub crater, showing local gravitational anomalies [note the blue]. Source: http://www.astro.uio.no/ita/nyheter/katastrofer_0901/chicxulb.gif
Evidence at Chicxulub There is a great deal of evidence that corroborates our theory that Chicxulub was formed by an immensely destructive impact event. Evidence for Chicxulub is also evidence for an impact event contributing to the extinction of the dinosaurs, as we know through detailed statistical modelling [and the occasional thermonuclear test] that any such impact would have disastrous consequences for life. Shocked Quartz
Ejecta Ejecta is the material released by an impact event. As an impactor strikes the earth’s surface, it displaces a certain amount of material, which is blasted out with great force and lands elsewhere, often far from the impact site. Due to the extreme conditions of an impact event, ejecta is often very noticeable, even far from it’s point of origin. Ejecta from Chixulub have been located in the Cayo District of central Belize, about 500 km southeast of the Chicxulub impact crater. (Ocampo et al. 2003) Multiple Impacts? The collision of Comet Shoemaker-Levy 9 with Jupiter in 1994 demonstrated that gravitational interference can fragment an impactor, allowing for multiple impacts over a period of a few days if the comet should collide with a planet. This scenario may have played out at the time of the KT boundary. Other craters of around the same age as Chicxulub have been discovered, all between latitudes 20°N and 70°N. They include the Silverpit crater in the United Kingdom, and the Boltysh crater in Ukraine. They are much smaller than Chicxulub but are
believed to have been have been caused by objects many tens of metres across striking the earth. This has led to the hypothesis that the Chicxulub impact may have been only one of several impacts that happened all around the time. In 1997, palaeontologist Sankar Chatterjee drew attention to a much larger 600 km (370 mi) Shiva crater, located in the Indian Ocean. Due to it’s monstrous size, it was tentatively suggested that this could have been an impactor in the KT scenario. However, there is currently argument in the astrogeological field as to whether Shiva was formed by an impact at all(Sankar). There is the possibility of more concurrent impacts, however any craters that might have formed in the Tethys Ocean would have been erased by tectonic events related to northward drift of Africa and India. More Proof – Rock Displacement, Shocked Quartz And The Iridium Anomaly Iridium is a transition metal which is extremely rare on the earth’s surface but common in asteroids. Iridium is rare on the earth’s surface as it often forms chemical bonds with iron, which as a heavy element, sinks to the earth’s core. Distributed through the material that makes up the KT layer there is an unusually high concentration of Iridium. This strongly suggests that an object with a high concentration of iridium impacted the earth with enough force to disperse the materials of which it was made all over the surface of the planet. This same iridium rich dust could have been responsible for the nuclear winter that blanketed the atmosphere and was so deadly to life. This layer is also very rich in soot.
Deccan Traps. Information points to the 600 meters (2000 feet) of lava pouring out of them in as little as 30,000 years. This is enough to have possibly released a climate-altering amount of sulphur gases, and is most probably a very significant contributor to the climate change that is thought to have occurred.(Geological Society Of America 2005) Additional evidence suggests that most of the Deccan Traps flood basalts were erupted in a <1 Million year interval which coincided with the K/T boundary. The global environmental effects from this volcanism could be similar to a large impact, such as global dimming due to particle release into the atmosphere. However, the timescale of the two processes would be different. The full consequences of an impact event may only take a few months to manifest, whereas the effects from volcanism would be spread over at least a few hundred thousand years. Therefore resolving these hypotheses requires estimating the duration of the K/T event. Unfortunately most chronological techniques do not have sufficient resolution to date geologically ‘instantaneous’ events The Deccan Traps could have caused extinction through several mechanisms, including the release of dust and sulfuric aerosols into the air which might have blocked sunlight and thereby reduced photosynthesis in plants. In addition, Deccan Trap volcanism might have resulted in carbon dioxide emissions which would have increased the greenhouse effect when the dust and aerosols cleared from the atmosphere.
“…it contains enough soot to correspond to burning down all of the forests of the world. This suggests that massive fires were touched off at the time of impact” (Hartmann n.d.). This soot evidence suggests forest fires of an unparalleled scale. Such a quantity of huge fires could have caused a large conversion of oxygen to carbon dioxide, and thrown up even more detritus into the sky. This would have the effect of making environmental conditions even more inhospitable. Air would harder to breathe, and declining light would result in falling temperatures and available light for plant photosynthesis. Further proof – Stone In Peculiar Places The Chicxulub impact [which impacted on water] would have caused a Tsunami that must have churned up billions of tonnes of sand from the coast and dumped it on the ocean bed. This became the sandstone and when the sea level fell, the rock was exposed. The work of Hildebrand, a graduate student at the University of Arizona, found that such sandstone deposits occur in many locations, but seem to be concentrated in the Caribbean basin. A Final Clue One of the largest pieces of evidence of environmental destruction from the KT period was a high concentration of fern spores. Ferns flourish whenever all other plants have been killed off by some environmental devastation. The spores are to be found well distributed on the geological KT boundary(Fleming & Nichols 1990). Alternative theories The event could be linked to a combination of causes, as many of these are linked. Environmental changes and the Deccan Traps. For about half a million years before the KT boundary, the world suffered a period of extremely destructive vulcanism. Vast areas of the surface where covered by molten lava. A million cubic kilometres of material spewed out in what are known as the
The Deccan Traps – notice the ridged surface, which geologists believe was caused by the layered accumulation of thousands of years worth of lava. Source: http://farm4.static.flickr.com/3185/2575165118_c8c6c29282_o.jpg
Disease Another, possibly far flung explanation has been linked to falling sea levels. As sea levels fell, more and more land bridges started to appear on the earth. The dinosaurs would have been able to cross these bridges into new territory, bringing their microbes with them. Millions of years of careful evolution would mean that the migrating dinosaurs where immune to these bacteria, whereas dinosaurs native to the regions they were colonizing were not. This could have resulted in a kind of unintentional biological warfare, in which the species native to the regions where assailed by bacteria which they had not time to evolve immunity against, similarly, dinosaurs migrating to these new regions would also be entering a territory full of microscopic enemies unknown to their immune systems . Although perhaps far flung, this bacterial invasion has actually been seen documented in humans. Around the time that Europeans first visited the new world it has been estimated that European disease wiped out 95 percent of America's preColumbian population(Diamond 1999) Orbital Variation Changes in the Earth's orbit that could have been responsible for climactic variations which contributed to a more hostile environment. In this scenario, the dinosaurs couldn't adapt to the cold, but the furry mammals could. This theory is consistent with the climate in the late Cretaceous; toward the end of this period,
there was a drop in sea level, causing land exposure on all continents,. From the upset of the global thermodynamic system came more variance in seasonal conditions, and greater extremes between equatorial and polar temperatures. As of yet proof is not abundant for this theory and it would be exceptionally hard to test this hypothesis using the fossil record. Conclusion – The Experts Speak It seems there is ample proof that an asteroid struck at the time of the KT boundary. There is also no doubt that this impactor was powerful enough to severely disrupt the ecology of the earth. What is called into question is the idea that this impact could be the sole cause of the extinction of so many species. Evidence suggests that other causes could have played their part. A gradually worsening environment caused by increased seismic activity in regions such as the Deccan Traps. Darwinian pressures, due to disruption introduced by innovative newly evolved species, such as small, devious mammals. Lastly, additional speculation coming from astronomical explanations such as variations in the earth’s orbit and gamma ray bursts could also bear some scientific weight, given time and a little more proof. Perhaps Chicxulub was the finishing blow to a dying species? Jan Smit, Professor of Event Stratigraphy at the University of Amsterdam and an acknowledged expert on sedimentology, writes on his personal website; SMIT: “there is evidence for a decline of some of the biotic groups becoming extinct at or near the KT boundary, but decline is on different timescales, and attributable to various non-impact related causes (cooling, Deccan traps). There is little doubt however, that the mass- and final extinctions all occur very close to and at the KT boundary, suggesting a cause and effect relationship with the Chicxulub impact. These effects, despite almost two decades of research, are still poorly understood”(Smit n.d.). ARCHIBALD: “Six million years prior to the KT boundary there were about twenty species of ammonites in the world's oceans. Three million years before the KT boundary there were only fifteen or so and one million years prior to the KT boundary we have less than half of what we started out with, we have less than ten species so the extinction event has already been going on for millions of years. We see the same pattern in the fish record, in the terrestrial reptile record, even in the mammal record. All of these groups were undergoing an extinction event for millions of years and it would be absolutely amazing to me if dinosaurs weren't undergoing.. the same sort of long term extinction…Clearly dinosaurs were incredibly unlucky at the end of the Cretaceous to have all three things happen at the same time.” So we have established that the KT boundary is not a single point in time, and is instead a period with a length not yet agreed upon by scientific consensus. We must make a distinction between the KT impact event and the KT extinction, as evidence suggests they are not mutually exclusive. The KT impact event is clearly a contributor to the KT extinction, but cannot be deemed the sole cause. Lastly, as our evidence from this time is sparse and relies on the fossil record, which is incomplete at best, we cannot draw any certain conclusions. We can only offer more hypotheses and hope that in the coming years, additional improvements to the fossil record will give us a better picture of what was happening at the time. – Jack Oughton Bibliography) Diamond, J., 1999. Guns, Germs, and Steel: The Fates of Human Societies (Paperback) 1st ed., W. W. Norton & Company. Fleming, R. & Nichols, D.J., 1990. The fern-spore abundance anomaly at the Cretaceous-Tertiary boundary: A regional bioevent in western North America. In Extinction Events In Earth History. Springer Berlin / Heidelberg, pp. 347-349. Geological Society Of America, 2005. India's Smoking Gun: Dino-killing Eruptions. Sciencedaily.com. Available at: http://www.sciencedaily.com/releases/2005/08/050810130729.htm [Accessed March 2, 2010]. Goldberg, C., Unique Facts about Mexico: Chicxulub Crater. Sheppard Software. Available at: http://www.sheppardsoftware.com/Mexicoweb/factfile/Unique-facts-Mexico4.htm
[Accessed February 22, 2010]. Hartmann, W.K., The KT-boundary Impact. The Impact That Wiped Out The Dinosaurs. Available at: http://www.psi.edu/projects/ktimpact/ktimpact.html [Accessed March 2, 2010]. Images-Of-Elements.com, Hi-Res Images of Iridium. Images Of Elements. Available at: http://images-ofelements.com/iridium.php#a [Accessed February 22, 2010]. Kring, D.A. et al., Impact lithologies and their emplacement in the Chicxulub impact crater: Initial results from the Chicxulub Scientific Drilling Project, Yaxcopoil, Mexico. Meteoritics & Planetary Science, 39, 879-897. Mukhopadhyay, S., KT impact. Welcome to the Noble Gas Laboratory. Available at: http://www.people.fas.harvard.edu/~mukhop/KT.htm [Accessed February 27, 2010]. Ocampo, A. et al., 2003. New Location of Chicxulub's Impact Ejecta in Central Belize. Sankar, C., Multiple Impacts at the KT Boundary and the Death of the Dinosaurs. Journal of Geodynamics, 31-54. Smit, J., 2003. (7) CHICXULUB IMPACT CRATER AND THE K/T MASS EXTINCTION, REVISITED. Available at: http://www.geo.vu.nl/~smit. Smit, J., Global mass-extinction at the KT boundary. Space Telescope European Co-ordinating facility. Available at: http://www.stecf.org/~ralbrech/amico/intabs/smitj.html [Accessed February 28, 2010]. Strahan, D., 2004. BBC Horizon: What Really Killed The DInsoaurs? BBC: Horizon - What Really Killed The DInosaurs? Trexler, D., 2000. Dinosaur Treks - Extinction Theories. Thinkquest.org. Available at: http://library.thinkquest.org/C005824/extinction.html [Accessed February 22, 2010].