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| Tuesday, 20 July 2004 |
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When the world burned 65 million years ago by Derrick Schokman By now it is fairly well known that the impact of a cometor asteroid on planet earth 65 million years ago resulted in the extinction of the dinosaurs and more than 75 percent of plant and animal species. Science sometimes overwhelms science fiction in its capacity to startle and amaze. Such is the case for this impact as scientists describe what it could have looked like. So Huge This space intruder is said to have flashed through the sky at more than 40 times the speed of sound. It was so huge that when its leading edge made contact with the earth, its trailing edge was at least as high as the cruising altitude of a cruising airliner. The impact occurred in a shallow sea just south of the present North America when the continental drift was still in progress. It produced an explosion said to be equivalent to 1000 trillion tons of TNT, lofting rocky molten debris in vapourised form into the atmosphere, moving at speeds of 7000-40,000 kph and producing a fireworks display like trillions of meteors. The remains of that explosion lies below the tropical forest of Yucatan, the Maya ruins of Mayapan, the seaport village of Progreso and the Gulf of Mexico. The Chicxulub crater in Yucatan at the point of the impact is 180km in diameter, surrounded by a circular fault 240km across. Wildfires Under the influence of gravity the debris had to fall back to earth but not before it had severely heated the atmosphere and ignited wildfires. The two worst affected areas were the Chicxulub region and its antipode India farthest away on the opposite side, making it a focal point for debris. From these regions the fires spread to the south and central areas of North America, Central South America, Central Africa and S.E. Asia as the earth rotated below in a hail of re-entering debris. Studies suggest that plant and animal species were not immediately and directly lulled, but rather by a variety of severe and complex environmental conditions which spread the devastation worldwide. The fires wiped out critical habitats and produced severe air pollution. Soot and impact generated dust choked the sky over the whole planet, making it impenetrable to sunlight. Photosynthetic plants died and food chains collapsed. This phase of the aftermath of the impact has been likened to a "nuclear winter", a cold spell that some scientists have thought might follow a nuclear war. Billions of tons of carbon monoxide, carbon dioxide and methane were also released into the atmosphere. As a result the cold spell was followed by an interval of global warming. Some scientists believe that the amount of carbon in the atmosphere after the cataclysm would have been equivalent to 3,000 years of burning fossil fuels. The fires are also said to have produced debilitating gases like bromine and chlorine which helped destroy the ozone layer. Nitric acid and sulphuric acid rains compounded the total effect of climate change. Thin layer Geologically the imprint of that cataclysm may be seen in rocky outcrops in western USA, southernmost Europe and elsewhere. An especially good location is in the Raton Basin in Colorado and New Mexico. It is a thin layer of clay, one centimetre thick, sandwiched between the rocky layers of the Cretaceous and Tertiary periods. Analysis of th is clay had shown microscopic particles of soot - spherical particles of carbon clustered like grapes, with a composition that matches smoke from forest fires. It is the debris of that almighty collision. Globally the soot amounts to nearly 70 billion tons of residue. Recovery Fortunately not all areas on earth were devastated by this conflagration and its aftermath. In northernmost North America and Europe, where the heat was less intense, swamps and swamp margins afforded plenty of protection and began the long recovery. Ferns and algae were the first plant species to repopulate the planet. Followed by hardy shrubs and flowering plants until the forest canopy was replaced. The time taken for recovery is not known - it could have been several thousands of years. The impact also opened up niches for mammalian-evolution. Mammals who had lived like little moles in the undergrowth before, now had the opportunity to develop and evolve into our own species. "In this sense," said David Tring, one of a team of scientists, who identified the chicxulub point of impact, "the chicxulub crater could be considered the crucible of human evolution." The destruction of one world made way for another new one. |
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