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Theory of dinosaur extinction questioned
Much of the evidence points to the idea that an asteroid or comet collided with the Earth around 65 million years ago, triggering climate changes that eventually wiped out the dinosaurs. When the mostly hidden underwater crater was found off Yucatan, it seemed scientists had found the cause of the extinction that wiped out over 75 per cent of life on Earth.
"Since the early 1990s the Chicxulub crater on Yucatan, Mexico, has been hailed as the smoking gun that proves the hypothesis that an asteroid killed the dinosaurs and caused the mass extinction of many other organisms at the Cretaceous-Tertiary (K-T) boundary 65 million years ago," the researchers write in this week's issue of the Proceedings of the National Academy of Sciences.
Although a core drilled out of the middle of the crater suggests it dates back more than 300,000 years before the K-T boundary and "thus did not cause the end-Cretaceous mass extinction as commonly believed." The researchers studied a sample that extends over one kilometre below the current surface, in the middle of the more than 100 kilometre wide crater.
Other samples have included tiny pieces of glass-like rock that could have been melted during an asteroid impact, which seem to date back to the 65-million-year point, give or take a few hundred thousand years. But their core sample showed fossils that suggest the crater was blasted out 300,000 years before the K-T boundary. Magnetic evidence also suggests it is older than previously believed.
This finding would support an alternative theory that the dinosaurs and other forms of life were wiped out in a series of disasters that changed the Earth's climate. Although other craters dating to around this time are not big enough to have caused world-altering changes by themselves.
Any collision would have hit at the same time as a busy period of volcanic activity known as Deccan volcanism, North India, where a massive amount of molten material surged up from near the Earth's core. They would have brought vast amounts of carbon gases to Earth's surface, causing a warming effect that would have wiped out many species of plants and animals.
More info: Reuters
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