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New Extinction Clues Point to Deep Impact
by Paul Recer
May 10, 2001
New evidence shows that an extinction event in which more than half of all Earth species died 200 million years ago happened quickly, possibly as a result of an impact from outer space. The extinction, at the boundary of the Triassic and Jurassic periods of geologic history, is similar in its suddenness to two extinction events that have been linked to space rocks' impacts on the Earth. Researchers analyzing deposits from a rock formation on a remote beach front in Canada found evidence of a sharp shift in organic carbon levels at precisely the point in time that the Triassic-Jurassic extinction occurred. This is the first time scientists have found a clear carbon signature for what is called the TJ event, said Peter D. Ward, a researcher at the University of Washington... Similar evidence has been found for the Cretaceous-Tertiary extinction event 65 million years ago that killed off the dinosaurs, and for the much earlier Permian extinction 250 million years ago that killed 90 percent of all species... If the researchers find evidence that a space rock impact caused the TJ extinction, it will mean that three of the five major extinctions in the 4.5-billion-year history of the Earth are linked to the impact of asteroids or comets... Ward said that no impact crater on Earth has been shown to have a proven link to the TJ extinction event, although the Manicougan Crater in Quebec is considered a candidate. That crater was caused by a space impact, but it has been dated at 214 million years, well before the TJ event.