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Asteroid killed 90 percent of life on earth millions of years ago

ATLANTA (CNN) -- Before the dinosaurs were wiped out 65 million years ago, there was an even more devastating event millions of years before which wiped out 90 percent of life on earth, scientists said.

In a report in the journal "Science," researchers said 250 million years ago, before the dinosaurs existed, an asteroid four to eight miles across slammed into earth with the force of more than a million earthquakes. That impact caused volcanic eruptions that buried much of the earth in lava and kicked up so much dust and ash it blocked the sun's rays. The result was a dark and cold earth, which could no longer support most of the life on it, including cockroach-like creatures called trilobites.

"This is probably the most famous type of animal that existed in the Paleozoic era" said Richard Bambach of Virginia Tech, who added that the trilobites went "completely extinct."

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Ninety percent of the 15,000 species on earth became extinct in the aftermath, including shellfish and coral. Fish fared better than most, Bambach said.

"These very active animals actually made it through with only 40 percent rather than 90 percent extinction," he said.

No one knows where this asteroid hit. The one that scientists say caused the extinction of the dinosaurs hit in the Yucatan Peninsula in Mexico. Another smaller asteroid left a crater in Arizona.

Does this mean it could happen again? If so, when? Not to worry, scientists say. They calculate an asteroid hits earth every million years or so. We know where the big ones are and even if a smaller one was coming at us we'd get plenty of notice, said Chris Chyba of Stanford University.

"We would almost have decades, if not centuries, to go before that impact would happen so we would have a long time to think about what to do about it," he said.

Scientists discovered the earlier, devastating extinction event by digging deep into the earth's core. They found gases which are normally only found in outer space, trapped in carbon molecules called buckminsterfullerenes, or buckyballs.

Scientists say those alien gases rode in on a speeding asteroid and even though the devastating impact destroyed life, it paved the way for the dinosaur era 25 million years later.



RELATED STORIES:
Report: Asteroid storm pounded Earth, moon as life formed
December 7, 2000
Fossilized dinosaur heart rocks paleontology
May 11, 2000
U.S. biodiversity in jeopardy, study shows
March 17,2000

RELATED SITES:
Global Change Home Page
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