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A Comet, Not An Asteroid, Killed The Dinosaurs, New Study Suggests

Mar 22, 2013 10:55 AM EDT

Scientists have presented new evidence suggesting that it was likely a speeding comet - not an asteroid - that sent the dinosaurs to extinction some 65 million years ago.

The findings come from new geochemistry testing of the Chicxulub crater on the Yucatan Peninsula in Mexico, which analyzed levels of iridium and osmium.

The widely accepted belief that the impact of an extraterrestrial object caused an extinction event goes unchallenged, but the levels of iridium unleashed by the rock are lower than previous believed, the research concluded.

Lower levels of iridium suggest a smaller body hit Earth, so to account for the 125-mile-wide Chicxulub crater, the smaller space rock must have been traveling very fast, prompting the research team to conclude that a long-period comet was the most likely candidate.

"You'd need an asteroid of about [three miles] diameter to contribute that much iridium and osmium. But an asteroid that size would not make a [125 mile]-diameter crater," said Jason Moore, a researcher from Dartmouth College, according to BBC News.

"So we said: how do we get something that has enough energy to generate that size of crater, but has much less rocky material? That brings us to comets."

Long-period comets can take hundreds, thousands or in some cases millions of years to complete one orbit around the Sun.

However not everybody in the scientific community is onboard with Moore's proposal.

Dr. Gareth Collins, a researcher of impact cratering at Imperial College London, praised the teams work, but questioned their conclusion, the BBC reported.

"I don't think it is possible to accurately determine the impactor size from geochemistry," he said.

"The authors suggest that 75 percent of the impactor mass is distributed globally, and hence arrive at quite a small-sized impactor, but in reality this fraction could be lower than 20 percent," he said, which would still allow the possibility of the extinction event being caused by an asteroid.

Details of Moore and colleagues'' findings were detailed at the 44th Lunar and Planetary Science Conference in The Woodlands, Texas. 

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