for National Geographic News
A collision between two asteroids somewhere beyond the orbit of Mars set in motion the chain of events that led to the extermination of the dinosaurs, a new study suggests.
The crash showered the inner solar system with fragments of rock, doubling the rate of asteroid impacts on Earth, the moon, and Mars for many millions of years.
One of those giant fragments may have been the K-T impactor, which marks the boundary between the Cretaceous and Tertiary geologic periods.
That asteroid, which hit what is now Mexico's Yucatán Peninsula 65 million years ago, is widely believed to have wiped out the dinosaurs.
(Related: "Single Asteroid Impact, Not Two, Killed Dinos, Study Says" [November 30, 2006].)
Another fragment appears to have hit the moon, creating Tycho Crater, a dramatic feature that Apollo astronaut studies determined was formed 110 million years ago.
The study will appear in tomorrow's edition of the journal Nature.
The new discovery was an accident, said study leader William Bottke of the Southwest Research Institute in Boulder, Colorado.
"We didn't actually set about to track down the K-T impactor," Bottke said.
Rather, his team of U.S. and Czech scientists stumbled onto the find while studying a group of asteroids called the Baptistina family.
By studying the Baptistina asteroids' orbits, Bottke's team concluded that the group was formed in a collision about 160 million years ago.
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