Scientists say comet triggered extinctions

LOS ANGELES, Jan. 2 (UPI) -- A comet struck North America 13,000 years ago, triggering massive flooding and fires followed by a short ice age, researchers said Friday.

The team led by Douglas Kennett, an archaeologist, said its discovery of nanodiamonds -- diamonds visible only under a microscope -- associated with a layer of black soil containing burned debris shows that a comet was the cause, the Los Angeles Times reported.

"There's no other way we can interpret the presence of these diamonds other than an extraterrestrial impact," said James Kennett, a paleo-oceanographer and Douglas Kennett's father.

At least 35 species of large animals -- including mammoths and mastodons, the short-faced bear and the American camel -- became extinct during the 1,300-year cold spell known as the Younger Dryas. The research team said at least 15 of the extinctions were within a century of the comet impact.

In a paper published in the journal Science, the researchers said the series of cataclysms also caused a sharp drop in the human population of North America.

Some other scientists have questioned the findings, suggesting that the team has not yet proved its discovery of nanodiamonds.