The Comet that Destroyed AmericaS

Dinosaurs may not have been Earth's only creatures to face extinction from above. A team of researchers has found evidence that suggests a comet once hit North America, taking the continent's mammals down with it.

Researchers reported this week in Proceedings of the National Academy of Sciences that they found have found shock-synthesized diamonds — known to result from impact events — in the Arlington Canyon on Santa Rosa Island in California, and have previously found similar diamonds in the Greenland Ice Sheet. The placement of the Arlington Canyon diamonds coincide with North America's oldest known human remains — from the Clovis people, who went extinct nearly 13,000 years ago — and the disappearance of the pygmy mammoth from Santa Rosa. This fits with the team's earlier speculation that a comet strike led to a mass mammalian extinction across North America:

In 2007 researchers theorized that a comet set off continental fires that led to the mysterious disappearance of the Clovis people and the extermination of 35 mammal genera, including mammoths, mastodons, ground sloths and camels. The team documented a "black mat" of charcoal throughout North America that contains high levels of iridium, magnetic spheres, and nano-diamonds, which are consistent with such an airburst.

However, the hypothesis remains controversial, and other geologists and archeologists are reluctant to buy the diamonds as evidence of a comet-induced die-off, especially given the absence of an impact crater.

Did a Comet Cause a North American Die-Off around 13,000 Years Ago? [Scientific American]