A comet impact didn't set off a 1,300-year cold snap that wiped out most life in North America about 12,900 years ago, scientists say. Though no one disputes the frigid period, more and more researchers have been unable to confirm a 2007 finding that says a collision triggered the change, known as the Younger Dryas. The drop in temperature, plus fires from the impact, wiped out sabertooths, mastodons, and other giant animals, and may have caused the decline of an early civilization. (source: news.nationalgeographic.com)
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