Ice Age 3: The Killer Comet

These days, it seems as if everything is being blamed on astronomical impacts--the extinction of the dinosaurs 65 million years ago, the potential extinction of the human race 10 (or 100, or 10,000) years from now, and (now) the prolongation of the last Ice Age, which wiped out the mammoths as well as the ancient North American Clovis civilization.

According to a new study by researchers at the University of Cincinnati, the earth was just climbing out of its most recent Ice Age 13,000 years ago when a massive comet impact over Canada threw enough dust and ash into the air to block out the sun (and thus lower worldwide temperatures) for another couple of thousand years. The comet is estimated to have been a full mile in diameter, and it would have exploded high up in the atmosphere--which explains the lack of a telltale crater.