In May 2008, a scientific team made worldwide headlines by announcing evidence of a previously unsuspected impact from space that had devastated prehistoric North America at the end of the last Ice Age. According to this controversial new claim, the extinction of more than 34 types of large prehistoric animals (or "megafauna") was caused not by climate change or the arrival of the first human hunters, but by the massive breakup of a comet over the Great Lakes region. NOVA explores this provocative new theory about what killed off America's mammoths and may have come close to extinguishing early human populations as well.

Note: Originally titled "Last Extinction"