What killed the mammoths? Near the end of the last ice age 13,000 years ago, these mighty beasts disappeared from North America together with some 35 other groups of mammals, including giant ground sloths, saber-tooth cats, and American lions. For four decades, debate has raged over the cause of their abrupt demise. In Last Extinction, NOVA presents an exclusive in-depth investigation of a bold and controversial new hypothesis, which suggests that a massive impact from space could be the culprit. According to the theory, an incoming comet broke up over North America in a devastating series of explosions, causing widespread forest fires and wiping out plants, animals, and prehistoric people. The evidence comes from a mysterious black mat layer discovered at more that fifty sites across the continent. The black mat contains exotic materials including rare microscopic nanodiamonds that are claimed to be the signature of an extraterrestrial impact. But other scholars question the evidence