The NOVA program "Megabeasts' Sudden Death" aired Tuesday February 23, 2010 on PBS, and is now available online.  To start the video on the PBS site, click the mammoth picture.

Fifteen thousand years ago, North America was like the Serengeti on steroids, with mega-creatures roaming a continent teeming with incredible wildlife. But then, in a blip of geologic time, between 15 and 35 magnificent large types of animals went extinct. In this television exclusive, NOVA joins forces with prominent scientists to test a startling hypothesis that may finally explain these sudden and widespread extinctions—that a comet broke apart in the atmosphere and devastated North America 12,900 years ago.

Follow the heated, decades-long controversy over North America's Ice Age extinctions, and more on the program's companion website.

Watch the program online now.