Watch "Last Extinction" Online

After screening on PBS in America in March, the 1 hour documentary "Last Extinction" is now available for viewing online:
http://www.pbs.org/wgbh/nova/clovis/program.html

The doco investigates the possibility of a comet causing widespread large mammal extinctions 12,900 years ago. Currently the most academically accepted theory is that migrating humans hunted the megafauna to extinction. However recently discovered evidence suggests that a comet may have struck at that time:

• Earth's temperature, according to geologic records, dropped 18 degrees in two years
• Scientists found iridium, rarely found on earth, in elevated levels across Northern America. Iridium is often an indicator of meteors and comets, and was also found in the layer correlating with the extinction of the dinosaurs 65 million years ago.
• Found alongside the iridium were hexagonally shaped microscopic diamonds, which don’t occur naturally on earth

All that stops this theory from becoming scientific fact is the lack of a crater, (although this hasn't been the case with Tunguska...). The show suggests that either the comet broke up into thousands of small pieces - Carolina Bays anyone?, or struck a glacier, which acted as a bullet-proof vest.