May 2007
Geological evidence suggests that a 5km-diameter meteor may have exploded over North America around 13,000 years ago. This could explain the disappearance of several species of mammal around that time, including North American camels and the sabre-tooth tiger. Nature news item including impressive picture (subscription needed to get past abstract), BBC article.
The basis of the article on the bbc site is a mass extinction and a layer of charcoal that is attributed to a meteorite event 13000 years ago.
Yet another mass extinction that had nothing to do with modern humans turning up, killing everything in sight and setting the place on fire then?
Nice idea, but almost certainly not. Although the exact date of our arrival in North America is still a matter of dispute, it was probably around 11,000 years ago…