There was an interesting paper given at the American Geophysical Union meetings in Mexico last week that argued that there is evidence that a comet exploded over the Laurentide ice sheet in the central plains of Canada near the Great Lakes about 12,900 years ago. Apparently, there's no crater (Canada was covered by a glacier at the time and there may not have been an impact), but areas which have a thick carbon mat, the presence of an abundance of iridium, and glass-like carbon deposits have been found all over the North American continent.

Researchers argue that the theory explains why the Murray Springs site in Arizona has a thick carbon mat, a deposit similar in age and context to ones seen at other Paleoindian sites such as Lindenmeier (Colorado), Hell Gap (Wyoming), and Lange-Ferguson (South Dakota). The radiocarbon dates on the mat are uniformly about 10,800 +/- 200.

What the affect a near-impact of a comet might have had on the Clovis people living on the North American continent at the time could have included a wide dispersal of small bands of survivors, which certainly describes Clovis settlement patterns. Should be an interesting discussion around this issue.

• Catastrophic Comet Chilled and Killed Ice Age Beasts, Live Science
• Murray Springs, Arizona, a site description and sources
• Clovis