Supernova

An interesting new- ish theory on mammoth extinction can be seen here. A supernova caused what are carefully being called "comet- like" events about 13,000 years ago, may have wiped out most of the mammoths, leaving traces in their tusks.

This would be a rather local, that is, North American, event, not resposible (probably) for all Pleistocene extinctions. It also might have had an impact on early American humans:

"In addition to the tusk evidence, the scientists said arrowheads from North America's prehistoric Clovis culture, which went extinct around 13,500-13,000 years ago, Icelandic marine sediment, as well as sediment from nine 13,000-year-old sites in North America, contain higher-than-normal amounts of radiation in the form of potassium-40 levels."

I have a notion that a similar theory was proposed a few years ago, but cannot find a thing. Reader info would be welcome!