Rich Firestone a nuclear expert, has been working for years now on the hypethesis that the North American megafauna (mastodons, woolly mammoths etc) went extinct due to a supernova. He presented this idea on two recent congresses so it's getting some media coverage now: http://weblog.physorg.com/news3399.html http://www.lbl.gov/Science-Articles/Archive/NSD-mammoth-extinction.html I'm familiar with evidence. It's there. One element in particular is striking, the unexplained atmospheric radio-active carbon14 spikes in those periods (the last one actually 12,770 years ago) suggesting that something indeed was going on. We have discussed some of this briefly here but Vela-X does not seem the correct candidate. My questions: What would our experts think of his mechanism? Is there a known supernova that matches the dates and that could be close enough for all this? Isn't that radio-active comet a bit fast? covering 250 LJ in 28,000 years? or was it *less than* 250LJ perhaps? *** Off the record, the continental Siberian mammoths seemed totally unaffected by the 13,000 years event and continued to thrive at least another 1700 years, the oldest dated fossils being around 11,200 calendar years. After that a relict population survived on Wrangel island until some 4000 calender years ago.