Whodunnit?

There's a television programme called Cold Case, where unsolved crimes are re-examined in the light of new evidence. I think. I haven't seen it. What was I going to say? Oh, yes. The case of the dead elephants. There are a number of ideas as to the demise of the mammoths, mastodons and other exciting megafauna of North America about 13,000 years back. You know - when all this was fields. At the same time, a paleo-Indian people known as Clovis, famous for their stone spear points, seem to die out. The demise of the big, hairy animals and the spear-toting man would appear closely linked.

Well, three years ago a nuclear scientist, Richard Firestone, and geologist Allen West published a paper suggesting a supernova explosion some 41,000 years ago fired out a series of comet-like missiles, one of which piled into North America around 28,000 years later (that's about 13,000 years ago, to save you the maths). Aha - a suspect. The story went that initially there had been an early shockwave, 34,000 years ago, of tiny, hot, radioactive, magnetic iron-rich lumps from the supernova which had hit earth and caused considerable misery. Famously, three mammoth tusks found in Siberia and Alaska were pitted with flecks of what's thought to be this early supernova grit. Secondly, the impact of the comet at the 13,000 year-ago point had an immediate and severe effect on the wildlife, particularly anything right underneath. Then thirdly the landing created a series of wildfires that spread across the continent burning up all the vegetation and generally roasting stuff. Firestone and West proposed the extent of these fires was sufficient to eventually result in the extinction of the missing North American megafauna and the Clovis culture.

These claims were received with a degree of scepticism and recent research published in the Proceedings of the National Academy of Sciences lays out a number of concerns. There is evidence enough to support the meteorite impact, and there are certainly signs of large-scale fires at around the right time. What's dubious is the sweeping nature of the hypothesis. It seems very unlikely to me that such wildfires would be quite so all-pervasive and apocalyptic. I'm sure populations took a big hit but people, plants and animals usually find a way through things one way or another. So - was the death of the mammoths down to a big space explosion? Verdict - not guilty. Not completely. Aren't I decisive?