ScienceNow, Nature, BBC, etc: Comet as N. America mammoth killer takes a heavy impact – some say the idea is now deader than a ground sloth. R.I.P.
A few years ago researchers, with intriguing if not uniformly solid evidence, told a big AGU meeting that maybe the great die-off in North American megafauna 13,000 years ago or so was because a comet (maybe asteroid) slammed into Canada’s Laurentide ice sheet. They cited indirect evidence including shocked minerals, signs of second-splash elongated crater-like things elsewhere in N. America, and even – this was far fetched – mammoth tusks that appeared riddled with tiny blemishes as though shotgunned with debris from an exploded bolide.
I have to admit rooting for the hypothesis, even while thinking it was too fine a yarn to be anything more than a yearn. Put “comet mammoth” in this site’s search box and see how often we’ve tracked the story’s peregrination. It’s been chipped away over the years. Adherents have gamely gathered more evidence to counter doubts. In this last weekend’s Proceedings of the National Academy of Sciences came a heavy blow against the killer comet. It concluded that one of the pro-comet arguments, that nanodiamonds scattered in sediments from the time could only mean something had mightily pummeled the crust, had one flaw. They’re not nanodiamonds, just some carbon sheet bits mistaken for them.
Proponents say it’s not over yet. Several news reporters spell out the state of play:
Stories:
- AAAS ScienceNow – Richard Kerr: Mammoth-Killer Impact Rejected ;
- NatureNews – Rex Dalton: Comet theory carbonized ;
- BBC – Jonathan Amos: Mammoth-killing space blast ‘off the hook’
- CBS News – Charles Cooper: Comet Impact Refuted as Cause for Mammoths’ Extinction;
Grist for the Mill: Washington Univ.- St. Louis Press Release ;
