Comets, Climate Change, and Extinctions—2

 

by Emil Morhardt

When a large meteorite struck the earth 65 million years ago, it killed off the dinosaurs by abrupt climate change; the energy of the strike sharply raised global temperatures, ignited massive wildfires, and filled the atmosphere both with smoke from the fires and dust ejected from the crater which presumably prevented plants from thriving for a long enough time to starve all but the smallest animals (allowing, as it happened, the evolution of humans.) That’s a different cause of climate change than now, and most of us, if we worry about climate change at all, don’t much worry about it being caused by another meteorite strike. But, on August 16, I wrote about a paper published in 2007 that proposed a similar, though not so severe, extraterrestrial impact and abrupt climate change about 12,800 years ago—the initiation of the Younger Dryas (YD) cooling episode that stopped the

recovery from the last glacial maximum in its tracks for a thousand years, and probably killed off the North American megafauna. The ensuing discussions, like those following the discovery of the meteorite strike that killed the dinosaurs, have been highly contentious, with a great many papers, both supporting and refuting the claim. The latest volley in that round was just pre-published on August 26 in The Journal of Geology (Kinzie et al., 2014), and seems fairly convincing to me: nano-diamonds (and we’re really talking nano here—diamond-like objects no bigger than 0.003 millimeters in diameter, one tenth the diameter of the finest human hair) found at 24 locations across the US and Europe, all statistically in exactly the time period of the Younger-Dryas Boundary (YDB), the year, or year-and-a-half it took to reverse the global warming that was then taking place. If the 26 authors from research institutions throughout the strike zone are correct, these nano-diamonds could only have come from a cosmic impact.

Why should we care? Aside from the fact that this is a fascinating science detective story with two heavily entrenched points of view, one of which will eventually prevail, the incident suggests that the relative stability of the climate, which we are only recently beginning to question, may be illusory. There may be many potential tipping points, and many sources of tipping. Increasing atmospheric CO2 levels might also lead to abrupt changes, maybe through mechanisms similar to those triggered by the presumed YDB comet—a release of freshwater into the North Sea sufficient to stop the Gulf Stream (and the associated global ocean currents), radically altering regional global temperatures. In any case there is a rich and interesting scientific literature here, and there will soon be papers refuting the one that is the subject of this post…stay tuned.

Charles R. Kinzie, Shane S. Que Hee, Adrienne Stich, Kevin A. Tague, Chris Mercer, Joshua J. Razink, Douglas J. Kennett, Paul S. DeCarli, Ted E. Bunch, James H. Wittke, Isabel Israde-Alcántara, James L. Bischoff, Albert C. Goodyear, Kenneth B. Tankersley, David R. Kimbel, Brendan J. Culleton, Jon M. Erlandson, Thomas W. Stafford, Johan B. Kloosterman, Andrew M. T. Moore, Richard B. Firestone, J. E. Aura Tortosa, J. F. Jordá Pardo, Allen West, James P. Kennett and Wendy S. Wolbach. Nanodiamond-Rich Layer across Three Continents Consistent with Major Cosmic Impact at 12,800 Cal BP.

Published Online August 26, 2014. The Journal of Geology. Full paper at: http://www.jstor.org/stable/10.1086/677046

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