The session PP33B. Younger Dryas Boundary: Extraterrestrial Impact or Not? II was standing room only.
The question: What caused the thousand plus year Younger Dryas cold snap that likely killed off the mammoths, saber-toothed cats, and other iconic ice-aged creatures ~12,000 years ago?
In one corner were those who believe that impact from a swarm of comets caused the cooling event. In the other: the skeptics.
Wallace Broecker of the Lamont-Doherty Earth Observatory started the talk out with fighting words: “As far as a comet goes, I never believed it.” He claimed that the only evidence for a blast from outer space is the presence of nano-sized diamonds in the layer of sediment from that time period, and those don’t even prove impact.
Allen West of GeoScience Consulting led the pro-impact camp. He and his colleagues rocked the field when they published a paper in 2007 and another in 2009 suggesting the idea. He argued that the nanodiamonds are, in fact, proof of a major bang, since no other situation could produce the anaerobic conditions and the pressures and temperatures to make them