16 December 2009
Dukin’ out the Younger Dryas Boundary
Posted by Michael McFadden
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.
Still, there’s a nagging problem: if something slammed into Earth that was big enough to set off more than a millennium of cooling, then where’s the crater?
Pete Schultz of Brown Unviersity suggested that the absence of crater evidence was not necessarily evidence of an impact’s absence. Perhaps a thick layer of ice covered the impact site, and the ice absorbed some of the impact. Then, when the glaciers melted, they washed away all the evidence.
Or maybe it wasn’t a traditional impact at all. Instead, could the high pressures surrounding a meteor hurtling towards earth create microdiamonds? No way, said H. J. Melosh. Could these air bursts create nanodiamonds? Maybe, but then they aren’t proof of impact.
In the end, I wasn’t sure that anyone had delivered a knockout piece of evidence to convince the other side. But it sure was a good show.
-Tia Ghose, UC Santa Cruz Science Communication Graduate Student
Social comments and analytics for this post…
This post was mentioned on Twitter by theAGU: Scientists at #AGU09 battle over whether Younger Dryas was caused by an impact. See http://bit.ly/7NbRsx…
As a rank amateur, I’ve been reporting finding evidence via Google Earth and Maps and direct on the ground exploration for many fractal fields of round, oval, and irregular shallow craters — especially easy to find on dry plateaus above 1 km. I also find what seem to be black or white mineral coatings on target rocks that appear to have been deposited by high temperature blasts. Target rocks are cracked, fragmented, tumbled, and tossed widely over local area, but don’t seem to have been melted or vaporized. ——-
exact Carolina Bay crater locations, RB Firestone, A West, et al, two YD reviews, 2008 June, 2009 Nov, also 3 upcoming abstracts: Rich Murray 2009.11.14 http://rmforall.blogspot.com/2009_11_01_archive.htm Saturday, November 14, 2009 http://groups.yahoo.com/group/astrodeep/message/31 ——-
nanodiamond evidence for 12,900 BP Clovis extinction impact, Santa Rosa Island, discussion on Scientific American website, Carolina Bay type craters east of Las Vegas, NM: Rich Murray 2009.09.15 http://rmforall.blogspot.com/2009_06_01_archive.htm Friday, July 24, 2009 http://groups.yahoo.com/group/AstroDeep/28 ——-
widespread Carolina Bay type craters from Clovis comet 12,900 Ya BP? — 0.7 M long NS crater with fractured red sandstone on SW rim, CR C 53A, 20 miles E of Las Vegas, NM: Rich Murray 2009.06.08 http://rmforall.blogspot.com/2009_06_01_archive.htm Monday, June 8, 2009 http://groups.yahoo.com/group/AstroDeep/27 ——-
Rich Murray, MA Boston University Graduate School 1967 psychology, BS MIT 1964, history and physics, 1943 Otowi Road, Santa Fe, New Mexico 87505 505-501-2298 [email protected] http://groups.yahoo.com/group/AstroDeep/messages