Posted on | December 11, 2009 | 1 Comment
Mānoa Graduate Assistant François Paquay led an international team of researchers, including Associate Professor Gregory Ravizza, that has found no evidence supporting an extraterrestrial impact event at the onset of the Younger Dryas (approximately 13,000 years ago). The results were published in the online edition of the Proceedings of the National Academy of Sciences.
The Younger Dryas is an abrupt cooling event in Earth’s history. It coincided with the extinction of many large mammals including the woolly mammoth, the saber toothed jaguar and many sloths. This cooling period is generally considered to be the result of the complex global climate system, possibly spurred on by a reduction or slowdown of the thermohaline circulation in North America.
This paradigm was challenged two years ago by a group of researchers that reported finding high iridium concentrations in terrestrial sediments dated during this time period, which led them to theorize that an impact event was instead the instigator of this climate shift. Paquay’s team also investigated this theory but not only were they unable to replicate the results found by the other researchers, but additional lines of evidence failed to support an impact theory for the onset of the Younger Dryas.
The idea that an impact event may have been the instigator for this cooling period was appealing because of several alleged impact markers, especially the high iridium concentrations that the previous team reported. However, it is difficult for proponents of this theory to explain why no impact crater of this age is known.