A View from the Beach: New Claim for Comet Impact at Younger Dryas

Tuesday, July 28, 2015

New Claim for Comet Impact at Younger Dryas

I've covered the Younger Dryas controversies as they have arisen over the past few years. The Younger Dryas event was a rapid cooling back to near glacial conditions as the the climate warmed at the end of the last major glaciation, between 12,800 and 11,500 years BP. There have been competing explanations over its cause, between a collapse of the ice sheets causing freshwater to shut down the global thermohaline circulation, or a cosmological impact event and the resulting "astronomical winter". Several groups reports evidence of impact debris, around the right time, but no impact site has been reported. A new report claims to narrow the time of the impact debris from many sites to a narrow time window just prior to the start of the Younger Dryas cooling:

Younger Dryas cooling event said to be comet related

At the end of the Pleistocene period, approximately 12,800 years ago — give or take a few centuries — a cosmic impact triggered an abrupt cooling episode that earth scientists refer to as the Younger Dryas.

New research by UC Santa Barbara geologist James Kennett and an international group of investigators has narrowed the date to a 100-year range, sometime between 12,835 and 12,735 years ago. The team’s findings appear today in the Proceedings of the National Academy of Sciences.

The researchers used Bayesian statistical analyses of 354 dates taken from 30 sites on more than four continents. By using Bayesian analysis, the researchers were able to calculate more robust age models through multiple, progressive statistical iterations that consider all related age data.

I wish I knew more about Bayesian statistics. I distrust the kind of arm-waving that claims to "correct" all these various dates to the "right" range. It wouldn't be the first time scientists fooled themselves into finding the data their hypothesis demanded.

“This range overlaps with that of a platinum peak recorded in the Greenland ice sheet and of the onset of the Younger Dryas climate episode in six independent key records,” explained Kennett, professor emeritus in UCSB’s Department of Earth Science. “This suggests a causal connection between the impact event and the Younger Dryas cooling.”

Unfortunately, the impact site continues to elude researchers. Was it submarine and not yet found, or on top of a glacial cap which melted, erasing the evidence?

In a previous paper, Kennett and colleagues conclusively identified a thin layer called the Younger Dryas Boundary (YDB) that contains a rich assemblage of high-temperature spherules, melt-glass and nanodiamonds, the production of which can be explained only by cosmic impact. However, in order for the major impact theory to be possible, the YDB layer would have to be the same age globally, which is what this latest paper reports.

“We tested this to determine if the dates for the layer in all of these sites are in the same window and statistically whether they come from the same event,” Kennett said. “Our analysis shows with 95 percent probability that the dates are consistent with a single cosmic impact event.”