Cosmic Impact that Triggered the Cool Younger Dryas Pinpointed

Scientists have found that at the end of the Pleistocene period about 12,800 years ago, a cosmic impact triggered the Younger Dryas.

The new research actually narrows the date of the cosmic impact to a 100-year range. In fact, the scientists believe that the impact occurred between 12,835 and 12,735 years ago.

So how did they narrow this range? 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.

"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," said James Kennett, one of the researchers, in a news release. "This suggests a causal connection between the impact event and the Younger Dryas cooling."

The researchers examined six instances of independently derived age data that used other dating methods. In most cases, they counted the annual layers in ice and lake sediments.

Two core studies taken from the Greenland ice sheet actually revealed an anomalous platinum layer, which was a marker for the Younger Dryas Boundary (YDB). A study of tree rings in Germany also showed evidence of the YDB, as did freshwater and marine varves, the annual laminations that occur in bodies of water.

"The important takeaway is that these proxy records suggest a causal connection between the YBD cosmic impact event and the Younger Dryas cooling event," said Kennett. "In other words, the impact event triggered this abrupt cooling. The chronology is very important because there's been a long history of trying to figure out what caused this anomalous and enigmatic cooling. We suggest that this paper goes a long way to answering that question and hope that this study will inspire others to use Bayesian statistical analysis in similar kinds of studies because it's such a powerful tool."

The findings are published in the journal Proceedings of the National Academy of Sciences.

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