The layer, which has been found mostly in the Northern Hemisphere at sites across the Americas and Europe, also contains peak abundances of platinum and iridium, as well as metallic melt spherules, shocked quartz, and minerals fused together forming meltglass.
“They’re preserved in marine sediments as deep as about 2,000 meters,” Kennett said. The presence of these proxies doesn’t say anything in particular about the actual shocks, he explained, but rather illustrate their force, reach and allude to the event’s subsequent climatological impacts. “The material was thrown up into the atmosphere, and was globally transported and deposited in a broadly distributed layer that we earlier have described.”
Potentially the first known crater of Younger Dryas Boundary (YDB) Age
Impacts with Earth by extraterrestrial material vary in magnitude from the daily bombardment of Earth by tons of fine extraterrestrial dust to the dinosaur killers that occur on a timescale of tens of millions of years. Because the more extreme events leave their marks on Earth in the form of craters, much of the “gold standard” evidence of cosmic impacts is aligned with these structures and the character of associated material. As a result, proving the occurrence of a touchdown airburst becomes a challenge, given that there are typically no deformations in the landscape. This makes it very difficult to prove such an occurrence in the same way that the Chicxulub crater off Mexico’s Yucatán Peninsula has been linked to the massive impact that led to the extinction of dinosaurs.
“Previously, there has been no evidence for the Younger Dryas boundary (YDB) event of any crater or possible crater,” said Kennett. “So these events are more difficult to detect, especially when they are older than a few thousand years and after being buried, leave little or no superficial evidence.”