Explanation of ancient climate change undermined by new research

ST. LOUIS, Dec. 19 (UPI) -- New research undermines the consensus explanation for the Younger Dryas period, an interval of rapid cooling beginning 12,900 years ago. Scientists have previously hypothesized that the impact of one or more comets triggered the period.

The Younger Dryas period was one of several interruptions in the gradual warming of Earth's climate after the end of the Last Glacial Maximum, 27,000 years ago. For roughly 15 millennia prior the the Younger Dryas period, Earth's ice caps slowly receded and temperatures gradually rose. But 12,900 years ago, temperatures plunged once more.

Previous studies have pointed to a series of impact-derived nanodiamonds sourced from sediment dated to the beginning of the Younger Dryas as proof of the prevailing hypothesis. Other studies have detailed supposed evidence of continent-spanning wildfires caused by a massive, climate-changing impact.

But a pair of new studies, both published in the Journal of Quaternary Science, refute the evidence.

"Impact proponents report the rare form of diamond, lonsdaleite, that is usually associated with shock processing; however, we show that they misidentified polycrystalline aggregates of graphene and graphane as lonsdaleite," Tyrone Daulton, lead author of one of the two papers, said in a news release. "Further, we show that the nanodiamond concentration measurements reported by impact proponents are critically flawed. There is no evidence for a spike in the nanodiamond concentration at the onset of the Younger Dryas to suggest that an impact event occurred."

"The idea of a Younger Dryas impact was an interesting one that has drawn much attention; however, increasingly methodological research over the past few years has failed to corroborate that story," added Andrew Scott, lead author of the second paper. "Our research has shown that many of the markers for such an event have been misinterpreted or misidentified."