12,800-Year-Old Climate Mystery Solved: The Greenland Platinum Spike Came From Volcanoes, Not a Comet

One of the most hotly contested puzzles in climate science — the origin of a mysterious platinum spike preserved in Greenland's ancient ice — has been solved, and the answer is not from outer space. New research led by Professor James Baldini of Durham University's Department of Earth Sciences concludes that the anomalous concentration of platinum found in the Greenland Ice Sheet Project (GISP2) core almost certainly originated from volcanic eruptions, not from a comet or asteroid impact, overturning a theory that gained significant traction in scientific and popular circles over the past two decades.

The platinum spike in question is preserved in ice layers dating to approximately 12,800 years ago, at the very beginning of the Younger Dryas — a sudden and severe cold snap during which northern hemisphere temperatures plunged more than 15 degrees Celsius below present levels, an event that lasted roughly 1,200 years and abruptly reversed the warming that had been melting the last great ice sheets. The cause of the Younger Dryas has never been definitively established, and for years a group of researchers advocated the Younger Dryas Impact Hypothesis: the idea that a cosmic collision triggered the cooling by sending debris into the atmosphere, igniting wildfires, and disrupting ocean circulation.

The platinum spike seemed to support this hypothesis. Platinum is a platinum-group element often associated with meteorites and cosmic debris. Its appearance at precisely the Younger Dryas boundary looked, to impact proponents, like the chemical fingerprint of an extraterrestrial event.

Baldini's team, publishing in PLOS One, found two critical problems with that interpretation. First, the platinum spike appeared approximately 45 years after the Younger Dryas cooling began and persisted for about 14 years. If a cosmic impact had caused the cooling, its chemical signature should appear at the very start of the cooling event, not nearly half a century later. The timing alone rules out an impact as the trigger.

Second, the researchers analyzed 17 pumice samples from Germany's Laacher See volcano — a major eruption that occurred around 13,000 years ago and has been proposed as a partial driver of Younger Dryas cooling. Platinum levels in all 17 samples were at or below detection limits, eliminating Laacher See as the source of the Greenland platinum.

The most likely alternative source, the researchers argue, is unidentified submarine or subglacial volcanic eruptions in Iceland. Historical comparisons support this hypothesis: an eruption from Katla, one of Iceland's most active volcanoes, produced a 12-year metal surge in ice cores from the 8th century. The Eldgjá eruption in the 10th century left a distinctive cadmium signal preserved in the same ice archive. The pattern of the Younger Dryas platinum spike closely resembles these known volcanic signatures.

"This research significantly weakens the case for the Younger Dryas Impact Hypothesis," Baldini said in a statement accompanying the paper's publication. The finding does not resolve what caused the Younger Dryas itself — the platinum spike, as a post-hoc chemical signal, could not have triggered the cooling even if it were of cosmic origin. But it removes one of the key pieces of evidence that impact proponents had cited, and points scientists toward volcanic processes as a more productive area of investigation.