New evidence from Greenland ice cores suggests that a large cosmic impact may have struck North America approximately 12,900 years ago, according to US scientists. A spike in platinum levels in the ice coincides with a period of abrupt climate change known as the Younger Dryas, which has been linked to the decline of the Clovis people and the extinction of large mammals such as the mammoth.
The findings, published in the Proceedings of the National Academy of Sciences by Michail Petaev and colleagues at Harvard University, reveal a 100-fold increase in platinum concentration in ice dated to around 12,890 years ago. This spike aligns with rapid cooling indicated by oxygen isotope measurements, marking the onset of the Younger Dryas period.
The Younger Dryas, which began and ended abruptly, is one of several short climate shifts since the last glacial maximum. It may have involved temperature changes occurring over as little as a decade, potentially triggered by debris from an impact that dimmed the sun. This rapid change could explain the extinction of massive mammals and the disruption of native cultures like the Clovis people.
The platinum data support earlier disputed reports of microscopic diamond and lonsdaleite grains in lake sediments from the same era, similar to remnants of the Tunguska meteorite impact in Siberia. However, critics note that no impact site has yet been identified. The research adds to growing interest in cosmic impacts as drivers of major biological changes, including the dinosaur extinction 66 million years ago and the Permian mass extinction 252.3 million years ago.
