New evidence suggests comet impact cooled Earth 12,800 years ago

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Technological Innovation Website Editorial Team - 08/08/2025

Fe- and silica-rich impact microspherules (a and b) and metallic dust particles (c and d) were interpreted as cometary dust. The yellow arrows show FeSi, FeS, and FeCr particles in the microspherules (a and b) and NiFe, low-O2 Fe, and native Fe in the metallic particles (c and d). Note the folded edges in panel d, indicative of an impact. [Image: Christopher R. Moore et al. - 10.1371/journal.pone.0328347]

Comet impact

Last year, geologists found rocks that support the idea that a comet impact changed Earth's climate .

Now, after expanding their search area, the same team has found similar evidence on the seabed.

This hypothesis proposes that a comet collided with Earth's atmosphere 12,800 years ago, causing widespread climate change that, among other things, led to an abrupt reversal of Earth's warming trend and an anomalous quasi-glacial period called the Younger Dryas.

The era is named after the white dryad plant ( Dryas octopetala ): The Younger Dryas and the Older Dryas were named for the large amounts of this plant's pollen found in soil samples dating from those periods. During these cold periods, the white dryad was much more widespread than it is today, when tundra dominated areas now covered by forests. During the abrupt cooling—the Younger Dryas event—temperatures dropped by about 10°C (50°F) in a year or less, with the lowest temperatures lasting about 1,200 years.

Many researchers believe there was no comet involved, and that it was glacial melt that cooled the Atlantic Ocean, significantly weakening the currents that carry warm tropical water northward. The Younger Dryas Impact hypothesis, however, posits that Earth passed through debris from a disintegrating comet, with numerous impacts and shock waves destabilizing ice sheets and causing massive floods of meltwater—and it was this water that disrupted major ocean currents.

To clarify the issue, geologists have long been searching for evidence of comet debris. And now they've found several.

Different samples of microspheres collected and analyzed for evidence of a comet impact. [Image: Christopher R. Moore et al. - 10.1371/journal.pone.0328347]

Signs of impact

Christopher Moore and colleagues at the University of South Carolina in the US analyzed the geochemistry of four cores from the seafloor of Baffin Bay, near Greenland. Radiocarbon dating suggests the cores contain sediments deposited at the beginning of the Younger Dryas event.

Detailed analysis, using various techniques, revealed metallic debris whose geochemistry is consistent with cometary dust. This debris is in microscopic spherical particles, whose composition indicates a predominantly terrestrial origin, with some materials considered extraterrestrial—suggesting that these microspherules may have formed when fragments of the comet exploded just above or upon impact with the Earth, fusing together terrestrial and extraterrestrial materials. The analysis also revealed even smaller nanoparticles, with high levels of platinum, iridium, nickel, and cobalt, which may be indicative of extraterrestrial origin.

Taken together, the results indicate a geochemical anomaly that occurred around the beginning of the Younger Dryas event. However, they do not provide direct evidence to support the impact hypothesis. More research will be needed to confirm whether these results are indeed evidence of an impact and to firmly link this impact to climate cooling.

"Our identification of a Younger Dryas impact layer in deep-sea sediments highlights the potential of ocean records to expand our understanding of this event and its climatological impacts," Moore concluded.

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