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About 13,000 years ago, a chunk of a comet or asteroid hurtled into the atmosphere at a shallow angle, superheating the atmosphere around it as it careened toward the surface. The air grew hot enough to ignite plant material and melt rock below the object’s flight path. Within a few microseconds, atmospheric oxygen was consumed and the freed carbon atoms condensed into nanodiamond crystals. An air shock followed several seconds later, lofting these nanodiamonds and other carbon particles into the atmosphere, spreading them around. Mega mammals starved, unable to forage on the scorched earth, and human populations dwindled. The shock on the atmosphere was enough to lower global temperatures for a thousand years. This is according to a new study of ancient Mexican nanodiamonds, and it’s another salvo in a longstanding ancient-climate dispute. The study bolsters the controversial argument that an asteroid impact might have chilled the planet during the Younger Dryas, an abrupt and very short cold interval that started about 12,900 years back.
The sediment layer came from a a 27-meter-long core sample drilled from Lake Cuitzeo as part of a paleoclimate study. The team focused on several microparticles they attribute to widespread burning — such as carbon particulates — and nanodiamonds, which they measured using even more precise techniques than Kennett et al. two years ago. These particles can’t be explained by any terrestrial mechanisms, the authors say. They rule out a rain shower of cosmic particles; wildfires; volcanism; human-related activities; and even particle misidentification (like finding fool’s nanodiamonds). They say a cosmic impact is the only viable hypothesis.