
Spherules from archaeological sites in the study. The microscopic particles have marred surface patterns from being crystallized in a molten state and then rapidly cooled.
If such an impact took place, it did not leave behind any obvious clues like a crater. But microscopic melted rock formations called spherules and nano-sized diamonds in ancient soil layers could be telltale signs of a big collision. The mix of particles could only have formed under extreme temperatures, created by a comet or asteroid impact.
Researchers first reported in 2007 that these particles were found at several archaeological sites in layers of sediment 12,900 years old. Now an independent study published in the (Sept.17) in the Proceedings of the National Academy of Sciences (PNAS) says those findings hold up.
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