Geology.com writes:
Researchers believe that they have found physical evidence of a cosmic impact that might have caused the extinction of an estimated 35 mammal and 19 bird genera about 12,900 years ago. Their findings are inconsistent with the popular theory that overhunting by Clovis people led to these extinctions.
The researchers have found hexagonal nanodiamonds within a dark layer of sediment on Santa Rosa Island off the coast of Southern California. These are not ordinary diamonds. Instead, they are lonsdaleite, a shock-synthesized mineral with a hexagonal crystalline structure. It forms under extreme temperatures and pressures, similar to those produced by a cosmic impact.
Lonsdaleite diamonds, are typically found in meteorites, impact craters and impact ejecta. Their presence in the dark sediment layer suggests that materials in the layer might be ejecta produced by a large impact event.
link: Impact Nanodiamonds and Soot Explain Clovis-Age Extinctions?
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