I briefly mentioned two weeks ago that the Clovis impact theory had been rejected. The argument being that nanodiamonds (lonsdaleite or n-diamonds) were not such but mere graphene.
But now researchers from US universities, working with Greenland ice cores, have found the controversial "diamonds" in an ice layer roughly dated to that same fateful date of c. 12,900 years ago. Furthermore, the analysis seems to confirm these are genuine n-diamonds and that:
... the shape and size of the Greenland n-diamonds suggest that they formed not by shock metamorphism but rather by processes such as high-temperature CVD and/or high-explosive detonation, which duplicate conditions known to occur during a cosmic impact.
The authors also examined lonsdaleite from Caravaca (Spain) and Needles Point (New Zealand), concluding that they also seem to support the impact theory.
Of course, it is possible that the NDs in Greenland formed through some as-yet undiscovered natural process other than cosmic impact; however, that seems unlikely, since intense diamond research spanning more than a century indicates that the formation of NDs, and lonsdaleite in particular, requires extraordinary temperature, pressure and redox conditions that rule out natural processes that occur either on or below the surface of the Earth (DeCarli and others, 2002).
The theory known as 'Clovis imapact' or 'Younger Dryas event' claims that a sizable meteorite hit Earth, possibly in North America, c. 12,900 years ago, causing the cold millennium known as Younger Dryas, just before the definitive post-glacial warming that marks the beginning of the end of the Paleolithic era. This impact would have been decisive in the megafauna extinctions that defined that time
Ref. Andrei V. Kurbatov et al., Discovery of a nanodiamond-rich layer in the Greenland ice sheet. Journal of Glaciology, 2010. (Direct PDF link).
Found originally at Science Daily.