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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.
5 comments:
"This impact would have been decisive in the megafauna extinctions that defined that time"
Two days ago you were adamant that climate warming was responsible for the megafauna extinction. This week you accept the asteroid hypothesis. Doesn't this simply indicate you are desperate to cling to any hypothesis for the extinction as long as the hypothesis doesn't implicate humans to any great extent?
But the asteroid hypothesis has even larger holes in it than the climate warming one. At first glance, though, the hypothesis merely demands we accept that the collision wiped out the megafauna through the cold temperate regions of Eurasia and North America. Only in North America was the warm temperate region affected, perhaps also believable. The megafauna of the warm temperate regions of Eurasian was already extinct, so do we need to postulate an earlier asteroid collision as well?
The hypothesis then begins to fall to pieces completely. Why only larger animals? Surely if an asteroid was responsible the extinction would not target only the larger animals. In fact small herbivores would have been most at risk. Large animal can survive longer without food.
And the hypothesis becomes even more unbelievable when we consider the Southern Hemisphere. It wiped out megafauna only in South America. I'll grant that Australia's megafauna was already extinct (through an asteroid collision 46,000 years ago?). But the authors mention the presence of nano-diamonds in New Zealand, where the asteroid collision surprisingly caused no extinctions. We have to wait another 12,300 years before the large birds disappear from that country, at which time we come across an amazing coincidence. The birds died out within 200 years of human arrival. Or was there another asteroid at that time?
I'm not adamant of anything, just that there were issues bigger than a bunch of hunters in all this. You are the one who has a theory and insists in it all the time, in this as in so many other things, you "know the answer" without knowing.
I don't think they are saying that the asteroid physically killed the animals, it caused and abrupt and somewhat short-lived climate change to cold conditions (Younger Dryas, it's mentioned in the article). Large animals are just more susceptible to such changes because they exist in smaller numbers because of their size and resource demands. They are also easier to follow in the archaeological record.
"I'm not adamant of anything"
You certainly gave the impression of being extremely adamant on the subject.
Not sure if you've seen this at Julien's blog:
http://averyremoteperiodindeed.blogspot.com/2010/09/todd-surovell-late-pleistocene.html
Quote:
"Critics of overkill argue that anthropogenic extinction will remain highly controversial until unambiguous material evidence of human hunting of a large number of taxa is discovered. In contrast, I will argue that a huge amount of circumstantial evidence points to humans as the primary causal agents of extinction, and that the associational critique puts forth unrealistic if not impossible requirements for the overkill hypothesis to fulfill".
Not exactly CCTV footage, but Todd A. Surovell has no doubt what killed the megafauna.
I did not because it refers to a conference in Denver and I live far away.
But sure: the debate is open. Circumstantial evidence also points to climate-driven extinction, so...
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