Posted By crates on April 4, 2009

              About 12,900 years ago, most of the large megafauna of the New World disappeared.  This included the Mammoth, Mastodons, giant ground sloths, saber tooth tigers, camels, horses and many others.  This happened very rapidly and has been a source of speculation amongst scientists.  Most of the speculation has fallen into one of the following categories:

A. Climatic Change: Apparently at this time there was a period of intense cold which some say could have initiated the extinctions.  Others say that since this was at the end of the last glaciation, the warming temperatures could have caused the extinctions.  Others say that the climate became more “continentalized” with colder winters and hotter summers. However these same fauna survived previous interglacials without the large extinctions, so something doesn’t seem quite right about this hypothesis.

  B. Human overkill: Some say (I think Paul Martin popularized this hypothesis) that the extinctions coincided with one of the large human migrations into the area.  They point to other extinctions in other parts of the world (e.g. Australia) where extinctions coincided with the advent of humans into the area.

    This is succinctly summarized thus: “1- animals go extinct soon after the introduction of humans and 2- extinctions are greatest where humans have arrived last – the New World – and are least where humans were first – Africa. This is based on the reasoning that in Africa animals learned and evolved as H. sapiens developed new hunting techniques. The animals of new territories were naive about hunting and were more vulnerable – there was a greater gap between the ability of the hunter to kill and the ability of the animal to evade being killed. This predicts that the later H. sapiens entered a territory the more animals will be killed. “    For a fun, informative site that explores these questions see here.

C.  Disease:  A third hypothesis suggests that the invading humans brought some sort of pathogen with them that wiped out the megafauna.

Up until now the previous three hypotheses or combinations thereof were the only serious reasons put forth for these extinctions at this time.  However, I just saw a NOVA program which presents a fourth hypothesis:

D. Extraterrestrial body impact with the earth as shown on Nova’s program, The Last Extinction.   This program gave tantalizing evidence that a comet or asteroid impacted the earth approximately 13,900 years ago and which could have contributed to the extinctions.  The idea can be summarized thus:

• There is a dark band of material separating the strata at this age.  Before this band the megafauna was widespread in North America, and after the band the megafauna was basically extinct.  This “black mat” made up of cinders and burnt plant remains has been examined at over fifty sites in North America.
• There is a high amount of Iridium in this layer.  Iridium is found in high concentrations in meterors and comets, but not that common in the earth.  Louis Alvarez found a similar high concentration of Iridium at the Cretaceous/Tertiary border which indicated that an asteroid impact probably was a factor in the extinction of dinosaurs.
• Investigation of the Greenland ice layers also showed a high amount of Iridium in the ice of this time.
• In this black mat was also found nanodiamonds of a hexagonal crystaline structure which is formed only under high impact situations.
• Upon examining the Greenland ice layers of the same age, they found the same hexagonal nanodiamonds.  Both the Iridium and nanodiamonds were not found in layers just before (older) and just after (younger) than the layers of 13,900 years ago.
• They hypothesize that if the comet fell onto the ice or into the sea and if it was comprised of a group of small bodies instead of one large one, then there would be no impact crater.  One is reminded of the Tunguska Siberian Comet impact of 1908 which devastated a large area but left no impact crater. 
• It seems highly likely that a large extraterrestrial body hit the earth 13,900 years ago.
• This could have had an impact upon the sudden disappearance of the megafauna.

   They didn’t really address the impact upon the human population.  I wonder if there’s any evidence of this?   I know they said that the Clovis Culture was present before the “black mat” layer, but not after.  Oops!  I just found this site which discusses this same subject!  It also lists some objections as follows:

    “However, it is not clear why megafaunal extinctions caused by an impact event in northern North America would have extended all the way across northern Eurasia and down to the southern tip of South America (presuming a single primary cause for these similar and roughly contemporaneous regional extinctions), while sparing some of the small, isolated (and thus potentially most vulnerable) megafaunal populations on nearby islands. In the cases of the wooly mammoths of Wrangel Island or St. Paul Island, the Steller’s sea cows of the Commander Islands, and the ground sloths of the Antilles, the island populations survived for thousands of years after related populations on nearby continental land masses died out.”

   If  you get a chance watch this Nova program.  It is absolutely fascinating.

Categories: Extinction, nature
Tags: Clovis Culture, megafauna extinction, Nova, pleistocene extinctions