The Half-Astrophysicist Blog

Where DId the Wooly Mammoths Go?

A report today in the Journal Science (subscription required) argues that comet or metorite impacts may have lead to the demise of the wolly mammoth as well as early human settlers in North America.  You can read a BBC article on the research here.

It’s pretty widely accepted that impacts can cause mass extinctions.  The most famous example is the dinosaurs about 65 million years ago.  We have found multiple lines of evidence that an impact caused this extinction including iridium and other unusual elements in sedimentary rocks from this time period and the impact crater off the coast of the Yucatan peninsula (I am not going to try and spell the name of the crater!)

The impact in question would have occurred about 12,900 years ago.  They have found iridium in rock layers (called the Younger Dryas or YD Boundary) as well as evidence of large wildfires that can be started by large impacts.  They also found nanodiamonds at various sites around North America.  Nanodiamonds don’t form naturally on Earth’s surface, but can form in impacts (if you want go get really technical, they found both cubic diamonds and what are called n-diamonds which have unusal indicies of refraction.  n-diamonds are known to occur in metorites but not form naturally on Earth’s surface).

But what about the crater?  One idea is that the impactor never hit the ground but instead gave rise to an air burst.  This would not produce a crater.  The Tunguska impact in 1908 was an airburs and leveled quite a large area of forest in Siberia.

This would be an exciting discovery if they could prove an impactor caused this extinction.  The more we learn about impacts, their frequency and effects on Earth, the better prepared we will be to handle potential future events.


January 2, 2009 - Posted by | Uncategorized

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