National Geographic News, Reporting Your World Daily

Thursday, October 28, 2010

Photo: Comets Didn't Wipe out Sabertooths, Early Americans?


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North America's Great Lakes (pictured in an aerial shot on May 4, 2002) were created during glacial retreats and advances over millions of years—including the brief cold snap called the Younger Dryas, which occurred about 12,900 years ago.

What caused the cold snap, though, has proved controversial: Recent research has weakened a theory that a giant comet caused the drop in temperatures and wiped out much of North America's wildlife, scientists said in October 2009.

Photograph courtesy Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC