Were Wooly Mammoths And Saber-Tooth Tigers Killed By Comet Collision?

By Josh Lieberman on January 31, 2014 4:09 PM EST

wooly mammoth
A comet was responsible for the extinction of the wooly mammoth and other megafauna, according to a controversial 2007 study which was recently recreated. (Photo: Wikimedia Commons)

A comet wiped out North America's wooly mammoth and other megafauna like the giant ground sloth and saber-toothed tiger 12,000 years ago, according to a much-debated 2007 study by James Kennett of UC Santa Barbara. Now another team of UC Santa Barbara researchers has tested Kennett's controversial hypothesis and concluded that it is in fact plausible (with some qualifications). Kennett's hypothesis, known as the Younger Dryas Boundary hypothesis, hinges on the presence of nanodiamonds along Bull Creek in the Oklahoma Panhandle, which Kennett believes are the result of an earth-changing comet collision. 

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In order to see if they could reproduce the 2007 study's evidence, the researchers reexamined nanodiamond distribution in Bull Creek's sedimentary record, analyzing 49 sediment samples representing different time periods. They found that soil formation, environmental settings and cultural activities were not responsible for the presence of nanodiamonds, so it was likely something else.

"We were able to replicate some of their results and we did find nanodiamonds right at the Younger Dryas Boundary," said Alexander Simms, an associate professor in at UC Santa Barbara and a coauthor of the new study. "However, we also found a second spike of nanodiamonds more recently in the sedimentary record, sometime within the past 3,000 years." Simms added that despite the nanodiamond abundance at the Younger Dryas Boundary, the team "did find it at one other site, which may or may not be caused by a smaller but similar event nearby."

In September 2013, a National Science Foundation study suggested that a comet struck Quebec 13,000 years ago, wiping out megafauna. Those researchers based their findings not on nanodiamonds but on spherules found at Younger Dryas Boundary layers in Pennsylvania and New Jersey. Spherules are droplets of molten rock which come result from comet or meteor collisions. The impact led to human hunters known as the Clovis people adopted a new hunter-gatherer lifestyle in which they went after smaller game and began to gather roots and berries.

Since 2008, the Younger Dryas Boundary theory has been criticized for a number of reasons, among them the fact that the human population didn't decline at the time, and that after the alleged impact the megafauna didn't go extinct all at once. Some critics also believe that the crystals were not nanodiamonds at all.

While scientists believe that the earth cooled around the time of the Younger Dryas, the reason is not so readily agreed upon. The most prominent theory is that a North American ice sheet broke apart, flooding the Atlantic Ocean with an enormous amount of freshwater. This rush of water prevented ocean currents from moving warmer water north, which resulted in a colder and drier climate. 

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