Large Mammals Of Younger Dryas Wiped Out By Asteroid
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Lawrence LeBlond for redOrbit.com – Your Universe Online
Scientists long fascinated with trying to understand a dramatic global climate shift have revealed new evidence that could explain a few things.
A new study, funded by the National Science Foundation and to be published online in the Proceedings of the National Academy of Sciences (PNAS) Early Edition, has found that a cataclysmic asteroid or comet impact in the Canadian province of Quebec nearly 13,000 years ago wiped out many of the world’s large mammals and may have prompted early humans to move from a hunting lifestyle to start growing and gathering some of their food.
Dartmouth College researchers explain that this impact, which occurred at the beginning of the Younger Dryas period, marks an abrupt global shift to colder climes that had far-reaching effects on both animals and humans. In North America, large mammals such as mastodons, camels, giant sloths and saber-toothed cats all disappeared due to the cataclysmic event. Because of this, human hunters, known as the Clovis people, started taking a hunter-gatherer lifestyle, subsisting not only on smaller game, but also roots and berries.
“The Younger Dryas cooling impacted human history in a profound manner,” says Dartmouth Professor Mukul Sharma, a co-author of the study. “Environmental stresses may also have caused Natufians in the Near East to settle down for the first time and pursue agriculture.”
While other experts in the field are not disputing the powerful changes that occurred during this period, controversy still surrounds the cause of them. Most experts previously concur that the cooling period seen in the beginning of the Younger Dryas period was caused by an ice dam in the North American ice sheet that ruptured, releasing massive amounts of freshwater into the Atlantic Ocean. It has been theorized that this influx of water shut down the ocean currents that move tropical waters northward, resulting in colder, drier climates seen in the Younger Dryas.
However, Sharma and his colleagues’ evidence show that a cataclysmic impact is much more reliable in determining the environmental changes seen. The team is basing their results on spherules (droplets of solidified molten rock expelled by comet or meteor impacts). These spherules have been recovered from Younger Dryas boundary layers in Pennsylvania and New Jersey. The team found that the geochemistry and mineralogy profiles of the spherules are identical to rock found in southern Quebec, where Sharma argues the impact occurred 12,900 years ago.
“We have for the first time narrowed down the region where a Younger Dryas impact did take place,” says Sharma, “even though we have not yet found its crater.” The team said that one known crater in Quebec – the 2.5-mile-wide Corossal crater – is not the one they are looking for, stating the geochemical and mineralogical analysis shows no similarities with the spherules discovered in PA and NJ.
Studies of spherules around the world have led to theories of impacts that may have previously gone unnoticed. Sharma says it could be likely that it took “multiple concurrent impacts” to bring about evident climate shifts during the Younger Dryas. “However, to date no impact craters have been found and our research will help track one of them down.”