02 August 2008

New Clovis-Age Comet Impact Theory

Two University of Oregon researchers are on a multi-institutional 26-member team proposing a startling new theory: that an extraterrestrial impact, possibly a comet, set off a 1,000-year-long cold spell and wiped out or fragmented the prehistoric Clovis culture and a variety of animal genera across North America almost 13,000 years ago...Kennett said that 35 animal genera went extinct at the end of the Pleistocene, with at least 15 clearly being wiped out close to 12,900 years ago. There would have been major ecological shifts, driving Clovis survivors into isolated groups in search of food and warmth. There is evidence, he said, that pockets of Clovis people survived in refugia, especially in the western United States.

Researchers argue that the theory explains why the Murray Springs site in Arizona has a thick carbon mat, a deposit similar in age and context to ones seen at other Paleoindian sites such as Lindenmeier (Colorado), Hell Gap (Wyoming), and Lange-Ferguson (South Dakota). The radiocarbon dates on the mat are uniformly about 10,800 +/- 200.

Researchers say the comet - a ball of ice, rock and dust from outer space - hit the Laurentide ice sheet in Canada."It wouldn't have left a crater because it would have exploded and sent a shower of debris and chunks of ice," said Erlandson, adding the impact would have been ice on ice.Heat from impact may have sparked fires across the continent, and the melting of the ice sheet may have caused flooding. Researchers say the comet may have contributed to human population reduction and localized animal extinction.Researchers say the comet may have helped cause a cold climate period that lasted for about 1,300 years, called the Younger Dryas, and may have wiped out or fragmented the prehistoric Clovis tribe. A carbon-rich black layer found at more than 50 sites around North America is evidence for the impact, according to the article published in the Proceedings of the National Academy of Sciences. The layer contains iridium, carbon spherules and fullerenes with helium 3. Evidence of mammoths and other animals, along with early human hunters, are found beneath the black mat, but are missing within or above the strip.More evidence is found in the Carolina Bays, which are depressions from New Jersey to Florida. Erlandson says the depressions point toward the ice sheet, possibly a result of the comet.The theory, which is known as the "YDB Comet Theory," was first proposed by University of California at Santa Barbara paleoceanographer James Kennett, Douglas Kennett's father, Richard Firestone of the Lawrence Berkeley National Laboratory and Arizona researcher Allen West. Douglas Kennett often collaborates with his father.

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