Researchers have disapproved a theory that states that Younger Dryas, a brief return to near glacial conditions at the end of the Ice Age, was caused by a comet hitting the earth.
The team of archaeologist David Meltzer, Southern Methodist University, Dallas, and a lead author on the study and an expert in the Clovis culture, the peoples who lived in North America at the end of the Ice Age, found that nearly all sediment layers purported to be from the Ice Age at 29 sites in North America and on three other continents are actually either much younger or much older.
Meltzer and his co-authors found that only three of 29 sites commonly referenced to support the cosmic-impact theory actually date to the window of time for the Ice Age.
The team including Vance T. Holliday and D. Shane Miller, both from the University of Arizona; and Michael D. Cannon, SWCA Environmental Consultants Inc., Salt Lake City, Utah reported that the supposed impact markers are undated or significantly older or younger than 12,800 years ago.
They said that either there were many more impacts than supposed, including one as recently as 5 centuries ago, or, far more likely, these are not extraterrestrial impact markers.
Meltzer and his colleagues tested that hypothesis by investigating the existing stratigraphic and chronological data sets reported in the published scientific literature and accepted as proof by cosmic-impact proponents, to determine if these markers dated to the onset of the Younger Dryas.
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They sorted the 29 sites by the availability of radiometric or numeric ages and then the type of age control, if available, and whether the age control is secure.
The researchers found that three sites lack absolute age control: at Chobot, Alberta, the three Clovis points found lack stratigraphic context, and the majority of other diagnostic artifacts are younger than Clovis by thousands of years; at Morley, Alberta, ridges are assumed without evidence to be chronologically correlated with Ice Age hills 2,600 kilometers away; and at Paw Paw Cove, Maryland, horizontal integrity of the Clovis artifacts found is compromised, according to that site's principal archaeologist.
The remaining 26 sites have radiometric or other potential numeric ages, but only three date to the Younger Dryas boundary layer.
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