An international team of scientists says melted glass material in a thin layer of sedimentary rock in Pennsylvania and South Carolina, and in Syria, was formed at temperatures of 3,100 to 3,600 degrees Fahrenheit and is the result of a cosmic body impacting Earth.
The findings support a controversial hypothesis that proposes a cosmic impact occurred at the onset of an unusual cold climatic period called the Younger Dryas.
This event occurred at or close to the time of major extinction of the North American megafauna, including mammoths and giant ground sloths, and the disappearance of the prehistoric and widely distributed human Clovis culture, researchers said.
"These scientists have identified three contemporaneous levels more than 12,000 years ago, on two continents yielding siliceous scoria-like objects (SLO's)," H. Richard Lane of the National Science Foundation's Division of Earth Sciences, which funded the research, said. "SLO's are indicative of high-energy cosmic airbursts/impacts, bolstering the contention that these events induced the beginning of the Younger Dryas. That time was a major departure in biotic, human and climate history."
Analysis of the melt-glass confirms the material is not volcanic or of human-made origin, researchers said.
"The very high temperature melt-glass appears identical to that produced in known cosmic impact events such as Meteor Crater in Arizona, and the Australasian tektite field," James Kennett, professor of earth science at UC Santa Barbara, said.
"The melt material also matches melt-glass produced by the Trinity nuclear airburst of 1945 in Socorro, New Mexico," he said. "The extreme temperatures required are equal to those of an atomic bomb blast, high enough to make sand melt and boil."
The researchers' findings have been published in the Proceedings of the National Academy of Sciences.
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