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   Space

Last Update: 11-07-2012  
Related category(ies):
Environment  |  Space

 

Countries involved in the project described in the article:
United States
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An extraterrestrial collision of international importance

An 18-member international team of researchers has found exciting new evidence that supports the theory of an extraterrestrial impact that occurred nearly 13 000 years ago. Their evidence lies in material found in a thin layer of sedimentary rock in Pennsylvania and South Carolina in the United States and in Syria. This material stands out because at the time it was created it could only have been formed at 1 700 to 2 200 degrees Celsius and as a result of a cosmic body impacting Earth. All together this points to evidence that could strongly support the controversial Younger Dryas Boundary (YDB) hypothesis. The finding was published in the journal PNAS.

Exciting new evidence that supports the theory of an extraterrestrial impact © Shutterstock
Exciting new evidence that supports the theory of an extraterrestrial impact
©  Shutterstock

The Younger Dryas Boundary hypothesis, also known as the Clovis comet hypothesis, theorises that a large air burst or an earth impact of an object or multiple objects from space initiated the Younger Dryas cold period around 12 900 years ago. This occurred either at or roughly close to the time of the major extinction of the North American megafauna, including mammoths and giant ground sloths, and the disappearance of the prehistoric and widely distributed Clovis culture. This theory has not had much traction; the lack of confirmatory data is one of the reasons for this. This new discovery, however, appears to strongly support the controversial Younger Dryas Boundary hypothesis.

'These scientists have identified three contemporaneous levels more than 12 000 years ago, on 2 continents yielding siliceous scoria-like objects (SLOs),' said H. Richard Lane, program director of the United States-based National Science Foundation's Division of Earth Sciences, which funded the research. 'SLOs 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.'

Crucial to the confirmation is the discovery of the melt-glass which provides morphological and geochemical evidence, confirming that the material is not cosmic, volcanic or of human-made origin. '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,' said James Kennett, professor of earth science at the University of California Santa Barbara in the United States.

'The melt material also matches melt-glass produced by the Trinity nuclear airburst of 1945 in Socorro, New Mexico,' he continued. 'The extreme temperatures required are equal to those of an atomic bomb blast, high enough to make sand melt and boil.'

According to the researchers, the material evidence supporting the YDB cosmic impact hypothesis currently spans three continents, covering almost one third of the planet, from California to western Europe, and into the Middle East. The discovery extends the range of evidence into Germany and Syria, the easternmost site yet identified in the northern hemisphere. The researchers have yet to identify a limit to the debris field of the impact.

'Because these three sites in North America and the Middle East are separated by 1 000 to 10 000 kilometres, there were most likely 3 or more major impact/airburst epicenters for the YDB impact event, likely caused by a swarm of cosmic objects that were fragments of either a meteorite or comet,' said Professor Kennett.

The paper also cites examples of recent independent research that supports the YDB cosmic impact hypothesis, and backs two independent groups that found melt-glass in the YDB layers in Arizona and Venezuela. 'The results strongly refute the assertion of some critics that "no one can replicate" the YDB evidence, or that the materials simply fell from space non-catastrophically,' Professor Kennett noted.

He added that the archaeological site in Syria where the melt-glass material was found — Abu Hureyra, in the Euphrates Valley — is one of the few sites of its kind that record the transition from nomadic hunter-gatherers to farmer-hunters who live in permanent villages. 'Archaeologists and anthropologists consider this area the 'birthplace of agriculture,' which occurred close to 12 900 years ago,' Professor Kennett said.

'The presence of a thick charcoal layer in the ancient village in Syria indicates a major fire associated with the melt-glass and impact spherules 12 900 years ago,' he went on to say. 'Evidence suggests that the effects on that settlement and its inhabitants would have been severe.'


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Proceedings of the National Academy of Sciences
National Science Foundation's Division of Earth Sciences





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