Nano Diamonds clues to beasts’ demise

By | January 5, 2009

The controversial idea that space impacts may have wiped out woolly mammoths and early human settlers in North America has received new impetus.

Black layer at Murray Springs (Kennett et al)Nano-diamonds and other exotic impact materials have been unearthed in thin sediments, Science magazine reports.

The age of these materials coincides with the start of a millennium-long climate cooling event known as the Younger Dryas – some 13,000 years ago.

Many large animals vanish from the archaeological record at this time.

It is also the period in Earth history that sees the demise of Clovis culture – the prehistoric civilisation that many regard as the first human occupation of North America.

Taken together, it all makes for a compelling story, claims the team behind the latest research.

Question of origin

The group used transmission electron microscopy (TEM) to identify tiny impact diamonds found at a range of sites – four of them Clovis archaeological digs – across North America. Diamonds form through intense pressure and heat.

“We’ve discovered nano-diamonds that are not normally produced through average processes on the surface of the Earth,” said James Kennett, a geologist at the University of California, Santa Barbara, and author on the Science paper.

“They indicate there was an extra-terrestrial event on Earth 12,900 years ago,” he told BBC News.

Scientists last year reported the discovery of five types of nano-diamonds along with impact material such as iridium and magnetic microspherules in the Younger Dryas impact layer, a thin blanket of sediment 12,900 years old.

50 nanometres (billionths of a metre)The new analysis with TEM, they said, confirmed an abundance of diamonds in carbon spherules – melt material that forms in a fraction of a second – and the identification of lonsdalite, or hexagonal diamonds, associated with meteorite explosions.

The sheer number of diamonds – up to a million times that found in neighbouring sediment – and their presence inside spherules, refutes the speculation that the material is the normal rain of meteorite debris, says Allen West, a retired geophysicist in Arizona and a co-author.

“There is no other way that hexagonal diamonds could have ended up in a carbon spherule in this number,” said Dr West….

The absence of some traditional impact material and visible craters in North America led researchers to speculate that a meteoroid or comet disintegrated before exploding in a cluster of airbursts. …

BBC NEWS | Science & Environment | Diamond clues to beasts’ demise.

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