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