Minuscule diamond fragments found in a sediment layer dating from thousands of years ago are bolstering the theory that a catastrophic comet impact wiped out many forms of life in North America, including what are thought to have been the first human settlers of the continent, the so-called Clovis people. The nano-diamonds
are buried at a level that corresponds to the beginning 12,900 years ago of the Younger Dryas, a 1,300-year-long cold spell during which North American mammoths, saber-toothed cats, camels and giant sloths became extinct. The Clovis culture of American Indians also appears to have fallen apart during this time [Reuters].
The new study adds evidence to the controversial theory, but
some skeptics are not convinced. “The whole thing still does not make sense, and there are lots of contradictions,” said Christian Koeberl, a professor of geological sciences.... His chief reservation is that there is no crater. “A body of this size does not just blow up without a trace in the atmosphere,” Dr. Koeberl said. “Physics won’t have it” [The New York Times].
In reply, supporters of the theory say that some of the comet fragments may have exploded in midair, while others may have hit an ice sheet that was several miles thick, lessening the possibility of a crater forming. In the study, published in Science [subscription required], researchers used transmission electron microscopy to identify nanodiamonds at a number of North American sites, from Arizona to South Carolina to Manitoba, Canada.
"We've discovered nano-diamonds that are not normally produced through average processes on the surface of the Earth," said [study coauthor] James Kennett.... "They indicate there was an extra-terrestrial event on Earth 12,900 years ago" [BBC News].
The tiny diamonds are encased in carbon spheres that form through instantaneous melting, and the diamond crystals have a hexagonal pattern rather than the usual cubic structure, indicating that they were formed by intense heat and pressure. Such diamond crystals have been found only within meteorites at at impact craters, the researchers say.
The causes of the woolly mammoth extinction, the collapse of Clovis culture and the onset of the cold snap have long been debated. But only the impact theory accounts for the simultaneous occurrence of all three, said Doug Kennett [BBC News].
He says that the comet fragments' explosions and impacts could have destabilized the massive ice sheet that covered much of North America, sending a burst of fresh water into the North Atlantic and interfering with the ocean currents that play an important role in climate. Related Content: DISCOVER: Were the First Americans Wiped Out By an Asteroid?
Image: Doug Kennett
