for National Geographic News
The discovery of tiny "nanodiamonds" supports a controversial theory that a catastrophic bombardment of space rocks altered the course of Earth history.
About 12,900 years ago, Earth was escaping the grips of an ice age when something triggered a sudden refreeze.
The resulting 1,300-year cold spell coincides with the extinction of a host of massive mammals such as woolly mammoths, dire wolves, and sabertooths.
The Clovis culture, among the earliest humans in North America, may have suffered as well, according to Douglas Kennett, an archaeologist at the University of Oregon in Eugene, whose research appears in the current issue of the journal Science.
Kennett and colleagues found the layer of microscopic diamonds in sediments across North America that date to the start of the abrupt cooling.
The gems, the researchers argue, are consistent with a theory that Earth crossed a swarm of comets or carbon-rich meteorites that triggered cooling and die-offs.
(Related: Did Comets Cause Ancient American Extinctions? [May 6, 2008].)
According to the theory, the impacts sparked catastrophic wildfires and destabilized ice sheets in North America, allowing a giant lake to drain into the North Atlantic.
The influx of fresh water temporarily shut down an ocean current that shuttles warm water—and a warmer climate—north from the tropics.
The inferno and sudden environmental changes apparently proved disastrous for at least 16 North American mammals.
No remains of mammals such as woolly mammoths are known from above the soil layer containing the newfound diamonds.
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