NATIONAL

Did global cooling come from the sky?

JOHN INTINI June 18 2007
NATIONAL

Did global cooling come from the sky?

JOHN INTINI June 18 2007

Did global cooling come from the sky?

JOHN INTINI

A team of American scholars is theorizing that about 12,900 years ago a powerful comet—measuring an estimated five kilometres in diameter and packing a punch comparable to 10 million megatonnes of TNT—exploded above the earth or crashed down just north of the Great Lakes region. Either way, they say this event likely triggered the deadly 1,000-year cold spell at the end of the Clovis Age known as the Younger Dryas. If they’re right, this would replace the commonly held belief that glacial melting in North America led to this period of rapid global cooling. It would also disprove the notion that human hunting caused the extinction of at least 17 animal species (including mammoths, mastodons, giant ground sloths, horses and camels) that disappeared rather abruptly at about this time.

The 26-member team, which presented its early findings at a conference in Acapulco last month, is basing the comet theory on carbonrich sediment found at more than 20 North American research sites (including two locations in Alberta: Wally’s Beach at St. Mary Reservoir and another near Edmonton). Metals rare to our planet—including iridium, which is associated with the impact of an asteroid 65 million years ago that most scientists think wiped out the dinosaurs—have been found at the sites from coast to coast. The Great Lakes region has the highest concentrations, making it the most likely impact site. Researchers also plan to study ancient animal DNA, looking for abnormalities in the populations of those animals that survived during this period—including species of elk, moose and bison.

No crater was found, but Douglas Kennett, an archaeologist at the University of Oregon and member of this multidisciplinary team, says the huge ice sheet covering the Great Lakes region at the time was likely thick enough to have absorbed the blow. It would not, however, have stopped the flooding and continent-wide wildfires that the team believes occurred after impact. Put simply, “this was not a good day in North America,” says Kennett. M