You can see Clovis spear points, long polished leaves of agate and chalcedony, in Tacoma’s Washington State History Museum. Clovis points, named after the town in New Mexico where they were first found more than 70 years ago, have pushed back the date of human settlement in North America to at least 13,200 years ago.
The Tacoma spear points formed part of a cache unearthed in East Wenatchee 22 years ago by a couple of farm workers digging a trench through an orchard. Others have turned up virtually all over the continent. Some archaeologists think the Clovis people scattered quickly across North America; others think it was their technology that scattered quickly — among people who were already living here.
The Clovis culture that created the distinctive points disappeared 12,900 years ago, and the giant sloths and mammoths and a host of other Ice Age fauna they hunted disappeared along with them, at exactly the same time. They all vanished right at the start of the cold spell known as the Younger Dryas, which interrupted 5,000 years of warming at the end of the last ice age, plunging the northern hemisphere back into cold for another 1,100 years.
So, where did they all go? An intriguing theory has been getting lots of attention since a one-page article by Douglas J. Kennett, a University of Oregon archaeologist, and his colleagues, appeared in Science in January.
”People have been puzzling about the extinctions for a very long time,” Kennett says. Some scientists think that climate change did in the mammoths and all those other critters, and that Clovis hunters vanished along with their prey. But why, Kennett asks, would whole genera of animals “highly adapted to Ice Age conditions” die of cold? And why would they all die at once?
Other scientists suggest that the first human hunters killed the last of the ice age megafauna, basically hunting themselves out of business. There are two problems with that. One is political. If those early hunters were forebears of current Native Americans and Native Americans were the "first conservationists," then they just couldn't have killed off whole species. The other is basically logistical. Mammoths and mastodons weren't the only critters that disappeared. Sixteen whole genera vanished. Kennett doubts the small populations suggested for North America 13,000 years ago were large enough to pull this off.
Regardless of why the Clovis hunters and their prey disappeared, why should a world growing warmer suddenly head back to ice? There have been 10 glaciations and warmings in the past 700,000 years, explains University of California Santa Barbara paleoclimatoligist James Kennett (who happens to be Douglas Kennett’s father). This abrupt cooling seems to have been unique. All else being equal, he says, “the Younger Dryas should not have occurred,” No long-term pattern explains it. The earth was getting warmer. The amount of solar radiation reaching the northern hemisphere was near its peak. “So why have a cooling?”
You may remember Al Gore warning against the perils of global climate change. He suggested that an accelerated melting of the Greenland ice cap could send enough fresh water into the north Atlantic to disturb the so-called North Atlantic conveyor, the northbound current of relatively warm ocean water that moderates the temperature of North America and northern Europe.
In fact, fresh water has screwed up the North Atlantic conveyor before. As the last ice age waned, the huge Laurentide Ice Sheet started melting, releasing huge volumes of fresh water that formed the giant Lake Agassiz in what is now central Canada and the northern Midwest, and flowed down the Mississippi Valley to the Gulf of Mexico.
Then, suddenly, 12,900 years ago, the flow of meltwater shifted. Lake Agassiz largely drained. The freshwater torrent started flowing east, perhaps along the St. Lawrence valley, to the north Atlantic, and north to the Arctic. The conveyor was indeed disturbed, and cold weather returned to much of the northern hemisphere for another thousand years. That was the Younger Dryas. James Kennett suggests the change in ocean currents that caused the Younger Dryas was the prototype of the process Gore describes.
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