Retracing the footprints of time
Two U of A researchers make a disputed claim about human antiquity in North America
Anthropologists Bryan and Chlachula: Luck and intuition ina Calgary gravel dump.
Gut instinct and sheer serendipity: those were th e factors that may force North American scientists to redefine their ideas regarding the antiquity of human habitation in North America. In an otherwise unremarkable gravel bluff on the banks of the Bow River in Calgary, University of Alberta researchers Jiri Chlachula and Alan Bryan believe they have unearthed the remains of what could be the oldest human artifacts in North America, the pair announced this month. If substatiated, the discovery pushes back the known date of human settlement in North America by several thousand years. Other earth scientists are sceptical about the find's authenticity: U of A geomorphologist Rob Young describes it as "based only on pure speculation."
Scientists generally agree that humans first arrived in North American between about 10,000 and 13,000 years ago via the Bering Strait land bridge which then connected northeast Asia and Alaska. However, it is known that much earlier, from around 45,000 to 21,600 B.C., the continent teemed with animal species, including giant lions, bears, several species of elephants, muskox and camels. That suggests humans could have survived comfortably--had any been present.
But from approximately 21,000 to 18,000 B.C., cooler earth temperatures resulted in enormous ice sheets spreading across Canada. From the east, the encroaching Laurentide sheet, a sprawling mass covering eastern Canada and much of the northern U.S., draped the majority of Alberta with one to two kilometres of ice.
From the west, Alberta was invaded by another amoeboid ice mass, the smaller Cordilleran ice sheet. The two collided in the Porcupine Hills region in the foothills of the Alberta Rocky Mountains.
For most of an 8,000-year period, Alberta and the rest of Canada were almost completely icebound. But after 18,000 B.C., global temperatures began to rise slowly, beginning the lengthy process of deglaciation. At the front of the receding ice sheets, proglacial lakes were formed by accumulating meltwater. According to University of Calgary archaeologist Gerry Oetallar, one such lake was Glacial Lake Calgary. " The lake, formed about 15,000 to 16,000 B.C., later drained and incised the current Bow River Valley," he explains. It is in this ancient gravel lakebed that the theorized 20,000-year-old human artifacts lie.
Prof. Bryan, an anthropologist, recalls how his Czech research partner, Prof. Chlachula, stumbled across the site accidentally as a U of C student in 1990. Disregarding the scientific orthodoxy which held that no human remnants could be found in the deeper sediments of the gravel deposit located in Calgary's Varsity Estates neighbourhood, "he took a chance, and as a result found stone tools eroding out of the contact between two glacial deposits."
In all, about 50 instruments used by prehistoric people for pounding and crushing have been identified by the pair since 1990. Prof. Bryan believes they were fashioned from the abundant pulverized rock produced by glacial movement.
Prof. Bryan explains that the biface tools--flaked on both sides--could not have been carried b y ice or water to the Calgary site because they have sharp edges, not worn, rounded ones. He is confident that they must have been discarded by people who first migrated to the area at least 20,000 years ago, extrapolating this number from radiocarbon dati ng of similar Edmonton sites known to have been created during the same period.
Direct radiocarbon dating of the Calgary site is not possible because the ancient artifacts were not found in conjunction with organic matter, such as bones or decayed plant matter, which is necessary for such testing. Absent such verification, Prof. Young dismisses the find. For one thing, he says, the artifacts are so simple they could merely be naturally-occurring rocks; he says that most informed scientists are doubtful th ey are tools. And even if they are tools, he adds that there is no way to be sure that they were originally situated where they were found under the gravel, since the site has served as an exposed gravel pit for the last 100 years. Comments Prof. Young: "Any dude could have put that rock there."
One approach that might resolve the debate is by dating the inorganic materials from the site through a technique known as thermoluminescence. In this process, the electrons of sediments react on their last exposure to the sun, a phenomenon that can sometimes be used as a geologic clock. Prof. Bryan says some of the material will be tested with the method, but he concedes it may be inconclusive. Still, he is certain that the 20,000-year-old estimate will ultimately be proved accurate.
Prof. Young counters that if the artifacts prove authentic, it is a virtual certainty that they will subsequently found to be about 12,000 to 13,000 years old, in accord with known radiocarbon-dated dig sites elsewhere. Until now, the earliest remains in Alberta have been in the Vermilion Lakes region near Banff. "Anything estimated earlier from these sites is incredible," says Prof. Young. " And why do you call a newspaper conference before you do your dating? There are no fossils, no radiocarbon dates. Just bad correlation."
Prof. Oetalaar reports opinion on the Calgary site is divided among other earth scientists. "Some believe in the legitimacy of the site, while others are much more hesitant." Plains archaeologist Rod Vickers says the discord is no surprise. "You put three archaeologists in a room together," he chuckles, "and you're bound to get five different opinions."
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