By Michael Marshall
Mads Thomsen
HUMANS seem to have been living in the Americas as early as 33,000 years ago – 15,000 years before the most widely accepted date. The finding implies that people arrived there before the peak of the last glacial period and there is a long American prehistory we are yet to uncover.
The first American settlers were probably Homo sapiens, but we can’t rule out extinct groups like Neanderthals and Denisovans. The settlers probably entered from north-east Asia across a land bridge linking Asia and Alaska. This was submerged by rising seas when the ice sheets melted at the end of the last glacial period.
Most archaeologists accept that humans were in the Americas 18,000 years ago. Now two studies bolster the idea that people got there much earlier.
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Ciprian Ardelean at the Autonomous University of Zacatecas in Mexico and his colleagues have spent the past decade excavating Chiquihuite cave in Zacatecas. They have found almost 2000 stone tools buried in sediments in the cave, including blades, points and scrapers. No human remains or DNA have been found.
The youngest samples of sediment are at least 12,200 years old, and the oldest may be 33,150 years old (Nature, DOI: 10.1038/s41586-020-2509-0). This suggests that people lived in the Americas before a crucial event: the last glacial maximum – the peak of the last glaciation. Between 26,500 and 19,000 years ago, ice sheets extended across much of North America. This was thought to make condition too harsh for people to enter the Americas, but the new findings suggest humans were already present.
The second study compiles reliably dated archaeological sites to track the spread of people across North America. Lorena Becerra-Valdivia at the University of New South Wales in Australia and Thomas Higham at the University of Oxford, who are also on Ardelean’s team, assembled dates from 42 sites in North America and north-east Asia. Chiquihuite cave was the oldest reliably dated site (Nature, DOI: 10.1038/s41586-020-2491-6).
During and just after the last glacial maximum, North America seems to have been sparsely populated, with numbers exploding about 14,700 years ago as the ice receded, says Becerra-Valdivia.
The two studies offer “strong evidence for an earlier presence of humans in North America than has been fully accepted”, says Deborah Bolnick at the University of Connecticut.
Until now, it has been widely assumed that only modern humans reached the Americas, since groups like Neanderthals died out millennia before anyone was thought to have got there. Ardelean says we shouldn’t assume that any more. “I don’t see why other species wouldn’t have entered America,” he says.
But Bolnick and Becerra-Valdivia both say the first Americans were most likely to have been modern humans.
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