Pieces of limestone from a cave in Mexico are perhaps the oldest human tools ever found in the Americas and suggest that people first entered the continent 33,000 years ago – much earlier than we never thought so before.
The findings, published Wednesday in two articles in the journal Nature that include the discovery of the stone tools, challenge the idea that people first entered North America on a land bridge between Siberia and the ‘Alaska and an ice-free corridor in the interior of the continent.
The precise archaeological dating of the earliest human sites in North America, including the Cave of Mexico, suggests instead that they may have entered along the Pacific coast, the research finds.
Ciprian Ardelean, an archaeologist at the Autonomous University of Zacatecas in Mexico, and lead author of one of the articles, said the finds were the result of years of careful excavation in the Chiquihuite cave in north-central Mexico.
The steeply sloping cave is set high on the mountainside and filled with layers of crumbling gravel: “The deeper you go, the more the walls are likely to collapse,” he said.
The excavations paid off with the discovery of three deliberately formed pieces of limestone – a pointed stone and two cut flakes – which are perhaps the oldest human tools found in the Americas.
They date from a time when the continent appears to have been occupied by only a few groups of early humans – possibly “lost migrations” that have left little mark on the landscape and in the genetic register, Ardelean said.
The tools were found in the deepest layer of sediment they excavated, which dates back 33,000 years, long before the last Ice Age, which occurred between 26,000 and 19,000 years ago.
The generally accepted time for the first people to arrive in North America is approximately 16,000 years ago, and recent studies estimate that this happened as much as 18,000 years ago. But the latest discoveries push the date back more than 10,000 years.
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Ardelean said even reaching the cave was a challenge for the team.
“You have to live there and cook there, because it takes you a whole day to come and go from town, and it’s a five hour climb,” he says. “It’s a logistical nightmare.”
Other tools have been found in sediments deposited during and after the Ice Age, and indicate that the cave was occupied for short periods over thousands of years, possibly by nomads who knew it from legends. ancestral.
“I think it was a refuge used occasionally and periodically,” Ardelean said. “Even though you’ve never seen the site before, your grandparents told you about it and there were indications when you arrived. “
The presence of Ice Age stone tools – known to archaeologists as the Last Glacial Maximum, or LGM – suggested that people occupied the cave even before that.
Much of North America was then covered with thick ice caps that would have made migrations impossible, he said: “If you have people during LGM, it’s because they came in. on the mainland before the LGM.
Lorena Becerra-Valdivia, archaeologist at the University of Oxford and the University of New South Wales, and Thomas Higham, radiocarbon dating specialist at the University of Oxford, compared the dates of sediments from the cave with other archaeological sites in North America.
Their research indicates that very small numbers of humans likely lived in parts of North America before, during, and immediately after the last ice age, but the human population grew much more after a period of abrupt global warming that started about 14,700 years ago.
The study also suggested that some people entered the Americas 29,000 years ago, possibly along the Pacific coast, when the land bridge between Siberia and Alaska was completely or partially submerged, said Becerra-Valdivia.
Ardelean hopes archaeologists will now look for evidence of human occupation from the earliest dates proposed in the new studies.
He believes the stone tools and perhaps ancient human DNA from that time could be hidden under the traces of the largest human population that lived in North America after the Ice Age.
“Instead of stopping digging when you reach a certain layer… you have to go as far as you can because there are things there,” he says.
Other scientists are wary of the implications of the new research.
Anthropologist Matthew Des Lauriers of California State University, San Bernardino, who was not involved in the studies, said they “pushed the boundaries” of knowledge of the first human arrival in the Americas.
But he wondered how ancient peoples who had been in the Americas for more than 25,000 years could have remained “archaeologically invisible” for more than 10,000 years.
He said archaeologists from Australia and Japan, for example, had no difficulty finding evidence of human occupation from this era.
“Archaeologists in the Americas have done some very bad things over the past 90 years, or here we have [an] anomaly that must be taken into account, ”he said.