Paris (AFP) – Tools excavated from a cave in central Mexico are strong evidence that humans lived in North America at least 30,000 years ago, about 15,000 years earlier than previously thought, scientists said on Wednesday.
The artifacts, including 1,900 stone tools, showed human occupation of the Chiquihuite cave at high altitude over a period of approximately 20,000 years, they reported in two studies, published in Nature.
“Our results provide new evidence of the antiquity of humans in the Americas,” Ciprian Ardelean, an archaeologist at the Autonomous University of Zacatecas and lead author of one of the studies, told AFP.
“There are only a few artifacts and a couple of dates in that range,” he said, referring to radiocarbon dating results that locate the oldest samples between 33,000 and 31,000 years ago.
“However, the presence is there.”
No traces of human bone or DNA were found at the site.
“Humans are likely to use this site relatively constantly, perhaps in recurrent seasonal episodes that are part of larger migration cycles,” the study concluded.
The stone tools, unique in the Americas, revealed a “mature technology” that, according to the authors, was brought from elsewhere.
The saga of how and when Homo sapiens arrived in the Americas, the last great land mass populated by our species, is fiercely debated among experts, and the new findings are likely to be questioned.
– ‘Clovis-first’ discredited –
“That happens every time someone finds sites that are more than 16,000 years old; the first reaction is denial or tough acceptance,” said Ardelean, who excavated the cave in 2012 but did not discover the oldest elements until 2017.
Until recently, the widely accepted story was that the first humans to set foot in the Americas crossed a land bridge from present-day Russia to Alaska some 13,500 years ago and moved south through a corridor between two massive ice sheets.
Archaeological evidence, including spearheads specially designed to kill mammoths and other prehistoric megafaunas, suggested that this founding population, known as Clovis Culture, spread across North America, giving rise to distinct Native American populations.
But the so-called first Clovis model has crumbled in the past two decades with the discovery of several ancient human settlements dating back two or three thousand years ago.
Furthermore, the remains of tools and weapons at these sites were not the same, showing different origins.
“Clearly, people were in the Americas long before the development of Clovis technology in North America,” Gruhn, professor emeritus of anthropology at the University of Alberta, said in commenting on the new findings.
In a second study, researchers at the University of Oxford Radiocarbon Accelerator Unit, Lorena Becerra-Valdivia and Thomas Higham used radiocarbon, supported by another luminescence-based technique, to date samples from 42 sites in North America.
Using a statistical model, they showed a widespread human presence “before, during, and immediately after the Last Glacial Maximum” (LGM), which lasted from 27,000 to 19,000 years ago.
– Megafauna annihilated –
The timing of this deep cold is crucial because it is widely accepted that humans migrating from Asia could not have penetrated the huge sheets of ice that covered much of the continent during this period.
“So if humans were here DURING the Last Glacial Maximum, that’s because they had arrived BEFORE,” Ardelean said in an email.
Human populations scattered across the continent during an earlier period also coincide with the disappearance of once-abundant megafauna, including mammoths and extinct species of camels and horses.
“Our analysis suggests that the widespread expansion of humans across North America was a key factor in the extinction of large land mammals,” the second study concluded.
Many key questions remain unanswered, even if the first of our species to roam the frozen Beringia tundra headed south on an inland route or, as recent research suggests, moving along the coast, either to foot or in boats of some kind.
It is also a mystery “why no archaeological site of equivalent age to the Chiquihuite cave has been recognized in the continental United States,” Gruhn said.
“With an entry point to the Bering Strait, the first people to expand south must have passed through that area.”
