An international team of scientists said that the tools extracted from a cave in central Mexico provide strong evidence that humans lived in North America at least 30,000 years ago, i.e. 15,000 years earlier than previously thought.
In two studies published in the journal Nature, the researchers showed that artifacts, including 1,900 stone tools, demonstrated human occupation of the high-rise Chiquihuite Cave Cave for nearly 20,000 years.
Humans passed through here
"Our results provide new evidence for the ancient times of humans in the Americas," said Cyprien Ardelin, an archaeologist at the University of Autonoma de Zacatecas, Mexico, the lead author of one of the studies, told AFP news agency as Science Alert reported.
"There are only a few artifacts and some dates in this range," and "nevertheless, the humans were there," even if no traces of human bones or DNA were found at the site, indicating the results of the history with radiocarbon that The oldest samples are placed between 33,000 to 31,000 years ago.
The study concluded that "it is possible that humans have used this site relatively consistently, perhaps in frequent seasonal episodes as part of large migration cycles, where stone tools - unique in the Americas - revealed a" mature technique "that the authors speculate that humans came It from somewhere else.
The saga of how and when Homo sapiens reached the Americas - the last major land mass inhabited by humankind - is a matter of debate among experts, and new findings are likely to be debated.
Clovis' hypothesis first collapsed
"This controversy occurs every time anyone finds sites over 16,000 years old ... the first reaction is to deny or accept hard," said Ardelen, who first dug the cave in 2012 but did not discover the oldest items until 2017.
Until recently, the widely accepted story was that the first humans to step foot in the Americas crossed a land bridge from present-day Russia to Alaska about 13,500 years ago and moved south through a corridor between two huge ice sheets.
Archaeological evidence indicates that this founding population, known as the Clovis culture, spread throughout North America, leading to the emergence of the distinct indigenous Native Americans.
But the so-called "Clovis is the first" model has collapsed over the past two decades with the discovery of many ancient human settlements dating back two or three thousand years before this date.
Moreover, neither the tools nor the remnants of weapons found at these sites were the same, which indicates that the inhabitants of America were of distinct origins.
Major mammal offset
In the second study, also published in Nature, Lorena Becerra Valdivia and Thomas Hegham, researchers at the University of Oxford's Radiant Carbon Acceleration Unit, have used radioactive carbon - backed by another luminescence-based technology - so far on samples from 42 locations across North America.
Using a statistical model, they demonstrated a widespread human presence "before, during and after the last Last Glacial Maximum" (LGM) ice, which lasted from 27,000 to 19,000 years.
And as Ardelen pointed out, "If humans had found here during the last ice cap, it is because they had already arrived here before that," because it was difficult for them to have moved during that very cold period.
The presence of human groups scattered throughout the continent during a previous period also coincided with the disappearance of large animals that had been in abundance, including mammoths and extinct species of camels and horses.
The second study concluded that "the widespread spread of humans across North America was a major factor in the extinction of megafauna."