Paris (AFP)

It is a upheaval for the world of archeology: going back 30,000 years, the settlement of North America, the last continent to have been occupied by man, is twice as old as estimated so far, two studies reveal Wednesday.

While excavating the cave of Chiquihuite, in northern Mexico, archaeologists unearthed hundreds of cut stone tools revealing a still unknown lithic industry, dating back to 33,000 years before our era.

They prove that this site, perched in altitude, was occupied for 20,000 years, according to two studies published in the journal Nature.

"Our research brings new evidence on an ancient presence of humans in America", the last continent to have been occupied by modern man, welcomed AFP archaeologist Ciprian Ardelean, main author of one of the two studies.

The oldest specimens have been dated with radiocarbon (or carbon-14) over a range of between 33,000 and 31,000 years before our era. "They are few, but they are there," commented this researcher from the Universidad Autonoma de Zacatecas in Mexico.

They reveal a method of stone carving unique in America, using thin slat debitage - an advanced technology that would have come from elsewhere, according to the authors.

While no human bone or DNA was found at the site, "it is likely that humans have used it as a fairly fixed base, presumably during recurrent seasonal episodes as part of larger migratory movements," says study.

The origins of Homo sapiens' arrival in America - the last continent inhabited by our species - are hotly debated among anthropologists and archaeologists.

For decades, the most widely accepted thesis has been that of a settlement originating in eastern Siberia, which crossed a land bridge - the present-day Bering Strait - to land in Alaska, then spread further south.

- "Culture Clovis" -

Archaeological evidence, including spearheads used to kill mammoths, has long suggested a 13,500-year-old stand associated with a so-called Clovis culture - named after a city in the state of New Mexico in the United States - considered like the first American culture from which the ancestors of Native Americans came.

This model of the "primitive Clovis culture" has been called into question for 20 years, with new discoveries which have pushed back the age of the first populations. But only up to 16,000 years old.

The results of this research are therefore likely to be hotly contested. “It happens as soon as someone finds sites older than 16,000 years: the first reaction is either denial or strong approval,” according to the researcher who began excavating the cave in 2012.

"It is clear that stands were found in the Americas long before the development of the Clovis culture," writes Ruth Gruhn, professor of anthropology at the University of Alberta, in a commentary accompanying the publications.

In the second study, researchers were able to date samples from 42 sites across North America, using radiocarbon and luminescence dating.

Using statistical models, they demonstrated a distribution of human presence "before, during and immediately after the period of the last glacial maximum", between 27,000 and 19,000 years.

This episode of glaciation is crucial, because it is commonly accepted that the ice caps covering at the time most of the north of the continent made any human migration from Asia impossible.

"So if humans were there during this last ice age, it is necessarily because they had arrived before", notes Professor Ardelean.

The very ancient presence of populations across the continent also coincides with the disappearance of North American megafauna, including mammoths and other extinct species of camels and horses.

"Our analyzes suggest that the widespread expansion of humans across North America was a key factor in the extinction of large land mammals," the study concludes.

Many questions remain unanswered, notably that of the routes taken by the first arrivals, either through the Bering Strait or, as recent discoveries suggest, along the Pacific coast, on foot or by small boats.

© 2020 AFP