Findings of stone tools move back the first immigration of humans to America at least 15,000 years. This is revealed in a new international study from the University of Copenhagen, where researchers have analysed ancient material from a Mexican mountain cave.
The first humans arrived in America at least 30,000 years ago, approximately 15,000 before science was hitherto able to render it probable. This is the conclusion in new study published in the scientific journal, Nature.
The team behind the article consists of archaeologists and DNA experts from the University of Copenhagen and universities in Mexico, the UK, the US and Brazil, among others.
"The article in Nature is a scientific hand grenade. The fact that it moves back the time of early immigration to America significantly is guaranteed to ignite a heated debate," says Eske Willerslev, Professor and Head of Lundbeck Foundation Centre for GeoGenetics, Globe Institute at the University of Copenhagen.
Eske Willerslev and his two colleagues, Associate Professor Mikkel Winther Pedersen and Assistant Professor Martin Sikora, made up the Danish contribution to the international team of researchers.
The three scientists from UCPH have conducted the DNA analyses of ancient remains from animal and plant material found during the excavations of the Chiquihuite Cave in Northern Mexico.
1,900 stone tools
As far back as 30,000 years ago, humans had already developed techniques for producing tools. In the Mexican cave, researchers found 1,900 stone tools.
The unique feature of the Chiquihuite Cave is the "floor", which consists of six layers of detritus and dust - all in all, a ten-foot column of ancient remains - which is so compressed and stable that by using various advanced measuring methods, it has been possible to date the layers one by one, from top to bottom.
Each layer has contained deposits of stone tools such as knives, scrapers and arrowheads, which the researchers have also been able to date.
"The cave finds are extremely interesting. These archaeological finds are so far the oldest in America. And the excavated stone tools are of a type unique to America," Professor at Universidad Autónoma de Zacatecas, Mexico, Ciprian F. Ardelean, states.
Ice Cap Across North America
Until now, science has assumed that the earliest immigration to America took place approx. 15,000 years ago. At the time, a narrow opening in the ice along the northern Pacific coastline was created, which made it possible to walk from Siberia onto the American continent.
At the time, there were no other access routes to the continent, because North America was covered by a thick ice cap, which only later - approx. 13,000 years ago - melted enough to enable passage.
30,000 years ago, when the first stone tools were left in the Chiquihuite Cave, the massive ice cap had not yet covered all of North America, which means that it would have been possible to walk from Siberia and down through the American continent, Eske Willerslev explains.
"And that's how we must understand the presence of these humans in Mexico at this particular time - unfortunately though, we have no idea who they were. Because although we searched very thoroughly for human DNA in the samples we gathered during the ten days we spent at the Chiquihuite Cave, there were no human traces to be found. However, we may still be able to find some in the hundreds of earth samples we gathered, because we've not yet had time to analyse all of them."
According to Mikkel Winther Pedersen who was in charge of the DNA analyses, their finds contain DNA samples from numerous plants as well as animals. He elaborates:
"For example, we found DNA from an American black bear, a wide range of rodents, several types of bats as well as sparrow and falcon. These are all animals we would expect to find in Mexico at the time. Simultaneously, we were able to ascertain how the plant composition changed over time in step with the climate changes that occurred during this period."
The study was supported by the Lundbeck Foundation, Novo Nordisk Foundation and Carlsberg Foundation, among others. Read the entire study "Evidence of human occupation in Mexico around the Last Glacial Maximum" in Nature.
