Up until now, it had been thought humans entered North America across the Bering Strait around 14,000 years ago. Now, new evidence has shown beyond a doubt that it was in fact 10,000 years earlier than that.

Researchers from Canada and the UK have re-examined and radiocarbon-dated bones excavated from the Bluefish Caves in the Yukon region of northwest Canada, near the Alaska border, and found undeniable traces of human activity that date back 24,000 years. Their research is published in PLOS One.

The site was first excavated by archaeologist Jacques Cinq-Mars between 1977 and 1987. Cinq-Mars discovered a wealth of animal bones, and based on the radiocarbon dating, proposed that humans first settled in North America towards the end of the last ice age, around 30,000 years ago.   

However, with the absence of any other archeological sites of a similar age, as well as a lack of evidence that the animal bones found – which included horse, mammoth, bison, and caribou – were there due to human activity such as hunting, Cinq-Mars’ hypothesis proved controversial.

To settle the matter once and for all, doctoral student Lauriane Bourgeon and her supervisor Professor Ariane Burke of the University of Montreal spent two years examining the 36,000 bone fragments from the Bluefish Caves that had been preserved at the Canadian Museum of History in Gatineau. 

They found undeniable traces of human activity in 15 bones, with a further 20 fragments also showing probable traces of the same type of activity.

There was evidence that a "series of straight, V-shaped lines on the surface of the bones were made by stone tools used to skin animals," said Burke in a statement. "These are indisputable cut-marks created by humans."

They also sent the bones off to the Radiocarbon Accelerator Unit at Oxford University in the UK to be radiocarbon-dated again. They dated the oldest bone, a horse mandible with stone marks from a tool used to remove its tongue, back to between 23,000 and 24,000 years ago.

"Our discovery confirms previous analyses and demonstrates that this is the earliest known site of human settlement in Canada," said Burke. “It shows that Eastern Beringia was inhabited during the last ice age."

According to Burke, previous studies in population genetics have shown that a group consisting of a few thousand individuals lived in isolation in Beringia – a vast region that stretches from the Lena river in Russia to the Mackenzie river in Canada – around 15,000 to 24,000 years ago.

Burke confirmed that their discovery verifies the “Beringian standstill [genetic isolation] hypothesis” that “during the Last Glacial Maximum, Beringia was isolated from the rest of North America by glaciers and steppes too inhospitable for human occupation to the West.” 

This means the earliest human presence in North America can now be dated back to the last ice age. These people, potentially taking refuge in the Bluefish Caves, would therefore be the ancestors of the people who would colonize the entire continent.