It appears glaciers in western North America receded leaving a corridor that supported life only after humans had already spread south.

It appears glaciers in western North America receded leaving a corridor that supported life only after humans had already spread south.
Photo Credit: Mikkel Winther Pedersen

New findings raise doubts about first migration to Americas

For decades it was believed that the first humans came to North America from Siberia over the Bering Land Bridge and then moved south through a corridor of land opened up by melting glaciers. But new research has found that this western corridor did not support life that the humans would have needed until about 12,000 year ago.

‘How did they get there?’

“The problem with that 12,000-years-ago date is that we already have humans that have somehow got south of these big glaciers and are living in places like Montana and South America at 14,000 years ago. So how did they get there if they didn’t come through the ice-free corridor,”asks Cynthia Zutter, professor of anthropology at MacEwan University in western Canada and a researcher on the project.

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Researchers gathered cores from lake sediments to find out what lived there and when.
Researchers gathered cores from lake sediments to find out what lived there and when. © Mikkel Winther Pedersen
Microscopic DNA was analyzed to reconstruct environments from 12,000 years ago.
Microscopic DNA was analyzed to reconstruct environments from 12,000 years ago. © Mikkel Winther Pedersen

Innovative technique can reconstruct past environments

Rather than using bones and teeth to date and document what life was in the 1,500-km-long corridor, researchers gathered samples from the bottom of lakes and colleagues in Denmark analyzed microscopic DNA to learn about the early environment.

“The workers from Denmark…provided this innovative research methodology that’s going to open up a whole new suite of reconstructing what past environments and vegetation and plant and animal communities were like,” says Zutter.

This map illustrates the difference between the time the western corridor could have supported life and the time humans arrived.
This map illustrates the difference between the time the western corridor could have supported life and the time humans arrived. © Mikkel Winther Pedersen

Tough to confirm coastal travel

The findings support newer theories that early humans came to North America by boat by island-hopping and living off whatever resources they found along the coast. They would have moved south of the ice sheets and spread out over land from there. More research is needed to confirm this, but Zutter says it is difficult.

Sites now under water

“Our challenge is that along that west coast most of those archaeological sites have been flooded because when those ice sheets melted the sea levels essentially rose substantively and any archaeological evidence or evidence of humans living there has now been flooded and is deep underwater. So how do we find it?”

Canadian researchers along the Pacific coast have been looking for evidence for years. Zutter hopes these new techniques will help support them and the theory that early humans first used coastal travel to make their ways south through the Americas. They would have used the western corridor much later when the ice receded and it became home to bison, mammoths, rabbits and other animals and plants.

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