A new study challenges the theory that humans populated the Americas using a corridor between ice sheets more than 12,600 years ago.

After humans arrived from Siberia to Alaska via a land bridge, the route south from there was blocked by two huge ice sheets in what is now Canada, called the Cordilleran and the Laurentide. As those ice sheets melted, a corridor opened between them, estimated to be about 930 miles long.

But the study released Wednesday uses an interesting method to demonstrate that that corridor couldn’t have supported human traffic until about 12,600 years ago, even if it was physically open before that. And as such, the researchers argue that people who arrived before then must have traveled down the Pacific coast by boat.

Scientists took samples from the materials beneath two modern bodies of water— Charlie Lake and Spring Lake in Canada— standing on the ice during the winter and drilling down. The point they chose to analyze was key, because it represents one of the last parts of the corridor to actually open, and was what the study refers to as a “bottleneck.”

Then, they analyzed the ancient DNA they found, and that told them a story about how the once-glaciated landscape became colonized. The researchers found evidence, starting about 12,600 to 12,500 years ago, of mammoth and bison; then voles and jackrabbits; and after that, bald eagles, elk, and moose roamed the landscape, their data demonstrated.

In short, while the corridor they studied was open beforehand, it wasn’t until about 12,600 years ago that enough plants and animals lived there to support humans on their journey. The study is published in the journal Nature.

Because of this, the researchers hypothesize that ancient people who journeyed south before that had to come down the Pacific coast.

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“The bottom line is that even though the physical corridor was open by 13,000 years ago, it was several hundred years before it was possible to use it,” Eske Willerslev, a professor at St. John’s College, Univeristy of Cambridge, and the lead researcher on the study, said in a statement. “That means that the first people entering what is now the US, Central and South America must have taken a different route.”

After the corridor did open, people used it to go south, or even travel north, according to the study.

Tom Dalton Dillehay, a professor of anthropology, religion, and culture at Vanderbilt University, and author of book The Settlement of the Americas: A New Prehistory, said a study like this one had been needed for a while, but that it was just a start.

“It is a well documented interdisciplinary work that attempts to resolve the early corridor route beyond standard archeology and geology,” Dillehay wrote in an email to FoxNews.com. “I would like to see more studies of this nature done in other areas of the corridor to confirm this hypothesis, especially at the entrance and exits points of the corridor.”

Follow Rob Verger on Twitter: @robverger