How did early humans first enter the Americas?

After crossing into Alaska, the Ice Age adventurers may have trekked along two routes: either by foot through the interior of present-day Canada through a grassy passageway between two large ice sheets, or they moved south along the Pacific Coast.

Scientists have debated the two theories, and in recent years support for the coastal route has grown from archaeological finds, such as 13,000-year-old footprints on an island in British Columbia. Now, geologists studying boulders and bedrock on Alaska’s southeastern islands have found evidence of an ice-free route some 17,000 years ago down the coast that would have allowed human travel.

“We’re not definitively saying they took the coastal route,” said Alia Lesnek, a graduate student at the University at Buffalo and lead author of the study. “We have some of the first direct evidence that that was something that could be done.”

The finding, published Wednesday in the journal Science Advances, supports the theory that the first people to populate the Americas were seafarers traveling from island to island.