NEW YORK — Researchers have found new evidence that the first Americans migrated south from Alaska via the Pacific Coast, rather than a route hundreds of miles inland along the Rocky Mountains.

The colonization of the Americas began after people arrived from Siberia, crossing an ancient land bridge into Alaska. Huge ice sheets largely blocked the way south, but a gap in Canada was long thought to provide an ice-free corridor for migration into the continent.

That idea ran into a problem as archeologists documented human presence in the Americas at earlier and earlier times. The corridor appeared some 15,000 to 14,000 years ago as the ice sheets retreated, but studies suggest that people had reached South America by at least 14,700 years ago. Even if one accepts the earliest date for the corridor, it’s hard to believe the migration could have gone so far south, so fast.

So in recent years many scientists have concluded the first southward migrants traveled along the Pacific Coast instead, either in boats or on land.

The new research, released Wednesday by the journal Nature, casts further doubt on the inland corridor. It suggests that even after the corridor appeared, it wasn’t suitable for migration until about 12,600 years ago. That’s because it lacked plants and game that people would need to sustain themselves on the long journey, researchers said.