Geography of Beringia and levels of UV radiation ... This population was genetically isolated for 2,500-9,000 years because of the ice to the east and extensive mesic tundra to the west.

Instead of a mix of grassland, tundra, and ice sheet, the connection between Asia ... creating an enormous region known as Beringia. Or at least it was assumed the land was dry.

New genetic evidence supports the hypothesis that the first people in the Americas all came from northeast Asia by crossing a land bridge known as Beringia ... after the last ice age the land ...