For most of the last ice age, enormous glaciers covered western Canada. And yet people still managed to cross deep into the Americas from their settlements in western Alaska. How did they do it? Archaeologists once thought a narrow strip of land opened up between the glaciers, allowing them passage. But others suspect the migrants hopped down the Pacific coast in boats long before that happened. Now, a new study of bison fossils offers the most precise date yet for the opening of the ice-free corridor: 13,000 years ago. Combined with evidence of earlier occupations in the lower 48, it suggests the corridor could not have been the first route people took into the New World.
http://www.sciencemag.org/news/2016/06/humans-didn-t-wait-melting-ice-settle-americas
