Question

What events allowed for the early settlement of the Americas during the Ice Age?

Answer 1

Indigenous Amerindian genetic studies indicate that the "colonizing founders" of the Americas emerged from a single-source ancestral population that evolved in isolation, likely in Beringia.[15][16][17][18][19] Age estimates based on Y-chromosome micro-satellite place diversity of the American Haplogroup Q1a3a (Y-DNA) at around 10,000 to 15,000 years ago.[5][20] This does not address if there were any previous failed colonization attempts by other genetic groups, as genetic testing can only address current population ancestral heritage.[5]
Migrants from northeastern Asia could have walked to Alaska with relative ease when Beringia was above sea level. But traveling south from Alaska to the rest of North America may have posed significant challenges. The two main possible routes proposed south for human migration are: down the Pacific coast; or by way of an interior passage (Mackenzie Corridor) along the eastern flank of the Rocky Mountains.[18] When the Laurentide and Cordilleran ice sheets were at their maximum extent, both routes were likely impassable. The Cordilleran sheet reached across to the Pacific shore in the west, and its eastern edge abutted the Laurentide, near the present border between British Columbia and Alberta. Geological evidence suggests the Pacific coastal route was open for overland travel before 23,000 years ago and after 15,000 years ago. During the coldest millennia of the last ice age, roughly 23,000 to 19,000 years ago, lobes of glaciers hundreds of kilometers wide flowed down to the sea.[16] Deep crevasses scarred their surfaces, making travel across them dangerous. Even if people traveled by boat—a claim for which there is currently no direct archaeological evidence as sea level rise has hidden the old coastline — the journey would have been difficult with abundant icebergs in the water.
read more at: http://en.wikipedia.org/wiki/Settlement_of_the_Americas