 The earliest possible viability of the ice-free corridor as a human migration route has been estimated at 11.5k cal years BP.Birch forests were advancing across former herb tundra in Beringia by 14.3ka 14C years BP (17k cal years BP) in response to climatic amelioration, indicating increased productivity of the landscape.The archaeological community is in general agreement that the ancestors of the Indigenous peoples of the Americas of historical record entered the Americas at the end of the Last Glacial Maximum (LGM), shortly after 20,000 years ago, with ascertained archaeological presence shortly after 16,000 years ago.