The first people to arrive in the Americas were unlikely to have migrated via a corridor in western Canada opened by retreating ice sheets at the end of the last ice age, concludes a paper published this week in Nature. The corridor has long been considered to be the most likely route for the migration of the first people into the Americas from Siberia. However, the new study suggests that although the corridor opened around 14-15,000 years ago, it was not colonized by plants and animals - and was therefore unable to support human migration - until thousands of years later
The ice-free corridor between the Cordilleran and Laurentide ice sheets, which together covered much of present-day Canada and much of the northern United States, was long thought to be the only way into North America for humans who had crossed the Bering Land Bridge. Recent evidence instead suggests human presence in the Americas before the corridor had opened, leading many to now favour an alternative migration route along the Pacific coastline for these early Americans. Although the ice-free corridor could have provided an entryway for later migrations, it has been unclear whether there would have been sufficient sources of food and shelter to support humans travelling this route into the Americas.
Eske Willerslev and colleagues analysed nine sediment cores from Charlie Lake and Spring Lake in British Columbia and Alberta, Canada, representing the last areas of the corridor to become ice-free. Their reconstruction of the environment from plant remains and environmental DNA reveals that the landscape had become vegetated by about 12,600 years ago and was concurrently occupied by animals, including the bison and mammoth that were an important food source hunted by early Americans. The findings suggest that the first Americans are unlikely to have travelled by this route into the Americas, but that later groups may have used this north-south passageway.
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