The age of the opening of the Ice-Free Corridor and implications for the peopling of the Americas

The Clovis-first model for the peopling of the Americas by similar to 13.4 ka has long invoked the Ice-Free Corridor (IFC) between the retreating margins of the Cordilleran and Laurentide ice sheets as the migration route from Alaska and the Yukon down to the Great Plains. Evidence from archaeology and ancient genomics, however, now suggests that pre-Clovis migrations occurred by at least similar to 15.5 to 16.0 ka or earlier than most recent assessments of the age of IFC opening at similar to 14 to 15 ka, lending support to the use of a Pacific coast migration route instead. Uncertainties in ages from the IFC used in these assessments, however, allow for an earlier IFC opening which would be consistent with the availability of the IFC as a migration route by similar to 15.5 to 16.0 ka. Here, we use 64 cosmogenic (Be-10) exposure ages to closely date the age of the full opening of the IFC at 13.8 +/- 0.5 ka. Our results thus clearly establish that the IFC was not available for the first peopling of the Americas after the Last Glacial Maximum, whereas extensive geochronological data from the Pacific coast support its earlier availability as a coastal migration route.

Automated summary

The Clovis-first model suggests the migration of humans in the Americas occurred through the Ice-Free Corridor (IFC) between the retreating Cordilleran and Laurentide ice sheets. However, new archaeological and ancient genomic evidence suggests earlier migrations before the Clovis people, possibly through a Pacific coast route. Uncertainties in the IFC's opening age allow for the possibility of an earlier opening, consistent with a migration route around 15.5 to 16.0 ka. Using cosmogenic exposure ages, this study establishes the full opening of the IFC at 13.8 +/- 0.5 ka, proving it was not available for the initial peopling of the Americas after the Last Glacial Maximum, while supporting an earlier availability as a coastal migration route based on geochronological data from the Pacific coast.