An international team of researchers has found evidence that suggests the Ice-Free Corridor (IFC) proposed to have existed between ice sheets along a route from Beringia to the Great Plains came to exist approximately 13,800 years ago. In their paper published in Proceedings of the National Academy of Sciences, the group describes using cosmogenic nuclide surface exposure dating to date boulders left behind by the ice sheets that once covered the IFC, and their conclusion that early travelers likely came by boat.