How did glaciers affect routes into North America during the Pleistocene Epoch?

During the Pleistocene Epoch, glaciers significantly influenced migration routes into North America by both creating and obstructing pathways for human and animal movement.

As global temperatures dropped, glaciers absorbed vast amounts of water, causing sea levels to fall by as much as 400 feet. This process exposed Beringia, a broad land bridge connecting northeastern Asia to northwestern North America. While this bridge provided an entry point, early migrants were often held back in the northwestern sector of the continent by impenetrable glacial formations.12

For a long period, massive ice sheets—specifically the Cordilleran Ice Sheet and the Laurentide Ice Sheet—blocked movement into the interior of the continent. It was once believed that humans traveled through an "ice-free corridor" between these sheets, but recent evidence suggests this route was not viable until approximately 12,600 years ago. Because archaeological sites indicate human presence in the Americas well before this date, it is now understood that initial migrations likely occurred along the Pacific coast, potentially utilizing both walking and boat travel.341