Analysis of how long erratics have been exposed on ice-free ground in the hypothesized “Late Pleistocene ice-free corridor migration route” suggests that route was not fully open until about 13,800 years ago.

The ice sheets “may have been 1,500 to 3,000 feet (455 to 910 m) high in the area where they covered the ice-free corridor,” according to study lead author Jorie Clark, a geologist and archaeologist at Oregon State University.

Clark said, “we now have robust evidence that the ice-free corridor was not open and available for the [Late Pleistocene] first peopling of the Americas.”

If evidence of humans in the Americas prior to the 30,000 years ago is ultimately found, that evidence does not preclude the possibility of ice-free corridor migration before closure of the corridor.