Anthropology

before the LGM. Now there is proof.

It took time for the glaciers to reach a point of making travel on the Pacific coast impossible. During that time, as global temperatures cooled, water levels would have been continually dropping while glaciers formed in many parts of the earth, taking up moisture. The distances between islands would have become smaller, making it more possible for people to island hop.

The Aleutians stretch nearly to Asia, forming "stepping stones" between Asia and North America. Humans were using water travel as long as 50,000 years ago to reach Australia. So reaching North America by boat 30,000 years ago is not only plausible, but seems to be the only explanation for the dating of these footprints. No need for a complete land bridge to walk across. Once in North America, people could follow rivers, streams, and lakes inland. Ancient waterways would be the best places to find ancient artifacts or human remains, I think.

Since the footprints date from 21,000 years ago to 23,000 years ago in New Mexico, people must have been in North America for some time before that to get that far south and inland from the Alaskan coast.