The land bridge is under the icecap. And supposedly these people did not have boats. A maritime technology capable of traveling along the edges of the glacier where it meets the sea did not appear until the Neolithic. Traveling along the ice sheet would give ancient mariners the ability to hunt seals on the ice pack, plus provide ice 'islands' and 'bays' where they could pull in for shelter.

Or is it possible that advanced Neolithic cultures capable of coastal seafaring (like the Pacific islanders, or the Inuit) evolved much earlier than we believe, but just left no archeological evidence? The present-day Inuit would be a remnant of these ancient maritime cultures, not a more recent development.

If these people made it to the American Southwest 20k years ago, they must represent migrations that came from the Asian landmass much, much earlier.

In any event, this is fascinating stuff. Let's hope more evidence starts showing up soon, now that information about this early wave of "illegal aliens" can no longer be dismissed outright by anthropological orthodoxy. This is exciting news.