The most commonly discussed alternative is a coastal route.

The Pacific Coast of North America, during the Last Glacial Maximum, was partially glaciated in the north but may have had ice-free refugia — areas where the coast was accessible — that could have allowed people to move southward by boat or along the shore.

This coastal migration hypothesis has been gaining support from multiple lines of evidence over the past two decades.

The White Sands dates are consistent with it, though they do not prove it specifically.

There is another possibility that some researchers have been reluctant to entertain: that people arrived in the Americas far earlier than either the Clovis timeline or the coastal migration timeline suggests — not 15,000 years ago, not 23,000 years ago, but perhaps 30,000 or even 40,000 years ago.

A handful of sites have produced evidence that proponents argue supports this possibility, though most of these claims remain contentious.