[jcranmer]

It's been known since around the mid-90s that the "ice-free gap" opened up too late to allow for humans to arrive before Clovis, and that Clovis-first was an untenable theory. However, it takes a long time for scientific consensus to work its way into textbooks and popular imagination. When I was learning about this stuff in school around 2005-ish, the textbooks still suggested the ice-free migration route, although coastal migration was suggested as a plausible alternative. Even as late as 2017, there's still a popularly cited anthropology writer (but not an anthropologist) who believes in Clovis-first and vociferously argues against pre-Clovis migration.