Good point.......human migration to the Americas was most probably through the Bering Straits. I am skeptical about the sea route theories because later Amerindian tribes do not appear to have the necessary technology.
Additionally, they were not a trading people. If they were, we would see more evidence of trade between the South American and North American tribes. Intercontinental trade (and by extension, travel) appears to have existed only in the "old world."
There are also substantial finds of South American culture in Mississippian sites.
You have to read more ~ there's lots of stuff that's gone on right under your nose.