Twenty-five years ago it was taken as gospel truth that the people collectively known as native Anmericans had all arrived via the Bering land bridge, no more than 10,000 years ago. Modern students in the field now ponder at least three separate waves of Immigration to the Americas, roughly between 10,000 and 30,000 years ago. I think they are generally referred to as Trans-Pacific, Trans-Atlantic, and Beringean. And, of course, if one group made any of the crossings successfully, there's no reason to believe that they would have been the only group to do so. Some Native American legends look back to the earliest arrivals as having been some 30,000 years ago. The great variety of languages and phenotypic groupings of Native American peoples also argue for multiple origins. Perhaps the biggest problem in understanding the anthropo-history of the Americas is the eurocentric baggage investigators have traditionally brought with them. These things move slowly, and seemingly in spurts. "hard evidence" is often just not available, so an open mind is of great value.