Below is what Official History says Now.
That humans populated the Americas by coming across the Land bridge from Asia.
But What if this Scenario was all wrong?
What if it turns out that Hapgood and Flem-ath were right. That mankind arose out of what is now the Antarctica - back when it was called Atlantis - And that the planet was RE-populated from the south upwards, and not from the north downwards?
I have always wondered why it was, that we could find African faces in Central America and Pyramids on three different continents - Egypt, Mexico and South East Asia. That cannot have been a coincidence. It bugs me when archaeologists say that each civilisation arose in ISOLATION. That cannot be correct. Humans do not live in isolation. Humans live in societies.
Just look at the Silk road for example. I think the Silk road was a perfect example of DIVERSITY - where ideas and inventions arose in China and spread to the west.
As for the questions on who exactly discovered the America's first... I think the Americas have always been discovered. I think the Phoenicians from 2000 years ago, who were great sailors and who actually did circumnavigate the continent of Africa, could easily have decide to try sailing west, just to see what was out there. It is well known and accepted that the Vikings did know about the Americas after they settled in the area of Newfoundland that we now call L'anse aux Meadows.
The thing about History is that, on order to be preserved, it has to be written down. The Vikings did preserve their history, They spoke their history orally or verbally, as stories, or SAGAS. These Sagas were not written down until many centuries later.