The Vikings certainly got there. But didn't you see that excellent programme on TV, showing evidence that might prove the Solutrean peoples, (from what's now Spain), got to the present-day US around 20,000 years ago, well before the asiatic migration across the Bering Straits?
Then there is the mystery of Tobacco and Cocaine found in ancient Eyptian mummies. Both South American in origin. How did they get from South America to Egypt 3000 years ago?