Well c'mon, NO ONE thinks that Columbus was the one who discovered America! There is plenty of evidence that there were multiple groups from Europe, and the Vikings left behind several entire settlements in Newfoundland. That's not even counting Asian migrations over the land bridge that become the Eskimos and Native Americans.
What's interesting is that there is some pretty compelling evidence that the peoples we know as "Native Americans" where NOT the original group of settlers in the Americas, and there were even earlier migrations from Asia (likely by sea) But whenever an archeologist wants to dig up remains to check for evidence of this, the Native Americans refuse permission based on a law that gives them rights over any ancient remains discovered in the US, because they don't want it to be proven they weren't the first humans over here!