There's genetic information that a lot of Nordic blood was infused into the Native American population as far back as Ice Age times. Both a chromosome that only shows up in European races, and a type of Clovis toolmaking that was only seen in stone age times in Western Europe, are showing up in ancient bones and relics in North America.
Which leads you to the crazy image of seafaring cavemen launching themselves across the Atlantic, in large numbers, long before Columbus or Eric the Red.
I'm visualizing skin boats made with mammoth hides or something...mind-boggling. But the scientists are still arguing over it.