No, but it does give lie to Columbus "discovering" America. Especially since he only tooled about the Caribbean and never hit the Continent.
Wasn't there some excitement a while ago about a discovery that the Phoenicians were crossing the Atlantic rather regularly? And didn't they find evidence of a West African presence in S. or C. America?
Wish my memory worked. It was like on some PBS special. (There, if that isn't an acceptable bibliographic source, I don't know what is!
Also...don't forget Brendan the Voyager. I mean, while I doubt the old Saint made the journey himself, the landfalls mentioned in the accounts match up fairly well with geographical areas on the NE coast of North America. And if the Vikings could do it in longboats, why not Irish monks in a curragh? Especially if they got into the Guinness beforehand.