Yeah, the is essentially hard evidence that the vikings made it over circa 1000AD.
There was a very good documentary on concerning this subject a while back. Several cultures were reported to have possibly made it over here pre-Columbus. The Chinese, Japanese, the Irish, etc. The Polynesians in particular looked quite likely to have made it to parts of the western coast as some of the canoes used by the western tribes were very close to Polynesian canoes in design, and the tribes referred to them by a term that was quite close to the Polynesian word for canoe (not to mention it's quite obvious that they made it at LEAST as far as Hawaii, having been the group to settle that island).
In reality, I think the truth is that a number of different groups made it over here at various times throughout history.
The documentary is "Who Really Discovered America"? It was aired on History channel the other night again. A well thought out program that should be watched for IMO.
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