Look up the Solutrean Hypothesis. Based on the similarity between Clovis and Solutrean spear points, Stanford & Bradley suggested that originally, Europeans crossed into North America during the last Glacial Maximum. Interestingly, a dig in Allendale SC demonstrated spear points with designs between the Solutrean and Clovis points, which is what was predicted if a westward migration had occurred. DNA evidence somewhat disputes this, but then a Blackfoot man was recently located whose ancestry apparently traced back through Peru from Polynesia. People have been sailing ships across the ocean for at least 60,000 years, otherwise the Australian Aborigines wouldn't have gotten across the 2000 miles from Indonesia. I wouldn't worry about it too much. My kids are Gaelic, Celtic, Swedish, Norwegian and Cherokee. We consider them ethnically American.