We might add that Old World mariners from the Phoenicians to the Romans had plenty to interest them on the coasts of the Mediterranean and Black Seas and few if any reasons to venture out into the Atlantic. The Vikings of course were a different story, great sailors and out at the edge of the known world. Having discovered Iceland and Greenland it would not be at all unreasonable for them to continue to venture westward, as indeed they did. To date they remain the ONLY documented pre-Columbian Old World contact.