Ugh, I remember this one. Thought it was pretty good at the time, until you realize that there's a lot of embellishment and poor logic that goes into the conclusions.

Plus, if any culture would have "discovered" the New World between Leif Erikson and Columbus, it would have been the Polynesians. They were cultivating the sweet potato as early as the 13th century, a crop that previously only existed in South America.