Hapgood's book was published in 1966. It was when he identified the previously unidentified land-mass on the Piri Reis map as being Antartica pre-6,000 BC that his book caused a sensation! This is Antarctica but shown without its full ice cover! This provoked incredulity. But after much scholarly research it is clear that Piri Reis re-compiled his early 15th century map from a series of highly accurate and possibly very ancient regional maps of South America etc...with longitudes correctly shown. This pre-dates Columbus. And the (alleged) Chinese imperial naval foray to South America in the early 1400's. How so? Is this evidence of a high civilization at the end of the last Ice Age (12,000 to 8,000 BC)? Graham Hancock vigorously supports such a theory. Hapgood mentions his other (controversial) theory about crustal shift.