 He used that to propose that a 15° pole shift occurred around 9,600 BCE (approx.11,600 years ago) and that a part of the Antarctic was ice-free at that time and that an ice-age civilization could have mapped the coast.He concludes that "Antarctica was mapped when these parts were free of ice" and took the view that an Antarctic warm period coincided with the last ice age in the Northern hemisphere and that the Piri Reis and other maps were based on "ancient" maps derived from ice-age originals.