When the sea level was a few hundred feet lower during the Ice Age, the Bering land-bridge connected Asia to Alaska, a vast swath of land recorded in the ancient source maps which Hadji Ahmed in 1559 must have used in making his map, and in 1531 Oronteus Finaeus having done the same, but his of Antarctica (supposedly not discovered until 1818 by the Russians), its outline very accurate, but of the land (and mountain ranges) beneath the polar icepack there now in places ten thousand feet thick!
