The mainland on Lantea is the only known location of dry land on the planet and it masses about fifteen million square miles. The Athosians had lived on the mainland since it was discovered and grew and harvested crops to keep themselves and the Atlantis expedition self-sufficient. They, however, left the mainland sometime later when the Ancients on the warship Tria reclaimed Atlantis. (ATL: "Suspicion", "The Return, Part 1")