The rock of the escarpment is very old. Approximately 400 million years ago, this area was covered by a shallow tropical sea teeming with life in the form of plant-like animals, crustaceans, living corals and mollusks. It would have looked much like the present-day Great Barrier Reef of Australia. When the sea began to dry up, the minerals dissolved in it became more and more concentrated. Magnesium in the water was absorbed into the limestone, which then became a harder, slightly different sort of rock, called dolomite.