Researchers sampled and dated corals from two fossil reefs of different ages on the islands of Great Inagua and San Salvador, in the Bahamas. This photo shows a large individual fossil coral from the younger reef, which grew directly on the remains of an older generation of similar corals. The two reefs are separated by a wave-cut surface, also visible in the photo, which was eroded in the swash zone after sea level fell. Since both generations of corals grew in about 3 m of water, and the wave-