The atoll is comprised of ancient corals that originally grew as a reef around a volcano. With time, the volcano began to lower, but the corals kept the reef close to the ocean surface. During the several ice ages, the corals rose and submerged again and again.
In fact the Aldabra we know, is called Aldabra Three, as it is the third time, that the atoll is exposed long enough to support a complex terrestrial biodiversity. About 5000 years ago tidal movements and general erosion breached the outer rim, and the lagoon flood. The daily rise and lower of the sea level deepened the channels, and shaped Aldabra.
The atoll still holds surprises and treasures, this week SIF senior ranger Terence Mahoune found below amazing Giant Clam fossil on Picard Island.