Charles Darwin proposed that the Atolls of the Maldives developed as the mountain range gradually subsided into the sea or sea levels rose. The fringing reefs surrounding these mountains built up and became more distant from the center of the range untill there was nothing left but a circle of reefs enclosing a lagoon, called an Atoll.

During a seismic survey by Esso in 1980, a well sunk near Bandos concluded that a volcanic base lay beneath 2100 meters of limestone, supporting the subsidence theory of Darwin.

Coral reefs are created by a tiny animal, called a polyp, which secretes a hard limestone skeleton and provides the reef framework. Fragile branching coral may grow between 20 to 30 centimeters per year, while massive boulder-shaped coral may grow only a few millimeters per year. Coralline algae, which thrives in areas exposed to wave action and places too deep and dark for the coral, cement framework of dead and broken coral together forming a solid limestone base.

The type and shape of the reef developed depends to a great extent on the depth and shape of the ocean floor, the currents, the recent geological history of the area and degree of exposure to wave action. Yet coral reefs have not always existed as they do today.

During the ice ages, falls in sea-levels forced reef building coral away from the reefs to colonize new areas. At the same time reefs were left high out of the water. The limestone reefs were readily eroded by fresh water and this led to the formation of caves and canyons of all shapes and sizes. After they were again flooded by the sea, marine life re-established itself and layers of coral and coralline algae continue to grow upon the eroded gutters and valleys. These eroded substrata largely govern the shapes of modern reefs. Today, many of these features remain submerged providing divers with spectacular natural attractions.

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