How do coral reefs form islands?



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    Living coral basically builds upon the dead skeletons of its predecessors, creating larger and larger reefs. However, since living coral can grow only in the top 100 meters of ocean, Charles Darwin suggested that the first layer of coral began building upon a volcano. As the volcano sank into the ocean floor, and as sea levels changed, eventually a coral island, or atoll, was formed. The final form of the atoll is a circular island ringing around a central lagoon, and this process can take 30 million years. Even if a coral island has sandy beaches and rich vegetation, it basically consists of dead coral.

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