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How did drilling at Enewetak Atoll support Darwin’s theory of atoll formation?

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coral reef The Great Barrier Reef, off the coast of Queensland, Australia, is the world's largest coral reef.

Geologic drilling at Enewetak Atoll in 1952 provided critical empirical evidence for Charles Darwin’s subsidence theory of atoll formation.1

Darwin proposed that atolls originate as coral reefs fringing a volcanic island. As the island gradually sinks, the reef continues to grow upward to remain near the surface, eventually forming a barrier reef and finally an atoll once the volcanic peak is completely submerged.12

The drilling at Enewetak confirmed this model by revealing the presence of volcanic rock approximately 1,400 metres (4,600 feet) below the modern reef surface. This discovery demonstrated that the reef had indeed grown atop a subsiding volcanic foundation, supporting Darwin's hypothesis that the deep structure of an atoll is built upon the remains of a sunken volcanic island.1