Revising Darwin’s sinking-island theory
The three different formations of South Pacific coral-reef islands have long fascinated geologists. Tahiti’s coral forms a “fringing” reef, a shelf growing close to the island’s shore. The “barrier” reefs of Bora Bora are separated from the main island by a calm lagoon. Finally, an “atoll,” such as Manuae, appears as a ring of coral enclosing a lagoon with no island at its center. The question of how reefs develop into these shapes over evolutionary time produced an enduring conflict between two hypotheses, one from English naturalist Charles Darwin and the other from geologist Reginald Daly. But in a paper (see PDF) recently published in the journal Geology, researchers at MIT and Woods Hole Oceanographic Institution (WHOI) use modern measurements and computer modeling to resolve this old conundrum. Darwin proposed that fringing reefs, barrier reefs and atolls reflect different stages in a dramatic process that occurs as an island sinks...