How did Charles Darwin explain the formation of coral reefs?

In 1842, Charles Darwin proposed a theory of coral reef formation based on the gradual subsidence of the Earth's crust. He concluded that reefs evolve through a sequence of stages as the landmass they surround sinks.12

• Fringing Reefs: These begin as reefs growing directly along the shores of a volcanic island or mainland mass.13
• Barrier Reefs: As the landmass slowly subsides, the coral continues to grow upward to remain within optimal light and temperature conditions. This upward growth creates a lagoon between the reef and the now-distant shore.12
• Atolls: When the original volcanic island or landmass becomes completely submerged, the remaining ring of coral forms an atoll, enclosing a central lagoon.13

While modern science recognizes that rising sea levels following the Pleistocene Epoch also play a significant role in reef development, Darwin’s fundamental concept regarding the relationship between subsidence and upward coral growth remains a valid and foundational contribution to geology.1