An atoll is a ring-shaped coral reef that encircles a lagoon, typically formed from the remains of a volcanic island that has eroded over time. Atolls are found in warm ocean waters, primarily in the Pacific Ocean and Indian Ocean. They are composed of coral and sand, providing a unique habitat for various marine life, including fish, sea turtles, and birds. The formation of an atoll begins with a volcanic island, which gradually sinks as the surrounding coral grows. Over thousands of years, the island erodes, leaving behind a circular reef structure. Atolls are important for biodiversity and serve as natural barriers against storms, protecting coastal areas from erosion.