Interestingly, coral reefs are found in the ocean along the equator around the world, but they are not formed from geological processes. Reefs were built over the years by tiny organisms called corals. Corals belong to the same family of animals as jellyfish. They begin life as small, microscopic polyps that float in the sea, but eventually settle in colonies of the same creatures. Their tiny body extracts minerals from seawater (calcium carbonate) and uses it to form a hard shell around the body. An interesting fact that after a coral dies, its protective shell remains in the clutch of existing reefs. This process is called accretion and, as you can imagine, it is a very slow process. Over the course of many thousands of years, the accumulation of these tiny organisms has built entire mountains in the ocean.
Coral reefs are also commonly found in the warmer, tropical seas around the equatorial belt. The Great Barrier Reef, off the southern coast of Australia, is the largest coral reef in the world. It stretches for 1, 600 miles (2, 600km) and covers over 133, 000 square kilometers of ocean floor and is made up of 2, 900 individual reefs. It is estimated that over 350 different coral species live on the Barrier Reef. Scientists estimate that the reef is about 20, 000 years old, but geologists who took samples from the depths of the reefs gave the date 500, 000 years.