How Coral Reefs Are Made

      Coral reefs are home to 25% of marine life on our planet while covering less than 1% of the ocean floor. These complex reefs are basically made of skeletons of hard coral. A coral polyp has a skeleton made from calcium carbonate. Calcium carbonate is made as calcium from the water mixed with carbon dioxide. As the coral grows taller, the skeleton on its base grows with it. New coral is then able to grow on the skeleton. This way a coral reef can grow several centimeters per year.