The document discusses the major bodies of water on Earth. It notes that there are four oceans - Pacific, Atlantic, Indian, and Arctic - with the Pacific being the largest and deepest. Coral reefs form in shallow, warm seas and are made up of coral polyps' skeletons growing on top of old skeletons. The ocean is divided into zones from sunlit down to sunless, with different plants and animals inhabiting each layer depending on access to light.