Did you know that most of the Earth's oxygen comes from its marine habitats? The marine habitats are the largest in the world. They includes the five main oceans and are a source of food, air and water for plants, animals and people all over the world. Learn about the geography and resources of marine habitats as well as how animals and people have adapted to and changed marine environments. Explore this habitat's future and what people can do to help keep it safe. Part of the Exploring Earth's Habitats series.