Oceans cover more than 70 percent of Earth's surface. They are the reason why Earth is known as "the blue planet." Learn more in Oceans, part of the Aquatic Ecosystems series. Each title helps readers explore an ecosystem's plants and animals, how the ecosystem is important to humans, and which threats face the ecosystem today. Aquatic Ecosystems is a series of AV2 media enhanced books, A unique book code printed on page 2 unlocks your interactive eBook. These books come alive with video, audio, weblinks, slideshows, activities, and much more.