Figure 6-3Earth’s Dynamic Oceans This image shows the relative size of Earth compared to a sphere containing all of Earth’s water. The sphere is about 1380 km (860 mi) in diameter and includes freshwater, oceans, ice, and even water in the atmosphere. Nearly three-quarters of Earth’s surface is covered with water, a substance that is essential to the existence of life. In contrast, there is no liquid water at all on the surfaces of Mercury, Venus, Mars, or the Moon.