The hydrosphere is made up of all the water on Earth. Water exists in three forms-liquid, solid, and water vapor-and changes from one form to another. Water moves around Earth in the water cycle in which some of the water in oceans and rivers turns into water vapor that goes into the air to form clouds. The water is then returned to the surface of Earth as rain or snow. This cycle repeats over and over. Water is necessary for life on Earth to exist...