GEF

Unit 2  |  Water Science and the Water Cycle 48 Despite the difficulties presented by availability and distribu- tion, water is fundamentally renewable. The water we drink has been on our planet for billions of years. It is the same water where the first life-forms evolved, that the dinosaurs drank, and which froze into mile-high glaciers during ice ages. Water flowing over the surface of the Earth has continually reshaped continents and eroded huge mountains. In other words, the total amount of water on Earth never changes. Water is recycled over and over as it continuously flows around Earth in a gigantic and dynamic system known as the hydro- logic, or water cycle . The water cycle is the system that transforms and transports water around the Earth. Evaporation is the process in which water changes from a liquid to a vapor. Powered by the sun and wind, it is the engine that keeps the water cycle running. Most water entering the atmosphere evaporates from the surfaces of water bodies; including oceans, lakes, and rivers, but water can also evapo- rate from soil, snow, or ice. In the atmosphere, water vapor is WATER CYCLE A biogeochemical cycle that tracks the movement of water through earth systems. EVAPORATION The change of matter from a liquid to a gas.