Water Cycle: The water cycle describes the existence and movement of water on, in, and above the Earth. Earth's water is always in movement and is always changing states, from liquid to vapor to ice and back again. The water cycle has been working for billions of years and all life on Earth depends on it continuing to work; the Earth would be a pretty stale place without it. The water cycle has no starting point. But once the water is evaporated from its source (seas, oceans, ponds, lakes, etc.), it is taken to the atmosphere by vapor current. When the vapor is in the atmosphere the water condenses into the cloud and it falls back to the earth in the form of cloud particles. This is known as precipitation. Nitrogen Cycle: