The solar radiation that heats the Earth's crust is the driving force behind the water cycle. The water cycle is sometimes referred to as the hydrologic cycle and is a process through which Earth's water continuously moves between the surface of the planet and the atmosphere.
Earth's water is in constant motion as water at the surface exchanges places with the gaseous moisture and water droplets found in the atmosphere. As the sun warms the Earth, liquid water found in lakes and oceans on the planet's surface evaporates. Moisture within the atmosphere eventually cools and condenses, until liquid water or snow falls back to the Earth as precipitation. Runoff from rain eventually finds its way back to lakes and oceans, completing the most direct version of the water cycle.
The water cycle is able to move 495,000 cubic kilometers of moisture through the atmosphere each year. Without the sun's heat, there would be no evaporation to power the cycle. The heat of the sun is responsible for the formation of clouds and weather patterns. Without heat from the sun to drive the water cycle, there could be no weather, and all of Earth's water would exist in a frozen state.