The continuous changes of the state and movement of water throughout the Earth system, i.e., the atmosphere, biosphere, lithosphere and hydrosphere is known as the water cycle. The water cycle is driven by energy from the Sun rays, which cause liquid water from Earth's surface to change into gas in a process called evaporation. As gaseous vapour rises and circulates in the atmosphere, it cools and changes back into a liquid, a process known as condensation. When water vapour condenses, tiny droplets form clouds, which return the water to Earth as precipitation.