Facts At Your Fingertips: Matter and materials – The water cycle
Earth’s water is constantly changing state as it circulates between the sea, the land, and the sky. This process is known as the water cycle.
Although water is always moving, the total amount of water in the world always stays exactly the same.
Water and the atmosphere
The Sun’s heat causes liquid water to evaporate, turning it into a gas called water vapor. As it rises in the sky, the vapor cools, condensing into tiny droplets, which gather together as clouds. Water falls back to the surface as rain or snow and eventually returns to the oceans—where the process begins again.
Evaporation
Water heated by the Sun evaporates, forming water vapor
Condensation
When water vapor cools high in the sky, it condenses and forms clouds
Precipitation
Small water droplets in clouds merge together to become larger ones, eventually falling to Earth as precipitation, such as rain and snow, when they become too big
Melting
Liquid water that has fallen as rain or melted from snow collects in rivers and streams
Freezing
At low temperatures, water freezes into solid snow as it falls
Over time, flowing groundwater can slowly wear away rocks, forming underground caves and pools
Some water sinks into the Earth as groundwater, and eventually returns to the surface as springs or marshes