Earth's Water: A Never-Ending Journey
The water on Earth today is the same water that was here when the dinosaurs roamed. It is constantly moving and changing forms in a continuous process called the water cycle (or the hydrologic cycle). The water cycle has no starting point, but it's a giant loop that describes the movement of water on, above, and below the Earth's surface.
The Engine of the Cycle: The Sun
The entire water cycle is powered by energy from the sun. The sun's heat causes water to change state, driving it from the oceans and land into the atmosphere.
The Main Stages of the Water Cycle
1.Evaporation: This is the process where a liquid turns into a gas. The sun heats up the surface of oceans, lakes, and rivers, giving the water molecules enough energy to change into a gas called water vapor. This water vapor rises into the atmosphere.
Transpiration: Plants also release water vapor into the atmosphere from their leaves. This process is called transpiration, and it's like plants are 'sweating'.
2.Condensation: This is the process where a gas turns back into a liquid. As the warm, moist air rises, it cools down. The cool air can't hold as much water vapor. The water vapor changes back into tiny droplets of liquid water, forming clouds.
3.Precipitation: When the water droplets in a cloud get too numerous and heavy, they fall back to Earth. Precipitation is any form of water that falls from clouds, including rain, snow, sleet, or hail.
4.Collection: This is where the water that has fallen back to Earth goes.
Some of it collects in oceans, lakes, and rivers.
Some of it soaks into the ground in a process called infiltration, becoming groundwater.
Some of it flows over the land surface as runoff, eventually making its way back to a river or ocean.
And then, the cycle begins all over again. The sun's energy causes the collected water to evaporate, and the journey continues. This cycle is essential for life, as it provides the freshwater that plants and animals need to survive.