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The water on our planet is always moving. From the sky to the ground
and back again, water is constantly in motion!
This journey is called the water cycle. It's also known as the
hydrologic cycle. (Hydrology is a word that means the science of water.)
The water cycle is what makes clouds ... rain and snow ... and causes
most weather. Water is essential for life on earth, and the water
cycle is how it gets where it needs to be.
The cycle begins when water on the earth's surface, in lakes, oceans,
rivers, and even puddles, is heated up by the sun. This heat
causes the water to evaporate, or turn from a liquid into a gas.
This gaseous water, called water vapor, rises into the air. As the
water vapor rises high into the sky, colder temperatures cause it to
condense - or change from a gas to a liquid - into tiny water
droplets. These tiny water droplets group together to form clouds.
Although a cloud can easily weigh many tons, the individual water
droplets are at first not heavy enough to fall from the sky.
Eventually, though, the water droplets crash into each other and join
together into larger drops, until they are heavy enough to fall to
earth as precipitation - that is, as rain, snow, or ice.
Once back on the surface, the water collects in puddles, streams,
lakes, and oceans, and the cycle begins all over again.
The earth's water is constantly being recycled. We cannot make any
new water, but water is not destroyed when we use it, either. The
amount of water on the earth now is the same as there was when
dinosaurs lived here. The water you used to brush your teeth today
might be some of the same water that a dinosaur drank a long, long
time ago!
I hope you enjoyed learning about the water cycle today. Goodbye till
next time!