Water on the earth is constantly on the move from one location and physical state to another, it evolves and recycles over and over again. This movement is called the water cycle.
Heat from the sun causes water to evaporate from oceans, lakes and streams. Evaporation occurs when liquid water on Earth’s surface turns into water vapor in our atmosphere. Warm water vapor rises up through Earth’s atmosphere. As the water vapor rises higher and higher, the cool air of the atmosphere causes the water vapor to turn back into liquid water, creating clouds. When a cloud becomes full of liquid water, it falls from the sky as rain or snow—also known as precipitation. Rain and snow then fill lakes and streams, and the process starts all over again.
According to scientific research, water in the atmosphere is replaced about 35 times in one year, river water 32 times a year. It is also estimated that the full renewal time of the ocean may take 2,500 years, groundwater 1,400 years, ground ice of the permafrost zone 10,000 years, polar ice 9,700 years, mountain glaciers 1,600 years, lakes 17 years for atmospheric moisture.
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