Water molecules are so small that you can only see them when a number of them are clumped together to form a droplet. And they are constantly on the move. After a rain, they will eventually evaporate into water vapor. These airborne water molecules get carried back up into the sky to form clouds and then more rain.
The water on Earth plays a major role in the naturally occurring phenomena called the Hydrological Cycle, which can be described by four major steps: evaporation, condensation, precipitation and collection:
- Condensation: As water vapor rises into the Earth's atmosphere, it condenses on particles in the air. The water vapor condenses when air temperature decreases, as a result of higher elevation, forming clouds in the sky.
- Evaporation: During this stage, water from rivers, lakes and oceans transforms from liquid to water vapor, a gas. This transformation happens because the sun heats the Earth's surface, causing water to evaporate.
- Collection: The water that falls over land irrigates plants, trees and crops, and eventually makes its way back to rivers, lakes and oceans.
- Precipitation: As clouds become heavier, they release the condensed water particles, which fall back to the Earth as rain, snow or hail (depending on air temperature).
During the hydrologic cycle, water that evaporates from the ocean leaves its salt content behind because the salt in the water does not evaporate. So, the water cycle is, in essence, filtering saltwater, creating freshwater for the natural irrigation of plants, trees and crops.
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