The hydrologic cycle; describes the continuous movement of water on, above and below the surface of the Earth. Water changes states between liquid, vapor, and ice at various stages in the cycle.
Basically, the sun drives the cycle and heats water in the oceans. Water evaporates into the air. Rising air currents take the vapor up into the atmosphere where cooler temperatures cause it to condense into clouds. Air currents then move water vapor around the globe, cloud particles collide, and rain occurs. Some precipitation falls as snow or hail. Most water falls back into the oceans or onto land as rain. A proportion of water enters rivers, which can then enter the oceans. Over time, water returns to the ocean and the water cycle starts again.
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