The Water Cycle
The WATER CYCLE describes how water moves between the ocean, atmosphere, land, and underground. Powered by SUNLIGHT and gravity, it never stops. Every drop you drink today might have been Cleopatra's drinking water. Earth has a fixed amount of water, but it cycles continuously.
Steps. (1) EVAPORATION: sun warms water (mostly oceans) — it becomes vapor. (2) TRANSPIRATION: plants release water vapor too. (3) CONDENSATION: vapor cools high in the sky, becoming droplets — clouds. (4) PRECIPITATION: droplets fall as rain, snow, sleet, or hail. (5) RUNOFF: water flows across land into rivers and seas. (6) INFILTRATION: some water soaks into the ground (becoming groundwater). (7) Repeat — forever.
The water cycle is POWERED by:
Time scales. Water in the atmosphere cycles in days. River water reaches the sea in days to weeks. Glaciers hold water for thousands of years. Some groundwater dates back tens of thousands of years. The same water molecule has cycled countless times since Earth formed.
Mini Cycle
Put water in a glass. Cover with plastic wrap. Set in sunlight. Watch droplets form on the inside of the wrap (condensation), then drip back down (precipitation). You've made a tiny water cycle.
The water cycle is one of nature's most beautiful and essential processes. It powers ecosystems, weather, agriculture — and you.
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