The Water Cycle

The water on Earth today is the same water that has been here for millions of years. It travels in a loop called the water cycle, and the Sun is the engine that keeps it moving.

First, the Sun heats water in oceans, lakes, and puddles until it evaporates - turning from liquid into an invisible gas that rises into the air. High up, where the air is cold, the gas condenses back into tiny droplets. Billions of droplets together make a cloud.

When the droplets bump together and grow heavy, they fall as rain or snow. The water flows into streams and rivers and back to the ocean, ready to rise again. The rain on your window might once have fallen on a mountain a thousand years ago.