|Figure A: The Water Cycle
The water on Earth now is the same water thatâ€™s been on Earth since the beginning. The rain that falls on us is the same water that rained on the dinosaurs, King Tut and George Washington. What makes that awesome feat possible? The water cycle. The water cycle is the process that re-circulates water so we can have bodies of water as well as clouds and precipitation.
The first step of the water cycle is evaporation. About 85% of the water vapor in the air comes from water that evaporated from the oceans. The other 15% comes from evapotranspiration, which is a catch-all term for water that evaporates from over land. This includes water vapor produced by plants during transpiration (vegetation link), water from lakes, streams, puddles and soil moisture, direct evaporation of snow and even water vapor from the breath of animals.
The second step of the water cycle is condensation. Now that the atmosphere is full of water vapor, that water vapor condenses into water droplets. Sometimes, like early in the morning, the water vapor condenses on the grass as dew and seeps back into the soil, ready to be evaporated again. But most of the water vapor condenses higher up in the air and forms clouds. Once the water droplets are in a cloud, two things can happen. Either the cloud will dissipate and the water droplets will become vapor again, or the cloud will grow and it will begin to precipitate.
The third and final step of the water cycle is precipitation. Precipitation includes all water that falls from the sky, both in liquid and frozen form, which reaches the ground. Once the precipitation makes its way to the ground it can end up soaking into the ground, run off into streams and lakes, become snow cover, be used by plants, be inhaled by animals or fall directly back into the ocean. Then the water cycle can begin again and continue for millions of years to come.