ENERGY FOR LIFE: What happens when solar radiation reaches the earth?

Solar energy, like all radiant energy, travels through space in electromagnetic waves. What happens to the tiny fraction of the sun's energy that shines on the earth?

• About 30% is reflected back into space by clouds, deserts, and snow.
• Some, in the ultraviolet part of the electromagnetic spectrum, is absorbed by the earth's ozone layer.
• Some drives the water cycle: Solar energy is absorbed by water which evaporates and later falls back to earth as rain and snow.
• Some drives the winds: Solar energy heats up the earth's surface and the blanket of air surrounding it. Since the air is heated unevenly, currents of hot air expand upward while cool air moves down to take its place. The sun is the source of all our weather.
• Some is captured and stored by green plants and green one-celled organisms in a process called photosynthesis. The sun is the source of food for almost all life on earth.

NEXT: Photosynthesis—Turning Sunlight into Food