Despite their extensive applications in communication systems, radio waves and microwaves are not the only form of EM waves present in our atmosphere. Another form of EM radiation plays an even more important role in our life (and the life of our planet): sunlight. The sun emits over a wide range of frequencies; however, the fraction of its radiation that reaches the earth's surface is mostly in the visible spectrum. (Note that about 35% of the radiation coming from the sun is absorbed directly by the atmosphere before even reaching the earth's surface.) The earth, then, absorbs this radiation and reemits it as infrared waves.