Earth, the third planet from the Sun, is the most wondrous of the planets in the solar system. Scien- tists are now virtually certain that it is the only body in the solar system supporting the most peculiar of all phenomena: life, particularly human life. This image shows the planet’s vast oceans of water, its clouds of water vapor, and its thin rim of atmos- phere—all fundamental to the evolution and survival of life. Scientists believe that life origi- nated in the oceans and eventually migrated to land, where it was supported by rain and atmospheric gases such as carbon dioxide and oxygen. 
    In many ways, the Earth is not so different from the other rocky planets, Mercury, Venus, and