The Earth Biosphere; An oxygen-rich and protective atmosphere, moderate temperatures, abundant water, and a varied chemical composition allow earth to support life, the only planet to do so. The earth's relatively thin zone of air, soil, and water that is capable of supporting life, ranging from about 10 km (about 6 mi) into the atmosphere to the deepest ocean floor. Life in this zone depends on the sun's energy and on the circulation of heat and essential nutrients. The biosphere remained sufficiently stable for hundreds of millions of years to sustain the evolution of today's life forms. Large-scale divisions of the biosphere into regions of different growth patterns are called biomes. This slightly pear-shaped planet is composed of rock and metal, which are present in molten form beneath its surface. This photograph, taken by the Apollo 17 spacecraft in 1972, shows Arabia, the African continent, and Antarctica (most of the white area near the bottom).