Many other animals, including many mammals, either make their homes in the soil or hunt animals that do. The atmosphere is a gas envelope that rises 960 kilometres above the planet's surface and protects organisms from the harmful rays of the sun. Yet most life exists in the few kilometres nearest the earth's surface. The air contains the gases needed by organisms to live. Air moves around the globe on jet streams powered by the sun.
Sunlight is the principal source of energy for the biosphere.
Energy cannot be created or destroyed, only transferred or transformed. Unlike the constant recycling of water, carbon, nitrogen, and phosphorus, light energy can only be used once. Most of the light energy that strikes the earth from the sun goes unused. Only one or two percent of the light energy that reaches the earth is used by green plants. Using the process of photosynthesis, green plants convert light energy into chemical energy and then into a simple sugar.