Air

The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth's planetary surface, known collectively as air, with variable quantities of suspended aerosols and particulates, all retained by Earth's gravity. The atmosphere serves as a protective buffer between the Earth's surface and outer space, shields the surface from most meteoroids and ultraviolet solar radiation, keeps it warm and reduces diurnal temperature variation through heat retention, redistributes heat and moisture among different regions via air currents, and provides the chemical and climate conditions allowing life to exist and evolve on Earth. Read more on Wikipedia