This article is about the general term "atmosphere". For specific information about the Earth's atmosphere, see Atmosphere of Earth.
For other uses, see Atmosphere (disambiguation).
An atmosphere (New Latin atmosphaera, created in the 17th century from Greek ἀτμός [atmos] "vapor"[1] and σφαῖρα [sphaira] "sphere"[2]) is a layer ofgases that may surround a material body of sufficient mass,[3] and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low. Some planets consist mainly of various gases, but only their outer layer is their atmosphere.
The term stellar atmosphere describes the outer region of a star, and typically includes the portion starting from the opaque photosphere outwards. Relatively low-temperature stars may form compound molecules in their outer atmosphere. Earth's atmosphere, which contains oxygen used by most organisms forrespiration and carbon dioxide used by plants, algae and cyanobacteria for photosynthesis, also protects living organisms from genetic damage by solarultraviolet radiation. Its current composition is the product of billions of years of biochemical modification of the paleoatmosphere by living organisms.
