Reducing atmosphere Reducing atmosphere A reducing atmosphere is an atmospheric condition in which oxidation is prevented by removal of oxygen and other oxidizing gases or vapours, and which may contain actively reducing gases such as hydrogen, carbon monoxide, and gases such as hydrogen sulphide that would be oxidized by any present oxygen. In metal processing, a reducing atmosphere is used in annealing ovens for relaxation of metal stresses without corroding the metal. A non oxidizing gas, usually nitrogen, is used, or for more extreme conditions, hydrogen gas. A reducing atmosphere is also used to produce specific effects on ceramic wares being fired.
History of Earth melting in basalt. Earth is often described as having had three atmospheres. The first atmosphere, captured from the solar nebula, was composed of light (atmophile) elements from the solar nebula, mostly hydrogen and helium. A combination of the solar wind and Earth's heat would have driven off this atmosphere, as a result of which the atmosphere is now depleted of these elements compared to cosmic abundances. After the impact which created the moon, the molten Earth released volatile gases; and later more gases were released by volcanoes, completing a second atmosphere rich in greenhouse gases but poor in oxygen. Finally,