Atmosphere of Earth the border between the atmosphere and outer space. Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around . Several layers can be distinguished in the atmosphere, based on characteristics such as temperature and composition. The study of Earth's atmosphere and its processes is called atmospheric science (aerology). Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann. The three major constituents of Earth's atmosphere are nitrogen, oxygen, and argon. Water vapor accounts for roughly 0.25% of the atmosphere by mass. The concentration of water vapor (a greenhouse gas) varies significantly from around
Extraterrestrial atmosphere in atmospheric methane, as well as the presence of kerogen and other complex organic compounds. The four outer planets of the Solar System are gas giants. They share some atmospheric commonalities. All have atmospheres that are mostly hydrogen and helium and that blend into the liquid interior at pressures greater than the critical pressure, so that there is no clear boundary between atmosphere and body. Jupiter's upper atmosphere is composed of about 75% hydrogen and 24% helium by mass, with the remaining 1% consisting of other elements. The interior contains denser materials such that the distribution is roughly 71% hydrogen,