Earth

=== Upper atmosphere ===
[[File:Antarctic aurora ESA313457.jpg|thumb|upright=1.3|Earth's atmosphere as it appears from space, as bands of different colours at the horizon. From the bottom, [[afterglow]] illuminates the [[troposphere]] in orange with silhouettes of clouds, and the [[stratosphere]] in white and blue. Next the [[mesosphere]] (pink area) extends to just below the [[Kármán line|edge of space]] at one hundred kilometers and the pink line of [[airglow]] of the lower [[thermosphere]] (invisible), which hosts green and red [[aurora]]e over several hundred kilometers.]]
The upper atmosphere, the atmosphere above the troposphere,<ref>{{cite web |last=Morton |first=Oliver |title=Upper atmosphere Definition und Bedeutung |website=Collins Wörterbuch |date=26 August 2022 |url=https://www.collinsdictionary.com/de/worterbuch/englisch/upper-atmosphere |language=de |access-date=26 August 2022}}</ref> is usually divided into the [[stratosphere]], [[mesosphere]], and [[thermosphere]].<ref name="atmosphere" /> Each layer has a different lapse rate, defining the rate of change in temperature with height. Beyond these, the [[exosphere]] thins out into the magnetosphere, where the geomagnetic fields interact with the solar wind.<ref name=sciweek2004 /> Within the stratosphere is the ozone layer, a component that partially shields the surface from ultraviolet light and thus is important for life on Earth. The [[Kármán line]], defined as {{Convert|100|km|mi|abbr=on}} above Earth's surface, is a working definition for the boundary between the atmosphere and [[outer space]].<ref name=cordoba2004 />

Thermal energy causes some of the molecules at the outer edge of the atmosphere to increase their velocity to the point where they can escape from Earth's gravity. This causes a slow but steady [[Atmospheric escape|loss of the atmosphere into space]]. Because unfixed [[hydrogen]] has a low [[molecular mass]], it can achieve [[escape velocity]] more readily, and it leaks into outer space at a greater rate than other gases.<ref name="jas31_4_1118" /> The leakage of hydrogen into space contributes to the shifting of Earth's atmosphere and surface from an initially [[redox|reducing]] state to its current oxidizing one. Photosynthesis provided a source of free oxygen, but the loss of reducing agents such as hydrogen is thought to have been a necessary precondition for the widespread accumulation of oxygen in the atmosphere.<ref name="sci293_5531_839" /> Hence the ability of hydrogen to escape from the atmosphere may have influenced the nature of life that developed on Earth.<ref name="abedon1997" /> In the current, oxygen-rich atmosphere most hydrogen is converted into water before it has an opportunity to escape. Instead, most of the hydrogen loss comes from the destruction of methane in the upper atmosphere.<ref name="arwps4_265" />