What is Atmosphere of Earth?
{{redirect|Atmosphere|the unit of measure|Atmosphere (unit)}} The Earth's '''atmosphere''' is the layer of [[gas|gass]]es around the [[Earth]]. It is held in place by Earth's [[gravity]]. It is today made up mainly of [[nitrogen]] (78.1%). It also has plentiful [[oxygen]] (20.9%) and small amounts of [[argon]] (0.9%), [[carbon dioxide]] (~ 0.035%), [[water vapor]], and other gases. The atmosphere protects [[life]] on Earth by [[Absorption|absorbing]] (taking) [[ultraviolet]] rays from the [[Sun]]. It makes our [[day]]s cooler and our [[night]]s warmer. Solid [[particulate]]s, including [[ash]], [[dust]], [[volcanic ash]], etc. are small parts of atmosphere. They are important in making [[cloud]]s and [[fog]]. The atmosphere does not end at a specific place. The higher above the Earth, the thinner the atmosphere. There is no clear [[border]] between the atmosphere and [[outer space]], though the [[Kármán line]] is sometimes treated as a border. Even higher, for some purposes the edge of the [[magnetosphere]] is treated as a border. 75% of the atmosphere is within {{convert|11|km|abbr=off}} of the Earth's [[surface]]. == History of Earth's atmosphere == An important thing to remember about the [[Earth]] and other planets is that ''they do not come from the [[Sun]]''. They or their materials were picked up by the Sun's [[gravitation]] as it moved through space. The Sun is just composed of [[hydrogen]], with a little bit of [[helium]]. The material which makes up [[rocky planet]]<nowiki/>s and their satellites is almost entirely heavier elements whose origin was in earlier [[Supernova|supernovae]] explosions. The planets do give off small quantities of hydrogen and helium: this comes from the decay of larger [[radioactive]] molecules whose origin is also ancient supernovae. Originally, the Earth's atmosphere had almost no free [[oxygen]]. #The first atmosphere consisted of gases in the [[solar nebula]], mainly [[hydrogen]]. There might also have been simple [[hydride]]s such as those now found in the [[gas