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{{redirect|Atmosphere|the unit of measure|Atmosphere (unit)}}

{{redirect|Atmosphere|the unit of measure|Atmosphere (unit)}}

The atmosphere is the layer of [[gas]]es around the [[Earth]]. It is held in place by Earth's [[gravity]]. It is 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.

The atmosphere is the layer of [[gas]]es around the [[Earth]]. It is held in place by Earth's [[gravity]].There are total 5 layers of atmosphere, named stratosphere, troposphere, mesosphere, thermosphere, and exosphere. It is 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]].

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]].

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 ==

== History of Earth's atmosphere ==

#In the [[Great Oxygenation Event]] the atmosphere changed to the kind we have now, with oxygen replacing the carbon dioxide. Our atmosphere is still mostly nitrogen, but most living organisms interact more with oxygen than with nitrogen. Oxygenation began with [[cyanobacteria]] making free oxygen by [[photosynthesis]]. Most organisms today need oxygen for their [[respiration]]: only a few [[anaerobic organism]]<nowiki/>s can grow without oxygen.<ref>Heinrich D. Holland: ''The oxygenation of the atmosphere and oceans.'' In: ''Phil. Trans. R. Soc.'' B, vol. 361, 2006, p. 903–915 http://rstb.royalsocietypublishing.org/content/361/1470/903.full.pdf</ref><ref>Knoll, Andrew H. 2004. ''Life on a young planet: the first three billion years of evolution on Earth''. Princeton, N.J. {{ISBN|0-691-12029-3}}</ref>

#In the [[Great Oxygenation Event]] the atmosphere changed to the kind we have now, with oxygen replacing the carbon dioxide. Our atmosphere is still mostly nitrogen, but most living organisms interact more with oxygen than with nitrogen. Oxygenation began with [[cyanobacteria]] making free oxygen by [[photosynthesis]]. Most organisms today need oxygen for their [[respiration]]: only a few [[anaerobic organism]]<nowiki/>s can grow without oxygen.<ref>Heinrich D. Holland: ''The oxygenation of the atmosphere and oceans.'' In: ''Phil. Trans. R. Soc.'' B, vol. 361, 2006, p. 903–915 http://rstb.royalsocietypublishing.org/content/361/1470/903.full.pdf</ref><ref>Knoll, Andrew H. 2004. ''Life on a young planet: the first three billion years of evolution on Earth''. Princeton, N.J. {{ISBN|0-691-12029-3}}</ref>

== Temperature and the atmospheric layers ==

== Temperature the atmospheric layers ==

[[File:Profil temperature atmosphere.png|thumb|Temperature at various altitudes]]

[[File:Profil temperature atmosphere.png|thumb|Temperature at various altitudes]]

*[[Mesosphere]] - Starts at {{convert|50|km|abbr=off}}. Ends at {{convert|80|or|85|km|abbr=off}}. The higher, the colder. [[Wind]]s in this layer are strong, so the temperature is not stable.

*[[Mesosphere]] - Starts at {{convert|50|km|abbr=off}}. Ends at {{convert|80|or|85|km|abbr=off}}. The higher, the colder. [[Wind]]s in this layer are strong, so the temperature is not stable.

*[[Thermosphere]] - Starts at {{convert|80|or|85|km|abbr=off}}. Ends at {{convert|640|km|abbr=off}} or higher. The higher, the hotter. This layer is very important in [[radio]] [[communication]] because it helps to reflect some [[radio wave]]s.

*[[Thermosphere]] - Starts at {{convert|80|or|85|km|abbr=off}}. Ends at {{convert|640|km|abbr=off}} or higher. The higher, the hotter. This layer is very important in [[radio]] [[communication]] because it helps to reflect some [[radio wave]]s.

*[[Exosphere]] - Above the thermosphere. This is the top layer, and merges into interplanetary space.

*[[Exosphere]] - Above the thermosphere. This is the top layer. At the magnetopause, it merges into the [[heliosphere]] of interplanetary space.

Where one layer changes to the next have been named "-pauses." So the [[tropopause]] is where the troposphere ends ({{convert|7|to|14|km|abbr=off}} high). The [[stratopause]] is at the end of the stratosphere. The [[mesopause]] is at the end of the mesosphere.  

Where one layer changes to the next have been named "-pauses." So the [[tropopause]] is where the troposphere ends ({{convert|7|to|14|km|abbr=off}} high). The [[stratopause]] is at the end of the stratosphere. The [[mesopause]] is at the end of the mesosphere.  

The average temperature of the atmosphere at the surface of Earth is {{convert|14|°C}}.

The average temperature of the atmosphere at the surface of Earth is {{convert|14|°C}}.

== Pressure ==

== Pressure and density ==

The atmosphere has [[pressure]]. This is because even though [[air]] is a gas, it has [[weight]]. The average [[atmospheric pressure]] at [[sea level]] is about {{convert|101.4|kPa|psi}}.

The atmosphere has [[pressure]]. This is because even though [[air]] is a gas, it has [[weight]]. The average [[atmospheric pressure]] at [[sea level]] is about {{convert|101.4|kPa|psi}}.

The [[density]] of air at [[sea level]] is about 1.2 kilograms per [[cubic meter]].  This density becomes less at higher altitudes at the same rate that pressure becomes less. The total [[mass]] of the atmosphere is about 5.1 &times; 10¹⁸ kg, which is only a very small part of the Earth's total mass.

The [[density]] of air at [[sea level]] is about 1.2 kilograms per [[cubic meter]].  This density becomes less at higher altitudes at the same rate that pressure becomes less. The total [[mass]] of the atmosphere is about 5.1 &times; 10¹⁸ kg, which is only a very small part of the Earth's total mass.