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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]].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.
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]].
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 ==
The most 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]]. Nothing else. The material which makes up planets 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]].
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 giant]]s ([[Jupiter]] and [[Saturn]]): [[water vapor]], [[methane]] and [[ammonia]].<ref name=Zahnle>{{Cite journal |last1=Zahnle |first1=K. |last2=Schaefer |first2=L. |last3=Fegley |first3=B. |doi=10.1101/cshperspect.a004895 |title=Earth's Earliest Atmospheres |journal=Cold Spring Harbor Perspectives in Biology |volume=2 |issue=10 |pages=a004895 |year=2010 |pmid=20573713 |pmc=2944365}}</ref>
#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 giant]]s ([[Jupiter]] and [[Saturn]]): [[water vapor]], [[methane]] and [[ammonia]].<ref name=Zahnle>{{Cite journal |last1=Zahnle |first1=K. |last2=Schaefer |first2=L. |last3=Fegley |first3=B. |doi=10.1101/cshperspect.a004895 |title=Earth's Earliest Atmospheres |journal=Cold Spring Harbor Perspectives in Biology |volume=2 |issue=10 |pages=a004895 |year=2010 |pmid=20573713 |pmc=2944365}}</ref>
#The atmosphere gradually changed to mostly [[carbon dioxide]] and [[nitrogen]]. The lighter gases, like hydrogen and [[helium]], cannot be held by the Earth's [[gravity]], and would escape. For a long time (say two billion years or more), the atmosphere was dominated by carbon dioxide.
#The atmosphere gradually changed to mostly [[carbon dioxide]] and [[nitrogen]]. The lighter gases, like hydrogen and [[helium]], cannot be held by the Earth's [[gravity]], and would escape. For a long time (say two billion years or more), the atmosphere was dominated by carbon dioxide.
#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 the atmospheric layers ==
== Temperature and 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. At the magnetopause, it merges into the [[heliosphere]] of interplanetary space.
*[[Exosphere]] - Above the thermosphere. This is the top layer, and merges into interplanetary space.
Regions 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.
These are called boundaries.
These are boundaries.
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 and density ==
== Pressure ==
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}}.
==Density and 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 × 10<sup>18</sup> 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 × 10<sup>18</sup> kg, which is only a very small part of the Earth's total mass.
[[Category:Atmosphere]]
[[Category:Atmosphere]]
[[Category:Earth]]
[[Category:Meteorology]]