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Line 30: − + + + + + + + + + + + + + + + + + + + + + + − ==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. + + − −
KS update 1.3
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 ==
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.
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.
#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 and 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]]
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 ==
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.
== Atmosphere Of Earth Media ==
<gallery widths='160px' heights='100%' mode='traditional' caption=''>
File:Top of Atmosphere.jpg|View of the crescent moon through the top of the Earth's atmosphere. Photographed above 21.5°N, 113.3°E by International Space Station crew Expedition 13 over the South China Sea, just south of Maca
File:Atmosphere gas proportions.svg|Composition of Earth's atmosphere by molecular count, excluding water vapor. Lower pie represents trace gases that together compose about 0.0434% of the atmosphere (0.0442% at August 2021 concentrations). Numbers are mainly from 2000, with {{CO2}} and methane from 2019, and do not represent any single source.
File:Earth's atmosphere.svg|Earth's atmosphere. Lower four layers of the atmosphere in three dimensions as seen diagonally from above the exobase. Layers drawn to scale, objects within the layers are not to scale. Aurorae shown here at the bottom of the thermosphere can actually form at any altitude in this atmospheric layer.
File:ISS-46 Soyuz TMA-17M reentry.jpg|[[Afterglow]] of the [[troposphere]] (orange), the [[stratosphere]] (blue) and the mesosphere (dark) at which [[atmospheric entry]] begins, leaving smoke trails, such as in this case of a [[spacecraft]] reentry.
File:ISS-47_Islands_In_The_Sky,_Indonesia.jpg|A picture of Earth's troposphere with its different [[cloud types]] of low to [[high altitude]]s casting shadows. Sunlight is reflected off the ocean, after it was filtered into a redish light by passing through much of the troposphere at sunset. The above lying [[stratosphere]] can be seen at the [[horizon]] as a band of its characteristic glow of [[Rayleigh scattering|blue scattered]] sunlight.
File:Msis_atmospheric_composition_by_height.svg|The volume fraction of the main gases in Earth's atmosphere according to height. The boundary between the homosphere (left) and heterosphere (right) is at about 100 km. The outermost layer of the exosphere (off the chart) is dominated by hydrogen.
File:Atmospheric Temperature Trend.jpg|Temperature trends in two thick layers of the atmosphere as measured between January 1979 and December 2005 by [[microwave sounding unit]]s and [[advanced microwave sounding unit]]s on [[NOAA]] weather satellites. The instruments record microwaves emitted from oxygen molecules in the atmosphere. Source:
File:Atmosphere model.png|Temperature and mass density against altitude from the [[NRLMSISE-00]] [[International Standard Atmosphere|standard atmosphere]] model (the eight dotted lines in each "decade" are at the eight cubes 8, 27, 64, ..., 729)
File:Atmospheric electromagnetic opacity.svg|Rough plot of Earth's atmospheric [[transmittance]] (or opacity) to various wavelengths of electromagnetic radiation, including [[visible light]].
File:SB DouglasPreserve SunAtmosphericEffects 2017 3 cropped.jpg|Distortive effect of [[atmospheric refraction]] upon the shape of the sun at the horizon.
File:Watching the Earth Breathe.ogv|Animation shows the buildup of tropospheric {{CO2}} in the Northern Hemisphere with a maximum around May. The maximum in the vegetation cycle follows in the late summer. Following the peak in vegetation, the drawdown of atmospheric {{CO2}} due to photosynthesis is apparent, particularly over the [[boreal forests]].
</gallery>
== Related pages ==
== Related pages ==
* [[Air]]
* [[Air]]
* [[Template:Life timeline|Life timeline]]
* [[Template:Life timeline|Life timeline]]
== References ==
== References ==
{{Reflist}}
{{Reflist}}
== Other websites ==
== Other websites ==
*[http://www.ux1.eiu.edu/~cfjps/1400/atmos_struct.html The Atmosphere]
*[http://www.ux1.eiu.edu/~cfjps/1400/atmos_struct.html The Atmosphere]