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

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

'''Earth's atmosphere''' is the layer of [[gas]]es around the [[Earth]]. The atmosphere is held in place by Earth's [[gravity]]. It is made up of [[nitrogen]] (78.1%) and [[oxygen]] (20.9%), with 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]]. 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 something is, the thinner the atmosphere around it is. There is no clear [[line]] between the atmosphere and [[outer space]]. 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. 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 ==

Originally, the Earth's atmosphere had almost no free [[oxygen]]. It gradually changed to what it is today, over a very long time (see [[Great Oxygenation Event]]). The process began with [[cyanobacteria]]. They were the first [[organism]]s to make free oxygen by [[photosynthesis]]. Most organisms today need oxygen for their [[metabolism]]; only a few can use other sources for [[respiration]].<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>

Originally, the Earth's atmosphere had almost no free [[oxygen]]. The first atmosphere consisted of gases in the solar nebula, primarily [[hydrogen]]. There might be 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 2 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>

 

== Temperature and the atmospheric layers ==

== Temperature and the atmospheric layers ==

Some parts of the atmosphere are hot or cold, depending on [[height]]. If something climbed straight up, it would get colder, but then it would get hotter as the object climbed higher. These changes of [[temperature]] are divided into layers. These are like layers of an onion. However, no difference can be seen between each layer. They are just places where the temperature changes differently.

 

 

Some parts of the atmosphere are hot or cold, depending on [[height]]. Starting from the surface and climbing straight up, the air gets colder in the troposphere, but then it becomes hotter, higher in the stratosphere. These changes of [[temperature]] are divided into layers. These are like layers of an onion. The difference between the layers is the way the temperature changes.

These are the layers of the atmosphere, starting from the ground:

These are the layers of the atmosphere, starting from the ground:

*[[Troposphere]] - Starts at the ground. Ends somewhere between {{convert|7|to|14|km|abbr=off}}. The higher, the colder. [[Weather]] in this layer affects our daily life.

*[[Troposphere]] - Starts at the ground. Ends somewhere between {{convert|0|to|18|km|abbr=off}}. The higher, the colder. [[Weather]] in this layer affects our daily life.

*[[Stratosphere]] - Starts at {{convert|7|to|14|km|abbr=off}}. Ends at {{convert|50|km|abbr=off}}. The higher, the hotter. There is little [[water vapor]] and other [[substances]] in this layer. [[Airplane]]s fly in this layer because it is usually stable and [[air resistance]] is small.

*[[Stratosphere]] - Starts at {{convert|18|km|abbr=off}}. Ends at {{convert|50|km|abbr=off}}. The higher, the hotter. The heat comes from the [[Ozone layer]] at the top of the stratosphere. There is little [[water vapor]] and other [[substance]]s in this layer. [[Airplane]]s fly in this layer because it is usually stable and [[air resistance]] is small.

*[[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 [[AM 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.

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.  

These are called boundaries.

These are called 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==

== Pressure ==

The atmosphere has [[pressure]]. This is because even though [[air]] is a gas, it has [[weight]]. The average pressure of the atmosphere 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==

==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 &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.

== References ==

== References ==

[[Category:Atmosphere]]

[[Category:Atmosphere]]