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Comparing the atmospheric compositions of Earth with our nearest neighbours:

enter image description here

As the table shows, the Earth's atmospheric nitrogen concentration is 78%, compared to 3.8% for Venus and 2.7% for Mars Image source.

I have read the excellent question and answer Why do Earth and Venus have different atmospheres?, but the answer focuses on the $\ce{CO2}$ content of the planets, this question is about the $\ce{N2}$ content. Also, have read Why do some planets have lots of $\ce{N2}$ and others none?, but in this question, I am looking at how nitrogen concentrations dominated over the other chemicals in Earth's atmosphere, not looking at similarities between planetary processes.

In modern Earth, the nitrogen cycle maintains nitrogen levels, however the early pre-biotic atmosphere, was believed by

most of the scientific community now believes that the early Earth's atmosphere was not reducing. Instead, scientists beleive the atmosphere was full of oxidants, such as $\ce{CO2}$ and $\ce{N2}$.

Source: Duke University Pre-Biotic Earth webpage

What is the origin of the dominant atmospheric nitrogen content in Earth's atmosphere?

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    $\begingroup$ It would be fantastic if you could add an image caption/transcript to make your question more accessible to folk with low/no vision. Screen-readers are a thing! :-) $\endgroup$
    – kaberett
    Nov 3, 2014 at 21:50
  • $\begingroup$ @kaberett a written captions is included $\endgroup$
    – user889
    Nov 14, 2014 at 9:31
  • $\begingroup$ @Michael true, have linked to that good question in my question. $\endgroup$
    – user889
    Dec 9, 2014 at 6:16

5 Answers 5

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According to the recent paper in Nature Geoscience: Nitrogen speciation in upper mantle fluids and the origin of Earth's nitrogen-rich atmosphere, $N_2$ originates from regions of the Earth where plates are converging. Venus and Mars lack plate tectonics and therefore lack $N_2$ in their atmospheres. In other regions of Earth upper mantle, and in Venus and Mars, nitrogen is expected to exist as aqueous ammonium and not enter the atmosphere.

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  • $\begingroup$ +1. That certainly is a timely paper with regard to this question! $\endgroup$
    – David Hammen
    Nov 3, 2014 at 20:56
  • $\begingroup$ Excellent paper! precisely answers the question in a way I never expected - definitely accepting this answer. $\endgroup$
    – user889
    Nov 4, 2014 at 0:05
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    $\begingroup$ +1 Though I'm a bit dubitative regarding the statement that "Venus [...] lack N2 in their atmospheres". 3% of the atmosphere, considering the density of Venus atmosphere is still a lot. I think it corresponds to a partial pressure of more or less 3 bars. $\endgroup$
    – plannapus
    Nov 4, 2014 at 7:23
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    $\begingroup$ @plannapus good point, the paper is discussing the ratio of $N_2$ to noble gases, rather than absolute amount of or percent $N_2$, alternate link: drsamimikhail.files.wordpress.com/2014/02/… ; supplemental material: drsamimikhail.files.wordpress.com/2014/02/… $\endgroup$
    – DavePhD
    Nov 4, 2014 at 12:59
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Nitrogen is volatile in most of its forms here on Earth. It is fairly non-reactive with most materials that make up the solid part of Earth, and it is very stable in the presence of solar radiation in the atmosphere. Even though, nitrogen is 4 times more abundant than oxygen in the atmosphere, we must also consider the relative abundances of nitrogen and oxygen over the entire Earth, where oxygen is about 10,000 times more abundant (water, sand). In life forms, nitrogen is less abundant than oxygen, mainly due to the abundance of water.

Venus and Mars, though, have lots of CO2 in the atmosphere. Plant life on Earth (Ocean + Land) and precipitation have taken CO2 out of the atmosphere... plants created the oxygen reserve. Earth is a distinctly unique planet because it undergoes hydrologic, geologic, and biological processes that take CO2 out of the atmosphere.

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  • $\begingroup$ This does not explain the origin of atmospheric nitrogen, as per the question. $\endgroup$
    – user889
    Nov 3, 2014 at 20:19
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    $\begingroup$ @Omen All atomic matter on Earth came from the solar nebula. The point is that the nitrogen molecule is not being consumed because it is very stable in sunlight. It has no place to go and noone wants it. Oxygen is too attractive of a molecule. $\endgroup$
    – f.thorpe ♦
    Nov 3, 2014 at 23:58
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    $\begingroup$ @farrenthorpe but it's true for the other planets as well. So why the difference? $\endgroup$
    – Gimelist
    Dec 9, 2014 at 6:05
  • $\begingroup$ @Michael sorry could you clarify what you mean? $\endgroup$
    – f.thorpe ♦
    Dec 9, 2014 at 15:21
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    $\begingroup$ @Michael Earth is distinctly unique because it undergoes hydrologic and biological processes that take CO2 out of the atmosphere. Large gaseous giants still have large reserves of atmospheric molecular hydrogen so they are not a good comparison. Venus and Mars have lots of CO2 in the atmosphere but plant life on Earth (Ocean + Land) and precipitation have taken CO2 out of the atmosphere... plants of course created an Oxygen reserve. $\endgroup$
    – f.thorpe ♦
    Dec 9, 2014 at 22:44
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The two major sources of atmospheric nitrogen are volcanoes and bottom-dwelling denitrifying bacteria, who produce it from nitrate ion dissolved in seawater. If anyone knows the relative importance of these two sources, I'd very much appreciate knowing. Tx.

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The reason Earth has so much nitrogen is because it is non reactive and builds up. The origin of the nitrogen is covered in previous answers. Also, Venus has as much nitrogen in its atmosphere as Earth, but it is a much smaller percentage due to the large amount of CO2. Here is a nice graph showing what gases can exist in a planetary atmosphere based on temperature and escape velocity (mass/radius) of a planet http://abyss.uoregon.edu/~js/ast121/lectures/lec14.html .

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Where all that nitrogen comes from. The two terrestrial planets plus one moon, in order of the amount of Nitrogen that they possess in their atmospheres: are Venus, Titan, finally Earth. Our planet is last. Everyone seems to not understand the difference between quantity and percentage. Venus has an atmospheric pressure of 92 bars, unlike Earth's of one bar at sea level. This means that at 3.5 % Venus has at least more than double the amount of nitrogen than Earth in its atmosphere. Saturn's moon Titan has an atmosphere mainly of nitrogen with a hint of methane. Nasa reports that its atmosphere is four times as dense as ours and Wikipedia says Titan's surface pressure is 1.5 bar. Again, Titan has more nitrogen than Earth. What is startling is the non-effect of gravity on atmospheric density. What do all three have in common that Mars lacks? Magnetic protective fields. No Venus does not have an intrinsic magnetic field but the solar wind induces one in its atmosphere. Saturn does the same thing for Titan. I would suggest that ionized nitrogen from the solar wind or the magnetosphere of Saturn would be deposited on these two planets and a single planetoid. Once there and relatively protected from charged particles and radiation, nitrogen is enough of an inert gas to accumulate over time. Just as water does in the Plasma Water Theory on Earth. https://www.researchgate.net/publication/349685226_plasma_water_theory I could definitely be wrong here, but I would love to know how.

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