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A lot of people tend to narrowly focus on only Oxygen, Hydrogen, and carbon when considering the suitability for life. But the organic processes that we rely on require more elements than just those two, one of those often overlooked elements is Nitrogen.

In examining Venus for chemical suitability I noticed it only has like ~ %2 atmospheric Nitrogen concentration (from wiki). Where's all the Nitrogen?

My assumption is that there is a whole lot more trapped in liquid Nitric Acid or other acids or mineral deposits. If that is the case what is the estimated amount contained? If that is not the case, how did Earth end up with all the Nitrogen?

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    $\begingroup$ Well, Venus' atmosphere is about 50x more dense than Earth's, so the 2% nitrogen there is roughly comparable to Earth's 70% (depending on if your counting moles or kilograms). $\endgroup$
    – uhoh
    Oct 23, 2018 at 13:22
  • $\begingroup$ @anon - From the responses to your question, it sounds like there's more nitrogen in absolute measurements, but a great deal less proportional to other elements. And that's what you're really asking about, correct? $\endgroup$ Oct 23, 2018 at 15:47
  • $\begingroup$ Nitric acid would not be stable on Venus it would decompose to water and nitrogen dioxide. The nitrogen dioxide would also decompose to nitric oxide and oxygen and even that would decompose to nitrogen and oxygen. I doubt any nitrogen salts would be stable either. uhoh has the answer. $\endgroup$
    – Slarty
    Jan 28 at 14:12

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There is nitrogen in the atmosphere of Venus, four times the amount of nitrogen on Earth. Because Venus' atmosphere is so dense, made up almost entirely of carbon dixode, the percentage of nitrogen is rather small in comparison to Earth's atmosphere, but the nitrogen is there.

Space.com: Venus' Atmosphere: Composition, Climate and Weather

Atmospheric makeup:

The atmosphere of Venus is made up almost completely of carbon dioxide. It also includes small doses of nitrogen and clouds of sulfuric acid. The air of Venus is so dense that by mass, the small traces of nitrogen are four times the amount found on Earth, although nitrogen makes up more than three-fourths of the terrestrial atmosphere. This composition causes a runaway greenhouse effect that heats the planet even hotter than the surface of Mercury, although Venus lies farther from the sun. When the rocky core of Venus formed, it captured much of the gas gravitationally.

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    $\begingroup$ This doesn't answer the question. Sure, there is a lot more atmospheric nitrogen than on Earth, and the percentage is so low due to the sheer amount of carbon dioxide on Venus when in fact it's really dense, but... Still, that doesn't fully explain why the percentage of nitrogen is so low. Restated, why is the percentage of CO2 so high? $\endgroup$
    – matt_rule
    Oct 23, 2018 at 23:18
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    $\begingroup$ @matt_rule The proper question to ask is why Earth's atmosphere has such a low concentration of CO2 and other carbon based compounds compared to other planets. Of course, we know where that missing carbon is - it is bound in sedimentary rocks. If all the limestone like compounds littering the Earth surface were to decompose suddenly, we will end up with exactly the amount of CO2 to make Earth into Venus (such calculations were done before, most recently by Octave Levenspiel). $\endgroup$
    – oakad
    Oct 24, 2018 at 0:38
  • $\begingroup$ @oakad could you expand that into an answer? I think it would nicely complement this one $\endgroup$
    – Bear
    Oct 24, 2018 at 12:41
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    $\begingroup$ @Bear I asked and self answered a similar question some years ago. $\endgroup$
    – oakad
    Oct 25, 2018 at 1:38
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Earth probably had a similar atmospheric composition to Venus after it formed with vast amounts of water, carbon dioxide and smaller amounts of nitrogen plus traces of other gases. So the real question is what happened to make Venus different from Earth?

Firstly water can be split by UV light in the upper atmosphere into hydrogen and oxygen. The oxygen would have reacted rapidly on Earth and Venus forming oxides and carbonates on the surface the hydrogen would linger for a while but eventually escape. Over geological time water levels on both planets would have decreased significantly.

But the really big difference between Venus and Earth was the emergence of photosynthesis only on Earth (perhaps Venus was too hot). Photosynthesis saved Earth from the fate of Venus by flooding the atmosphere with a lot of oxygen. The UV splitting of water still happened as before, but in most cases any hydrogen formed that way would react fairly quickly with oxygen before it could escape (it has been calculate that today a mere 3 million tonnes a year is lost so it now takes roughly 4.5 billion years to lose 1% of the oceans.

In time photosynthesis on Earth consumed almost all of the carbon dioxide in Earth's atmosphere converting it to the vast amounts of oxygen we see today and leaving behind vast amounts of carbon in the form of coal, oil, gas and more importantly (>95%) as a 1-2% carbon based impurities in sandstone and other sedimentary rocks (there is an awful lot of sandstone on Earth).

Venus lost it's water due to UV reactions in it's upper atmosphere, the escape of hydrogen and the reaction of the oxygen with the crust. But it never lost it's vast blanket of carbon dioxide that remains to this day swamping the nitrogen.

Earth didn't lose much of its water, it was protected by the formation of far greater amounts of oxygen by photosynthesis. The carbon dioxide on Earth was consumed by photosynthesis leaving oxygen in the atmosphere and deposits of carbon and hydrocarbons in the crust. Earth appears to have much more nitrogen than Venus but Earths atmosphere is at a much lower pressure due to the loss of al that carbon dioxide so the nitrogen is more apparent.

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    $\begingroup$ What about the role of carbonate rock formation? Most CO2 on Earth has been so converted, but on Venus a widely hypothesized global volcanic resurfacing may have destroyed the carbonates and released the CO2. I suspect thus had more impact than photosynthesis. $\endgroup$ Jan 29 at 19:13
  • $\begingroup$ @Oscar Lanzi, there is a lot that we don't yet understand about the detailed history of Venus so it's hard to be too adamant. That said Venus is thought to have undergone a sudden resurfacing event 750 million years ago, but Earth also undergoes gradual resurfacing in perhaps as little as 500 million years. $\endgroup$
    – Slarty
    Jan 30 at 13:50
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Earth did not end up with "all the nitrogen". Neither planet has much nitrogen compared with the icy bodies farther out in the Solar System, such as Ceres with ammonium salts or the ammonia/ammonium compounds or the giant planets and some of their moons. Such minerals are volatile and thus more likely to be found on colder surfaces in the Solar System. See this answer for more discussion of these alternate sources.

Comparing just Earth and Venus, our atmosphere is higher in nitrogen percentage but also much less dense, so in the end Venus actually has more nitrogen in its atmosphere than Earth.

Most mineral nitrogen on Earth's surface (also on Mars) is in the form of nitrates. On Earth, nitrogen is oxidized in thunderstorms and the reactions end with nitric acid, which then reacts with various components of rock when delivered in rain or snow. On Venus, the high surface temperature would decompose most nitrates and (notwithstanding whether thunderstorms occur) there is very little oxygen. We would therefore expect very little mineral nitrogen on the surface of Venus.

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