# Life and the atmosphere
**URL:** https://boards.straightdope.com/t/life-and-the-atmosphere/671485
**Category:** Factual Questions
**Created:** [October 17, 2013, 3:03pm UTC](https://boards.straightdope.com/t/life-and-the-atmosphere/671485 "2013-10-17T15:03:26Z")
**Posts on this page:** 13
**Page:** 1
### Author:  [@pdunderhill](https://boards.straightdope.com/u/pdunderhill)
#### Post date: [October 17, 2013, 3:03pm UTC](https://boards.straightdope.com/t/life-and-the-atmosphere/671485/1 "2013-10-17T15:03:26Z")
Hello good people,
A thought came to me,
does any part of life on Earth utilize any of the gases with very low concentrations, Krypton Xenon, Iodine etc?
From wiki:Gas Volume
Nitrogen (N2) 780,840 ppmv (78.084%)
Oxygen (O2) 209,460 ppmv (20.946%)
Argon (Ar) 9,340 ppmv (0.9340%)
Carbon dioxide (CO2) 397 ppmv (0.0397%)
Neon (Ne) 18.18 ppmv (0.001818%)
Helium (He) 5.24 ppmv (0.000524%)
Methane (CH4) 1.79 ppmv (0.000179%)
Krypton (Kr) 1.14 ppmv (0.000114%)
Hydrogen (H2) 0.55 ppmv (0.000055%)
Nitrous oxide (N2O) 0.325 ppmv (0.0000325%)
Carbon monoxide (CO) 0.1 ppmv (0.00001%)
Xenon (Xe) 0.09 ppmv (9×10−6%) (0.000009%)
Ozone (O3) 0.0 to 0.07 ppmv (0 to 7×10−6%)
Nitrogen dioxide (NO2) 0.02 ppmv (2×10−6%) (0.000002%)
Iodine (I2) 0.01 ppmv (1×10−6%) (0.000001%)
Ammonia (NH3) trace
Assuage my curiosity please, I will allow one (1) joke about Krypton, first one gets the nice fluffy toy at the back.
NB this is not a question about Global Warming…
Peter
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### Author:  [@aNewLeaf](https://boards.straightdope.com/u/aNewLeaf)
#### Post date: [October 17, 2013, 3:17pm UTC](https://boards.straightdope.com/t/life-and-the-atmosphere/671485/2 "2013-10-17T15:17:44Z")
Nitrogen, Oxygen, Carbon Dioxide are all crucial to life. Ozone too, though we don’t breathe it and too much is poisonous.
Neon, Xenon, and other noble gases don’t participate in chemistry at ordinary pressures and temps.
Anything more than a trace of methane or ammonia is problematic and can be unhealthy. Humans use iodine but not from the atmosphere, I think.
Hydrogen is utilized as part of water, I don’t know how many organisms deal with hydrogen directly from air.
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### Author:  [@Quercus](https://boards.straightdope.com/u/Quercus)
#### Post date: [October 17, 2013, 4:11pm UTC](https://boards.straightdope.com/t/life-and-the-atmosphere/671485/3 "2013-10-17T16:11:55Z")
Short answer: no
For everything below Carbon Dioxide
Iodine (in some form, but certainly not I2) is used by mammals and probably many other organisms, but not obtained from the atmosphere.
Ammonia and hydrogen are present in some form in nearly all organisms but again not directly obtained from the atmosphere in those forms. There are probably some bacteria or what-not that can live off of methane in gas form, but only at higher concentrations than typical in the general atmosphere.
I believe NO2 and N2O are used by some organisms, but almost certainly synthesized internally from various other compounds.
As far as I know, the only compounds directly obtained from the atmosphere are O2, CO2, and N2. I think some organisms like lichens get some trace minerals from rainwater, which absorb the minerals from suspended particles in the atmosphere (not actual gases).
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### Author:  [@Smeghead](https://boards.straightdope.com/u/Smeghead)
#### Post date: [October 17, 2013, 4:49pm UTC](https://boards.straightdope.com/t/life-and-the-atmosphere/671485/4 "2013-10-17T16:49:20Z")
Nitrogen-fixing bacteria, incidentally, use N2 as their starting material, which is at the top of the list, not the bottom. As far as I’m aware, other nitrogen compounds are not absorbed from the atmosphere for direct use by any life forms. But, biology being biology, there are probably exceptions out there that I’m not aware of.
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### Author:  [@njtt](https://boards.straightdope.com/u/njtt)
#### Post date: [October 17, 2013, 4:57pm UTC](https://boards.straightdope.com/t/life-and-the-atmosphere/671485/5 "2013-10-17T16:57:32Z")
I do not know what **iodine** is doing on your list, as it is a solid, and thus not found in the atmosphere. (It is also highly reactive, and thus not naturally found anywhere on Earth in its elemental form, but only as compounds. But none of those compounds are present in the atmosphere either.) Human beings and many other animals need it as a component of thyroid hormone. It also participates in the chemistry of life as the iodide ion which will be found, in low concentration, in most if not all aqueous fluids, including cell cytoplasm, in all living things. However, it is probably not _necessary_ in this latter role, and could be replaced by other halogen ions, such as bromide and chloride, the latter of which is far, far more abundant in these fluids anyway.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [October 17, 2013, 5:13pm UTC](https://boards.straightdope.com/t/life-and-the-atmosphere/671485/6 "2013-10-17T17:13:08Z")
Iodine is ordinarily a solid under Earthly conditions, but there’s still going to be a trace of vapor pressure of it, in much the same way that there’s water vapor in the atmosphere despite water being a liquid (and where is water vapor on that list, anyway?).
And anything on that list that’s used at all will be at least indirectly gotten from the atmosphere. Anything that’s found in the air will also be found in water, and vice-versa, in a dynamic equilibrium. There’s always some in the air that’s settling out into the water, and some in the water evaporating out into the air, and the relative concentrations are such that the rates of both processes are the same. If you magically sucked all of the ammonia, say, out of the atmosphere, it would be quickly replenished from the oceans to nearly the same level. If you kept on removing the ammonia from the atmosphere, you’d eventually deplete the oceans, and that would have an effect on life.
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### Author:  [@TroutMan](https://boards.straightdope.com/u/TroutMan)
#### Post date: [October 17, 2013, 5:18pm UTC](https://boards.straightdope.com/t/life-and-the-atmosphere/671485/7 "2013-10-17T17:18:04Z")
Elemental iodine (I2) is present in the atmosphere at extremely low concentrations, as noted in the OP. The fact that it is a solid at room temperature isn’t really important. Water is a liquid at room temperature yet there is plenty in air. Molecules escape from solids in the same way; the amount is so small that we usually ignore it.
ETA; ninja’d by **Chronos** , right down to the water example.
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### Author:  [@njtt](https://boards.straightdope.com/u/njtt)
#### Post date: [October 17, 2013, 5:38pm UTC](https://boards.straightdope.com/t/life-and-the-atmosphere/671485/8 "2013-10-17T17:38:31Z")
OK, but that is going to be true of virtually any solid (or liquid) element. Why isn’t bromine, or mercury, or even iron, come to that, listed?
The tiny trace of elemental iodine in the atmosphere can’t be there because it has sublimed off solid elemental iodine, anyway, since, as I noted, there is no natural elemental iodine around on Earth. If elemental iodine is in the atmosphere in higher concentrations than, say, bromine or mercury, I think that must be because it (or some quickly broken down iodine compound) is released by some living organism (at a guess, some sort of seaweed).
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### Author:  [@TroutMan](https://boards.straightdope.com/u/TroutMan)
#### Post date: [October 17, 2013, 6:21pm UTC](https://boards.straightdope.com/t/life-and-the-atmosphere/671485/9 "2013-10-17T18:21:00Z")
You are correct that elemental iodine as I is not found, but it is certainly found in nature as I2, which is what people are referring to as Iodine. It is naturally occurring in sea water and liberated to the atmosphere from the ocean. It is also concentrated within seaweed and released from that.
Mercury occurs in nature at lower levels than iodine so isn’t found at the same levels in the atmosphere. I’m not sure about the relative prevalence of bromine, but it is definitely more reactive than iodine and therefore you wouldn’t expect it at the same levels.
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### Author:  [@pdunderhill](https://boards.straightdope.com/u/pdunderhill)
#### Post date: [October 18, 2013, 12:00am UTC](https://boards.straightdope.com/t/life-and-the-atmosphere/671485/10 "2013-10-18T00:00:46Z")
Hence the question, do we need anything other than Nitrogen, Oxygen and CO2?
P
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### Author:  [@TroutMan](https://boards.straightdope.com/u/TroutMan)
#### Post date: [October 18, 2013, 12:03am UTC](https://boards.straightdope.com/t/life-and-the-atmosphere/671485/11 "2013-10-18T00:03:45Z")
See post #3 by **Quercus**.
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### Author:  [@aNewLeaf](https://boards.straightdope.com/u/aNewLeaf)
#### Post date: [October 18, 2013, 12:07am UTC](https://boards.straightdope.com/t/life-and-the-atmosphere/671485/12 "2013-10-18T00:07:20Z")
> [@pdunderhill](#):
>
> Hence the question, do we need anything other than Nitrogen, Oxygen and CO2?
> P
That question isn’t in the OP. Answer: not from air, no.
We have to have a certain amount of water in the air though, or it’s hideously uncomfortable.
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### Author:  [@j\_sum1](https://boards.straightdope.com/u/j_sum1)
#### Post date: [October 18, 2013, 12:29am UTC](https://boards.straightdope.com/t/life-and-the-atmosphere/671485/13 "2013-10-18T00:29:19Z")
The thing that is missing from the list is sulfur compounds. H2S and SO2 spring to mind. These are released by geothermal and volcanic processes and concentrations would vary greatly. I know that many bacteria release sulfur compounds as a waste. I seem to recall that there are some bacteria that utilise sulfur compounds. Presumably there are some that do this either directly or indirectly from the atmosphere.