# Atmospheric deterioration

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I've posed this question once already, but the discussion devolved into semantics and stuff, with no real answer coming out of it. So, I once again turn to the nerds of the forum: If all the oxygen-producing processes on Earth were to suddenly stop, how long would it take for the atmosphere to become inhospitable to human life?

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Without knowing the actual reabsorption rate/reaction rate or the mechanisms involved, in the limit of small changes in the concentration of oxygen, the absorption/reaction of atmospheric oxygen will likely occur in a linear fashion with time. Over longer time periods, it may start to approach an expotential decay of some sort. But it's possible that within the range of oxygen levels that would support humans, absorption and reaction of oxygen would be linear enough that a linear approximation may get you in the ballpark.

If you assume that the current oxygen levels represent an equilibrium between oxygen production by plants and oxygen absorption and reaction, then you need to find out how much oxygen is produced by plants yearly. If you make the assumption that without plants, oxygen absoprtion and reaction would continue at the same rate, then you can thus get a ballpark estimate of how long it would take for oxygen levels to drop below habitable levels, by using the aforementioned linear approximation by subtracting the oxygen production rate of plants from the atmosphere until levels fall below habitability. This will probably under-estimate the time it would take, but that's OK, since we're just looking for a ballpark figure.

In reality, the moment plants die then there is a quick drop in oxygen levels (probably only by a fraction of a percent though) because much of the decay of plant matter will involve reactions with oxygen.

ANYWAY, in summary, look up the rate of oxygen production by plants, and make an estimate based off of the assumption that we're currently in an equilibrium state between oxygen consuming and oxygen producing processes.

Edited by |Velocity|

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Well, most of the oxygen removed now is due to animals & decomposing fungi/bacteria/etc, and these would die off quickly (many within weeks, scavengers/decomposers/detritivores would live significantly longer) due to starvation.

From a search, the mass of oxygen in the atmosphere is vastly greater than the biomass, so the rotting away of most life wouldn't reduce it much. After that, it would be geological processes, which are slow (most rocks are oxidized already).

A search gives me about 4 million years, but that's to remove all of it, and I don't know whether it's a linear decrease or what. But, very roughly, it would probably take hundreds of thousands of years for the oxygen to drop to unbreathable levels. Maybe longer depending on who you are -- if you live in the Andes or Tibet with low oxygen partial pressure, you might be able to live at sea level with a significantly lower oxygen concentration.

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It would be a very short time on the geological scales. If all life was suddenly removed, it would take more, but in this case we just have the production stopped. There's a lot of reducers in the nature to reduce oxygen to water. All of the biomass on the world suddenly turns into exclusive oxygen consumers by rotting.

Apart from organisms, consumers would be not only reductive compounds made by geological processes, but also compounds made by the bacteria. Amount of anaerobic bacteria below the silty ocean floors is enormous. Their metabolism gives off hydrogen sulphide and methane, and they don't care about what's happening above. There's plenty of food for them.

I can't say for sure, but my hunch says it would be a blink of time on the geological scale even knowing that the surface of Earth is mostly oxidized.

Edited by lajoswinkler
lapsus

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It would be a very short time on the geological scales. If all life was suddenly removed, it would take more, but in this case we just have the production stopped. There's a lot of reducers in the nature to reduce oxygen to water. All of the biomass on the world suddenly turns into exclusive oxygen consumers by rotting.

Sure, but the biomass is tiny compared to the mass of oxygen in the atmosphere. The CO2 levels might become problematically high, though.

Apart from organisms, consumers would be not only reductive compounds made by geological processes, but also compounds made by the bacteria. Amount of anaerobic bacteria below the silty ocean floors is enormous. Their metabolism gives off hydrogen sulphide and methane, and they don't care about what's happening above. There's plenty of food for them.

There may well be a huge amount of very deep endolithic bacteria, but I'm not sure whether their metabolic products actually enter the atmosphere or ocean, and anyway their metabolism is glacially slow (1 cell division per century kind of thing).

I don't think the ones interacting with the ocean in black smokers/cold seeps are that abundant since their habitats are small & localized.

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Sure, but the biomass is tiny compared to the mass of oxygen in the atmosphere. The CO2 levels might become problematically high, though.

There may well be a huge amount of very deep endolithic bacteria, but I'm not sure whether their metabolic products actually enter the atmosphere or ocean, and anyway their metabolism is glacially slow (1 cell division per century kind of thing).

I don't think the ones interacting with the ocean in black smokers/cold seeps are that abundant since their habitats are small & localized.

Well it would obviously take thousands of years or more to destroy it all, but it's all a fragment on the geological scales of eons. The current situation is one frame in the film featuring dynamic balance where one of the actors is a highly reactive gas. It would take a serious scientific study to increase the security of statements involving numbers, though.

However, problems for the autotrophes would become apparent a lot sooner. The whole grid would collapse very fast.

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