If all plant life stopped how long would it take for oxygen in air to drop to zero?

[repoman]

Including ocean algae of course.

This is a silly academic question, but also sort of fun to think about.

There would be organic respiration making carbon dioxide and also rusting and so on...

One thing is that in the far future as the sun warms and the geochemical cycle restricts carbon dioxide in the atmosphere and therefore plant life, then oxygen levels will drop as well, right? Lower replenishment rate.

Will oxygen be say 19% in 100 million years from now?

 

[Loren Pechtel]

A long, long time--life would die out and oxygen would only be removed by oxidation.

 

[barbos]

True, but numerically it would take about 1000 years. This assumes rate of oxygen consumption stays the same. But again it's true that there is simply not enough readily available stuff to burn out all the oxygen in the atmosphere. We have basically 2 meters of liquid oxygen covering whole planet.

relevant number is here:
https://skepticalscience.com/human-co2-smaller-than-natural-emissions.htm

 

[rjh01]

Most animals would starve to death first.

 

[DBT]

First the herbivores would go, carnivores soon after. Some humans surviving on stored food for a while. It would all wind down quite quickly.

 

[Loren Pechtel]

True, but numerically it would take about 1000 years. This assumes rate of oxygen consumption stays the same. But again it's true that there is simply not enough readily available stuff to burn out all the oxygen in the atmosphere. We have basically 2 meters of liquid oxygen covering whole planet.

relevant number is here:
https://skepticalscience.com/human-co2-smaller-than-natural-emissions.htm

The rocks would eventually get rid of it. Oxygen atmospheres are not stable and thus are a very strong indication of life creating the oxygen.

 

[steve_bank]

Simple math. Liters per hour O2 by species and number into liters O2 in the atmosphere. As a rough approximation look up human O2 consumption.

 

[Jokodo]

Simple math. Liters per hour O2 by species and number into liters O2 in the atmosphere. As a rough approximation look up human O2 consumption.

Bullshit in bullshit out. If all plant life stops, the vast majority of humans will be dead within months, and the rest within years at the best, and most other animals will be d dead within weeks, hibernating ones within e weeks after they wake up. After that, only a few cave dwellers and deep sea critters, sustaining themselves on trace amounts of organic matter slowly dissipating from the surface, will survive a few more decades at most. Within little more than 100 years, the only animal life left on the planet will be around hydrothermal vents.

A simple math that assumes a constant rate of consumption is as wrong as it is simple.

(If we're pedantic, we might object that plants aren't the only oxygen producers - cyanobacteria are no plants, and neither are under the term's modern meaning single celled algae; I'm assuming the op means all phototrophic life. )

 

[Jokodo]

True, but numerically it would take about 1000 years. This assumes rate of oxygen consumption stays the same. But again it's true that there is simply not enough readily available stuff to burn out all the oxygen in the atmosphere. We have basically 2 meters of liquid oxygen covering whole planet.

relevant number is here:
https://skepticalscience.com/human-co2-smaller-than-natural-emissions.htm

The rocks would eventually get rid of it. Oxygen atmospheres are not stable and thus are a very strong indication of life creating the oxygen.

Sure, but that's a process that will take many (probably tens of) million years. The rocks currently facing the atmosphere aren't enough, it would require substantial resurfacing to complete the job.

 

[Valjean]

Oxygen is quite a reactive element. It's taken up not just organically but by rocks and water. If the forests were cut/killed, and the phytoplankton poisoned, we might see a measurable diminution in months or years.

 

[Jokodo]

Oxygen is quite a reactive element. It's taken up not just organically but by rocks and water.

On a planet that didn't have oxygen in its atmosphere, true.

On a planet that has had an atmosphere with around 20% oxygen for hundreds of millions of years, mostly everything at the surface that easily oxygenates is already oxygenated.

 

[steve_bank]

http://scienceline.ucsb.edu/getkey.php?key=3097

From a controlled study in anesthesiology humans average 5ml/minute O2 while resting.

The estimate is about 1000 years for humans alone. The OP excludes other factors but obviously everybody starves to death well before that.

The current estimate is 16% atmospheric O2 and is dropping. It has always been dropping.Technology and fossil fuels consume O2. More people consume O2. There does not appear to be a balance.

Ask somebody like Trump and anti environment regulation conservatives where O2 they breath comes from and they probably have no clue.

 

[barbos]

True, but numerically it would take about 1000 years. This assumes rate of oxygen consumption stays the same. But again it's true that there is simply not enough readily available stuff to burn out all the oxygen in the atmosphere. We have basically 2 meters of liquid oxygen covering whole planet.

relevant number is here:
https://skepticalscience.com/human-co2-smaller-than-natural-emissions.htm

The rocks would eventually get rid of it. Oxygen atmospheres are not stable and thus are a very strong indication of life creating the oxygen.

Sure, but that's a process that will take many (probably tens of) million years. The rocks currently facing the atmosphere aren't enough, it would require substantial resurfacing to complete the job.

I don't know what LP means by "rock" but most of the stone is already oxidized form of elements which can't be oxidized anymore. OK, diamond can be burned, what else?
The only thing which is available in measurable quantities is organic matter which is close to the surface. Coal and even oil is not really close to the surface.

 

[Loren Pechtel]

Sure, but that's a process that will take many (probably tens of) million years. The rocks currently facing the atmosphere aren't enough, it would require substantial resurfacing to complete the job.

I don't know what LP means by "rock" but most of the stone is already oxidized form of elements which can't be oxidized anymore. OK, diamond can be burned, what else?
The only thing which is available in measurable quantities is organic matter which is close to the surface. Coal and even oil is not really close to the surface.

I forget exactly what it is that reacts but I do recall that in the long run oxygen will oxidize out of an atmosphere, thus the presence of O₂ is a clear indication of something producing it--and no natural process does so.

 

[barbos]

Sure, but that's a process that will take many (probably tens of) million years. The rocks currently facing the atmosphere aren't enough, it would require substantial resurfacing to complete the job.

I don't know what LP means by "rock" but most of the stone is already oxidized form of elements which can't be oxidized anymore. OK, diamond can be burned, what else?
The only thing which is available in measurable quantities is organic matter which is close to the surface. Coal and even oil is not really close to the surface.

I forget exactly what it is that reacts but I do recall that in the long run oxygen will oxidize out of an atmosphere, thus the presence of O₂ is a clear indication of something producing it--and no natural process does so.

Question is not about producing O2, question is about how it gets consumed. The reason why dead planets don't have O2 is O2 does not exist in space in the first place - it will react with everything starting with hydrogen and carbon.
Coal, oil and iron is no longer accessible for atmospheric oxygen.
Initially there was plenty of iron but once O2 started to be produced all the available iron in the ocean and on the surface was oxidized.

So if life on earh suddenly stops, O2 will most certainly persist for hundreds of millions of years because the only major thing which can be oxidized is coal and it is deep underground

 

[Valjean]

I forget exactly what it is that reacts but I do recall that in the long run oxygen will oxidize out of an atmosphere, thus the presence of O₂ is a clear
indication of something producing it--and no natural process does so.

Am I reading this right, no natural process produces O2? So where's it coming from?

 

[Jokodo]

I forget exactly what it is that reacts but I do recall that in the long run oxygen will oxidize out of an atmosphere, thus the presence of O₂ is a clear
indication of something producing it--and no natural process does so.

Am I reading this right, no natural process produces O2? So where's it coming from?

I think what Loren wants to say is no abiotic process produces oxygen in sufficient quantities.

 

[Loren Pechtel]

I forget exactly what it is that reacts but I do recall that in the long run oxygen will oxidize out of an atmosphere, thus the presence of O₂ is a clear
indication of something producing it--and no natural process does so.

Am I reading this right, no natural process produces O2? So where's it coming from?

I think what Loren wants to say is no abiotic process produces oxygen in sufficient quantities.

Yeah, that's what I meant. I was distinguishing chemistry from life.

 

[Politesse]

First the herbivores would go, carnivores soon after. Some humans surviving on stored food for a while. It would all wind down quite quickly.

If all plants died? The majority of humanity would be dead from malnutrition by the end of the year. We need plants, and the stored ones would get hoarded like mad by those who could. So I would concur with post two, life would cease to exist before it started meaningfully impacting oxygen depletion.

 

[barbos]

First the herbivores would go, carnivores soon after. Some humans surviving on stored food for a while. It would all wind down quite quickly.

If all plants died? The majority of humanity would be dead from malnutrition by the end of the year. We need plants, and the stored ones would get hoarded like mad by those who could. So I would concur with post two, life would cease to exist before it started meaningfully impacting oxygen depletion.

So you agree with DBT.
As for plant life, I think people will switch to fully synthetic food pretty soon, 100 years from now.