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

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

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?

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

3. 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-c...-emissions.htm

4. Most animals would starve to death first.

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

6. Originally Posted by 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-c...-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.

7. 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.

8. Originally Posted by 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.
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. )

9. Originally Posted by Loren Pechtel
Originally Posted by 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-c...-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.

10. 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.

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