[inbetweenus]

Hello! This may be a silly question, but I wanted to get some additional feedback from others. So here it is... and thanks in advance for your *delete me*

How would life on earth change if there was only 10% oxygen in the atmosphere? How would things like burning, rusting and other metabolic processes in humans and plants be affected?

Thanks! 

[Yggdrasil]

According to the Forum Rules, you should post what you think of the question before we help you with it.  So, what is your guess as to what will happen to burning, rusting, and metabolic processes in an atmosphere with 10% oxygen?  How do all of these processes depend on oxygen?  Is oxygen a reactant?  A product?  Do animals (such as humans) and plants use different metabolic processes which might be affected differently by a low oxygen atmosphere?

[inbetweenus]

Ok...

Well my guess is that if oxygen was present at only 10%, burning, rusting and things of that nature would occur at a much slower rate, and less frequently. As far as plants and animals go, I would imagine they would need to adjust their eating and breathing habits. There are a lot of possibilities, but to be honest I am having a hard time coming up with specific examples. That is why I posted my question here.

[Yggdrasil]

I agree that rusting and burning would occur at much slower rates.  I also think that plants and animals which evolved in a low oxygen environment would have major differences.  Since most energy production in most organisms uses oxygen, a low oxygen environment would greatly slow down energy production in these plants and animals in the same way that low oxygen slows the rates of rusting and burning.  So, these plants and animals would either have to be more energy efficient, more sluggish, or have some other way of producing energy.

On the other hand, plants produce sugars by photosynthesis, which produces oxygen.  One problem with photosynthesis is that the enzyme which captures carbon dioxide (RuBisCo) has a hard time differentiating between carbon dioxide and oxygen.  When RuBisCo uses oxygen instead of carbon dioxide, a process known as photorespiration occurs which wastes the plant's energy and does not produce any sugars.  As a result, many modern plants have evolved mechanisms to prevent oxygen from interfering with photosynthesis (e.g. CAM and C4 plants).  Presumably, in a low oxygen environment, plants would not have to worry as much about photorespiration and photosynthesis may even be more efficient.

[Dan]

Since most energy production in most organisms uses oxygen, a low oxygen environment would greatly slow down energy production in these plants and animals in the same way that low oxygen slows the rates of rusting and burning.

This could also result in smaller organisms. I read a somewhere about a theory that dinosaurs and other massive organisms all those years ago were able to grow so large because the oxygen content of the air was really high. I think 35% was what they reckoned.

[Borek]

AFAIR it was much more prominent in arthropods, as they don't have a breathing/blood circulation system that can transport oxygen. That's why at some time they were much larger then today. And 35% is what I remeber too.

[constant thinker]

Since most energy production in most organisms uses oxygen, a low oxygen environment would greatly slow down energy production in these plants and animals in the same way that low oxygen slows the rates of rusting and burning.

This could also result in smaller organisms. I read a somewhere about a theory that dinosaurs and other massive organisms all those years ago were able to grow so large because the oxygen content of the air was really high. I think 35% was what they reckoned.

My first thought about organisms when I read the question was that they'd wind up smaller too.

[Ψ×Ψ]

AFAIR it was much more prominent in arthropods, as they don't have a breathing/blood circulation system that can transport oxygen. That's why at some time they were much larger then today. And 35% is what I remeber too.

Centipedes are arthropods, right?  Extant giant centipedes are large enough for me

[Borek]

AFAIR it was much more prominent in arthropods, as they don't have a breathing/blood circulation system that can transport oxygen. That's why at some time they were much larger then today. And 35% is what I remeber too.

Centipedes are arthropods, right?  Extant giant centipedes are large enough for me

Yep. Insects, spiders, scorpions, crabs, shrimps and so on. Especially some scorpions were huge.

http://en.wikipedia.org/wiki/Sea_scorpion

[billnotgatez]

I guess the original question assumed that nitrogen would make up 89%, oxygen would be 10% and the rest of the gases would be 1%. The answer might be very different if the percentages were not as above.

Consider
79% nitrogen, 10% oxygen, 10% carbon dioxide and 1% other gases
Or
79% nitrogen, 10% oxygen, 10% chlorine and 1% other gases
Or
79% nitrogen, 10% oxygen, 10% helium and 1% other gases
Or
49% nitrogen, 10% oxygen, 40% carbon dioxide and 1% other gases


Recollect that the current atmosphere is about
79% nitrogen, 20% oxygen and 1% other gases
Correction
78% nitrogen, 21% oxygen and 1% other gases

The question should have been more precise. Ok so I am nit picking.