Why has life evolved around oxygen? Many lifeforms require oxygen to breakdown bio-molecules and release energy. I think there are two possibilities:

  • Reactions with oxygen tend to release more energy, so it is profitable to use oxygen for metabolic activities.
  • It is chance that it got to be oxygen; it could have been anything.

Which is right? Or is there some other possibility?

Edit: Yes, it is true that there are organisms to which oxygen is toxic. But you can't ignore the large numbers of organisms to which it is absolutely necessary for living. Why could it not have been some other molecule? Which property of oxygen drives it to become the most useful in bio-processes?


closed as off-topic by anongoodnurse, another 'Homo sapien', David, theforestecologist, Bryan Krause Apr 24 '17 at 1:38

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    $\begingroup$ Have you done any research before asking this question? If you have, we would like to see it (edit it into your question.) Thanks! $\endgroup$ – anongoodnurse Apr 21 '17 at 13:35

I think you need to consider that oxygen is toxic to large groups of microorganisms, because it poisons their electron transport chains.

Strict anaerobes does not tolerate the presence of oxygen at all and as such I would argue that life can survive and thrive without O2.

Also life on earth evolved under conditions were O2 levels were extremely low, in fact when some organisms started to release oxygen into the atmosphere it caused an extinction event (Great Oxygenation Event).

So I think you need to change your question to why did life adapt to the presence of oxygen?

  • $\begingroup$ The reason life adapted to the presence of oxygen is that if it hadn't, it would have died - and so we wouldn't be around to ask the question :-) Just a larger version of why bacteria become resistant to antibiotics, plants develop resistance to herbicides, insects to insecticides, &c. $\endgroup$ – jamesqf Apr 21 '17 at 19:39
  • $\begingroup$ @jamesqf You cite the reason why organisms became adapted to the presence of oxygen. But why did oxygen become so vital to a large number of organisms? If it is because of the abundance of oxygen, aren't plants major contributors to stable oxygen levels during the oxygen cycle? So does it not mean that life also contributed to the abundance of oxygen and so it could not be the reason why life evolved around it? $\endgroup$ – prlfak1 Apr 22 '17 at 1:45
  • $\begingroup$ @prlfak1: I think what I'm trying to say is that asking "why" really isn't all that meaningful in evolutionary terms. Photosynthetic organisms hit on the trick of using light for energy, releasing oxygen. Then other organisms evolved ways of using this energetic waste product for their metabolism, which allowed them to survive & reproduce. Lots of photosynthesis eventually meant lots of O2, so lots of O2-using organisms. But there are other ways, like chemosynthetic bacteria that react CO2 & H2S to produce carbohydrates & sulfur. It's just that H2S isn't all that plentiful... $\endgroup$ – jamesqf Apr 22 '17 at 5:19

The main drive towards oxygen is it's efficiency. When you consider the order in which different energy generation pathways evolved you will see the improvement. Here are the main ones

  1. Glycolysis - produces 2 NADH and 4 ATP. Plus you end up with two pyruvates ()
  2. Pyruvate Decarboxylation - 3 NADH, 1 FADH2, and 1 GTP (equivalent to 12 ATP)
  3. Electron Transport Chain (final electron acceptors other than O2) - 2-36 ATP equivalent. This number varies so much because bacteria have a whole range of different systems and their efficiency varies greatly. However efficiency mostly depends on the final acceptor redox potential which is highest for O2
  4. Oxydative phosphorelation (ETC with O2 as final acceptor) - 10 NADH (equivalent to 30-36 ATP)

In addition to that 2.3 bya Great Oxygenation Event occured. What happened is that cyanobacteria was releasing a lot of oxygen as part of photosynthesis for a while but it was all instantly bound to Iron diluted in ocean waters (and other compounds). Then 2.3 bya, oxygen levels got saturated and atmospheric oxygen levels increased rapidly driving many obligate anaerobes to extinction.


Yes, oxygen is crucial for all of the processes mentioned above, where it is used as electron acceptor. The reason why oxygen was "chosen" over other electron acceptors, which are in fact better electron acceptors, was due to the abundance of water and therefore how easily accessible oxygen is. There are in fact certain organisms, such as lithotrophic bacteria, that instead of oxygen use sulfur. You can also read up more about when the production of oxygen first occurred on Earth and which were the first organisms to use oxygen here: https://en.wikipedia.org/wiki/Great_Oxygenation_Event.


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