Quote:
Originally Posted by spacecowboy
It’s pretty much the only constant occurring in nature as much as it being the only thing needing to be constant. If oxygen were random and we evolved from goo, are lungs would not be what we have today.
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Oxygen is not random because of a little phenomenon called diffusion. In a mixture of gases (such as the atmosphere), all gases present will diffuse until they are of approximately equal concentration throughout the mix. For example, if you're in a car with someone and they fart, there will be a very high concentration of fart-gas around the person for a few seconds, but the gas will diffuse throughout the car within a few seconds or minutes, becoming lower in concentration as it goes.
In fact, though, oxygen concentration in the air varies minutely due to conflicting air masses; not by huge amounts, never more than about 1% and rarely that, but it does vary. And as you go higher in elevation, oxygen concentration does go down. In fact, once you get out of the troposphere, oxygen levels start to decline rapidly; by the time you reach the upper thermosphere, the main constituents of the atmosphere are hydrogen and helium with small amounts of nitrogen and other gases, including monatomic oxygen and ozone, which is formed by solar radiation knocking off electrons from O2 molecules, causing unstable ozone and monatomic oxygen to form.
And if oxygen did, by some phenomenon, vary more than it does (by more than 5-10%) then our lungs
would be different, through natural selection preferring those with lungs that could handle the wild changes in atmospheric composition without ill effects.