The air we breathe

Apollo 1 tested high-pressure pure oxygen cabin atmosphere, which turned out to be a stupid idea as a tiny spark turned the whole thing into an inferno in seconds.

>air is about 79% nitrogen, 20% oxygen, and 1% trace gases. does that mean that over 3/4 of the air we breathe does nothing for us?
If by 'us' you mean human beings, then yes.

>if we lived in a 100% oxygen environment, could we take shallower/fewer breaths per minute and still live?
Yes, but the human race would go extinct in a fairly short amount of time (say 5-10 years) due to oxygen toxicity.

>what about the trace gases, like Ar, Ne, He, etc. do they do anything for us, or could we live without them?
They don't do anything for us.

>would a 100% oxygen atmosphere filter light differently, so maybe the sky would be some color besides blue?
No, blue would still be scattered the most, and thus the sky would continue to be blue.

>also occurs to me a 100% oxygen atmosphere might make fires problematic.
Not really, fires would just be slightly more intense. Oxygen isn't flammable.

100% oxygen allows for the pressure to be lowered whilst keeping the partial pressure of the oxygen the same. It's used in environments that cannot maintain large pressure gradients (but only short term, because long term exposure causes oedema)
It's also used medically to saturate the blood with oxygen, and to treat gangrene caused by anaerobic (oxygen intolerant) bacteria.

>Not really, fires would just be slightly more intense. Oxygen isn't flammable

Excuse me? I think the astronauts of Apollo 1 and every hospital room using oxygen that bars smoking would disagree.

In most cases no. It's just inert. It does mess with combustion sometimes. Specially on uncomplete/abrupt cycles. Which generates NOx and harm the environment.

IIRC in the Early stages of live on earth, the oxygen levels where like 40% and that caused a LOT of problems with the early forests that populated earth, burning everyrhing away. Also. Insects could be MUCH bigger, since they bresthe through small holes like stomas, with a higher oxigen concentration, their breathing did not limit their body sizes as much.

Oxigen isn't flamable user. But it makes almost anything that contains any kind of stored oxidation chemical energy flamable. Like any hydrocarbon or organic material.

oxygen isnt flammable, it just increases the flammability of other things

>Oxygen toxicity
Why is evolution so retarded?

It's inert, meaning it doesn't react with anything. But what it does do is keep our alveoli from collapsing (called atelectasis). In anesthesia machines, accidents like this are known to occur when you set the FiO2 (inspired oxygen fraction) too high. Because the partial pressure of nitrogen isn't very different in the blood than in the alveoli, it doesn't diffuse into the blood at a large rate keeping the alveoli from collapsing from lack of air. On the other hand, the blood coming from the pulmonary artery is pretty low on oxygen and high on CO2, so the oxygen diffuses quickly into the blood and leaves the alveoli without air, making them collapse and stay shut.

Oh, and it's also toxic to your brain in high concentrations. You know this when you scuba dive under 40 m.

>It's inert, meaning it doesn't react with anything.

That's not really true. Nitrogen is the basis of many compounds like ammonia, cyanide and high-explosives. Nitrogen is also essential to amino acids, nucleic acids and adenosine, and is the fourth most abundant element in your body.

Sorry, I should have been more specific. Nitrogen GAS is inert in the HUMAN BODY. The nitrogen has to be fixed by bacteria out of its super stable diatomic gas before you can do shit with it, in nature that is.

Here I am just landed from a 6hr day into night sortie in a T6 on 100% O2 for half of it.. 100% O2 is used in aircraft all the time. Any time we're expecting to do high g maneuvering or even at altitudes that the cabin alt cant remain under 8000ft we'll chuck the switches up

>Astronauts breathe pure oxygen, but I think the pressure is lower.
That's GOT to be wrong.
MY job is tough enough, can you imagine being an astronaut? The pressure must be enormous.

The causes here are completely wrong (and don't make any sense, because O2 is exchanged with CO2; resulting in no net gas volume change). Higher levels of oxygen in the body result in the body being unable to effectively remove reactive oxygen species such as superoxide (O2-). These lead to oxidative stress, with more vascular areas, such as the lungs, having higher levels of these, and so being affected first. This results in inflammation and eventually collapse of the alveoli. This happens over the scale of days (unlike what you described, which would be much quicker).