How can the Earth’s air be made up of just 21% oxygen?

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Today’s [Triviatime](https://triviatime.app/) had a Q which asked what % of the earth’s air is made of Oxygen. The answer was 21% but this only left me with more questions!

How??? What else is there and what are the implications of those elements/things being literally everywhere in the air. Fellow laymen eggheads, please add to this list of thoughts you have about this which need to be addressed:

– How does our breathing filter the other stuff out?

– What actually is air if it’s made up of so many different things, I thought air basically = oxygen?

– How steady is this 21% level? Can this change overtime, is that dangerous, and if so how?

– Etc

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8 Answers

Anonymous 0 Comments

The percentage of oxygen does fluctuate, but that’s on timescales of hundreds of millions of years. Fun fact, the reason some prehistoric insects could grow so much larger than insects today is because their atmosphere was more oxygen-rich than ours.

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