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Earth's atmosphere has gone through "dramatic" composition changes over millions of years. A well-known example is the Great Oxidation Event. Currently the atmosphere is 78% nitrogen, 21% Oxygen, 1% Argon, and 0.04% Carbon Dioxide.

Atmospheric composition is changing because of human activity. Is it also changing because of natural forces? For example, have oxygen levels stabilised or will they continue to change because of oxidation cycles from life on Earth? Is volcanic activity, solar activity, or other natural factors slowly changing the atmospheric composition?

CODA: The motivation of my question is the fact that we humans evolved in and adapted to the current atmospheric composition, but we might not be adapted for future compositions if over millions of years the atmosphere continues to change.

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Yes the atmosphere is always in mild flux, humans are just changing it MUCH more severely than it does naturally.

the atmosphere even changes from season to season, that is the little up and down on the line in this graph. Since the amount of land receiving sunlight effects co2 and oxygen levels, which will change from winter to summer because the northern and southern hemisphere have different amounts of land. enter image description here

All kinds of factors cause small changes, volcanoes, forest fires, algae bloom, all have an impact. humans are just vastly overwhelming all those small natural fluctuations both in time and intensity.

If you look at ice core data humans only have a noticeable effect right at the end, basically all the rest of that fluctuation is natural. Even things like changes in tectonics has an impact, depending on what scale you want to look at you see different factors dominating humans are just overpowering all of them. Right now we should actually be cooling due to just natural factors, yet we are warming, which makes me wonder how bad it will be when the natural factors naturally cycle back to warming as well...

![enter image description here

we can even correlate things like changes due to individual volcanic eruptions. https://www.researchgate.net/figure/Volcanism-and-temperature-variability-during-the-migration-period-500-705-ce-a_fig3_279965759

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