Is the oxygen level fluctuating in our atmosphere in a slow cyclic rate? What % range would we expect?

Question

If the level goes below 15%, for example, does fire burn or our brains work well? And over 25%, does the world burn?

At the time chlorophyl was created, the oxygen level increased dramatically, killing many life forms. Is there evidence of other sudden changes?

Answer 1

The oxygen level in the atmosphere is pretty constant. It's about 21%. Nitrogen makes up 78%. Argon is about 1%. There are some trace gases, which include carbon dioxide at 0.01% With the sheer volume of the atmosphere, it would take a major event to change the amount of oxygen to a noticeable extent. Even the tons and tons of gases given off by volcanoes isn't much of an effect on the percentage of oxygen in the atmosphere.