Does anyone have a vague idea how many years does it take for half of free oxygen in the atmosphere to be recycled. For example if you had a giant hypothetical disaster that burned or converted to dioxide half the earths atmosphere, how many years would it take to the various oxygen producing lifeforms and various other chemical interactions to bring back that level of oxygen?
Do all oxygen breathing organisms, forest fires, and oxydation and combustion of various types, collectively consume 1% of the earth atmosphere's oxygen in a year or is it more like 0.000001%
Where does it mostly come from anyways, forests, grass, algue, bacteria/unicellular, gysers/eruption?
I heard somewhere that the earth's atmosphere may have had much higher oxygen concentration at the time when dinosaurs walked the earth, I dont know it thats true or not.