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4

Disclaimer: This is going to be a very mathematical answer. Before answering it, I assume that you are only asking about humans, assuming that all other organisms don't require $O_2$ to survive (as it will complicate the answer many many times). List of variables: V = total volume of air on earth (in l) V' = total volume of oxygen on earth (in l) ...


2

The answer above gives a nice calculation how much oxygen there is, and how much we use. There are some BIG other factors that warrant a second answer IMO. Starting at 371 thousand years (above). Animals: according to http://xkcd.com/1338/ (probably sourced somewhere reliable) humans make up only ~20% of the walking biomass, so we would burn through the ...


1

Not sure if there is a definite answer. However, from structural studies, its proposed that essentially the Chlorophyll a and pheophytin(Pheo) are positioned ~10A away, and the transfer of a radical electron from the P680 center to Pheophytin does occur. The exact mechanism is possibly mediated by a tyrosine Durant J.R et al (1995). Proceedings of the ...


1

The idea that the oxygen in the atmosphere would "last" for 15,000 years is probably incorrect. When the biosphere experiment was done, the finding was the following: "The oxygen inside the facility, which began at 20.9%, fell at a steady pace and after 16 months was down to 14.5%. This is equivalent to the oxygen availability at an elevation of ...



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