If oxygen came from CO2 by way of plant activity how much CO2 was needed to make the oxygen?

Question

Since there is ~10E18 kilograms of oxygen in thr atmosphere there had to be at least that much CO2 in the atmosphere which means the early atmosphere had to be at least 20% CO2 plus all the CO2 locked up in rocks.

Answer 1

A lot.  Not 20% (not all of the O2 came from CO2), but still, a lot.

Of course coastlines were very different then, and that would put most of our coastal cities underwater now.

Fortunately for us (those levels of CO2 are actually toxic) the natural "carbon cycle" buried a lot of it back then.

Unfortunately we're now digging a lot of it up and releasing it.  That's a dumb idea, and it will bite us.

Answer 2

CO2 toxic? We create CO2 within us.  Is it going to kill us?

It's not the co2 that can kill us.  It's the lack of oxygen.  Currently co2 makes up less than 0.003% of the air we breathe.

Answer 3

Presumably one CO2 makes one O2 molecule.  I think a good theory that explains the continuous CO2 necessary for precipitation of carbon bearing rocks is that hydrocarbons from the original accretion of the earth have been upwelling since the earth formed.  This theory isn't generally accepted by American geologist who favor the biogenic "fossil fuel" theory of methane and hydrocarbon formation.  I think the abiogenic makes more sense.  Methane upwells through cracks and encounters a deep hot biosphere that transforms some of it to petroleum.  Some methane gets trapped with the petroleum.  Some gets trapped deep below the ocean.  Some forms carbon deposits of high grade coal.  When methane encounters the atmosphere, it doesn't take too long to convert to CO2.  There are other portions of the carbon cycle that are not as well understood as sometimes believed.   There presumably were times when CO2 was much greater but I think the amount in the rocks is probably from continuous emission but you did hit on the crux of the matter.

Answer 4

It is thought that the early atmosphere (second atmosphere: produced by volcanic out gassing) WAS very rich in CO2. Not only that, it was 100 times heavier than the current atmosphere.

Answer 5

no - it is a slow process - oxygen breathing organisms began evolving well before the atmosphere hit the 21% O2 mark - in addition as atmospheric co2 levels fall co2 is drawn out from the ocean into the atmosphere - also the co2 level could have been maintained by volcanic activity or other- the atmosphere did not have 20% co2. It could have maintained a lower level and still produced 21% O2 atmosphere while being replinished by other sources - volconoes, oceans, breathing creatures ect. However, co2 levels were much higher way back then - upwards of 20 or so times higher i believe - in the 1% range.

Answer 6

its 1 mol of co2 containes 1 mol of 02 (oxygen). ie for every molecule of co2 you can make one of oxygen.