Acording to https://en.wikipedia.org/wiki/Carbon_cycle, organic carbon has a cycle. My question is how carbon entered to the cycle in first place. As far as I can say, inorganic carbon enters to the cycle only as CO2 that is transformed by photosynthesis.
If atmospheric CO2 can turn into organic carbon, and, as far as I know, only volcanoes add CO2 to the air. Current organic carbon comes from volcanoes or was always part of atmosphere?
If that is true. Photosynthetic life has ever been constrained to the carbon released by volcanic activity?

  • 1
    $\begingroup$ Much of the Earth's atmosphere was originally CO2. This was converted to O2 and carbon when life evolved photosynthesis. (It's more complicated than that, of course. See e.g. en.wikipedia.org/wiki/Great_Oxidation_Event for a basic introduction.) $\endgroup$
    – jamesqf
    Oct 1 '19 at 5:32

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