[Marika (OP)]

Donald wants to know:

The Earth's original atmosphere had a lot of carbon dioxide that apparently disappeared during the 'oxygen catastrophe'. Since there was little life on land, and life was involved in clearing the atmosphere, it follows that almost all the atmospheric carbon was trapped in the ocean. How did any ever get out, or has land based life been parsimonious in attaining and retaining the tiny overflow from the oceans?

What do you think?

[chiralSPO]

I believe that the bulk of the carbon from the primordial atmosphere is contained in limestone (not related to the oxygen production, but still biologically removed from the atmosphere), coal, oil, and natural gas (essentially all carbon in these fossil fuels was reduced from CO₂ by photosynthesis).

There is also quite a bit of carbon in currently (or recently) living biomass.