The Role of Plate Tectonic-Climate Coupling and Exposed Land Area in the
Development of Habitable Climates on Rocky Planets cites a few references for the global carbon cycle model.
The diagram on page 8 seems to imply that subduction is the only sink.
There aere too many unknowns to give reliable figures for the varying levels of oxygen in the atmosphere in Precambrian times. What can be said with a fair degree of certainty is that photosynthetic cyanobacteria evolved about 3.5 billion years ago. At first the oxygen they produced was absorbed by the ocean, but by about 3 billion years ago it began to ...