Fig. 3
From: Developing ecospheres on transiently habitable planets: the genesis project
Sketch of the organic carbon cycle (Jacob 1999; Sleep and Zahnle 2001). The overall amount of sedimentated organic carbon has been estimated to be of the order of \(1250 \times 10^{18}~\mathrm{mol}\). This implies, with about \(37 \times 10^{18}~\mathrm{mol}\) \(\mathrm{O}_{2}\) present nowadays in the air, that earth’s biosphere has produced at least \(1250/37\approx 34\) times more oxygen over the last four billion years than the one remaining in today’s atmosphere. The present-day fluxes are: \(8.7 \times 10^{15}~\mbox{mol}\) biological C per year global NPP (net primary production) (Field et al. 1998), with roughly equal contributions from land and oceans, and \(11\times 10^{18}~\mbox{mol}\) biological C/Ma buried in sediments (Sleep and Zahnle 2001)