The early Earth productivity paradox

Numerous lines of evidence suggest that the primary productivity of the Archean biosphere was considerably lower than it is today. Combined with isotopic evidence for only small changes in fractional organic burial through time, this implies lower-than-modern rates of total carbon burial in Archean marine sediments. However, other lines of evidence imply that rates of carbon input to Earth's surface reservoir - volcanism and weathering - were higher in the Archean than at present. It is well-established that negative feedbacks balance the carbon cycle on million-year timescales, meaning a long-term (>Myr) imbalance between inputs and outputs is implausible. So are we left with a paradox in Earth's early carbon budget? Here we compile literature estimates of carbon fluxes into and out of Earth's surface reservoir through geologic time and attempt to construct a balanced carbon budget through Earth's history. We find that in order to accommodate high outgassing rates and low biological productivity in the Archean, the burial efficiency of organic carbon in marine sediments must have been higher than it is today by 1-2 orders of magnitude. This is consistent with recent work that has argued for high Archean burial efficiency due to a scarcity of oxidants in seawater. We also consider the implications of high burial efficiency for the Archean redox budget, finding that atmospheric anoxia would have been difficult to maintain in a high-burial-efficiency world unless the flux of reductants from the mantle was greater than it is today. This supports recent studies that invoke an increase in mantle redox state in the late Archean as a possible trigger for the Great Oxidation Event.