Andrew P Ingersoll

Approximately 1.4 Ga after life first appeared, atmospheric O2 suddenly jumped by more than an order of magnitude over a 20-50 Ma period. The contrast between these two timescales does not seem to be due to any sudden, large-amplitude change in external forcing. However, it could be due to processes intrinsic to the geobiological system itself, namely, positive feedback between atmospheric O2 and photosynthetic bacteria: More O2 leads to more photosynthesis, which leads to more O2, and so on. The key to this feedback is the 15-fold greater efficiency of aerobic vs anaerobic respiration and the tight coupling of respiration and photosynthesis inside the cell. As in the climate system, feedback leads to tipping points, where a rapid, large-amplitude change in the state of the system occurs. Examples include transitions to a snowball Earth and/or a runaway greenhouse. For the geobiological system, the GOE is the tipping point, and the long, slow buildup before the GOE is the gradual oxidation of Earth’s surface and ocean, either due to burial of organic matter, oxidation of volcanic gases, and/or escape of hydrogen to space. The feedback hypothesis is offered as a framework for interpreting observations leading up to and during the GOE.