WHEN, WHY, AND HOW OF THE GREAT OXIDATION EVENT

Transition from the Archean, largely anoxic atmosphere and ocean to the Proterozoic oxidizing surface conditions has been inferred from geochemical and geological evidence as early as 1927 in Zimbabwe. Subsequent studies provided additional support for this interpretation, bracketed the transition between 2.45 and 2.32 Ga, and suggested temporal and cause-and-effect relationship with a series of the early Paleoproterozoic ice ages (including 4 discrete events). Recently recognized transient oxidation events of the Archean add texture to this pattern, but do not change it.

The rise of atmospheric oxygen requires a misbalance between oxygen sinks and sources and most attention was focused on sinks. In contrast, change in oxygen supply related to low organic productivity in Archean oceans with limited nutrient contents are considered here. Although carbon isotope values of carbonates and organic carbon indicate substantial relative burial rate of organic carbon during the Archean, most of the earlier buried organic matter was recycled to sediments at that time during continental weathering, implying very low productivity and burial of ‘new’ organic carbon. Low contents of redox-sensitive elements, such as Mo, Cu, Zn, and V, in Archean seawater could have kept organic productivity and oxygen production at low levels. The GOE was immediately preceded by deposition of giant iron formations, accounting for more than 70% of world iron resources, and worldwide emplacement of a number of LIPs between 2.5 and 2.45 Ga, indicating enhanced delivery of nutrients and redox-sensitive elements to the oceans via submarine hydrothermal processes and continental weathering under CO₂- and SO₂-rich atmosphere and associated terrestrial acidic runoff. The GOE could have thus been triggered by enhanced nutrient supply to the oceans lifting the limit on biological productivity during a period with intensive mantle plume activity, emphasizing an underappreciated role of endogenic processes as a driver of redox fluctuations in the atmosphere-ocean system.