Great Oxidation and Lomagundi events linked by deep cycling and enhanced degassing of carbon.

Abstract

For approximately the first 2 billion years of Earth history, atmospheric oxygen levels were extremely low. It wasn’t until at least half a billion years after the evolution of oxygenic photosynthesis, perhaps as early as 3 billion years ago, that oxygen rose to appreciable levels during the Great Oxidation event. Shortly after, marine carbonates experienced a large positive spike in carbon isotope ratios known as the Lomagundi event. The mechanisms responsible for the Great Oxidation and Lomagundi events remain debated. Using a carbon-oxygen box model which tracks surface and interior C fluxes and reservoirs while also tracking C isotopes and atmospheric oxygen levels we demonstrate that about 2.5 billion years ago a tectonic transition resulting in increased volcanic CO2 emissions could have led to increased deposition of both carbonates and organic carbon via enhanced weathering and nutrient delivery to oceans. Increased burial of carbonates and organic carbon would have allowed accumulation of atmospheric oxygen while also increasing delivery of carbon to subduction zones. Coupled with preferential release of carbonates at arc volcanoes and deep recycling of organic C to ocean island volcanoes we find such a tectonic transition can simultaneously explain the Great Oxidation and Lomagundi events without any change in the fraction of carbon buried as organic carbon relative to carbonate, which is often invoked to explain carbon isotope excursions.