COUPLING ATMOSPHERE AND SEDIMENT MELTS ACROSS THE ARCHEAN-PROTEROZOIC TRANSITION

The oxygenation of our planet’s atmosphere at ~2.35 Ga, termed the Great Oxygenation Event (GOE), irreversibly changed major biogeochemical cycles and provided the necessary chemical reservoirs for highly efficient aerobic metabolism that facilitated evolution of complex life. It remains a matter of debate whether a decrease in O₂ consumption or an increase in O₂ production led to the build-up of free oxygen. The profound impact of the GOE on Earth surface environments are imprinted on the geologic record via suppression of atmospheric mass-independent fractionation of sulfur isotopes (S-MIF). Recent studies show that fluctuations in atmospheric O₂ level are also captured in the igneous rock record and the deeper crust, e.g., through a change in average oxygen fugacity of strongly peraluminous granites and recycled S-MIF in igneous rocks. Coevally with the rise of atmospheric O₂, the triple oxygen isotope composition of shales (expressed as ∆¹⁷O) and the ¹⁸O/¹⁶O composition of felsic magmas were subject to a rapid change at ~2.35 Ga, which has been linked to the widespread emergence of continents above sea-level. We present triple sulfur in pyrite and oxygen isotopes in zircon and garnet from Archean and Proterozoic sediment-derived granitoids. These sediment-derived melts record a global increase in average garnet and zircon δ¹⁸O and a and a disappearance of pyrite S-MIF in the Paleoproterozoic. This coupled behaviour of sulfur and oxygen isotopes in these samples imply a causal link between continental emergence and the ~2.35 Ga rise of free oxygen. This rise is interpreted in the context of the mechanism subaerial continents removed carbon dioxide from the atmosphere and increased supply of nutrients to oceanic oxygenic phototrophs.