Oxygenation of the Earth aided by mineral–organic carbon preservation

Abstract

Photosynthesis produces molecular oxygen, but it is the burial of organic carbon in sediments that has allowed this O2 to accumulate in Earth’s atmosphere. Yet many direct controls on the preservation and burial of organic carbon have not been explored in detail. For modern Earth, it is known that reactive iron phases are important for organic carbon preservation, suggesting that the availability of particulate iron could be an important factor for the oxygenation of the oceans and atmosphere over Earth history. Here we develop a theoretical model to investigate the effect of mineral–organic preservation on the oxygenation of the Earth, supported by a proxy compilation for terrigenous inputs and the burial of reactive iron phases, and find that changes to the rate of iron input to the global ocean constitute an independent control on atmosphere–ocean O2 and marine sulfate levels. We therefore suggest that increasing continental exposure and denudation may have helped fuel the rise in atmospheric O2 and other oxidants over Earth history. Finally, we show that inclusion of mineral–organic preservation makes the global marine O2 reservoir more resilient to changes in nutrient levels by breaking the link between productivity and organic carbon burial. We conclude that mineral–organic preservation is an important missing process in current assessments of Earth’s long-term carbon cycle.