Response of the Nitrogen Cycle to Ocean Redox Chemistry During the Great Oxidation Event

This project is aimed at documenting feedbacks between the oceans, atmosphere, and biosphere in the time period spanning Earth's first major oxygenation.

A critical question in Earth science is how the global biosphere responded to and/or drove major transitions in Earth surface chemistry. This project focused on how the Earth’s geosphere, atmosphere, and biosphere interacted during the Great Oxidation Event (GOE), the largest such transition recorded in the geologic record.

The results of this study provided direct geochemical constraints on biogeochemical cycling and atmospheric chemistry on the run-up to the GOE (Zerkle et al., Nature Geoscience, 2012), as well as geochemical and modelling constraints on how the global nitrogen cycle responded to this event (Zerkle et al., Nature, in review). Specifically, we have produced high-resolution geochemical records of Earth surface chemistry spanning the Great Oxidation Event, and used numerical models to interpret them. We have found that the Earth's atmosphere rapidly oscillated between clear-skies and hydrocarbon haze-rich skies immediately prior to the Great Oxidation Event. We have further documented a significant change in the speciation and utilization of nitrogen in the biosphere following oxygenation of the atmosphere and surface oceans.

These key findings are of interest to a wide variety of scientists studying global change, nutrient cycling, and the chemical and biological evolution of the early Earth, as evidenced by their publication in high-impact journals. The fundamental question of how our planet evolved to its current state is also of wide interest to the general public, as evidenced by the widespread international media coverage of the 2012 study, which was featured in articles by New Scientist and National Geographic.