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Assessing the Effects of Rising O2 on Biogeochemical Cycles: Integrated Laboratory Experiments and Numerical Simulations

Final Report Summary - AEROBIC (Assessing the Effects of Rising O2 on Biogeochemical Cycles: Integrated Laboratory Experiments and Numerical Simulations)

Over the course of work on this ERC-funded research program, we performed experiments and observations, and developed several models to constrain the evolving chemistry of Earth's oceans and atmosphere and its interactions with the microbial biosphere and with climate, in response to an increasing oxidation state, decreasing heat production within the Earth, and a brightening Sun. For example, in one project we provided novel constraints on the evolution of seawater pH through time, from more acidic values (~6.5-7.0 approximately 3.5 billion years ago) to the mildly alkaline present-day value (8.2). We show that this evolution is a response to solar brightening, which has resulted in generally decreasing atmospheric CO2 concentrations over 4.5 billion years of Earth history, and to cooling of Earth's mantle, which has resulted in less intense removal of Mg from seawater in seafloor hydrothermal systems. In a second project we identified the Fe(II)-Fe(III) hydroxy-salt, green rust, as a key component of the early iron cycle, with implications for the genesis of banded iron formations, the main economic source of iron and an important archive of geochemical information about the redox evolution of the early oceans and atmosphere. In addition to its role in iron formation genesis, green rust is likely to have had major impacts on the concentrations and bioavailability of several key nutrients and trace metals, with implications for biological productivity, evolution and diversification. In a third example, we developed the first fully coupled biochemical-isotopic framework for understanding and predicting isotopic fractionation during metabolic activity. This novel framework is now providing a quantitative, mechanistic understanding of isotopic effects during several metabolic pathways, which evolved early and participated in the coupled evolution of the carbon, oxygen, sulfur and iron cycles over Earth history. These and other projects, carried out as part of this research program, valuably inform our understanding of the long-timescale biogeochemical evolution of Earth's surface environment.