Collaborative Research: PYRITE OXIDATION AND THE ENSUING TRIPLE O ISOTOPE COMPOSITION OF SULFATE

Understanding the environmental conditions that Earth experienced over the course of its lifetime is a story recorded in ocean sediments and rocks deposited over that time. In certain rare instances, those repositories offer a glimpse of what that ancient environment (and, in particular the atmosphere) looked like. It has been proposed that a certain type of oceanic mineral (called sulfate evaporites) directly reflects the composition of atmospheric O2 – critical to life on the planet – at the time it forms. Through this work, the researchers will explore the biogeochemical and microbial process behind the production of these sulfate minerals to better understand their role as a time capsule for the development of the atmospheric conditions conducive to life as we know it. This work will involve both detailed microbiological experiments paired with novel geochemical measurements and will provide interdisciplinary training opportunities for two doctoral students. Further, the researchers have partnered with Salish Kootenai College to provide immersive summer research internships for multiple Native undergraduate students at both research institutions. On geologic timescales oxidative weathering or minerals on land regulates atmospheric CO2, O2, and Earth's redox budget. Reconstructing these temporal records then falls to proxies, and of interest here, a powerful record of the triple oxygen isotope composition of sulfate minerals. As conceived, the isotope composition of sulfate can be used to assay paleo-atmospheric compositions and global biogeochemical features like gross primary production. The thread that ties all this together is the requirement for oxygen atoms in tropospheric O2 be transferred to sulfate through the oxidative weathering of pyrite minerals. Although seemingly true in the Proterozoic, new data now reveal that this string is broken with the dawn of land plants. The researchers posit that this fundamental change in Earth's sulfur cycle is buried in the details of pyrite oxidation itself, which has recently been shown to be mediated by microorganisms in circumneutral pH conditions. They propose to conduct targeted microbial experiments to untangle the physiologic and isotopic consequences of the steps involved in microbial pyrite oxidation. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.