Atmospheric oxygen is fundamental to life as we know it, but its concentration has changed dramatically over Earth’s 4.5 billion year history. An amazing qualitative story has emerged, in which Earth’s atmosphere was devoid of free oxygen for the first 2 billion years of planetary history, with two significant increases in concentration at ~2.4 and ~0.55 billion years ago. Both oxygenation events were accompanied by extreme climatic effects – the “snowball earth” episodes – and paved the way for massive reorganization of biogeochemical cycles such as the Cambrian radiation of macroscopic life. Despite these profound influences on the Earth system, we currently lack fundamental quantitative constraints on Earth’s atmospheric evolution. I am poised to add substantial quantitative rigor to Earth’s atmospheric history, by constraining the concentrations of important gases (e.g. O2, O3, CO2, CH4, organic haze) in ancient atmospheres to unprecedented accuracy. I will accomplish this via an innovative interdisciplinary program focused on the unusual mass-independent isotope fractionations observed in sedimentary rocks containing sulfur and oxygen. These signals are direct remnants of ancient atmospheric chemistry, and contain far more information than can currently be interpreted. This project combines novel experimental and methodological approaches with state-of-the-art numerical modelling to significantly advance our ability to decipher the isotope records. Novel analytical methodologies that are cheaper and less dangerous than existing, will vastly increase the global geochemical database. The experimental results and data will provide ground-truth for next-generation atmospheric models that will constrain atmospheric composition and its feedbacks with the Earth-biosphere-climate system during key points in our planetary history.
We vastly expanded the global database of oxygen and sulfur MIF measurements and made strong contributions to the framework for their interpretation. We were able to constrain periods when early earth went from primarly volcanic atmospheric composition (prior to 2.7 Ga) to one dominated by life (after 2.7 Ga). We revolutionized the models used to understand the great oxidation event, demonstrating dynamic behavior that drives the Earth's atmosphere between negligible concentrations and those within 2 orders of magnitude of the modern, without stabilizing in between. An independent framework developed to use the appearance/magnitude of mass-independent oxygen isotope fractionation to constrain paleo pO2 provides a complementary story. In addition, we undertook a through exploration of the driest place on Earth - and used geochemical measurements coupled with techniques of molecular biology to identify biosignatures as the imprint themselves onto abiotic atmospheric inputs.
