Atmospheric evolution: from early Earth to exoplanets

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Terrestrial planet atmospheres are awesome. They are the mixing pot of every waste gas from the planet, gasses from everything from microbes to the mantle, processed by photochemistry and geochemistry. Atmospheric composition largely determines what life can live at the surface and controls planetary climate by setting the strength of the greenhouse effect and how much sunlight is absorbed. As we enter the age of exoplanets, atmospheres are our window to other worlds; remote atmospheric characterization is the means by which exoplanets may be explored and ultimately life may be detected. My research program is about the evolution of planetary atmospheres, for inhabited planets (just Earth right now), for comparison planets and moons in the solar system (Venus, Mars, Titan and more) and, increasingly, for exoplanets. The objectives of the proposed research are: to improve our understanding of the coupled climate-geochemical-biosphere evolution of Earth throughout its history; to develop theory of planetary evolution in a comparative planetology framework, linking Earth to the other terrestrial planets; and to apply this theory to developing methodology for discerning whether exoplanets are habitable or inhabited. We will research across four themes: (A) Evolution of Earth's atmosphere, modelling cycles of nitrogen, carbon and oxygen and the atmospheric inventories of N2, O2, CO2, CH4, N2O and NH3, linking geochemical and climate changes. We will look at the Great Oxidation and snowball Earth glacials, and change throughout Earth history. (B) Climate of Earth's deep past, using 3-D climate models to understand the climate system and clouds in particular, and a project to verify the accuracy of the radiation codes used in these models. (C) Atmospheric evolution on other planets and moons, studying the transition of Venus through a runaway greenhouse and the weird atmosphere of Titan (D) (Exo)planet habitability, developing theory on which planets could harbour life, and how the "habitable zone" depends on atmospheric composition and water inventory. The proposed work addresses fundamental "blue-sky" questions relating, contributing novel theory to how the Earth and terrestrial planets have evolved. It will directly contribute to developing methodology for exoplanet life detection and characterization, which will be a rapidly expanding field over the next few decades and utilize major Canadian assets. It will be applied to improved understanding of anthropogenic climate change, as exploring Earth history provides the context for modern-day changes. A particularly novel aspect of my research program is the interdisciplinary breadth: we tackle problems in climate science, geochemistry and atmospheric chemistry, geology, astronomy and planetary sciences as necessary to understand the evolution of our, and other, atmospheres.