DAWN · The dawn of the Hadean atmosphere

During the Hadean eon, the first 500 million years of Earth's geological history, the atmosphere underwent its most dramatic transformations. An abundance of greenhouse gases prevented runaway cooling in the face of a fainter Sun, but the concentration, chemistry, and decline rates of these gases are unknown. Retracing this intriguing metamorphosis is impeded by the scarcity of Hadean samples, a vast parameter space, and volatile flux estimates that largely rely on empirical extrapolations. Here, I aim to decipher the formation and chemical evolution of the Hadean atmosphere using a pioneering multi-scale approach, bridging atomic to planetary scales. At the foundation of my project lies a unique combination of state-of-the-art atomistic simulations that cover different length and time scales. With ab initio calculations, I compute equilibrium thermodynamics and thermochemistry at the nanoscale. Subsequently, I employ these ab initio results to train new advanced machine-learning interatomic potentials tailored for liquid-vapor and vapor-solid interactions. These simulations quantify the devolatilization rates from the cooling magma ocean and reconstruct the volatile cycle during its crystallization, including the effects of redox changes and fugacity variations. I incorporate the results of the atomistic simulations into thermochemical calculations and global circulation modeling. In this way, I simulate the behavior and evolution of the atmosphere in Hadean, retrace the major volatile fluxes between geological reservoirs and their contributions to the atmosphere, and dynamically integrate gas losses to space, incoming meteoritic contributions, and fast-changing surface conditions, including the appearance of the hydrosphere. This modeling also gives feedback on the surface state that constrains the atomistic simulations. Thus, I can chart a comprehensive evolutionary path of the Hadean atmosphere and bridge the gap to the better-constrained state of the Archaean.