Chemical Pathways to Earth's Habitability: Constraints from the Origin, Distribution, and Delivery of Life-Essential Elements in the Early Solar System

This is an all-day event. Location: Keith-Wiess Geological Laboratories   Speaker: Debjeet Pathak Doctoral Candidate Thesis Defense Department: Earth, Environmental and Planetary Sciences Location: Keith-Wiess Geological Laboratories The emergence and long-term habitability of Earth depend on the acquisition and redistribution of life-essential elements (LEEs), including C, N, P, S, H, and O, during planetary formation. This thesis investigates the chemical pathways that governed the origin, evolution, and delivery of these elements from the earliest stages of Solar System history to the formation of Earth. By integrating high-pressure-temperature experiments, meteoritic observations, geochemical reconstructions, and planetary accretion models, this work constrains the behavior of LEEs during core formation, planetary differentiation, and planetary growth. New experimental constraints on the partitioning of nitrogen and phosphorus between solid and liquid metallic alloys (Chapter 2 and 3), together with nitrogen partitioning between cohenite and metallic liquid (Chapter 4), are used to reconstruct the inventories of life-essential elements in the parent bodies of iron meteorites—the earliest differentiated planetesimals in the Solar System. Comparison of these reconstructed inventories with those of chondrites reveals the spatial and temporal evolution of life-essential elements during the earliest stages of Solar System formation and suggests that inner Solar system planetesimals were the major contributors of phosphorus and nitrogen to the growing Earth. Complementary electron probe microanalysis (EPMA) measurements significantly expand the existing nitrogen dataset for iron meteorites, providing improved constraints on their parent-body nitrogen inventories (Chapter 5). Furthermore, reconstructed zinc, sulfur, and gallium inventories provide evidence that disequilibrium condensation played an important role during the formation of these early planetary bodies (Chapter 6). Finally, numerical models of a Mars-sized last giant impactor demonstrate that its metallic core, rather than its silicate mantle, could have been an important source of volatile and life-essential elements delivered to the silicate Earth (Chapter 7). Collectively, this thesis provides new geochemical constraints on the origin, redistribution, and delivery of life-essential elements during planetary formation, offering a comprehensive framework for understanding the chemical pathways that ultimately led to Earth's habitability.   (Department : Earth, Environmental and Planetary Sciences)