Over geologic timescales, Earth's climate has varied between warm (ice-free) and cold (glacial) periods. Understanding the drivers of these secular changes is integral to understanding the habitability of planets, feedback in the modern carbon cycle, and the evolution of life. By combining the tectonic history of the Paleozoic (541 Ma - 252 Ma) with a coupled model of mineral weathering and the carbon cycle, I show that glaciations can be initiated by enhanced organic carbon burial due to the emplacement and weathering of mafic and ultramafic rocks during ophiolite obduction. Specifically, the high-surface-area clays formed as alteration products of these mafic and ultramafic rocks adsorb organic carbon, protect the carbon from remineralization and locking it in the lithosphere. This mechanism for global cooling is corroborated by an interrogation of δ13c records and whole rock geochemistry of shales.  The incongruent weathering reactions of ultramafic rocks, particularly the clay species which are formed, have implications far beyond the Paleozoic carbon cycle. This process could have caused substantial cooling of the early Martian climate and may even have a role to play in mediating anthropogenic climate change.

Joshua Murray is a geologist and PhD candidate at MIT, driven by a passion to understand the forces of Earth’s long-term climate. He couples field observations, geochemistry, and computational methods to evaluate the carbon sources and sinks associated with different tectonic processes. Originating from Scarborough, England, Josh earned his degree in Geosciences from Princeton University in 2018.