The Maintenance and Restoration of Habitable Conditions on Terrestrial Planets: from Snowball Earth to TRAPPIST-1

Abstract

This dissertation investigates how terrestrial planets sustain habitable conditions and recover from catastrophic perturbations, combining insights from Earth’s geologic record with the study of exoplanets. The first section examines Earth’s two “Snowball Earth” events in the Cryogenian period (720–635 Myr ago), when global ice cover persisted for millions to tens of millions of years. Using a numerical model of the geologic carbon cycle, Chapter 2 shows how the mass and rapid deposition of post-Marinoan “cap carbonates” – carbonate layers that directly overlie glacial deposits – can be explained by a multi-stage process of syn-glacial seafloor weathering, post-glacial continental weathering, and slow ocean mixing. Chapter 3 applies the same framework to show why the first glaciation (the “Sturtian”; ~56 Myr) lasted an order of magnitude longer than the second (the “Marinoan”; ~4 Myr), revealing how seafloor weathering and redox state modulated Earth’s recovery from snowball conditions. Together, these studies clarify the mechanisms by which Earth has repeatedly regained habitable climates after near-total glaciation. The second section extends this perspective to the TRAPPIST-1 exoplanet system, which contains seven terrestrial planets that are prime targets for atmospheric characterization. Chapter 4 combines magma chemistry and knowledge of volcanism on Earth, Mars, and Io to demonstrate that volcanic outgassing could supply long-lived secondary atmospheres rich in water vapor on the TRAPPIST-1 planets, counteracting escape processes. These results provide new constraints on the processes that control atmospheric evolution and underscore the potential for habitable conditions beyond the Solar System. Overall, this work advances the study of terrestrial planets as dynamic objects that can overcome barriers to habitability via a variety of processes.