Abstract

The habitability of the Earth is governed by volatile species and fundamental large-scale geological processes (i.e., plate tectonics) that transport volatiles between the surface reservoir and the interior. Volatiles are transported out of the mantle and into the atmosphere through volcanic outgassing and are returned to the mantle as hydrous phases within subducting slabs. Noble gases are powerful tools that allow us to trace volatile transport between the atmosphere and the mantle over Earth history. The noble gas isotopic composition of the present-day atmosphere and mantle is a time-integrated result of volatile transport processes that have occurred and their initial compositions have been muted over time. Identifying snapshots of what the isotopic compositions for the mantle and atmosphere were like at different points in Earth history would provide valuable constraints on how volatile transport has evolved. In this dissertation, I attempt to identify geological samples that contain preserved noble gas compositions of the ancient atmosphere and mantle. High-precision noble gas isotope measurements from these samples are paired with numerical modeling efforts as a means to identify constraints on past compositions for the ancient atmosphere and mantle. In chapter 2, I consider high-precision noble gas isotopic data within a 2.97 Ga SW Greenland anorthosite and use them to investigate compositions for the ancient mantle and atmosphere at that time. A mixing relationship is observed within our Ne isotopic data between a crustal component and a component with elevated 20Ne/22Ne from the modern atmosphere, which I argue is evidence for the presence of subduction-related flux melting. I also develop a model of Xe isotopic evolution within the upper and plume mantle and use the predicted compositions for 2.97 Ga within a mixing model to investigate four possible mixing scenarios that could explain our reported Xe isotopic data. The mixing model results favor scenarios that are dominated by the ancient atmosphere and possibly indicate a mantle signature. Regardless, the presence of an ancient atmospheric component would still be consistent with a subduction origin. The combination of an ancient mantle Ne and ancient atmospheric Xe provides direct isotopic evidence that flux melting was occurring on Earth as early as ~3 Ga. In chapter 3, I move forward in time and consider noble gas isotopic compositions within four anorthosites from two ages within the Proterozoic (1.4 Ga and 1.0 Ga). I show that all four samples reveal Ne isotopic compositions that have lower 20Ne/22Ne values than the modern atmosphere and infer that this reflects an ancient atmospheric component. This result is used to comment on the origin of atmospheric Ne and argue for the initial atmosphere to be from delivered gas-rich rocky solid material (e.g., chondrites). A mixing relationship within one sample between an ancient atmospheric component and a component with a 20Ne/22Ne ratio higher than the modern atmosphere is identified, which I argue reflects an ancient mantle signature. I show numerical models of Ne and Xe isotopic evolution within the atmosphere and mantle and compare the modeled Ne compositions to our extrapolated Ne compositions from our anorthosite sample. The modeled Ne compositions for the ancient mantle and our extrapolated Ne compositions are different but fall relatively close to one another. However, the predicted Ne atmospheric and extrapolated compositions do not match, and I argue that the disagreements observed between the modeled and extrapolated Ne compositions reflect an inaccurate model assumption for a smoothly decreasing mantle processing rate over time. Lastly, Xe isotopic compositions within one of the anorthosites reveal a mixing trend between an ancient atmospheric component and an ancient mantle component. However, the ancient mantle component does not agree with modeled mantle Xe compositions, and I argue for the presence of a previously unidentified component that is contributing to the mantle Xe budget. Lastly, in chapter 4, the evolution of Xe budgets between the MORB and plume mantles through forward numerical models are considered (similar to Chapters 2 and 3). Here, I use numerical models of Xe isotopic evolution to characterize the range of possible atmospheric influx histories into both mantle sources, and our results show that the atmospheric influx is inefficient early in Earth history but transitions to be an efficient process later. I show that the concentrations of Xe within subducting slabs that contribute to the plume mantle are higher than slabs that contribute to the MORB mantle. This indicates that the materials that contribute to the plume mantle source have inherent differences than those that contribute to the MORB source and could affect the material properties (e.g., viscosity) of the surrounding mantle over time. From these results, I suggest that future models must consider separate evolutions for the volatile budgets for the MORB and plume mantle sources.

Committee Chair

Rita Parai

Committee Members

David Fike; Guillaume Avice; Michael Krawczynski; Robert Dymek

Degree

Doctor of Philosophy (PhD)

Author's Department

Earth & Planetary Sciences

Author's School

Graduate School of Arts and Sciences

Document Type

Dissertation

Date of Award

5-6-2026

Language

English (en)

Author's ORCID

https://orcid.org/0000-0002-8432-2650

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Available for download on Tuesday, April 27, 2027

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Geochemistry Commons

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