Fates of Carbon

Citation

Zeichner, Sarah Soojin (2024) Fates of Carbon. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/vy9f-k705. https://resolver.caltech.edu/CaltechTHESIS:01022024-183348243

Abstract

This thesis investigates the organic matter relevant to the oldest rocks on the Earth and in the Solar System, along with novel methods for exploring the composition of that organic matter. Chapter II describes a novel method for using a gas chromatography-Orbitrap mass spectrometer system to simultaneously analyze multiple isotopic properties from multiple compounds within a complex mixture. This method is ideal for the study of environmental or extraterrestrial samples and was integral to the study described in Chapter III. Chapters III and IV highlight new isotopic properties that can be measured in extraterrestrial samples to constrain processes of abiotic organic molecule formation: These processes have direct implications for where the carbon on Earth comes from. Chapter III details the measurement of ¹³C, D, and double-¹³C contents of five polycyclic aromatic hydrocarbons in samples returned by the Hayabusa2 spacecraft mission to the Ryugu asteroid. The findings of this study support the formation of aromatic hydrocarbons---arguably the most abundant molecules in the Milky Way galaxy and other galaxies---through low-temperature reactions within molecular clouds in the interstellar medium. Chapter IV characterizes the position-specific carbon isotopic compositions of three structurally-distinct amino acids-- α-alanine, β-alanine and aspartic acid--from the Murchison meteorite, which provide constraints for how they were synthesized abiotically within the meteorite parent body. Chapters V-VI of this thesis relate to organic molecules on the early Earth. Chapter V is a scholarly review of prior data documenting the carbon isotope contents of organic carbon in Archean rocks. It also includes a model for the evolution of the carbon isotopic composition of organic matter as it goes through the rock cycle (i.e., diagenesis, catagenesis, metagenesis and metamorphism), which is then used to re-interpret carbon isotope data based on extant biology and models of metabolic evolution. Chapter VI uses sedimentological experiments to demonstrate that water-soluble organic compounds may have led to the rise of mud deposition concurrent with the evolution of land plants.

Thesis Files