Theses and Dissertations

Although nitrogen is the dominant element in Earth’s atmosphere, it is depleted in the bulk silicate Earth (relative to expected volatile abundances established by carbonaceous chondrites). To resolve this inconsistency, it has been hypothesized that this “missing nitrogen” may actually be stored within the Earth’s deep interior. In this work, we use multi-anvil press experiments to synthesize solid solution mixtures of the mantle transition zone mineral wadsleyite (Mg2SiO4) and silicon nitride (Si3N4). Successful synthesis of a 90% Si3N4, 10% Mg2SiO4 solid solution implies that nitrogen may not be sequestered within the most abundant mineral phases in the Earth’s mantle. Instead, nitrogen-rich accessory phases may hold the key to studying nitrogen storage within the deep interior. Ultimately, quantifying the amount of nitrogen within the mantle will further our understanding of the N cycle, which is vital to maintaining planetary habitability. Similar N cycling processes may be occurring on other rocky bodies; therefore, studying nitrogen storage may be an important part of determining habitability conditions on other worlds, both within in our solar system and beyond.

Lunar meteorites are created when an asteroid impacts the Moon. In such events, the lunar surface, known as regolith, can experience extreme pressures and temperature conditions. Some of this regolith material can be ejected from the Moon and enter interplanetary space where it can be captured by Earth's gravity. Even after falling to Earth, the minerals of lunar meteorites preserve the history and conditions of lunar impact processes. One such mineral that has gained attention recently is tissintite due to its relatively specific temperature and pressure formation conditions. The lunar meteorite NWA 13967 and its mineral assemblage provided an opportunity for comparison to other lunar meteorites (Zhang et al. 2021). Based on its mineralogy and petrography, NWA 13967 likely experienced peak pressures of 18 to 24 GPa and peak temperatures above 2000℃, as indicated by the presence of intergranular melt, vesicles, and corundum. The occurrence of tissintite-II and coesite suggest crystallization during cooling and decompression, while other high pressure minerals likely back-transformed to lower pressure polymorphs.