Matching Items (5)
Filtering by
- Resource Type: Text
Description
Lunar Reconnaissance Orbiter (LRO) and MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft missions provide new data for investigating the youngest impact craters on Mercury and the Moon, along with lunar volcanic end-members: ancient silicic and young basaltic volcanism. The LRO Wide Angle Camera (WAC) and Narrow Angle Camera (NAC) in-flight absolute radiometric calibration used ground-based Robotic Lunar Observatory and Hubble Space Telescope data as standards. In-flight radiometric calibration is a small aspect of the entire calibration process but an important improvement upon the pre-flight measurements. Calibrated reflectance data are essential for comparing images from LRO to missions like MESSENGER, thus enabling science through engineering. Relative regolith optical maturation rates on Mercury and the Moon are estimated by comparing young impact crater densities and impact ejecta reflectance, thus empirically testing previous models of faster rates for Mercury relative to the Moon. Regolith maturation due to micrometeorite impacts and solar wind sputtering modies UV-VIS-NIR surface spectra, therefore understanding maturation rates is critical for interpreting remote sensing data from airless bodies. Results determined the regolith optical maturation rate on Mercury is 2 to 4 times faster than on the Moon. The Gruithuisen Domes, three lunar silicic volcanoes, represent relatively rare lunar lithologies possibly similar to rock fragments found in the Apollo sample collection. Lunar nonmare silicic volcanism has implications for lunar magmatic evolution. I estimated a rhyolitic composition using morphologic comparisons of the Gruithuisen Domes, measured from NAC 2-meter-per-pixel digital topographic models (DTMs), with terrestrial silicic dome morphologies and laboratory models of viscoplastic dome growth. Small, morphologically sharp irregular mare patches (IMPs) provide evidence for recent lunar volcanism widely distributed across the nearside lunar maria, which has implications for long-lived nearside magmatism. I identified 75 IMPs (100-5000 meters in dimension) in NAC images and DTMs, and determined stratigraphic relationships between units common to all IMPs. Crater counts give model ages from 18-58 Ma, and morphologic comparisons with young lunar features provided an additional age constraint of <100 Ma. The IMPs formed as low-volume basaltic eruptions significantly later than previous evidence of lunar mare basalt volcanism's end (1-1.2 Ga).
ContributorsBraden, Sarah E (Author) / Robinson, Mark S (Thesis advisor) / Bell, James F. (Committee member) / Christensen, Philip R. (Committee member) / Clarke, Amanda B (Committee member) / Lawrence, Samuel J (Committee member) / Arizona State University (Publisher)
Created2013
Description
The distribution and transport of mercury in the human body are poorly constrained. For instance, the long-term persistence and intra-individual distribution of mercury in bones from dental amalgams or environmental exposure have not been studied. A robust method validated for accuracy and precision specifically for mercury in human bones would facilitate studies of mercury in anthropological, forensic, and medical studies. I present a highly precise, accurate mercury concentration analytical method targeted to human bone samples. This method uses commercially commonly available and reliable instruments that are not limited to elemental Hg analysis. This method requires significantly lower sample amounts than existing methods because it has a much lower limit of detection compared to the best mercury analyzers on the market and other analytical methods. With the low limit of detection achieved, this mercury concentration protocol is an excellent fit for studies with a limited amount of samples for destructive analysis. I then use this method to analyze the mercury concentration distribution in modern skeletal collections provided by three U.S. anthropological research facilities. Mercury concentration and distribution were analyzed from 35 donors’ skeletons with 18 different skeletal elements (bones) per donor to evaluate both the intra-individual and inter-individual variation in mercury concentration. Considered factors include geological differences in decomposition sites and the presence of dental amalgam filling. Geological differences in decomposition sites did not statistically affect the mercury concentration in the donor’s skeleton. The presence of dental amalgam significantly affected the inter-individual and intra-individual mercury concentration variation in donors’ skeletal samples. Individuals who had dental amalgam had significantly higher mercury concentration in their skeleton compared to individuals who did not have dental amalgam (p-value <0.01). Mercury concentration in the mandible, occipital bone, patella, and proximal phalanx (foot) was significantly affected by the presence of dental amalgam.
ContributorsRen, Yi (Author) / Gordon, Gwyneth GG (Thesis advisor) / Anbar, Ariel AD (Thesis advisor) / Shock, Everett ES (Committee member) / Knudson, Kelly KJ (Committee member) / Arizona State University (Publisher)
Created2022
Description
Impact craters are ubiquitous throughout the Solar System, formed by one of the principal processes responsible for surface modification of terrestrial planets and solid bodies (i.e., asteroids, icy moons). The impact cratering process is well studied, particularly on the Moon and Mercury, where the results remain uncomplicated by atmospheric effects, plate tectonics, or interactions with water and ices. Crater measurements, used to determine relative and absolute ages for geologic units by relating the cumulative crater frequency per unit area to radiometrically-determined ages from returned samples, are sensitive to the solar incidence angle of images used for counts. Earlier work is quantitatively improved by investigating this important effect and showing that absolute model ages are most accurately determined using images with incidence angles between 65° and 80°, and equilibrium crater diameter estimates are most accurate at ~80° incidence angle. A statistical method is developed using crater size-frequencies to distinguish lunar mare age units in the absence of spectral differences. Applied to the Moon, the resulting areal crater densities confidently identify expansive units with >300–500 my age differences, distinguish non-obvious secondaries, and determine that an area >1×104 km2 provides statistically robust crater measurements. This areal crater density method is also applied to the spectrally-homogeneous volcanic northern smooth plains (NSP) on Mercury. Although crater counts and observations of embayed craters indicate that the NSP experienced at least two resurfacing episodes, no observable age units are observed using areal crater density measurements, so smooth plains emplacement occurred over a relatively short timescale (<500 my). For the first time, the distribution of impact melt on Mercury and the Moon are compared at high resolution. Mercurian craters with diameters ≥30 km have a greater areal extent of interior melt deposits than similarly sized lunar craters, a result consistent with melt-generation model predictions. The effects of shaking on compositional sorting within a granular regolith are experimentally tested, demonstrating the possibility of mechanical segregation of particles in the lunar regolith. These results provide at least one explanation toward understanding the inconsistencies between lunar remote sensing datasets and are important for future spacecraft sample return missions.
ContributorsOstrach, Lillian Rose (Author) / Robinson, Mark S (Thesis advisor) / Bell Iii, James F (Committee member) / Christensen, Philip R. (Committee member) / Clarke, Amanda B (Committee member) / Garnero, Edward J (Committee member) / Arizona State University (Publisher)
Created2013
Description
Millions of people around the world daily engage in artisanal and small-scale gold mining (ASGM)––a vital part of total global gold production. For Colombia, this mining accounts for most of the precious metal’s output. It has also made Colombia, per capita, the worst mercury-polluted country in the world. Though cleaner, safer, and more effective methods exist, miners yet opt for mercury-use. Any success with interventions in technology, capacitation, or policy has been limited. This dissertation attends to mercury-use in ASGM in Antioquia, Colombia, via two gaps: a descriptive one (i.e., a failure to pay attention to, and to describe, actual practices in ASGM); and, a theoretical one (i.e., explanations as to why some decisions, including but not limited to policy, succeed or fail). In addition to an ecology of practices, embodiment, and situated knowledges, phenomenological interviews with stakeholders illuminate critical lived experience, as well as whether or how it is possible to reduce mercury-use and contamination. Furthermore, a novel application of speculative sound supplements this work. Finally, key findings complement existing scholarship. The presence of gold drives mining, but an increase in mining comes at a cost. Miners know mercury is hazardous, but mining legally, or formally, has proven too onerous. So, mercury-use persists: it is profitable, and the effects on human health can seem delayed. The state is pivotal to change in mercury-use, but its approach has been punitive. Change will invariably require greater attention to the lived experiences of miners.
ContributorsPimentel, Matthew (Author) / Fonow, Mary Margaret (Thesis advisor) / Parmentier, Mary Jane (Thesis advisor) / Coleman, Grisha (Committee member) / Arizona State University (Publisher)
Created2021
Description
Studying natural variations in the isotopic composition of oxygen-sensitive elements in ancient marine sediments is a powerful way to study the geochemical evolution of Earth’s environments in the past. My dissertation focused on two broad aspects of isotope geochemistry: 1) the development of rhenium (Re) isotopes as a paleoredox and nuclear forensics tool, and 2) the application of mercury (Hg) isotopes as a tool to trace Hg mobility in the environment and what this movement means for isotopic changes in sedimentary rocks used to study Earth’s past. Chapter 2 is the first examination of Re isotopes in sedimentary rocks that formed ~2.5 billion years ago during a period of ocean and atmospheric oxygenation prior to the Great Oxidation Event. The data show variations in Re isotope ratios coincide with evidence for changes in oceanic and atmospheric oxygenation, supporting the use of Re isotopes as a tool to track paleoredox conditions throughout Earth's history. Another application of rhenium isotopes is explored in the third chapter on nuclear forensics. Rhenium isotopes in uranium ore concentrates (UOC) from known production locations revealed more than double the range of isotope fractionation previously reported for any natural geologic samples so far. These first Re isotope ratio data indicate that Re is a promising new tool for provenance assessment of UOCs. Chapter 4 focuses on geochemical applications of Hg isotopes. Mercury isotopes in shales are a geochemical tool that can be utilized to study the prevalence of global volcanism and detect oxygen-depleted conditions in the photic zone of ancient oceans. I measured Hg isotope ratio data from a Devonian shale bed in a road cut with varying degrees of weathering that has been well characterized for variations in elemental concentrations and other isotopic ratios. I found significant variation in mass-dependent and mass-independent Hg isotope fractionation in weathered samples. Surprisingly, however, I observed both loss and gain of Hg, when only significant loss was expected based on prior weathering studies. These findings improve the understanding of Hg mobility in nature and indicate that mass-independent fractionation can be modified after deposition in surprising ways.
ContributorsSullivan, Daniel Louis (Author) / Anbar, Ariel D (Thesis advisor) / Gordon, Gwyneth W (Committee member) / Hartnett, Hilairy E (Committee member) / Hervig, Richard L (Committee member) / Zheng, Wang (Committee member) / Arizona State University (Publisher)
Created2023