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- All Subjects: Biogeochemistry
- All Subjects: Meteorites
- Creators: Shock, Everett L
Description
Carbonaceous chondrites (CCs) present a unique opportunity for learning about the earliest organic chemistry that took place in our Solar System. The complex and diverse suite of meteoritic organic material is the result of multiple settings and physicochemical processes, including aqueous and thermal alteration. Though meteorites often inform origin-of-life discussions because they could have seeded early Earth with significant amounts of water and pre-biotic, organic material, their record of abiotic, aqueous, and organic geochemistry is of interest as well.
CC materials previously resided on asteroidal parent bodies, relic planetesimals of Solar System formation which never accreted enough material to develop long-lived, large-scale geological processes. These bodies were large enough, however, to experience some degree of heating due to the decay of radiogenic isotopes, and the meteorite record suggests the existence of 100-150 parent bodies which experienced varying degrees of thermal and aqueous alteration for the first several 10 Myr of Solar System history.
The first chapter of this dissertation reviews literature addressing aqueous alteration as an essential participant in parent body geochemistry, organic synthesis, or both (though papers which address both are rare). The second chapter is a published organic analysis of the soluble organic material of Bells, an unclassified type 2 chondrite. Analytical approaches to assess terrestrial contamination of meteorite samples are also reviewed in the first chapter to allow introduction in chapter 3 of kinetic modeling which rules out certain cases of contamination and constrains the timing of thermal and aqueous alteration. This is the first known application of isoleucine epimerization for either of these purposes. Chapter 4 is a kinetic study of D-allo-isoleucine epimerization to establish its behavior in systems with large, relative abundances of alloisoleucine to isoleucine. Previous epimerization studies for paleontological or geological purposes began with L-isoleucine, the only protein amino acid of the four isoleucine stereoisomers.
Kinetic model calculations using isoleucine stereoisomer abundances from 7 CR chondrites constrain the total duration of the amino acids' residence in the aqueous phase. The comparatively short timescales produced by the presented modeling elicit hypotheses for protection or transport of the amino acids within the CR parent body.
CC materials previously resided on asteroidal parent bodies, relic planetesimals of Solar System formation which never accreted enough material to develop long-lived, large-scale geological processes. These bodies were large enough, however, to experience some degree of heating due to the decay of radiogenic isotopes, and the meteorite record suggests the existence of 100-150 parent bodies which experienced varying degrees of thermal and aqueous alteration for the first several 10 Myr of Solar System history.
The first chapter of this dissertation reviews literature addressing aqueous alteration as an essential participant in parent body geochemistry, organic synthesis, or both (though papers which address both are rare). The second chapter is a published organic analysis of the soluble organic material of Bells, an unclassified type 2 chondrite. Analytical approaches to assess terrestrial contamination of meteorite samples are also reviewed in the first chapter to allow introduction in chapter 3 of kinetic modeling which rules out certain cases of contamination and constrains the timing of thermal and aqueous alteration. This is the first known application of isoleucine epimerization for either of these purposes. Chapter 4 is a kinetic study of D-allo-isoleucine epimerization to establish its behavior in systems with large, relative abundances of alloisoleucine to isoleucine. Previous epimerization studies for paleontological or geological purposes began with L-isoleucine, the only protein amino acid of the four isoleucine stereoisomers.
Kinetic model calculations using isoleucine stereoisomer abundances from 7 CR chondrites constrain the total duration of the amino acids' residence in the aqueous phase. The comparatively short timescales produced by the presented modeling elicit hypotheses for protection or transport of the amino acids within the CR parent body.
ContributorsMonroe, Adam Alexander (Author) / Pizzarello, Sandra (Thesis advisor) / Williams, Peter (Thesis advisor) / Anbar, Ariel D (Committee member) / Shock, Everett L (Committee member) / Arizona State University (Publisher)
Created2014
Description
The occurrence of exogenic, meteoritic materials on the surface of any world presents opportunities to explore a variety of significant problems in the planetary sciences. In the case of Mars, meteorites found on its surface may help to 1) constrain atmospheric conditions during their time of arrival; 2) provide insights into possible variabilities in meteoroid type sampling between Mars and Earth space environments; 3) aid in our understanding of soil, dust, and sedimentary rock chemistry; 4) assist with the calibration of crater-age dating techniques; and 5) provide witness samples for chemical and mechanical weathering processes. The presence of reduced metallic iron in approximately 88 percent of meteorite falls renders the majority of meteorites particularly sensitive to oxidation by H2O interaction. This makes them excellent markers for H2O occurrence. Several large meteorites have been discovered at Gusev Crater and Meridiani Planum by the Mars Exploration Rovers (MERs). Significant morphologic characteristics interpretable as weathering features in the Meridiani suite of iron meteorites include a 1) large pit lined with delicate iron protrusions suggestive of inclusion removal by corrosive interaction; 2) differentially eroded kamacite and taenite lamellae on three of the meteorites, providing relative timing through cross-cutting relationships with deposition of 3) an iron oxide-rich dark coating; and 4) regmaglypted surfaces testifying to regions of minimal surface modification; with other regions in the same meteorites exhibiting 5) large-scale, cavernous weathering. Iron meteorites found by Mini-TES at both Meridiani Planum and Gusev Crater have prompted laboratory experiments designed to explore elements of reflectivity, dust cover, and potential oxide coatings on their surfaces in the thermal infrared using analog samples. Results show that dust thickness on an iron substrate need be only one tenth as great as that on a silicate rock to obscure its infrared signal. In addition, a database of thermal emission spectra for 46 meteorites was prepared to aid in the on-going detection and interpretation of these valuable rocks on Mars using Mini-TES instruments on both MER spacecraft. Applications to the asteroidal sciences are also relevant and intended for this database.
ContributorsAshley, James Warren (Author) / Christensen, Philip R. (Thesis advisor) / Sharp, Thomas G (Committee member) / Shock, Everett L (Committee member) / Hervig, Richard L (Committee member) / Zolotov, Mikhail Y (Committee member) / Arizona State University (Publisher)
Created2011
Description
Molybdenum (Mo) is a key trace nutrient for biological assimilation of nitrogen, either as nitrogen gas (N2) or nitrate (NO3-). Although Mo is the most abundant metal in seawater (105 nM), its concentration is low (<5 nM) in most freshwaters today, and it was scarce in the ocean before 600 million years ago. The use of Mo for nitrogen assimilation can be understood in terms of the changing Mo availability through time; for instance, the higher Mo content of eukaryotic vs. prokaryotic nitrate reductase may have stalled proliferation of eukaryotes in low-Mo Proterozoic oceans. Field and laboratory experiments were performed to study Mo requirements for NO3- assimilation and N2 fixation, respectively. Molybdenum-nitrate addition experiments at Castle Lake, California revealed interannual and depth variability in plankton community response, perhaps resulting from differences in species composition and/or ammonium availability. Furthermore, lake sediments were elevated in Mo compared to soils and bedrock in the watershed. Box modeling suggested that the largest source of Mo to the lake was particulate matter from the watershed. Month-long laboratory experiments with heterocystous cyanobacteria (HC) showed that <1 nM Mo led to low N2 fixation rates, while 10 nM Mo was sufficient for optimal rates. At 1500 nM Mo, freshwater HC hyperaccumulated Mo intercellularly, whereas coastal HC did not. These differences in storage capacity were likely due to the presence in freshwater HC of the small molybdate-binding protein, Mop, and its absence in coastal and marine cyanobacterial species. Expression of the mop gene was regulated by Mo availability in the freshwater HC species Nostoc sp. PCC 7120. Under low Mo (<1 nM) conditions, mop gene expression was up-regulated compared to higher Mo (150 and 3000 nM) treatments, but the subunit composition of the Mop protein changed, suggesting that Mop does not bind Mo in the same manner at <1 nM Mo that it can at higher Mo concentrations. These findings support a role for Mop as a Mo storage protein in HC and suggest that freshwater HC control Mo cellular homeostasis at the post-translational level. Mop's widespread distribution in prokaryotes lends support to the theory that it may be an ancient protein inherited from low-Mo Precambrian oceans.
ContributorsGlass, Jennifer (Author) / Anbar, Ariel D (Thesis advisor) / Shock, Everett L (Committee member) / Jones, Anne K (Committee member) / Hartnett, Hilairy E (Committee member) / Elser, James J (Committee member) / Fromme, Petra (Committee member) / Arizona State University (Publisher)
Created2011
Description
In many natural systems aqueous geochemical conditions dictate the reaction pathways of organic compounds. Geologic settings that span wide ranges in temperature, pressure, and composition vastly alter relative reaction rates and resulting organic abundances. The dependence of organic reactions on these variables contributes to planetary-scale nutrient cycling, and suggests that relative abundances of organic compounds can reveal information about inaccessible geologic environments, whether from the terrestrial subsurface, remote planetary settings, or even the distant past (if organic abundances are well preserved). Despite their relevance to planetary modeling and exploration, organic reactions remain poorly characterized under geochemically relevant conditions, especially in terms of their reaction kinetics, mechanisms, and equilibria.
In order to better understand organic transformations in natural systems, the reactivities of oxygen- and nitrogen-bearing organic functional groups were investigated under experimental hydrothermal conditions, at 250°C and 40 bar. The model compounds benzylamine and α-methylbenzylamine were used as analogs to environmentally relevant amines, ultimately elucidating two dominant deamination mechanisms for benzylamine, SN1 and SN2, and a single SN1 mechanism for deamination of α-methylbenzylamine. The presence of unimolecular and bimolecular mechanisms has implications for temperature dependent kinetics, indicating that Arrhenius rate extrapolation is currently unreliable for deamination.
Hydrothermal experiments with benzyl alcohol, benzylamine, dibenzylamine, or tribenzylamine as the starting material indicate that substitution reactions between these compounds (and others) are reversible and approach metastable equilibrium after 72 hours. These findings suggest that relative ratios of organic compounds capable of substitution reactions could be targeted as tracers of inaccessible geochemical conditions.
Metastable equilibria for organic reactions were investigated in a natural low-temperature serpentinizing continental system. Serpentinization is a water-rock reaction which generates hyperalkaline, reducing conditions. Thermodynamic calculations were performed for reactions between dissolved inorganic carbon and hydrogen to produce methane, formate, and acetate. Quantifying conditions that satisfy equilibrium for these reactions allows subsurface conditions to be predicted. These calculations also lead to hypotheses regarding active microbial processes during serpentinization.
In order to better understand organic transformations in natural systems, the reactivities of oxygen- and nitrogen-bearing organic functional groups were investigated under experimental hydrothermal conditions, at 250°C and 40 bar. The model compounds benzylamine and α-methylbenzylamine were used as analogs to environmentally relevant amines, ultimately elucidating two dominant deamination mechanisms for benzylamine, SN1 and SN2, and a single SN1 mechanism for deamination of α-methylbenzylamine. The presence of unimolecular and bimolecular mechanisms has implications for temperature dependent kinetics, indicating that Arrhenius rate extrapolation is currently unreliable for deamination.
Hydrothermal experiments with benzyl alcohol, benzylamine, dibenzylamine, or tribenzylamine as the starting material indicate that substitution reactions between these compounds (and others) are reversible and approach metastable equilibrium after 72 hours. These findings suggest that relative ratios of organic compounds capable of substitution reactions could be targeted as tracers of inaccessible geochemical conditions.
Metastable equilibria for organic reactions were investigated in a natural low-temperature serpentinizing continental system. Serpentinization is a water-rock reaction which generates hyperalkaline, reducing conditions. Thermodynamic calculations were performed for reactions between dissolved inorganic carbon and hydrogen to produce methane, formate, and acetate. Quantifying conditions that satisfy equilibrium for these reactions allows subsurface conditions to be predicted. These calculations also lead to hypotheses regarding active microbial processes during serpentinization.
ContributorsRobinson, Kirtland J (Author) / Shock, Everett L (Thesis advisor) / Herckes, Pierre (Committee member) / Hartnett, Hilairy E (Committee member) / Anbar, Ariel D (Committee member) / Arizona State University (Publisher)
Created2017
Description
Utilizing both 16S and 18S rRNA sequencing alongside energetic calculations from geochemical measurements offers a bridged perspective of prokaryotic and eukaryotic community diversities and their relationships to geochemical diversity. Yellowstone National Park hot spring outflows from varied geochemical compositions, ranging in pH from < 2 to > 9 and in temperature from < 30°C to > 90°C, were sampled across the photosynthetic fringe, a transition in these outflows from exclusively chemosynthetic microbial communities to those that include photosynthesis. Illumina sequencing was performed to document the diversity of both prokaryotes and eukaryotes above, at, and below the photosynthetic fringe of twelve hot spring systems. Additionally, field measurements of dissolved oxygen, ferrous iron, and total sulfide were combined with laboratory analyses of sulfate, nitrate, total ammonium, dissolved inorganic carbon, dissolved methane, dissolved hydrogen, and dissolved carbon monoxide were used to calculate the available energy from 58 potential metabolisms. Results were ranked to identify those that yield the most energy according to the geochemical conditions of each system. Of the 46 samples taken across twelve systems, all showed the greatest energy yields using oxygen as the main electron acceptor, followed by nitrate. On the other hand, ammonium or ammonia, depending on pH, showed the greatest energy yields as an electron donor, followed by H2S or HS-. While some sequenced taxa reflect potential biotic participants in the sulfur cycle of these hot spring systems, many sample locations that yield the most energy from ammonium/ammonia oxidation have low relative abundances of known ammonium/ammonia oxidizers, indicating potentially untapped sources of chemotrophic energy or perhaps poorly understood metabolic capabilities of cultured chemotrophs.
ContributorsRomero, Joseph Thomas (Author) / Shock, Everett L (Thesis advisor) / Cadillo-Quiroz, Hinsby (Committee member) / Till, Christy B. (Committee member) / Arizona State University (Publisher)
Created2018
Description
Many acidic hot springs in Yellowstone National Park support microbial iron oxidation, reduction, or microbial iron redox cycling (MIRC), as determined by microcosm rate experiments. Microbial dissimilatory iron reduction (DIR) was detected in numerous systems with a pH < 4. Rates of DIR are influenced by the availability of ferric minerals and organic carbon. Microbial iron oxidation (MIO) was detected from pH 2 – 5.5. In systems with abundant Fe (II), dissolved oxygen controls the presence of MIO. Rates generally increase with increased Fe(II) concentrations, but rate constants are not significantly altered by additions of Fe(II). MIRC was detected in systems with abundant ferric mineral deposition.
The rates of microbial and abiological iron oxidation were determined in a variety of cold (T= 9-12°C), circumneutral (pH = 5.5-9) environments in the Swiss Alps. Rates of MIO were measured in systems up to a pH of 7.4; only abiotic processes were detected at higher pH values. Iron oxidizing bacteria (FeOB) were responsible for 39-89% of the net oxidation rate at locations where biological iron oxidation was detected. Members of putative iron oxidizing genera, especially Gallionella, are abundant in systems where MIO was measured. Speciation calculations reveal that ferrous iron typically exists as FeCO30, FeHCO3+, FeSO40 or Fe2+ in these systems. The presence of ferrous (bi)carbonate species appear to increase abiotic iron oxidation rates relative to locations without significant concentrations. This approach, integrating geochemistry, rates, and community composition, reveals biogeochemical conditions that permit MIO, and locations where the abiotic rate is too fast for the biotic process to compete.
For a reaction to provide habitability for microbes in a given environment, it must energy yield and this energy must dissipate slowly enough to remain bioavailable. Thermodynamic boundaries exist at conditions where reactions do not yield energy, and can be quantified by calculations of chemical energy. Likewise, kinetic boundaries exist at conditions where the abiotic reaction rate is so fast that reactants are not bioavailable; this boundary can be quantified by measurements biological and abiological rates. The first habitability maps were drawn, using iron oxidation as an example, by quantifying these boundaries in geochemical space.
The rates of microbial and abiological iron oxidation were determined in a variety of cold (T= 9-12°C), circumneutral (pH = 5.5-9) environments in the Swiss Alps. Rates of MIO were measured in systems up to a pH of 7.4; only abiotic processes were detected at higher pH values. Iron oxidizing bacteria (FeOB) were responsible for 39-89% of the net oxidation rate at locations where biological iron oxidation was detected. Members of putative iron oxidizing genera, especially Gallionella, are abundant in systems where MIO was measured. Speciation calculations reveal that ferrous iron typically exists as FeCO30, FeHCO3+, FeSO40 or Fe2+ in these systems. The presence of ferrous (bi)carbonate species appear to increase abiotic iron oxidation rates relative to locations without significant concentrations. This approach, integrating geochemistry, rates, and community composition, reveals biogeochemical conditions that permit MIO, and locations where the abiotic rate is too fast for the biotic process to compete.
For a reaction to provide habitability for microbes in a given environment, it must energy yield and this energy must dissipate slowly enough to remain bioavailable. Thermodynamic boundaries exist at conditions where reactions do not yield energy, and can be quantified by calculations of chemical energy. Likewise, kinetic boundaries exist at conditions where the abiotic reaction rate is so fast that reactants are not bioavailable; this boundary can be quantified by measurements biological and abiological rates. The first habitability maps were drawn, using iron oxidation as an example, by quantifying these boundaries in geochemical space.
ContributorsSt Clair, Brian (Author) / Shock, Everett L (Thesis advisor) / Anbar, Ariel (Committee member) / Garcia-Pichel, Ferran (Committee member) / Hartnett, Hilairy (Committee member) / Arizona State University (Publisher)
Created2017
Description
Mantle derived basalts along the entirety of the Earth’s Mid-Ocean Ridge (MOR) spreading centers are continuously altered by seawater, allowing the hydrosphere to subsume energy and exchange mass with the deep, slowly cooling Earth. Compositional heterogeneities inherent to these basalts—the result of innumerable geophysical and geochemical processes in the mantel and crust—generate spatial variation in the equilibrium states toward which these water-rock environments cascade. This alteration results in a unique distribution of precipitate assemblages, hydrothermal fluid chemistries, and energetic landscapes among ecosystems rooted within and above the seafloor. The equilibrium states for the full range of basalt compositional heterogeneity present today are calculated over all appropriate temperatures and extents of reaction with seawater, along with the non-equilibrium mixtures generated when hydrothermal fluids mix back into seawater. These mixes support ancient and diverse ecosystems fed not by the energy of the sun, but by the geochemical energy of the Earth. Facilitated by novel, high throughout code, this effort has yielded a high-resolution compositional database that is mapped back onto all ridge systems. By resolving the chemical and energetic consequences of basalt-seawater interaction to sub-ridge scales, alteration features that are globally homogeneous can be distinguished from those that are locally unique, guiding future field observations with testable geochemical and biochemical predictions.
ContributorsELY, TUCKER (Author) / Shock, Everett L (Thesis advisor) / Till, Christy B. (Committee member) / Walker, Sara I (Committee member) / Anbar, Ariel D (Committee member) / Hartnett, Hilairy E (Committee member) / Arizona State University (Publisher)
Created2020