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Past studies in paleoenvironmental reconstruction have set out to bridge the gap that limits our understanding of the biogeochemical controls in the past oceans by developing redox proxies based on trace metal content, iron speciation, and pyrite formation. Many of those studies have relied on broad-scale temporal assumptions about ocean redox conditions inferred from idealized chemical processes and classifying past oceans into either oxygenated, ferruginous, or euxinic. The redox threshold values associated with these proxies can vary considerably among depositional systems and, for this reason, geochemical proxies should be scrutinized in multiple modern deposition systems of variable redox characteristics (stable and dynamic). This dissertation applies various geochemical tools to understand the biogeochemical controls on carbon, iron, and sulfur reaction rates during early diagenesis. Specifically, I test, refine, and expand the use of pyrite as a paleoredox proxy by expanding our understanding on the controls on pyrite formation and the incorporation of trace elements in pyrite during early diagenesis by investigating those relationships in modern marine depositional systems. First, I explore the early diagenetic processes occurring in marine sediments with emphasis on the carbon, iron, and sulfur cycle–the three main components in sedimentary pyrite formation. This effort is made by measuring nutrients, organic carbon, and iron and sulfur mineralogical characterization and coupling with reactive-transport diagenetic modelling to understand the diagenetic reactions that lead to iron-sulfide precipitation within the sedimentary profile. Two geographically distinct locations are studied in detail: (1) The Santa Monica Basin (SMB), an exceptionally iron dominated system, and (2) Saanich Inlet, BC, Canada, a fjord with high redox variability and transient euxinic bottom waters. Then, I explore the relationships between the chemical signatures in syngenetic and dia

Iron (Fe) is present over a very wide range of redox conditions and is one of most the important nutrients for phytoplankton growth in the ocean. In a marine environment, Fe composition in the sediments is intimately linked to the chemistry of the waters from which they precipitate. Particularly, the elemental and isotopic signature of Fe recorded in sediments provide clues about the nature of the redox state and the biogeochemical cycling of bio-essential metals, both of which are associated to primary productivity, carbon cycling, and the evolution of Earth through time.In this work, I firstly evaluate Fe, a fundamental regulator of ocean primary productivity and the global carbon cycle and a limiting micronutrient for phytoplankton growth, to draw connections between win-borne bioavailable Fe distribution and its potential impact on Fe-based climate feedbacks over the last 120,000 years. Our results from sediments in the North Atlantic suggest that atmospheric processing of Saharan dust enhances the solubility and hence bioavailability of dust-borne iron independent of grain size, and this transport-dependent processing scales with atmospheric residence time and thus transport distance. These observations and inferred processes may extend to many other regions beyond the North Atlantic and enlighten the global primary productivity distribution. A second study defines natural variations in water column redox of the southern Scotia Sea basins, Dove and Pirie from scientific drilling of the Scotia Sea sedimentary record during International Ocean Discovery Program (IODP) Expedition 382. The distinct trend in the pore water and sedimentary concentrations from two basins reveal the dominant control of Fe availability on primary composition and early diagenetic signals that affects the biogeochemical signals and its effects for interpreting Fe data towards the climate evolution of the Southern Ocean. Lastly, I examine the redox state of the late-Archean and Paleoproter

Since life took its earliest footholds, organisms have been in a perpetual arms race. Evolutionary trial and error has produced increasingly complex organisms. All with a single purpose, to utilize available resources as efficiently as possible and reproduce. This progression has led to things like photosynthesis and respiration, phagocytosis, multicellularity, differentiated cell types, neural networks, and apparently consciousness. This dissertation presents one account of the history of the push-and-pull relationship between life and the environment as both evolved together, centered around two case studies that contributed to the knowledgebase on which the larger argument is founded.Because the net outcome of biological activity is the concentration of reduced material, the net outcome is also environmental oxidation, so long as some of that material still exists. Oxygenic photosynthesis was not necessarily the path of least resistance to ecological success, but once the machinery was assembled, the substrates were nearly limitless in many environments. This intuitively leads to the utilization of O2 in respiration—is by far the best candidate for the job, assuming it is ambiently present. That statement suggests implicitly that evolution will continually exploit its environment to gain a competitive advantage. This effectively frames one side of a long-standing debate concerning the role that environmental O2 concentrations played the evolution of the eukaryotic clade. The chapters herein elaborate on this argument. It begins with a case study of the 1.4-billion-year-old Xiamaling Formation, presenting iron speciation, sulfur isotope, trace metal, and molybdenum isotope data; concluding that while the Xiamaling Formation was likely deposited in a restricted setting, it still holds geochemical indications that global oceans could have been more well oxygenated at the time than many previously thought. The middle chapters explore these ideas further. The disserta

Iron (Fe) is present over a very wide range of redox conditions and is one of most the important nutrients for phytoplankton growth in the ocean. In a marine environment, Fe composition in the sediments is intimately linked to the chemistry of the waters from which they precipitate. Particularly, the elemental and isotopic signature of Fe recorded in sediments provide clues about the nature of the redox state and the biogeochemical cycling of bio-essential metals, both of which are associated to primary productivity, carbon cycling, and the evolution of Earth through time.In this work, I firstly evaluate Fe, a fundamental regulator of ocean primary productivity and the global carbon cycle and a limiting micronutrient for phytoplankton growth, to draw connections between win-borne bioavailable Fe distribution and its potential impact on Fe-based climate feedbacks over the last 120,000 years. Our results from sediments in the North Atlantic suggest that atmospheric processing of Saharan dust enhances the solubility and hence bioavailability of dust-borne iron independent of grain size, and this transport-dependent processing scales with atmospheric residence time and thus transport distance. These observations and inferred processes may extend to many other regions beyond the North Atlantic and enlighten the global primary productivity distribution. A second study defines natural variations in water column redox of the southern Scotia Sea basins, Dove and Pirie from scientific drilling of the Scotia Sea sedimentary record during International Ocean Discovery Program (IODP) Expedition 382. The distinct trend in the pore water and sedimentary concentrations from two basins reveal the dominant control of Fe availability on primary composition and early diagenetic signals that affects the biogeochemical signals and its effects for interpreting Fe data towards the climate evolution of the Southern Ocean. Lastly, I examine the redox state of the late-Archean and Paleoproter

Since life took its earliest footholds, organisms have been in a perpetual arms race. Evolutionary trial and error has produced increasingly complex organisms. All with a single purpose, to utilize available resources as efficiently as possible and reproduce. This progression has led to things like photosynthesis and respiration, phagocytosis, multicellularity, differentiated cell types, neural networks, and apparently consciousness. This dissertation presents one account of the history of the push-and-pull relationship between life and the environment as both evolved together, centered around two case studies that contributed to the knowledgebase on which the larger argument is founded.Because the net outcome of biological activity is the concentration of reduced material, the net outcome is also environmental oxidation, so long as some of that material still exists. Oxygenic photosynthesis was not necessarily the path of least resistance to ecological success, but once the machinery was assembled, the substrates were nearly limitless in many environments. This intuitively leads to the utilization of O2 in respiration—is by far the best candidate for the job, assuming it is ambiently present. That statement suggests implicitly that evolution will continually exploit its environment to gain a competitive advantage. This effectively frames one side of a long-standing debate concerning the role that environmental O2 concentrations played the evolution of the eukaryotic clade. The chapters herein elaborate on this argument. It begins with a case study of the 1.4-billion-year-old Xiamaling Formation, presenting iron speciation, sulfur isotope, trace metal, and molybdenum isotope data; concluding that while the Xiamaling Formation was likely deposited in a restricted setting, it still holds geochemical indications that global oceans could have been more well oxygenated at the time than many previously thought. The middle chapters explore these ideas further. The disserta

Oxygen availability in the oceans and atmosphere has been one of the primary controls on evolutionary advances on Earth, but our inability to measure oxygen concentrations directly requires the use of proxies that have been calibrated in low-oxygen settings. The biogeochemical cycles of sulfur and carbon, among many other elemental cycles, have been closely linked to oxygen concentrations through time, and many proxies for oxygen have arisen from observations of their linked cycles. This dissertation applies a number of geochemical proxies in two different types of environments to constrain the role of sulfate reduction and its relationships to organic carbon burial. First, I explore the role of hydrocarbon seep environments as a source of methane and reduced sulfur to the oceans, atmosphere, and biosphere using a system of Cretaceous-aged seeps in Colorado, U.S.A. The connection between sulfur and carbon cycling in seep settings through coupled sulfate reduction and anaerobic methane oxidation suggests that sulfur isotope compositions of carbonate-bound sulfate can be used to track paleo-sulfate reduction rates and methane concentrations. The next chapters focus on reconstructing local and global redox conditions in the Miocene Monterey Formation. The Miocene was a time of elevated global temperatures, and the Monterey Formation's deposition into multiple sub-basins provides an ideal opportunity to study how preservation of geochemical signatures of basin redox conditions vary within and among basins as a function of local and global climatic and oceanic conditions. The first study presents commonly employed redox indicators, including iron speciation and redox-sensitive trace metal concentrations, to constrain paleoredox conditions from three basins with different hydrographic conditions during deposition, including degrees of restriction and intensities of upwelling. A second study builds on these interpretations, applying Mo and Tl isotope proxies to determine w

The rise of oxygen in Earth's atmosphere from negligible levels on the earliest Earth to the high levels that we enjoy today is the consequence of oxygenic photosynthesis and it is the most profound impact that life has had on Earth's surface environment. Yet details of this transition remain poorly constrained. This dissertation examines the cause-and-effect relationships between Earth's biosphere, atmosphere, and climate system with a particular focus on oxygen and its many impacts. Topics include: (1) the relationship between oxygen production and oxygen accumulation on early Earth, (2) the mechanisms that regulate oxygen levels in Earth's atmosphere, (3) the role of oxygen in early animal ecosystems, and (4) the interplay between oxygen and trace greenhouse gases. Understanding the relationships between life and its environment is essential to understanding not only the requirements and emergence of complex life on Earth but on other planets as well---and for ultimately recognizing the chemical fingerprints of life in the atmospheres of other inhabited worlds.

The rise of oxygen in Earth's atmosphere from negligible levels on the earliest Earth to the high levels that we enjoy today is the consequence of oxygenic photosynthesis and it is the most profound impact that life has had on Earth's surface environment. Yet details of this transition remain poorly constrained. This dissertation examines the cause-and-effect relationships between Earth's biosphere, atmosphere, and climate system with a particular focus on oxygen and its many impacts. Topics include: (1) the relationship between oxygen production and oxygen accumulation on early Earth, (2) the mechanisms that regulate oxygen levels in Earth's atmosphere, (3) the role of oxygen in early animal ecosystems, and (4) the interplay between oxygen and trace greenhouse gases. Understanding the relationships between life and its environment is essential to understanding not only the requirements and emergence of complex life on Earth but on other planets as well---and for ultimately recognizing the chemical fingerprints of life in the atmospheres of other inhabited worlds.

Oxygen availability in the oceans and atmosphere has been one of the primary controls on evolutionary advances on Earth, but our inability to measure oxygen concentrations directly requires the use of proxies that have been calibrated in low-oxygen settings. The biogeochemical cycles of sulfur and carbon, among many other elemental cycles, have been closely linked to oxygen concentrations through time, and many proxies for oxygen have arisen from observations of their linked cycles. This dissertation applies a number of geochemical proxies in two different types of environments to constrain the role of sulfate reduction and its relationships to organic carbon burial. First, I explore the role of hydrocarbon seep environments as a source of methane and reduced sulfur to the oceans, atmosphere, and biosphere using a system of Cretaceous-aged seeps in Colorado, U.S.A. The connection between sulfur and carbon cycling in seep settings through coupled sulfate reduction and anaerobic methane oxidation suggests that sulfur isotope compositions of carbonate-bound sulfate can be used to track paleo-sulfate reduction rates and methane concentrations. The next chapters focus on reconstructing local and global redox conditions in the Miocene Monterey Formation. The Miocene was a time of elevated global temperatures, and the Monterey Formation's deposition into multiple sub-basins provides an ideal opportunity to study how preservation of geochemical signatures of basin redox conditions vary within and among basins as a function of local and global climatic and oceanic conditions. The first study presents commonly employed redox indicators, including iron speciation and redox-sensitive trace metal concentrations, to constrain paleoredox conditions from three basins with different hydrographic conditions during deposition, including degrees of restriction and intensities of upwelling. A second study builds on these interpretations, applying Mo and Tl isotope proxies to determine w

The presence of marine oxygen is an essential precursor for faunal habitability, driving distribution in coastal systems today and linked to evolutionary patterns throughout the geologic past. In oxygen-deficient marine systems, the reducing capacity can be defined by the zonation of redox-sensitive elements (e.g. O, I, N, Mn, Fe, S, C), with their availability in the rock record in some cases linked to the water column redox state during deposition and subsequent burial processes. In this dissertation, I reconstruct paleoredox in environments defined by water column oxygen deficiency at biologically critical levels, specifically extreme low oxygen to mildly sulfidic, a redox window most representative of reducing systems today but largely underexplored in the geologic past. First, I present the initial surface ocean-specific Precambrian redox record, the location and period hosting the emergence of both oxygenic photosynthesis and multicellular life, evaluated through iodine-to-calcium-magnesium ratios in mostly shallow carbonate and supplemented through study of iodine retention during carbonate diagenesis. Oxygen became widespread in shallow marginal marine settings starting in the Paleoproterozoic, likely at levels necessary to support simple animals. The ensuing Proterozoic record was dynamic, with oxygen fluctuating at and below thresholds similar to waters within and directly overlying modern oxygen minimum zones and largely constrained to shallow settings, a condition particularly exacerbated during the middle Proterozoic. This is a new view of the Precambrian surface ocean and such variability and spatially restricted marine oxygen at critically low levels is hypothesized to explain the delayed emergence of animals until the Neoproterozoic. A second study defines natural variations in water column redox in the Baltic Sea over the Holocene, the world’s largest modern anthropogenically forced and spatially and temporally variable low-oxygen basin. An iron-man

The presence of marine oxygen is an essential precursor for faunal habitability, driving distribution in coastal systems today and linked to evolutionary patterns throughout the geologic past. In oxygen-deficient marine systems, the reducing capacity can be defined by the zonation of redox-sensitive elements (e.g. O, I, N, Mn, Fe, S, C), with their availability in the rock record in some cases linked to the water column redox state during deposition and subsequent burial processes. In this dissertation, I reconstruct paleoredox in environments defined by water column oxygen deficiency at biologically critical levels, specifically extreme low oxygen to mildly sulfidic, a redox window most representative of reducing systems today but largely underexplored in the geologic past. First, I present the initial surface ocean-specific Precambrian redox record, the location and period hosting the emergence of both oxygenic photosynthesis and multicellular life, evaluated through iodine-to-calcium-magnesium ratios in mostly shallow carbonate and supplemented through study of iodine retention during carbonate diagenesis. Oxygen became widespread in shallow marginal marine settings starting in the Paleoproterozoic, likely at levels necessary to support simple animals. The ensuing Proterozoic record was dynamic, with oxygen fluctuating at and below thresholds similar to waters within and directly overlying modern oxygen minimum zones and largely constrained to shallow settings, a condition particularly exacerbated during the middle Proterozoic. This is a new view of the Precambrian surface ocean and such variability and spatially restricted marine oxygen at critically low levels is hypothesized to explain the delayed emergence of animals until the Neoproterozoic. A second study defines natural variations in water column redox in the Baltic Sea over the Holocene, the world’s largest modern anthropogenically forced and spatially and temporally variable low-oxygen basin. An iron-man

The Neoproterozoic Era, from around 1000 to 570 million years ago, witnessed the widespread deposition of Iron Formations (IFs) in close association with global glaciations. These IFs record distinct iron isotope and rare earth element patterns that allow us to reconstruct their depositional environment. The Fulu Formation of South China is a regional example of a global phenomenon. The Fulu was deposited immediately following the breakup of the Supercontinent Rodinia, which provided a restricted rift basin and contributed to an ample supply of iron. Specifically, iron isotopes and rare earth element profiles point to hydrothermally sourced iron in an oxygen-limited environment as the major driver of deposition for the Fulu Formation.

By about 2.0 billion years ago (Ga), there is evidence for a period best known for its extended, apparent geochemical stability expressed famously in the carbonate-carbon isotope data. Despite the first appearance and early innovation among eukaryotic organisms, this period is also known for a rarity of eukaryotic fossils and organic biomarker fingerprints, suggesting low diversity and relatively small populations compared to the interval that followed. Nevertheless, the search for diagnostic biomarkers has not been performed within an independent paleoenvironmental context that should reveal the facies that were most likely hospitable to these oxygen-requiring organisms. Shales and mudstones obtained from drill core of the ca. 1.45 Ga Roper Group from the McArthur Basin of northern Australia provide one of our best windows into the mid-Proterozoic redox landscape. The group is well dated and minimally metamorphosed, and previous geochemical data show a relatively strong connection to the open ocean compared to other mid-Proterozoic records. Consequently, conditions captured in the Roper Group may better reflect the redox state of the ocean margin and may reveal eukaryote-favoring setting. Despite this potential, a comprehensive, multi-proxy study of the Roper Group had not been undertaken. Here we present one of the first integrated investigations of Precambrian biomarkers performed within a strict inorganic proxy context. Results show a textured paleoredox structure for the Velkerri Formation, vacillating between oxic and anoxic, even euxinic conditions in the water column. Despite this variability, including the likely presence of oxic bottom waters, we see no evidence for the sterane compounds that would point convincingly to the presence of eukaryotes in this marine basin roughly 1.45 Ga. Also missing are the aryl isoprenoids that would delineate shallow photic zone euxinia and thus the likelihood of appreciable anoxygenic primary production, even though the ir

The Neoproterozoic Era, from around 1000 to 570 million years ago, witnessed the widespread deposition of Iron Formations (IFs) in close association with global glaciations. These IFs record distinct iron isotope and rare earth element patterns that allow us to reconstruct their depositional environment. The Fulu Formation of South China is a regional example of a global phenomenon. The Fulu was deposited immediately following the breakup of the Supercontinent Rodinia, which provided a restricted rift basin and contributed to an ample supply of iron. Specifically, iron isotopes and rare earth element profiles point to hydrothermally sourced iron in an oxygen-limited environment as the major driver of deposition for the Fulu Formation.

By about 2.0 billion years ago (Ga), there is evidence for a period best known for its extended, apparent geochemical stability expressed famously in the carbonate-carbon isotope data. Despite the first appearance and early innovation among eukaryotic organisms, this period is also known for a rarity of eukaryotic fossils and organic biomarker fingerprints, suggesting low diversity and relatively small populations compared to the interval that followed. Nevertheless, the search for diagnostic biomarkers has not been performed within an independent paleoenvironmental context that should reveal the facies that were most likely hospitable to these oxygen-requiring organisms. Shales and mudstones obtained from drill core of the ca. 1.45 Ga Roper Group from the McArthur Basin of northern Australia provide one of our best windows into the mid-Proterozoic redox landscape. The group is well dated and minimally metamorphosed, and previous geochemical data show a relatively strong connection to the open ocean compared to other mid-Proterozoic records. Consequently, conditions captured in the Roper Group may better reflect the redox state of the ocean margin and may reveal eukaryote-favoring setting. Despite this potential, a comprehensive, multi-proxy study of the Roper Group had not been undertaken. Here we present one of the first integrated investigations of Precambrian biomarkers performed within a strict inorganic proxy context. Results show a textured paleoredox structure for the Velkerri Formation, vacillating between oxic and anoxic, even euxinic conditions in the water column. Despite this variability, including the likely presence of oxic bottom waters, we see no evidence for the sterane compounds that would point convincingly to the presence of eukaryotes in this marine basin roughly 1.45 Ga. Also missing are the aryl isoprenoids that would delineate shallow photic zone euxinia and thus the likelihood of appreciable anoxygenic primary production, even though the ir

The chemical composition of the ocean changed dramatically with the oxidation of the Earth's surface, and this process has profoundly influenced the evolutionary and ecological history of life. The early Earth is generally thought to have been characterized by a reducing ocean-atmosphere system, while the Phanerozoic Eon (<542 million years ago) is known for a stably oxygenated biosphere conducive to the radiation of animals. However, the exact redox landscape of the Earth's oceans is poorly constrained. Similarly, the redox characteristics of surface environments during Earth's middle age (1.8 to 1 billion years ago) are poorly known. I will provide several lines of evidence that even the mixed layer of the surfical ocean was anoxic in the Archean. Oxygen must have been restricted to very localized regions of the regions--`oxygen oases'. Further, I will present evidence that anoxic and Fe(II)-rich conditions were both spatially and temporally extensive across diverse paleogeographic settings in the mid-Proterozoic ocean. This is a new view of Proterozoic redox conditions; it has been commonly assumed for the last decades that the mid-Proterozoic was home to a globally sulfidic (euxinic) or oxic deep ocean. Lastly, I will explore the underlying controls behind the transition from the reducing state that characterized most of the Precambrian to the oxidized state typical of the Phanerozoic. More specifically, I propose based, on a new record of how marine phosphate concentrations have changed through time, that a spike in phosphate levels in the ocean in late Precambrian was key in causing the switch to a more oxidizing ocean atmosphere system.

The evolution of oxygenic photosynthesis has dramatically reshaped the chemistry of the surface Earth, and the presence of significant quantities of O2 in the atmosphere and ocean now drives the fundamental dynamics of nearly all quantitatively significant biogeochemocal cycles (C, S, P, N, Fe). Whether by direct consumption through the metabolic demands of large, complex organisms, or through the recycling of essential substrates within microbial ecosystems, biologically produced O2 provides nearly all of the compounds used in metabolic electron transfer on a global scale. Although it is widely accepted that the partial pressure of O2 in Earth's atmosphere has increased through time (with attendant, although somewhat complex, changes in ocean ventilation), there is still much debate surrounding the timing of the emergence of oxygenic photosynthesis and little is known about the detailed tempo and mode with which this metabolic innovation came to shape early Earth surface chemistry. This dissertation explores the early oxygenation of Earth's atmosphere and the relationship between atmospheric oxygen levels and ocean ventilation from a variety of perspectives. First, empirical data based on an integrated suite of paleoredox proxies is used to suggest that biological oxygen production emerged and began exerting significant effects on Earth surface chemistry at least 100 million years prior to the initial accumulation of large quantities of O2 in the atmosphere (often referred to as the "Great Oxidation Event", approximately 2.4 billion years ago). The implications of this time lag between metabolic innovation and large-scale biogeochemical reorganization are explored through a series of quantitative models, focusing on the thermodynamics and kinetics of mineral reactions under various Earth surface conditions, regional oceanographic modeling of surface ocean O2 cycling, and a global sulfur isotope mass balance model that explicitly incorporates rare sulfur isotope sys

The chemical composition of the ocean changed dramatically with the oxidation of the Earth's surface, and this process has profoundly influenced the evolutionary and ecological history of life. The early Earth is generally thought to have been characterized by a reducing ocean-atmosphere system, while the Phanerozoic Eon (<542 million years ago) is known for a stably oxygenated biosphere conducive to the radiation of animals. However, the exact redox landscape of the Earth's oceans is poorly constrained. Similarly, the redox characteristics of surface environments during Earth's middle age (1.8 to 1 billion years ago) are poorly known. I will provide several lines of evidence that even the mixed layer of the surfical ocean was anoxic in the Archean. Oxygen must have been restricted to very localized regions of the regions--`oxygen oases'. Further, I will present evidence that anoxic and Fe(II)-rich conditions were both spatially and temporally extensive across diverse paleogeographic settings in the mid-Proterozoic ocean. This is a new view of Proterozoic redox conditions; it has been commonly assumed for the last decades that the mid-Proterozoic was home to a globally sulfidic (euxinic) or oxic deep ocean. Lastly, I will explore the underlying controls behind the transition from the reducing state that characterized most of the Precambrian to the oxidized state typical of the Phanerozoic. More specifically, I propose based, on a new record of how marine phosphate concentrations have changed through time, that a spike in phosphate levels in the ocean in late Precambrian was key in causing the switch to a more oxidizing ocean atmosphere system.

The evolution of oxygenic photosynthesis has dramatically reshaped the chemistry of the surface Earth, and the presence of significant quantities of O2 in the atmosphere and ocean now drives the fundamental dynamics of nearly all quantitatively significant biogeochemocal cycles (C, S, P, N, Fe). Whether by direct consumption through the metabolic demands of large, complex organisms, or through the recycling of essential substrates within microbial ecosystems, biologically produced O2 provides nearly all of the compounds used in metabolic electron transfer on a global scale. Although it is widely accepted that the partial pressure of O2 in Earth's atmosphere has increased through time (with attendant, although somewhat complex, changes in ocean ventilation), there is still much debate surrounding the timing of the emergence of oxygenic photosynthesis and little is known about the detailed tempo and mode with which this metabolic innovation came to shape early Earth surface chemistry. This dissertation explores the early oxygenation of Earth's atmosphere and the relationship between atmospheric oxygen levels and ocean ventilation from a variety of perspectives. First, empirical data based on an integrated suite of paleoredox proxies is used to suggest that biological oxygen production emerged and began exerting significant effects on Earth surface chemistry at least 100 million years prior to the initial accumulation of large quantities of O2 in the atmosphere (often referred to as the "Great Oxidation Event", approximately 2.4 billion years ago). The implications of this time lag between metabolic innovation and large-scale biogeochemical reorganization are explored through a series of quantitative models, focusing on the thermodynamics and kinetics of mineral reactions under various Earth surface conditions, regional oceanographic modeling of surface ocean O2 cycling, and a global sulfur isotope mass balance model that explicitly incorporates rare sulfur isotope sys