© Copyright 2018 Matthew C. Koehler The co-evolution of life and the nitrogen cycle on the early Earth Matthew C. Koehler A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Washington 2018 Reading Committee: Roger Buick, Ph.D., Chair David Catling, Ph.D. Eric Steig, Ph.D. Program Authorized to Offer Degree: Earth and Space Sciences & Astrobiology University of Washington Abstract The co-evolution of life and the nitrogen cycle on the early Earth Matthew C. Koehler Chair of the Supervisory Committee: Roger Buick, Ph.D. Earth and Spaces Sciences & Astrobiology Nitrogen is an essential element for all life as we know it. Its abundance and speciation in the atmosphere and ocean has been dynamic through Earth’s history. The dynamic nature of nitrogen cycling is invariably linked to the dynamic nature of oxygenation on the early Earth, and the evolution of these two biogeochemical cycles influenced biological evolution and diversification. Exploration of the mode, tempo, and scale of such changes will add to our mechanistic understanding of these components of the inhabited Earth-system and should provide insight into how these cycles might operate on an alien planet that is different from our own. Here, I explore four critical points in Earth’s redox and biological evolution: Chapter 2 – The dominantly anoxic world of the Mesoarchean, when aerobic nitrogen metabolisms did not exist, and bioavailable nitrogen could only be obtained through biological nitrogen fixation or remineralized ammonium. Biological nitrogen fixation by the Mo-nitrogenase dominated. Chapter 3 – Incipient oxygenation ~300 Myr before the great oxidation event. We start to characterize the mode, tempo, and scale of these transient oxygenation events, and provide the oldest evidence of aerobic nitrogen cycling 2.66 Gyr ago. Chapter 4 – The state of nitrogen cycling during the Mesoproterozoic. We find further evidence that the Mesoproterozoic was characterized by an oceanic nitrate minimum, and that this nitrate scarcity could have prevented the radiation of early eukaryotes until the end of the Proterozoic. Chapter 5 – Nitrogen cycling across the Hirnantian glaciation and end Ordovician mass extinction event. We find that oceans during this period were characterized by widespread ocean anoxia that led to a scarcity in nitrate much like in the Mesoproterozoic. Nitrate scarcity was temporarily alleviated in near-shore settings during glaciation. Much like in the Pacific Ocean during the Last Glacial Maximum, the carbonate compensation depth at multiple sites seems to have deepened substantially during peak Hirnantian glaciation. These results highlight the relationship between ecology, evolution, nitrogen speciation/abundance, and surface oxygen. TABLE OF CONTENTS List of Figures ................................................................................................................................ vi List of Tables ............................................................................................................................... xiii Chapter 1: Introduction ........................................................................................................... 17 Chapter 2: Nitrogen isotope evidence for anoxic deep marine environments from the Mesoarchean Mosquito Creek Formation, Australia .................................................................... 22 2.1 Abstract ..................................................................................................................... 22 2.2 Introduction ............................................................................................................... 22 2.3 Geologic Setting........................................................................................................ 23 2.4 Methods..................................................................................................................... 28 2.5 Results ....................................................................................................................... 30 2.6 Discussion ................................................................................................................. 32 2.6.1 Isotopic fidelity ......................................................................................................... 32 2.6.2 Redox and paleoecology ........................................................................................... 34 2.6.3 Marine or non-marine? ............................................................................................. 36 2.6.4 Implications for microbial evolution ........................................................................ 40 2.7 Acknowledgements ................................................................................................... 40 Chapter 3: Transient surface ocean oxygenation recorded in the ~2.66 Ga Jeerinah Formation, Australia ..................................................................................................................... 41 3.1 Abstract ..................................................................................................................... 41 3.2 Introduction ............................................................................................................... 42 i 3.3 Geologic Setting........................................................................................................ 44 3.4 Results ....................................................................................................................... 45 3.4.1 AIDP-2 ...................................................................................................................... 48 3.4.2 AIDP-3 ...................................................................................................................... 48 3.5 Discussion ................................................................................................................. 51 3.5.1 Proxy Alteration ........................................................................................................ 51 3.5.2 Interpretation of nitrogen isotopic data ..................................................................... 53 3.5.3 Interpretation of selenium concentrations and isotopic ratios .................................. 54 3.5.4 Transient surface ocean oxygenation in the Neoarchean: mode and tempo ............. 55 3.6 Conclusion ................................................................................................................ 57 3.7 Methods..................................................................................................................... 58 3.8 Acknowledgements ................................................................................................... 58 Chapter 4: Spatial and temporal trends in Precambrian nitrogen cycling: a Mesoproterozoic offshore nitrate minimum ............................................................................................................. 60 4.1 Abstract ..................................................................................................................... 60 4.2 Introduction ............................................................................................................... 61 4.3 Precambrian nitrogen cycling ................................................................................... 64 4.4 Location and geologic setting ................................................................................... 68 4.4.1 Bangemall Supergroup.............................................................................................. 68 4.4.2 Roper Group.............................................................................................................. 71 4.5 Analytical methods ................................................................................................... 73 4.5.1 Sample preparation for bulk rock analyses ............................................................... 73 4.5.2 Kerogen extraction for organic nitrogen ................................................................... 73 ii 4.5.3 Isotopic analyses ....................................................................................................... 74 4.6 Results ....................................................................................................................... 75 4.6.1 Bangemall basin ........................................................................................................ 75 4.6.2 Roper basin ............................................................................................................... 76 4.7 Discussion ................................................................................................................. 77 4.7.1 Diagenesis and metamorphism ................................................................................. 77 15 4.7.1.1 Oxic diagenesis: effects on preserved δ Nbulk ...................................................... 77 15 4.7.1.2 Anoxic diagenesis: effects on preserved δ Nbulk .................................................. 81 4.7.1.3 Diagenetic effects on the δ 13 C of organic matter .................................................. 82 4.7.1.4 Metamorphism ...................................................................................................... 83 4.7.2 Carbon cycling in the Bangemall and Roper Basins ................................................ 85 4.7.3