2014 Annual Science Report

Astrobiology Roadmap Objective 7.2 Reports Reporting  |  SEP 2013 – DEC 2014

Project Reports

  • Biogenic Gases From Anoxygenic Photosynthesis in Microbial Mats

    This lab and field project aims to measure biogenic gas fluxes in engineered and natural microbial mats composed of anoxygenic phototrophs and anaerobic chemotrophs, such as may have existed on the early Earth prior to the advent of oxygenic photosynthesis. The goal is to characterize the biogeochemical cycling of S, H, and C in an effort to constrain the sources and sinks of gaseous biosignatures that may be relevant to the detection of life in anoxic biospheres on habitable exoplanets.

    ROADMAP OBJECTIVES: 4.1 5.2 5.3 6.1 6.2 7.2
  • Life Underground

    Our multi-disciplinary team from USC, Caltech, JPL, DRI, RPI, and now also Northwestern is developing and employing field, laboratory, and modeling approaches aimed at detecting and characterizing microbial life in the subsurface—the intraterrestrials. We posit that if life exists, or ever existed, on Mars or other planetary body in our solar system, evidence thereof would most likely be found in the subsurface. This study takes advantage of unique opportunities to explore the subsurface ecosystems on Earth through boreholes, mine shafts, sediment coring, marine vents and seeps, and deeply-sourced springs. Access to the subsurface—both continental and marine—and broad characterization of the rocks, fluids, and microbial inhabitants is central to this study. Our focused research themes require subsurface samples for laboratory and in situ experiments. Specifically, we are carrying out in situ life detection, culturing and isolation of heretofore unknown intraterrestrial archaea and bacteria using numerous novel and traditional techniques, and incorporating new and existing data into regional and global metabolic energy models.

    ROADMAP OBJECTIVES: 2.1 2.2 3.1 3.3 4.1 5.1 5.2 5.3 6.1 6.2 7.2
  • Biosignatures in Ancient Rocks – Kasting Group

    We have been working on two things: 1) the question of whether there are plausible “false positives” for life on extrasolar planets, i.e., high abiotic O2 and/or O3 levels that might be confused with evidence for photosynthesis, and 2) hydrodynamic escape of hydrogen from H2- or H2O-rich primitive atmospheres. We are developing a two-component model to describe this process. Old single-component models evidently do not obey the diffusion limit, so are are trying to remedy that.

    ROADMAP OBJECTIVES: 1.1 2.1 4.1 7.2
  • Project 3: The Origin of Homochirality

    A universal aspect of living systems on Earth is their homochirality: Life uses dextrorotary sugars and levorotary amino acids. The reasons for this are hotly debated and not close to being settled. However, the leading idea is that autocatalytic reactions grew exponentially fast at the origin of life, and whatever chiral symmetry breaking was accidentally present became amplified subsequently. We are calculating the way in which this can take place using statistical mechanics, and also trying to see how a uniform homochirality could be stable to spatial fluctuations.

    ROADMAP OBJECTIVES: 3.2 3.4 4.1 4.2 5.1 5.2 7.1 7.2
  • Coupled Energy Balance Ecosystem-Atmosphere Modeling of Thermodynamically-Constrained Biogenic Gas Fluxes Project

    The thermodynamically-constrained fluxes of gases to and from a biosphere has profound, planet-wide consequences. These fluxes can directly control the redox state of the surface environment, the atmospheric composition, and the concentration of nutrients and metals in the oceans. Through these direct effects, they also create strong forcings on the climate, the redox state of the interior of the planet, and the detectability of the biosphere by remote observations. This is a theoretical modeling study to constrain biomass, productivity, and biogenic gas fluxes given a range of geologic parameters.

    ROADMAP OBJECTIVES: 1.1 1.2 5.2 5.3 6.1 7.2
  • Biosignatures in Extraterrestrial Settings

    The Biosignatures in Extraterrestrial Environments group works on finding and characterizing exoplanets, in particular through very high resolution spectroscopy; and developing new techniques for finding exoplanets and characterizing their properties. It also works on understanding the evolution and dynamics of planetary systems, including the solar system, and the role of astrophysical processes in establishing and sustaining life in extraterrestrial environments.

    ROADMAP OBJECTIVES: 1.1 1.2 2.1 2.2 3.1 4.1 4.3 6.2 7.1 7.2
  • Earth as an Extrasolar Planet

    Earth will always be our best example of a habitable world. By studying Earth as a single point of light, which harkens back to the famous Pale Blue Dot image of our planet, we can develop ideas and techniques for characterizing other potentially habitable planets around distant stars. These techniques focus on remotely measuring or detecting fundamental planetary and atmospheric properties—-composition, total atmospheric mass, temperature, and the presence of a surface ocean.

    ROADMAP OBJECTIVES: 1.2 7.2
  • Astrophysical Controls – Task 7 – Update Catalog of Elemental Ratios in Nearby Stars

    Abundances of both common and trace elements can have substantial effects on the habitability of stellar systems. Elemental ratios can change the stellar evolution and mineralogy, geophysics, and surface processed of planets. We study the abundances of large samples of nearby stars and individual systems and the extent of their variation. We examine ratios of elements that have substantial effects of the mineralogy and interiors of planets. The relative abundances of common elements vary substantially among nearby stars. Extremely non-solar abundance ratios at the level that can produce substantial changes in planetary and stellar properties are present in interesting numbers.

    ROADMAP OBJECTIVES: 1.1 7.2
  • Biosignatures of Ancient Rocks – Hedges Group

    Our work involves the design, assembly, and release to the public of a tree of life calibrated to geologic time (timetree). It is needed by astrobiologists to help determine the source of biomarkers for the presence of life in the geologic record.

    ROADMAP OBJECTIVES: 3.3 3.4 4.1 4.2 7.1 7.2
  • Exoplanet Detection and Characterization: Observations, Techniques and Retrieval

    In this task, VPL team members use observations and theory to better understand how to detect and characterize extrasolar planets. Techniques to improve the detection of extrasolar planets, and in particular smaller, potentially Earth-like planets are developed, along with techniques to probe the physical and chemical properties of exoplanet atmospheres. These latter techniques require analysis of spectra to best understand how it might be possible to identify whether an extrasolar planet is able to support life, or already has life on it.

    ROADMAP OBJECTIVES: 1.2 2.2 7.2
  • Evolution of Protoplanetary Disks and Preparations for Future Observations of Habitable Worlds

    The evolution of protoplanetary disks tells the story of the birth of planets and the formation of habitable environments. Microscopic interstellar materials are built up into larger and larger bodies, eventually forming planetesimals that are the building blocks of terrestrial planets and their atmospheres. With the advent of ALMA, we are poised to break open the study of young exoplanetesimals, probing their organic content with detailed observations comparable to those obtained for Solar System bodies. Furthermore, studies of planetesimal debris around nearby mature stars are paving the way for future NASA missions to directly observe potentially habitable exoplanets.

    ROADMAP OBJECTIVES: 1.1 1.2 3.1 4.3 7.2
  • Project 6. Mining Archaeal Genomes for Signatures of Early Life: Comparison of Metabolic Genes in Methanogens

    Methanogenic archaea derive energy from simple starting materials, producing methane and carbon dioxide in the process. The chemical simplicity of the growth substrates and versatility of the organisms in extreme environments provide for a possibility that they could exist on other planets. By characterizing the evolution of methanogens from the most simple to most complex organism as well as their growth characteristics under controlled environments, we hope to address the question as to whether they could exist on planets such as Mars, where bursts of methane have been seen, yet no source has yet been identified.

    ROADMAP OBJECTIVES: 1.1 2.1 3.1 3.2 3.3 3.4 4.1 4.2 5.1 5.2 5.3 6.1 6.2 7.1 7.2
  • Exploring the Structure and Composition of Massive Exoplanets

    We have analyzed exoplanet transit and eclipse measurements with the Hubble Space Telescope (HST) and the Spitzer Space Telescope for a number of highly irradiated, Jupiter-mass planets, with a focus on confirming which planets exhibit water absorption or emission in transit and/or eclipse and measuring the characteristic brightness temperature at these wavelengths. Measurements of molecular absorption in the atmospheres of these planets offer the chance to explore several outstanding questions regarding the atmospheric structure and composition of hot Jupiters, including the possibility of bulk compositional variations between planets and the presence or absence of a stratospheric temperature inversion. We are also developing simulations of future observations with the James Webb Space Telescope, and we are in the process of designing a future balloon-borne telescope to conduct a large survey of hot exoplanet atmospheres.

    ROADMAP OBJECTIVES: 1.1 1.2 7.2
  • Biosignatures of Life in Ancient Stratified Ocean Analogs

    Instigated by Macalady and Kump in 2010, this project investigates biosignatures of life in modern analogs for stratified ancient and/or extraterrestrial oceans. The primary field site is a sinkhole in Florida. Other field site include stratified ocean analogs in the Bahamas, New York State, and the Dominican Republic. A website monitoring the activities of an informal working group on Early Earth Photosynthesis is maintained by Macalady (http://www.geosc.psu.edu/~jlm80/EEP.html).

    ROADMAP OBJECTIVES: 2.1 3.3 3.4 4.1 5.2 5.3 6.1 7.1 7.2
  • Project 1F: Chemolithotrophic Microbial Communities in Subglacial Sediments

    Recent interpretation of Yellowknife Bay, Gale Crater, Mars as an ancient lake basin characterized by low salinity, circumneutral pH, and Fe and S compounds in a range of redox states (1) motivates inquiry into the capability of analogous Earth systems to support microbiomes founded on Fe and S chemolithoautotrophy. The research progress outlined herein was conducted to improve understanding of the microbial metabolisms that promote Fe and S redox transformation in an analogous system – the subglacial environment Robertson Glacier (RG), Peter Loughleed Provincial Park, Alberta, Canada. We seek to better understand the mechanisms by which chemolithoautotrophs access mineral-bound electron donors and acceptors and the potential for biosignature preservation associated with this type of life. Geochemical attributes of the RG subglacial environment that are consistent with the former aqueous habitat at Yellowknife Bay include circumneutral pH, low salinity, and sulfur (S) and iron (Fe) existing in a range of oxidation states. Further, the structure, composition, and function of the endogenous subglacial microbiome at RG is largely shaped by redox transformation of pyrite (FeS2) and chemolithoautotrophic growth on released Fe and/or S intermediates. To achieve these goals we have assembled a collaborative, multidisciplinary team with expertise in molecular biology, microbial physiology, geochemistry, and thermodynamics.

    ROADMAP OBJECTIVES: 4.2 5.3 7.2
  • Project 2A: The Catalysis Effect of Extracellular Polymeric Substances Excreted by Fermentative Bacteria on Ca-Mg Carbonate Precipitation

    Experiments show that purified non-metabolizing biomass from pure cultures of both anaerobic fermenting and sulfate-reducing bacteria closely related to those organisms present in the consortium could also catalyze the precipitation of disordered dolomite. Polysaccharides that are the dominant components in the EPS act as catalysts for weakening surface water and Mg (II) boning and enhancing dolomite crystallization. Our study contributes to the understanding of the “dolomite problem” by revealing (1) the catalytic effect of bound EPS on Ca-Mg carbonate crystallization and (2) the possible involvement of anaerobic fermenting bacteria in sedimentary dolomite formation, which has not been reported previously.

    ROADMAP OBJECTIVES: 7.1 7.2
  • Titan as a Prebiotic Chemical System – Benner

    In 2007, NASA sponsored a committed of the National Academies of Science to explore whether life might exist in environments outside of the traditional habitable zone, defined as positions in a solar system where liquid surface water might be found. Alternative solvents which have analogous “habitable zones” farther away from their star include hydrocarbons, ammonia, and dinitrogen. The core question asked whether life having genetic biopolymers might exist in these solvents, which are in many cases (including methane) characterized by the need for “cold” (temperatures < 100K in the case of methane).

    These “weird” solvents would require “weird” genetic molecules, “weird” metabolic processes, and “weird” bio-structures. In pursuit of this “big picture” question, we turned to Titan, which has exotic solvents both on its surface (methane-hydrocarbon) and sub-surface (perhaps super-cooled ammonia-rich water). This work sought genetic molecules that might support Darwinian evolution in both environments, including non-ionic polyether molecules in the first and biopolymers linked by exotic oxyanions (such as phosphite, arsenate, arsenite, germanate) in the second.

    In the current year, we completed our studies that identified biopolymers that might work in hydrocarbon solvents. These studies have essentially ruled out biological processes in true cryosolvents. However, a series of hydrocarbons containing different numbers of carbon atoms (one, two, three, and four, for example, in methane, ethane, propane, and butane) cease to be cryosolvents as their chain lengths increase. These might be found on “warm Titans”. Further, they might exist deep in Titan’s hydrocarbon oceans, where heating from below would lead to warm hydrocarbon oceans.

    These studies showed that polyethers are insufficiently soluble in hydrocarbons at very low temperatures, such as the 90-100 K found on Titan’s surface where methane is a liquid at ambient pressures. However, we did show that “warm Titans” could exploit propane (and, of course, higher hydrocarbons) as a biosolvent for certain of these “weird” alternative genetic biopolymers; propane has a huge liquid range (far larger than water). Further, we integrated this work with mineralogy-based work that allows reduced molecules to appear as precursors for less “weird” genetic biomolecules, especially through interaction with various mineral species, including borates, molybdates, and sulfates.

    ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 3.2 3.4 4.1 5.3 6.2 7.1 7.2
  • Developing New Biosignatures

    This project works to develop new biosignatures based on element, molecules, or isotopes. For example, we are working with the method secondary ion mass spectrometry (SIMS) to analyze microorganisms or microfossils. We are also looking at the Isolation and analysis of F430, archaeol, and IPL-archaeol from the Cascadia Margin. We are also interested in DNA as a biosignature. For that work, we are extracting DNA from deep sea sediment and other difficult environments. Finally, we are also investigating prebiotic molecules in order to known which carbon-containing biomolecules can not be reasonable biosignatures.

    ROADMAP OBJECTIVES: 3.1 7.1 7.2
  • Project 2C: Developing the 13C-18O Clumped Isotope Thermometer

    One of the critical parameters in understanding the evolution of the Earth is the temperature of the oceans. Proposals, for example, that early life was hyperthermophilic would be supported if there was evidence for a “hot early ocean”, which some stable isotope data support. However, arguments against a “hot early ocean” include lower solar luminosity early in Earth history, and evidence for widespread glaciations. A new geothermometer is based on the enhanced thermodynamic stability of “clumped isotopes” (e.g., 13C-18O bonds) in carbonate minerals, which exhibits a temperature dependence. However, attempts to calibrate this temperature dependence have identified kinetic isotope effects that can give apparently anomalous results. In this project, experiments were designed to systematically probe formation rate effects on 13C-18O bonding during calcite mineral lattice assembly from aqueous solutions. Preliminary results do not show a correlation between precipitation rate and 13C-18O bonding over the range investigated but do provide evidence that is being used to deconvolute and identify physiochemical conditions and processes that lead to disequilibrium in 13C-18O bonding during carbonate mineral formation.

    ROADMAP OBJECTIVES: 4.1 6.1 7.1 7.2
  • Solar System Analogs for Exoplanet Observations

    The worlds of our Solar System represent only a fraction of the planetary diversity that likely exists in our Universe. Nevertheless, by studying and characterizing Solar System worlds, we can develop general models that can be applied and tested on exoplanets. Furthermore, by observing planets in the Solar System and studying these data within the context of exoplanet observations, we can provide new context and understanding to exoplanet data. Work in this area this past year includes observations of Titan as seen by Cassini, as an analog for exoplanet observations of hazy worlds; mapping observations of Venus below its cloud deck as an analog for processes and observations of hazy worlds; and the study of multiple atmospheres in the Solar System to understand the basic processes that control their atmospheric temperature structure.

    ROADMAP OBJECTIVES: 1.2 7.2
  • Laboratory Investigations Into Chemical Evolution in Icy Solids From the Interstellar Medium to the Outer Solar System to Meteorites

    NAI-GCA support in 2014 helped us continue our work on amino-acid stability. In 2014, we performed radiation experiments to measure the destruction rate of glycine in CO2 ice. In particular, we found that this rate depends on concentration and temperature, and is 20-40 times greater than for glycine in H2O-ice.

    ROADMAP OBJECTIVES: 2.1 2.2 3.1 7.1 7.2
  • Project 2D: Magnesium Isotopes in Carbonates as a Tracer of Marine Conditions in the Early Earth

    Massive dolomitization events affect seawater Mg concentration and have a profound influence on the carbonate cycle in seawater that ultimately controls seawater chemistry and atmospheric carbon dioxide levels. The Mg isotope fractionation factor between dolomite and aqueous Mg has been experimentally constrained at 130, 160, and 220 degrees C to derive a temperature-dependent fractionation factor. This Mg isotope fractionation function has been determined to allow evaluation of the Mg isotope composition of fluids that have produced dolomite. Based on these new data it is now possible to infer secular changes in seawater Mg isotope compositions based on the analysis of sedimentary dolomites. This information can be used to infer changes in the intensity of dolomitization which removes Mg from seawater and tectonism which controls mid ocean ridge hydrothermal circulation that largely removes Mg from seawater as well as impacts weathering.

    ROADMAP OBJECTIVES: 4.1 7.1 7.2
  • Stoichiometry of Life, Task 2a: Field Studies – Yellowstone National Park

    Yellowstone National Park harbors an array of hydrothermal ecosystems with widely varying geochemical characteristics and microbial communities. Our research aimed to understand how the geochemistry of these hot springs shapes their constituent microbial communities including their composition and function. To accomplish this aim, we measured (1) physical and geochemical properties of hot spring fluids and sediments, (2) the rates of biogeochemical processes (i.e., methane oxidation, nitrogen fixation, microbial Fe cycling, photosynthesis, de-nitrification, etc.), and (3) markers for microbial community diversity (i.e., SSU rRNA, metabolic genes, lipids, proteins).

    ROADMAP OBJECTIVES: 5.1 5.2 5.3 6.1 6.2 7.2
  • The Long Wavelength Limit of Oxygenic Photosynthesis

    Oxygenic photosynthesis (OP) produces the strongest biosignatures at the planetary scale on Earth: atmospheric oxygen and the spectral reflectance of vegetation. Both are controlled by the properties of chlorophyll a (Chl a), its ability to perform the water-splitting to produce oxygen, and its spectral absorbance that is limited to red and shorter wavelength photons. We seek to answer what is the long wavelength limit at which OP might remain viable, and how. This would clarify whether and how to look for OP adapted to the light from stars redder than our Sun.

    Previously under this project, with other co-investigators we spectrally quantified the thermodynamic efficiency of photon energy use in the chlorophyll d utilizing cyanobacterium, Acaryochloris marina str. MBIC11017, determining that it is more efficient than a Chl a cyanobacterium. The current focus of the project is aimed at understanding the adaptations of far-red/near-infrared (NIR) oxygenic photosynthetic organisms in general: what is their ecological niche where they are competitive against chlorophyll a organisms in nature, and what energetic shifts have been made in their photosynthetic reactions centers to enable their use of far-red/NIR photons. Field sampling and measurements are being conducted to isolate new strains of far-red utilizing oxygenic photosynthetic organisms, to quantify the spectral and temporal light regime in which they and previously discovered strains live in nature, and use these light measurements to drive kinetic models of photon energy use to ascertain light thresholds of survival.

    ROADMAP OBJECTIVES: 3.2 4.2 5.1 5.3 6.2 7.2
  • Review and Synthesis

    We reviewed aspects of biomarker formation and preservation. In one work, Briggs and Summons (2014), completed a review on Ancient biomolecules: their origin, fossilization and significance in revealing the history of life that was commissioned by the editor of Bioessays. The review was aimed at a general audience and outlined ways in which molecular biosignatures, ranging from the most unstable (DNA) to the most recalcitrant (lipids), could be informative about the evolution of life.

    A second review (Summons, 2014) was prepared for a paleontology short course and dealt with how molecules could be informative about life and the environments in which it lived. This review also touched on the production of highly oxidizing substances through radical chemistry operating in the Martian atmosphere has resulted in environmental conditions that promote the destruction of organic matter.

    ROADMAP OBJECTIVES: 7.2
  • Project 2G: Iron Isotope Fractionations Among Oxide Minerals Under Acidic Conditions

    The study of Fe isotope exchange and fractionation between aqueous Fe(II) and goethite was motivated by the inferred acidic environment for early Mars, where iron oxides (i.e. jarosite, goethite) were likely present. We found that the extent of atom exchange positively correlates with increasing pH during interactions between Fe(II)aq and goethite. The decrease in extent of exchange correlates with a decrease in the amount of sorbed Fe(II) to the goethite surface, which strongly suggests that sorbed Fe(II) is the primary catalyst for inducing Fe isotope exchange. The slow rate of isotopic exchange at acidic pH suggests that stable Fe isotope compositions may be resistant to change in acidic aqueous environments, thus leading to preservation of signatures that might contribute to the understanding of ancient Mars paleoenvironments.

    ROADMAP OBJECTIVES: 2.1 5.3 7.1 7.2
  • Project 3B: Genesis of High-δ18O Archean Chert, Pilbara Craton, Australia

    This investigation centers on the 3.43 – 3.35 Ga Strelley Pool Formation in the Pilbara craton of western Australia, which harbors some of the oldest convincing evidence for life. The research has three major components – 1) detection and characterization of habitable Paleoarchean environments to apply to the search for life-bearing extraterrestrial environments; 2) creating an isotopic guide to the sedimentary environments and relative timing and origin of these formation’s textures; 3) constrain paleoenvironmental evidence for the putative stromatolitic microfossils in the region. We are comparing conventional bulk analytical techniques vs. SIMS in-situ microanalysis to unravel the δ18O and δ13C isotopic and geochemical variation of the micro-textural, and generational quartz, dolomite, ankerite, and calcite varieties in these stromatolitic rocks. Understanding paleoenvironments supporting ancient biospheres aids in the understanding of the necessary conditions for life’s persistence, providing further basis for locating and identifying extraterrestrial life.

    ROADMAP OBJECTIVES: 4.1 7.2
  • Project 3C: The Role of Early Continental Weathering in Providing a Habitable Planet

    Recent studies of biogeochemical cycles recorded in Archean sedimentary rocks suggest an early diverse microbial ecology that may have required extensive continentally-sourced nutrients (i.e., phosphorus) early in Earth history. Widespread continental weathering is at odds, however, with studies that suggest a majority of continental crust was submerged and seawater chemistry was largely controlled by oceanic hydrothermal fluids. Here, we present new Sr and O isotope results from stratiform barite deposits from the 3.23 Ga Fig Tree Group, South Africa. The Sr and O isotope data indicate the barite was formed from a mixture of hydrothermal fluids and seawater, and that seawater was more radiogenic then previously predicted. The only appreciable source of radiogenic Sr is from continental weathering, and thus we propose that continental weathering was more extensive throughout the Archean than previously thought. This in turn has important implications for the availability of continentally-sourced nutrients to early marine environments on Earth.

    ROADMAP OBJECTIVES: 1.1 4.1 6.1 7.1 7.2
  • Task 4: Biogeochemical Impacts on Planetary Atmospheres

    Oxygenation of Earth’s early atmosphere must have involved an efficient mode of carbon burial. In the modern ocean, carbon export of primary production is dominated by fecal pellets and aggregates produced by the animal grazer community. But during most of Earth’s history the oceans were dominated by unicellular, bacteria-like organisms (prokaryotes) causing a substantially altered biogeochemistry. In this task we experiment with the marine cyanobacterium Synechococcus sp. as a model organism and test its aggregation and sinking speed as a function of nutrient (nitrogen, phosphorus, iron) limitation. We have found that these minute cyanobacteria form aggregates in conditions that mimic the open ocean and can sink gravitationally in the water column. Experiments with added clay minerals (bentonite and kaolinite) that might have been present in the Proterozoic ocean, show that these can accelerate aggregate sinking. In addition we find that Synechococcus could potentially export carbon 2–3 times of that contained in their cells via aggregation, likely due to the scavenging of transparent exopolymer particles and dissolved organic matter. Thus, aggregation and sinking by these small cyanobacteria could have constituted an important mode of carbon export in the Proterozoic ocean.

    ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1 7.2
  • Project 3D: A Microbial Iron Shuttle in Early Earth Marine Basins

    Iron-based metabolisms are deeply rooted in the tree of life, and yet comparatively little attention has been paid to searching for Fe-based biosignatures as compared, for example, photosynthetically-based metabolisms. Dissimilatory Iron Reduction (DIR) is found in both Archaea and Bacteria domains of life, its electron acceptors and donors are widespread in the solar system. This project focuses on determining the basin-scale footprint of DIR in well preserved samples of Mesoarchean age (~3 Ga) in the Witwatersrand Supergroup of South Africa. Preliminary results show a trend of iron enrichment that correlates with δ56Fe depletion from the proximal shelf to the deep distal basin, which is interpreted to indicate a DIR-driven “iron pump” or “shuttle”, where microbially-produced aqueous Fe(II) on continental shelves was pumped to the deep basin and trapped as Fe-bearing sulfides or oxides. These results not only confirm that Fe-based metabolisms were important on the early Earth ~3 b.y. ago, but that it had a substantial “footprint” in the biosphere on a basin-wide scale.

    ROADMAP OBJECTIVES: 4.1 5.2 6.1 7.1 7.2
  • Project 3F — Apatitic Latest Precambrian and Early Cambrian Fossils Provide Direct Evidence of Concentrations of Environmental Oxygen

    Means are not currently available to asses either quantitatively or semi-quantitatively the concentration of oxygen in Earth’s atmosphere over geological time. Despite this, the environmental availability of O2 has been repeatedly postulated to be a cause of major changes in Earth’s biota, most particularly at the Precambrian-Cambrian boundary-defining “Cambrian Explosion of Life,” a time in Earth history when large deposits of phosphate-rich apatite were deposited in shallow basins worldwide. This study shows that substitution of Sm+3 in the Ca I and Ca II sites of fossil-permineralizing, -infilling, and -encrusting apatite can differentiate between oxic, dysoxic, an anoxic settings of apatite formation. Further studies are to be undertaken to establish such REE-substitution as a quantitative O2 paleobarometer.

    ROADMAP OBJECTIVES: 4.1 4.2 6.1 6.2 7.2
  • Project 4B: New SIMS Procedures for in Situ Analysis of Mass-Independent Fractionation of S Isotopes

    An in situ sulfur four-isotope analysis technique with multiple Faraday cup detectors by ion microprobe was developed and applied to detrital pyrite grains in ~2.4 Ga glaciogenic sandstone from the Meteorite Bore Member of the Turee Creek Group, Western Australia.

    ROADMAP OBJECTIVES: 4.1 7.1 7.2