2015 Annual Science Report

Astrobiology Roadmap Objective 5.2 Reports Reporting  |  JAN 2015 – DEC 2015

Project Reports

  • Jon Toner NAI NPP Postdoc Report

    Aqueous salt solutions are critical for understanding the potential for liquid water to form on icy worlds and the presence of liquid water in the past. Salty solutions can form potentially habitable environments by depressing the freezing point of water down to temperatures typical of Mars’ surface or the interiors of Europa or Enceladus. We are investigating such low-temperature aqueous environments by experimentally measuring the low temperature properties of salt solutions and developing thermodynamic models to predict salt precipitation sequences during either freezing or evaporation. These models, and the experimental data we are generating, are being applied to understand the conditions under which water can form, the properties of that water, and what crystalline salts indicate about environmental conditions such as pH, temperature, pressure, and salinity.

    ROADMAP OBJECTIVES: 2.1 5.2 5.3
  • Life Underground

    Our multi-disciplinary team from the University of Southern California, California Institute of Technology, Jet Propulsion Lab, Desert Research Institute, Rensselaer Polytechnic Institute, and Northwestern University 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 3.2 3.3 4.1 5.1 5.2 5.3 6.1 6.2 7.2
  • Understanding Past Environments on Earth and Mars

    In this task we performed research to understand the evolution of habitable environments on Earth and Mars, both of which serve as potential analogs for habitable environments on extrasolar planets. We are expanding this line of work from past reports to span the entire histories of both planets. On Earth, we have sought to understand environments and time periods spanning the origins of life to the effects of human-generated greenhouse gas emissions on modern-day climate cycles. On Mars, we focus on the ancient conditions that could have allowed liquid water to be stable at the surface; on modern Mars, we focus on the debate on the presence, amount, and variability of methane in the Martian atmosphere.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1 4.2 5.1 5.2 6.1
  • Project 2: Function by Reduction: Do Extant Symbiont Enzymes Recapitulate Ancient Metabolic Generalists

    The origins of mitochondria and chloroplasts are two of the great unsolved mysteries in biology. It is now clear that these organelles used to be bacteria, but the evolutionary paths taken as they transitioned from bacteria to organelle are not well understood because they happened more than 1.5 billion years ago. Some insect endosymbionts have symbioses with bacteria which resemble organelles in many ways. We use these more recent symbioses as models to better understand the origins of organelles, one of the most critical events in the evolution of complex life.

    ROADMAP OBJECTIVES: 4.2 5.2 6.2
  • Field Activities at the Coast Range Ophiolite Microbial Observatory (CROMO)

    CROMO provides ongoing excellent exposure to samples of ophiolite-hosted serpentinites and associated rocks, access to monitoring wells important for observing serpentinization-related groundwater flow regimes, and serves as a community-building platform that fosters new scientific collaboration. CROMO has served as a test-bed for refining new experimental approaches, and progressing from basic observations to more complex, multi-disciplinary science.

    Within the past year, studies at CROMO have focused on the subsurface hydrogeochemical dynamics, by monitoring groundwater hydrology, measuring the concentrations and composition dissolved iron, sulfur, dissolved inorganic carbon, major inorganic anions and cations, dissolved hydrogen, carbon monoxide and methane gases, and organic compounds, in addition to time-series analyses.

    CROMO datasets are being incorporated into an exploratory database project aimed at addressing NASA’s public data requirements. Once developed, this database will help to address data sharing plans for collaborators and serve as a valuable tool for CROMO data management across collaborating labs.

    In 2015, project members Dawn Cardace, Masako Tominaga, Michael Kubo, Lauren Seyler, Mary Sabuda, Abigail Johnson, Ken Wilkinson, & Cameron Hearne participated in a field trip to CROMO from August 21-27, to continue seasonal bio/geo/chemical monitoring of the wells, as well as assessing the site for future geophysical measurements.

    ROADMAP OBJECTIVES: 5.1 5.2 5.3 6.1 6.2 7.1 7.2
  • Astronomical Biosignatures, False Positives for Life, and Implications for Future Space Telescopes

    In this task, we identify novel biosignatures and also identify “false positives” for life, which are ways for non-biological processes to mimic proposed biosignatures. Of primary concern are false positives that could mimic easier to detect biosignatures like O2, which we plan to search for with future space-based telescopes. This is a growing area of research that VPL’s past work has motivated, leading to multiple research teams across the planet following our example. Our work continues to be at the forefront of this area of work, as we have identified new non-biological mechanisms for mimicking signs of life. Further, we explained the ways in which these non-biological mechanisms could be identified, and “true positives” from biology confirmed with secondary measurements. Finally, we communicated these lessons to various teams that are studying concepts for future missions that would search for these signs of life. This connection to missions will ensure that our research is incorporated into those missions, so that they will not be “tricked” by these false positives.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1 4.3 5.2 5.3 7.2
  • Insights Into Geochemical and Biological Processes in Serpentinizing Systems From Hyperalkaline Seeps in Oman

    Rock-powered life makes its living from reactions between rocks and water as part of the overall processes of rock weathering. There can be energy available because rocks from deep in the Earth are moved by tectonic forces into regions populated by microbes faster than chemical weathering processes alone can act. Under the right conditions, energy left behind can be consumed by microbial communities, and resulting biogeochemical reactions expedite overall weathering processes. In many cases, these energy sources and the communities they support are independent of sunlight. Instead, their energy and nutrient requirements are met by a combination of slow tectonic and rapid fluid mixing processes. One particularly dramatic example of how the combination of these processes support microbial communities is found in an area of Oman called the Samail ophiolite. Owing to unusual geologic proceses, tectonic forces moved rocks normally in the Earth’s mantle to the surface of the continent on the Arabian peninsula about 65 million years ago. Ever since, the introduction of mantle rocks into the surface hydrosphere has been a source of energy tapped by microbes. At present, in the arid climate of Oman, small amounts of annual precipitation infiltrate these rocks, react, and reappear at springs. Owing to the unusual rock compositions, these springs have remarkably unusual compositions. Not only does the pH go to extremely basic values, nearly reaching 12, but the solutions are so reduced that they can bubble with escaping hydrogen and methane. Although these springs are not hot, they can look like they are boiling in places with lots of escaping gas.

    ROADMAP OBJECTIVES: 5.2 5.3 6.1
  • Project 5: Adaptation, Mutation Supply, and Evolution of Synergy in Biofilm Communities

    We will quantify the dynamics of adaptation and identify the mutational causes in evolving biofilms with high precision, and therefore illustrate how microbes colonizing a new surface can transform their environment and set the stage for primitive multicellularity. Biofilms resemble tissues in their subdivided labor, varied physical structure and shared metabolism. We predict that the stability of this ecological cooperation rests on population-genetic controls on selfish lineages associated with mutators, much as tissues are liable to selfish invasion by cancers.

    ROADMAP OBJECTIVES: 4.2 5.1 5.2 6.1 6.2
  • RPL and Expedition 357: Serpentinization and Life at the Atlantis Massif

    Circulating hydrothermal fluids associated with mid-ocean ridges represent some of the most prominent examples of the intersection between chemical energy and the biosphere. The Lost City Hydrothermal Field, which sits atop the Atlantis Massif near the Mid Atlantic Ridge hosts a microbial ecosystem which feeds off the products of serpentinization. IODP Expedition 357, which sailed in Fall 2015, obtained rock cores and fluids from the Atlantis Massif, which are being used for the coordinated investigation of serpentinization processes and life. Lost City is known to sustain abiogenic organosynthesis reactions and as such has been suggested to be an analogue to prebiotic early Earth environments and potential extraterrestrial habitats.

    ROADMAP OBJECTIVES: 3.1 3.4 5.1 5.2 5.3 7.2
  • Planetary Surface and Interior Models and SuperEarths

    We use computational and theoretical models to simulate the evolution of the interior and the surface of real and hypothetical planets around other stars. Our goal is to determine the characteristics that are most likely to contribute to making a planet habitable in the long run. Observations in our own Solar System show us that water and other essential materials are continuously consumed via weathering (and other processes: e.g., subduction, sediment burial) and must be replenished from the planet’s interior via volcanic activity to maintain a biosphere. The surface models we are developing will be used to predict how gases and other materials will be trapped through weathering and biological processes over time. Our interior models are designed to predict tidal effects, heat flow, and how much and what sort of materials will come to a planet’s surface through resurfacing and volcanic activity throughout its history.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1 5.2 6.1
  • High Temperature W/R Hosted Microbial Ecosystems in Yellowstone

    Geochemical data indicate that life on early Earth was dependent on chemical forms of energy. This attribute, when coupled with phylogenetic data indicating that early evolving forms of life were thermophilic, lead many astrobiologists to believe that life evolved in a high temperature environment and was dependent on chemical forms of energy to sustain its metabolism.

    Hydrothermal environments with temperatures >70ᵒC exclude life dependent on light energy, leaving only those life forms that can sustain themselves using chemical energy. The >14,000 hot springs in Yellowstone National Park therefore provide a unique field-based early Earth analog environment to examine the processes that sustain life dependent on chemical energy and to investigate the metabolic processes that sustain this life. Moreover, the chemical and physical variation present in these environments affords the opportunity to examine how this variation drove the diversification of life in these early Earth analog environments. RPL investigations in hot spring environments in Yellowstone in 2015 centered on answering questions related to the array of energy and carbon sources available to chemosynthetic life, the preferred carbon sources supporting this life, and the role of hydrogen transformation in the metabolisms of these organisms. By answering these interrelated questions, we will provide a framework by which we can use to begin to understand the processes that most likely sustained microbial life on the early Earth. Since it is possible, if not likely, that such processes would also sustain early life on other planetary bodies, this research has the potential to guide the search for life in non-Earth environments.

    ROADMAP OBJECTIVES: 3.2 3.3 4.1 5.2 5.3 6.1
  • Global Surface Biosignatures: Reflectance Spectra of Anoxygenic Phototrophs and Cyanobacteria

    This project investigates the spectral reflectance signature of anoxygenic photosynthetic bacteria, as an alternative to the “biosignature” of the vegetation “red-edge.” The vegetation red-edge is so called due to the sharp contrast in visible light absorbance by light harvesting pigments in plant leaves versus their high reflectance in the near-infrared (NIR). This contrast occurs around 700 nm in the red/far-red. This signature is ubiquitous among plants, which all utilize chlorophyll a. However, anoxygenic phototrophs contain a diverse array primary photopigments, including bacterichlorophylls (Bchl) a, b, d, e, and g. These Bchl pigments display different absorption maxima with peaks primarily in the NIR. There is an abundance of data on plant spectral reflectance thanks to the Earth remote sensing field. However, there is a dearth of data on anoxygenic phototrophs and cyanobacteria. For this project, we measured the reflectance spectra of pure cultures as well as environmental samples of laminated microbial mats to characterize their detectable biosignature features. This work will help inform the search for life on exoplanets at a similar stage of evolution or biogeochemical state as the pre-oxic Earth.

    ROADMAP OBJECTIVES: 4.1 5.2 7.2
  • Biosphere-Geosphere Stability and the Evolution of Complex Life

    Five times in the past 500 million years, mass extinctions have resulted in the loss of greater than three-fourths of living species. Each of these events is associated with a significant perturbation of Earth’s carbon cycle. But there are also many such environmental events in the geologic record that are not associated with mass extinctions. What makes them different? We hypothesize that mass extinctions are associated with an instability in the carbon cycle. This project attempts to specify, both theoretically and empirically,the conditions that result in such an instability.

    ROADMAP OBJECTIVES: 4.3 5.1 5.2 6.1
  • Project 7: Mining Archaeal Genomes for Signatures of Early Life: Comparison of Metabolic Genes in Methanogens

    Methanogens represent the largest diversity among the archaea and have the unique ability to generate methane from simple compounds such as carbon dioxide, acetate and methylamines which were common in the anaerobic environments of early Earth and perhaps Mars. Methane biosynthesis also requires the presence/uptake of important ions such as sulfates, sulfides, carbonates, phosphates, and various light metal ions. In this project, we are attempting to analyze the evolution of the methanogens’ central cellular functions of translation, transcription, replication, and metabolism. To accomplish this, we are constructing the metabolic and regulatory networks of Methanosarcina acetivorans, the most complex methanogen known, and using these models to establish a framework for studying the evolution of methanogens. Results will be tested through microfluidic studies using varying carbon and ion sources.

    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
  • Project 7: Error Rate and the Origin and Early Evolution of Life

    Our project investigates the evolutionary relationship between rates of genetic mutation and genetic recombination. It addresses very general questions about the stability of heredity and the implications of that stability for adaptation and persistence of organisms. Such questions are likely to apply wherever and whenever life evolves. In prior theory work we have shown that the mutation rate of a population will tend towards ever-higher values in the absence of genetic recombination. Because mutation is the ultimate source of the variation required for the evolution of a population, it might be thought that a high mutation rate would enable more rapid evolutionary adaptation. We and others have shown, however, that too high a mutation rate can cause extinction of a population. Because early life probably had very high mutation rates, early life would have been at considerable risk of evolving a lethal mutation rate. This should have produced strong pressure for genetic recombination to evolve. In our project we are using experimental evolution, analytical theory, and computer simulations to test the effect that recombination has on mutation rate evolution, the effect that high mutation rates have on population adaptation and persistence, and the effect of mutation on the evolution of cooperation among life forms.

    ROADMAP OBJECTIVES: 4.2 5.2 6.2
  • Project 2A: Application of the 13C-18O Clumped Isotope Thermometer to the Ancient Earth

    Application of the clumped isotope thermometer in carbonates, which is based on preferential bonding between 13C and 18O, offers the possibility of testing controversial proposals based on conventional stable isotope thermometry that the early Earth’s oceans were hot. In this project, we report on the results of a study of clumped isotope thermometry of the Neoarchean Campbellrand carbonate platform of South Africa. This platform is the best preserved Archean carbonate sequence known and was subjected to only very low grades of metamorphism, and hence offers the best opportunity to determine seawater temperature for the late Archean oceans. Comparison of clumped isotope temperatures retrieved from co-existing calcite and dolomite confirm that resetting of clumped isotope temperatures occurs at different rates for these minerals, where dolomite is closest to preserving primary temperatures. Despite slower re-equilibration rates for dolomite, however, the fact that the Campbellrand platform was buried at temperatures up to 170 oC for ~2 b.y., prevents use of clumped isotope thermometry from preserving Archean seawater temperatures. This would likely not be the case for carbonates on Mars, where early Mars carbonates would have had a relatively low temperature thermal history, suggesting that clumped isotope thermometry for Mars carbonates is a promising approach for determining ancient surface temperatures on Mars.

    ROADMAP OBJECTIVES: 4.1 5.2 7.1
  • Subglacial Environments as Water‐Rock Hosted Microbial Ecosystems

    Glaciers, ice sheets and ice caps cover ~11% of the earth’s surface, and likely covered up to 100% during Neoproterozoic glaciations. The beds of these ice masses can have significant sectors at the pressure melting point. The resulting water lubricates ice sliding and accelerates erosion, provides habitat for subglacial microbial ecosystems, and may have acted as refugia during past global glaciations on Earth. Such environments may also act as habitats for life on other planetary bodies.

    Grinding of bedrock by glaciers exposes fresh mineral surfaces capable of sustaining microbial metabolism. The foci of RPL investigations on subglacial environments are categorized into two key areas of relevance to habitability studies: i) determine the extent to which minerals support chemotrophic metabolism and the production of biosignatures (e.g., weathering products), and ii) quantifying the influence of water-rock interactions in supplying substrates to support energy metabolism. Through these interdisciplinary and collaborative studies, we aim to characterize the active microbial processes in subglacial environments and to define the sources of energy that sustains this microbial life.

    ROADMAP OBJECTIVES: 2.1 5.1 5.2 5.3 6.1 6.2 7.2
  • Advances in Gene Sequencing From Low-Biomass Water-Rock Hosted Ecosystems

    One of the approaches our team is taking to explore rock-powered life is to study microorganisms hosted within rocks that are undergoing potentially life-supporting reactions with water. The chemistry of the rock microenvironments shapes the abundance, diversity and distribution of microbial life. In turn, that microbial life locally affects the in-situ geochemistry. This project is currently focusing on the successful extraction and sequencing of the exceedingly small amounts of DNA that accumulates within rocks, in order to successfully detect and characterize the rock-hosted life. Ultimately our improved approaches will support the application of next-generation DNA sequencing technology in the study of natural microbial ecosystems that are key for understanding the mechanisms of rock-powered life.

    ROADMAP OBJECTIVES: 3.2 4.1 5.1 5.2 5.3 6.1 7.2
  • Rock Powered Life: Education and Communications

    The central theme of the Rock Powered Life research effort is to define how, where and when water/rock interactions release energy and how this energy is harvested to support microbial communities. These studies are of fundamental importance for improving understanding of how microbial life was supported on early Earth. Moreover, since similar reactions can be expected on any rocky planet with liquid water, these studies provide new constraints for predicting the distribution of life on other planetary bodies.

    The focus of our team – rock-hosted microbial ecosystems that are dependent on chemical rather than light energy – provides novel avenues to engage the next generation of astrobiologists and to disseminate knowledge to the broader public. Here we describe current and ongoing efforts by members of Rock Powered Life that are aimed at improving engagement and training in astrobiology. Of particular relevance are efforts to provide opportunities to provide underrepresented high school and undergraduate students hands on training opportnities in astrobiology-focused studies. We also describe advancements in Rock Powered Life’s digital-based information sharing technologies. Through these integrated team efforts we aim to attract and train future generations of astrobiologists and to provide greater access to the current knowledge base with which to understand the potential for life elsewhere on other planetary bodies.

    ROADMAP OBJECTIVES: 3.2 4.1 4.2 5.1 5.2 5.3 6.1 6.2
  • Mars Analog Studies: Ice Covered Lakes on Earth and Mars

    Ice-covered lakes in Antarctica provide models for sedimentary processes on ancient Mars and microbial ecosystems for early Earth. Ice affects sedimentation because sand grains can be blown onto the ice, where they can eventually go through the ice into the lake below. Understanding the details of these processes and resulting sediments will allow us to better reconstruct details of lake environments and their implications for climate on early Mars. Early Earth ecosystems, and those on early Mars if life ever existed there, consist exclusively of microorganisms, which is also true for many Antarctic lakes. Thus, these lakes provide the opportunities to investigate ecological principles for early ecosystems. Data from the microbial mats in these lakes are providing insights into the growth of stromatolite, the geochemical impacts of oxygen-producing photosynthesis, and environments that may have promoted the early diversification of animals.

    ROADMAP OBJECTIVES: 2.1 4.1 4.2 5.1 5.2 6.1
  • Theoretical Integration: Evolutionary Dynamics of Ecosystems Controlled by Multiple Autonomous Genomes

    The work of Co-I Smith during 2015 centered on two aspects of the role of ecosystem feedback in determining the relations among fitness functions and the co-evolutionary dynamics of multiple genomes.

    The first task concerns the optimal degree of genomic autonomy to carry out the aggregate metabolic functions of an ecosystem: when is it preferable to combine the control of multiple pathways within a single genome, and when is splitting the control among multiple autonomous genomes more stable under coevolution?

    The second task concerns the stochastic dynamics and the descriptive statistics of populations evolving under the control of feedbacks from potentially-complex ecological stoichiometric constraints. It incorporates recent methods in computational chemistry to produce exactly solvable, and biologically relevant, models of complex stoichiometric constraint that couple multiple evolving lineages.

  • Global Surface Biosignatures: Circular Polarization Spectra of Anoxygenic Phototrophs and Cyanobacteria

    This new project focuses on characterizing the chiral signature of biological molecules. The phenomenon of chirality is a powerful biosignature and, in principle, can be remotely observed on planetary scales using circular polarization spectroscopy. Molecules such as photosynthetic pigments are optically active and have several chiral centers, and influence the polarization of light. This can be measured using full Stokes spectropolarimetry. The goal of this interdisciplinary project is to characterize the circular polarization spectra of chiral photosynthetic pigments in anoxygenic phototrophs and cyanobacteria as global surface biosignatures.

    ROADMAP OBJECTIVES: 4.1 5.2 7.2
  • Project 10: Evolution Through the Lens of Codon Usage

    The sequences of protein encoding genes are subject to multiple levels of selection. First, amino acid changes that adversely alter protein function are unlikely to survive. In addition, the genetic code is degenerate; it includes alternative (synonymous) codons for most of the amino acids. The codon usages of genes reflect a balance between drift and selection for rapid and accurate translation of mRNAs into proteins, and in the case of horizontally transferred genes, the codon usages of their sources. Our studies of genes and their codon usages have led us to discover that: (i) most of the recently acquired genes come from such closely related organisms that their distinctive codon usages cannot be attributed to a phylogenetically distant source; (ii) the transfers commonly exceed recognized boundaries of microbial species; (iii) some genes do not drift to match the native codon usage of their current genome, but resemble the most recently acquired genes; (iv) many of the genes that are most up-regulated under starvation conditions also have this codon usage; and (v) a distinctive stress/starvation-associated codon usage is a recurring theme that is observed in diverse Bacteria and Archaea.

    These results have changed our understanding of the dynamics with which genetic novelties are shared in the biosphere, and revealed that there are selective forces on codon usage beyond those currently appreciated in the field.

    ROADMAP OBJECTIVES: 5.1 5.2 5.3 6.1
  • Project 2D: Carbonate-Associated Sulfate (CAS) as a Tracer of Ancient Microbial Ecosystems

    Our aim is to investigate and understand microbial communities that flourished much earlier in the Earth’s history. We have adapted a method used to investigate the isotopic compositions of ancient oceans, by analyzing rocks formed at those times, but applied it to the pore-waters present in ancient sediments inhabited by in the contemporaneous microbial communities. The isotopic compositions we measure tell us about the extent and progress of microbial metabolic processes. We have applied this method very successfully to 12 million year old sediments. Most recently in order to test and calibrate the approach most fully, we have been examining recent deposits in which we can analyze microbiological communities, the pore-waters in which they live and the rocks forming there.

    ROADMAP OBJECTIVES: 5.2 6.1 7.1
  • Physiology of Microbial Populations From W/R Hosted Ecosystems

    Microbial communities supported by chemical energy (chemotrophic communties) released through water / rock interactions are widespread in contemporary Earth environments, including the subsurface where light is excluded and in surface environments where physical or chemical conditions preclude photosynthetic metabolisms. Chemotrophic microorganisms are key targets of astrobiological investigation due to the strong likelihood that they predate photosynthetic metabolisms and because they can be physiologically tested to define the habitable limits for life on Earth, including those associated with extremes of temperature, pH, salinity, and energy availability. Research by RPL scientists is focused on identifying and characterizing the physiological strategies or mechanisms that allow life to persist under extreme conditions at the habitable limits. By combining this information with phylogenetic approaches, we aim to determine how and when these mechanisms evolved and what role they played in the diversification of early life. As such, this research effort is highly interdisciplinary and employs both traditional (e.g., activity assays, cultivation) and contemporary (genomics, transcriptomics, metabolomics) microbiological approaches in combination with geochemical approaches. In addition, RPL investigators are studying the evolution of these communities to hone in on the nature of key physiological processes (e.g., central carbon metabolism, nitrogen metabolism, and iron-sulfur metabolism) in chemotrophs prior to the onset of photosynthetic metabolisms. Field-based RPL investigations of microbial physiology in water/rock ecosystems to date have focused on populations inhabiting subglacial environments (cold-adaptation), hot springs (adaptation to acidity, high temperature), and subsurface peridotite environments (adapation to energy stress, nutrient stress, alkalinity).

    ROADMAP OBJECTIVES: 3.1 3.2 3.3 4.1 5.1 5.2 5.3
  • Project 3B: Biologically Recycled Continental Iron Is a Major Component in Banded Iron Formations

    Combined Fe- and Nd-isotope signatures suggest that banded iron formations (BIFs) contain a major component of continentally derived iron that was mobilized by microbial iron reduction followed by transport through an iron shuttle to the site of BIF formation in deep basin environments. This Fe source is in addition to the widely accepted submarine hydrothermal source of Fe in BIFs, and the two sources of Fe may be comparable in importance, although their proportions change over time dependent on basin-scale circulation. These results document a vigorous, basin-scale biological cycle for Fe at least 2.5 b.y. ago.

    ROADMAP OBJECTIVES: 4.1 5.2 7.1
  • Progress in the Elucidation of Microbial Biosignatures

    A number of discrete individual investigations have contributed to improved knowledge about the occurrence and interpretation of microbial molecular biosignatures across all geological timescales.

    A new analytical approach enabled a revised geologic distributions of fossilized biomarkers for anoxygenic sulfur bacteria. The prevalence of okenane and chlorobactane suggests that marine photic zone euxinia (PZE) was more intense and frequent in the geologic past. However, the presence of these compounds in some sediments and oils may also be a signature for basin restriction rather than one indicating more widespread marine anoxia.

    In a related work, pervasive photic zone euxinia and disruption of biogeochemical cycles was demonstrated for a sequence of rocks deposited on the northeastern Panthalassic Ocean during the end-Triassic extinction.

    A study of lipids and their isotopic compositions, combined with stable isotope probing experiments, demonstrated that streamer biofilm communities, which are a present in the high temperature zones of hydrothermal features of the Lower Geyser Basin of Yelowstone National Park, can alternate their metabolism between autotrophy and heterotrophy depending on substrate availability.

    Other collaborations with numerous colleagues resulted in documentation of lipid and isotopic biosignatures in cultured bacteria.

    ROADMAP OBJECTIVES: 3.2 4.2 5.1 5.2 5.3 6.1
  • Project 3C: A Redox-Stratified Ocean 3.2 Billion Years Ago

    A novel combination of stable Fe and radiogenic U–Th–Pb isotope data that demonstrate that significant oxygen contents existed in the shallow oceans at 3.2 Ga, based on analysis of the Manzimnyama Banded Iron Formation (BIF), Fig Tree Group, South Africa. This unit is exceptional in that proximal, shallow-water and distal, deep-water facies are preserved. When compared to the distal, deep-water facies, the proximal samples show elevated U concentrations and moderately positive 56Fe values, indicating vertical stratification in dissolved oxygen contents. Confirmation of oxidizing conditions using U abundances is robustly constrained using samples that have been closed to U and Pb mobility using U–Th–Pb geochronology. This documents the oldest known preserved marine redox gradient in the rock record. The relative enrichment of O2 in the upper water column is likely due to the existence of oxygen-producing microorganisms such as cyanobacteria. These results provide a new approach for identifying free oxygen in Earth’s ancient oceans, including confirming the age of redox proxies, and indicate that cyanobacteria evolved prior to 3.2 Ga.

    ROADMAP OBJECTIVES: 4.1 5.2 7.1
  • Early Animals: Modeling the Biotic-Abiotic Interface in the Early Evolution of Multicellular Form

    Multicellular organisms in the sea modify their local hydraulic environment. Modeling of the earliest-known multicellular communities of frond-like forms demonstrated that they were large enough and closely spaced enough to generate a distinctive canopy flow-regime. In this context diffusion at the surface of organism was limiting and height and attendant velocity exposure permitted escape from these limits (Ghisalberti et al. 2014). Building on these results, we are developing models of abiotic/biotic interactions at organismal surfaces, relevant to the morphology, development and orientation of other Neoproterozoic fossils. A subset of these are flat-lying forms such as Dickinsonia. These may interact with the sediment modifying redox gradients. Ultimately, this work will help illuminate how forms initially dependent on passive diffusion became more trophically, morphologically and behaviorally complex, during the diversification of animals.

    ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1
  • 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 6.1 7.2
  • Taphonomy of Microbial Ecosystems

    We perform experiments to understand shapes, molecules and isotopic signals of microbial processes in modern and old sediments. Experimental studies of microbial interactions with sediments, ions in the solution and the flow help us elucidate mechanisms that may have shaped sandy surfaces and preserved fossils on these surfaces at the dawn of animal life. Culture-based studies of isotopic fractionations produced by microbial processes and microbial membrane lipids help us interpret corresponding signals in the rock record and modern environments.

    ROADMAP OBJECTIVES: 2.1 4.1 4.2 5.1 5.2 6.1 7.1 7.2
  • Project 3G: A 3,400 Ma-Old Shallow Water Anaerobic Sulfuretum Evidences the Anoxic Archean Atmosphere

    Carbonaceous cherts of the ~3430 Ma Strelley Pool Formation contain innumerable “swirls” of fossilized sulfuretum bacteria encompassing quartz-replaced anhydrite nodules intermixed with layered assemblages of phototrophic filamentous fossil microbes. The geologic setting of the fossil-hosting unit, the preservation of the sulfuretum swirls adpressed to quartz pseudomorphs of precipitated anhydrite or gypsum, and the lack of physical disruption of the assemblage document its near-surface quiescent marine environment. The anaerobic physiology of the sulfuretum microbes indicates that Earth’s surface was anoxic. This exceedingly ancient biota is therefore interpreted to be composed of anaerobic H2S-producing sulfuretum microbes and H2S-using anoxygenic phototrophic bacteria. As such, this first-identified fossil microbial consortium provides firm evidence of the anoxia of Earth’s early environment.

    ROADMAP OBJECTIVES: 4.1 5.2 6.2 7.2
  • Earth’s Evolving Nitrogen Cycle – Implications for Community Complexity and Stability

    This project examines nitrogen isotope patterns in Proterozoic and Paleozoic rocks, as part of a broader effort to understand the co-evolution of Earth’s redox cycles and marine ecosystems. The results are being incorporated into a growing framework of data and models that have as their primary objective to show how planetary geochemical cycles evolve with and/or help to record signatures of living systems – both microbial and complex. The project aims to yield a better understanding of the transition from primarily anoxic to primarily oxic deep oceans, and how that transition is mirrored in nutrient budgets (i.e., nitrogen) and the marine ecosystems that depend on the stability of these cycles. Understanding N-cycling throughout Earth’s history has critical implications for the evolution of complex marine ecosystems on geologic timescales.

    ROADMAP OBJECTIVES: 4.1 4.2 5.2 5.3 6.1
  • Paleontological, Sedimentological, and Geochemical Investigations of the Mesoproterozoic-Neoproterozoic Transition

    As we learn more about the earliest evolutionary history of animals and other complex multicellular organisms, it becomes clearer that a satisfactory understanding of these events have to be set within the broader context of late Mesoproterozoic and Neoproterozoic biological and environmental change. To this end, several labs within our team have focused research effort of Mesoproterozoic and Neoproterozoic sedimentary successions. Over the reporting period, this has included stratigraphic and sedimentological fieldwork on rocks of this age in northwestern Canada, Death Valley, Mongolia, Peru, and anaylsis of drill cores from Russia, Congo and Zambia. Progress has also been made in new techniques for the discovery, description, and interpretation of Proterozoic microfossils, and several-fold improvements in the precision of oxygen-17 measurements, which can record the balance of atmospheric oxygen and carbon dioxide.

    ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1