2015 Annual Science Report

Astrobiology Roadmap Objective 7.1 Reports Reporting  |  JAN 2015 – DEC 2015

Project Reports

  • Deciphering the Mineralogy and Geophysical Properties of Serpentinized Rocks

    The transformation of mineral phases during water-rock interaction provides critical energy sources for life yet the reaction processes under low temperature conditions are enigmatic. Thus a key goal of the RPL NAI is to decipher the geochemical reaction path history recorded in rocks that have interacted with water at low temperatures. To that end, we are developing and optimizing analytical procedures for quantifying mineralogy, Fe oxidation state, and rock magnetism at the microscale. To date, we are applying an integrated suite of microsopic and spectroscopic techniques to mafic and ultramafic rocks that have undergone low temperature alteration in two ophiolite systems — surface and subsurface serpentinites from Oman and drill core material from the California Coast Range Microbial Observatory. The resulting integration of mineralogical and chemical images is critical in efforts to unravel the sequence of water/rock reactions. In future years, our approaches will be applied to a diversity of rocks to be recovered by drilling at sites undergoing active, low temperature reaction, such as the Atlantis Massif and the Oman ophiolite, as well as samples that will be generated from laboratory-based water/rock reaction experiments.

  • Project 1: The Origin of Homochirality

    Small biological molecules are frequently chiral, meaning that they can exist in both right-handed and left-handed forms. The two forms are identical except for the mirror symmetry that they break, and so would be expected to participate in chemical reactions in a way that does not depend on their chirality. When assembled into polymers, the resulting chains would therefore be expected to consist of a mixture of right and left-handed forms of the small molecules, a so-called racemic state. The surprise is that this is not true for the molecules of life. All chiral amino acids used by biology are left-handed and all chiral sugars are right-handed. That is, they are homochiral. This project is concerned with trying to find an explanation for this ubiquitous phenomenon, a universal aspect of all life on Earth. The specific question that is addressed is whether homochirality is a generic phenomenon of living systems, one that would be anticipated to arise if life were found elsewhere in the universe. Or is it instead some frozen accident related to the specific way that life arose on Earth? This question has been hotly debated in one form or other for over a hundred years, certainly since the time that Lord Kelvin coined the term “homochirality”. It is important for the Illinois NASA Astrobiology Institute for Universal Biology, because it is one of the two most evident universal phenomena of all life on Earth, the other being the universal genetic code. The phenomenon is important for another reason. The magnitude of the homochirality is 100%. It is not a slight imbalance in the abundance of right-handed vs. left-handed molecules. Thus, it is an unambiguous signal to measure, either from biological samples or remotely due to the effects of homochirality on the scattering of light waves. Specifically, homochiral solutions or suspensions will affect the polarization plane of electromagnetic waves, and so can readily be detected through optical means. The most exciting possibility in this regard is that if homochirality can be firmly established as a biological phenomenon, then its presence can be used as a biosignature of non-terrestrial life.

    ROADMAP OBJECTIVES: 1.2 3.2 3.4 4.1 4.2 7.1 7.2
  • Inv 2 – From Geochemistry to Biochemistry

    INV 2 focuses on experimentally simulating the geological disequilibrium in hydrothermal systems, and determining the role of minerals in harnessing these gradients toward the emergence of metabolism. Biology utilizes metals (to speed up reactions) and “engines” (such as electron bifurcators, to couple endergonic and exergonic reactions); these components in modern metabolism strongly resemble specific minerals found in hydrothermal environments. We focus on simulating these primordial geological components and processes that might have led to the beginning of metabolism in a seafloor system on a wet rocky planet.

    ROADMAP OBJECTIVES: 3.1 3.2 3.3 4.1 7.1
  • 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
  • Analytical Protocols and Techniques for Detection and Quantitative Analysis of Complex Organics in Planetary Environments

    Robotic planetary missions enable critical in situ investigations into the character, diversity and distribution of organic compounds in their native environments. The next-generation mass spectrometers being developed for planetary exploration promise enhanced capabilities to elucidate the molecular structure of detected organic compounds via tandem mass spectrometry (MS/MS), and to disambiguate potential biosignatures via ultra high-resolution mass discrimination. The in situ detection and potential sequencing of individual organic polymers using synthetic trans-membrane nanopores is another example of an innovative technology geared towards the identification of key organic compounds. We are engaged in evaluating and extending such innovative technologies to address astrobiological initiatives on future NASA missions.

    ROADMAP OBJECTIVES: 2.1 2.2 7.1
  • Inv 3 – Planetary Disequilibria: Characterizing Ocean Worlds and Implications for Habitability

    INV 3 looks at how, where, and for how long might
disequilibria exist in icy worlds, and what that may imply in terms of
habitability. A major interest for this work is how ocean composition affects habitability. We are investigating chemistry behaves under conditions of pressure, temperature, and composition not found on Earth. Our simulations of deep ocean world chemistry couple with models for ocean dynamics, ocean ice interaction, and tectonics within the ice. We are examining each of these, how they interact, and how they relate to what future missions may discover. Members of our team are involved in missions to Mars, Jupiter’s moon Europa, Saturn, and Pluto. We are also involved in studies of exoplanets, and are working to understand how ocean worlds like Ganymede and Europa might provide analogues for more distant watery super-earths.

    ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 4.2 6.2 7.1 7.2
  • Understanding Ancient Aqueous Environments on Mars

    Project 1: The goal of this project is to characterize ancient aqueous environments on Mars using Digital Terrain Model (DTM) analysis and mapping to understand the potential environments for past habitability. These include fluvial environments with morphological evidence for ponding, associated with hydrothermal systems and multiple episodes of surface and near surface flow in channelized systems. We will determine sediment and eroded volumes of fluvial landforms from DTM analysis and use transport equations and terrestrial analogs to understand likely discharges and flow durations.

    ROADMAP OBJECTIVES: 1.1 2.1 7.1
  • Biomarker Profiling Using the Life Detector Chip (LDChip)

    We have worked on the detection of molecular biomarkers in three relevant environments: Dry (Atacama), acidic (Río Tinto) and deep lake sediments (Andean lakes). Samples have been analyzed in situ by using a powerful biomarker detection chip with and antibody microarray sensor as well in the laboratory with other geomicrobiological tools.

    ROADMAP OBJECTIVES: 5.3 6.1 7.1
  • Inv 4 – Observable Chemical Signatures on Icy Worlds: A Window Into Habitability of Subsurface Oceans

    INV 4 aims to answer the Key Question: What can observable surface chemical signatures tell us about the habitability of subsurface oceans? We will shed light on the evolution of ocean materials expressed on the surface of airless icy bodies and exposed to relevant surface temperatures, vacuum, photolysis and radiolysis. To this end, we have initiated an experimental program designed to establish the extent to which chemical compositions of icy world surfaces are indicative of subsurface ocean chemistry. Our initial experiments have focused on freezing solutions of sodium, magnesium, sulfate and chloride – four commonly suggested major components of Europa’s Ocean.

    ROADMAP OBJECTIVES: 1.1 2.2 7.1
  • Exploring the Evolution of the Water and Organic Reservoirs in the Solar System

    This project investigates the evolution and stability of water and organic reservoirs in our Solar System, with particular emphasis on the characterization of the current and ancient habitability of planet Mars. We employ extremely powerful observatories (e.g., ALMA, Keck, VLT, future JWST) to acquire high spatial and spectral resolution maps of the isotopic and organic signatures on several bodies in the Solar System. These maps allow us to investigate the stability and evolution of their atmospheres, while localized plumes can be used to identify regions of active release. In this reporting period, we emphasized three areas:

    1. We advanced our pioneering work on characterizing the evolution of water on Mars, by developing a new observational plan that combines the power of ALMA, of Keck and of MAVEN to obtain maps of the water D/H signatures on Mars.

    2. We identified previously unknown chemical processes affecting singlet-O2 and odd-oxygen on Mars, which may be indicative of a much more active photochemical cycle (with the possible intervention of heterogeneous processes).

    3. We provided science leadership in the investigation of Mars with the James Webb Space Telescope (JWST), and established a variety of observing modes and scientific opportunities.

    ROADMAP OBJECTIVES: 1.1 2.1 3.1 3.2 4.1 7.1
  • Mars Analogs: Habitability and Biosignatures in the Atacama Deser

    This project focuses on the study of habitability in the Atacama Desert of northern Chile, one of the driest regions on Earth. We want to understand how life adapts and survives in an environment where liquid water is exceedingly rare, and how biosignatures are preserved in that environment after microorganisms die. These studies can become a very useful guide for future robotic missions to Mars. This year we focused on microbial communities that inhabit the interior of salt nodules in evaporitic lake deposits. These are the only known active microbial comunities in the driest parts of the Atacama. We wanted to understand how these microbial communities survive in an environment that excludes every other form of life. We suspected that the salt communities use atmospheric water vapor as a source of water to run their metabolic processes. We showed that this is indeed the case with a combination of field and laboratory tools. Our results suggest that the salt substrate could be one of the last possible habitats for life in extremely dry environments.

    ROADMAP OBJECTIVES: 2.1 5.1 5.3 6.1 6.2 7.1 7.2
  • Project 1F: Study of Modern Fe-Mn Nodules in Green Bay Sediments as Analog to the Fe-Nodules and Fe-Oxyhydroxide Minerals on Mars

    Fe-oxide nodules and concretions are common in terrestrial sedimentary rocks and also occur in Martial sediments. The precursors of the hematite are nano-phases of Fe-oxyhydroxides. Modern Fe-Mn nodules from Green Bay sediments were investigated by in-situ XRD, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Z-contrast imaging, and ab-initio calculations using the density functional theory (DFT) method. Nano-phase minerals for hosting trace elements of As, P, Ba, Co, Ni, and Zn have been identified. Structural sites of the trace elements and their incorporation mechanisms are also proposed. The Fe-Mn nodules can be used as analog for understanding the Fe-nodules and Fe-oxyhydroxide minerals on Mars.

  • Biosignature Capture and Preservation in Sulfate Evaporite Deposits

    Sulfate minerals are regarded as key exploration targets for Mars sample return. These minerals form in liquid water over a broad range of environmental conditions, thus providing sensitive measures of past habitability. We are studying the preservation potential of fossil kerogen in Miocene sulfate deposits of the Camp Verde Formation, central AZ. The primary tools used in the study were selected to emulate capabilities of the Mars 2020 payload. Our results suggest ways to enhance in situ kerogen detection in sulfates, as well as operational synergies that may improve mission operations.

  • Interstellar and Nebular Chemistry: Theory and Observations

    We continue to undertake theoretical and observational studies pertaining to the origin and evolution of organics in Planetary Systems, including the Solar System. In this performance period, we have focused on studies aimed at understanding the origin and processing of organics in the earliest evolutionary phases of stars like the Sun. These include formation pathways and related isotopic fractionation effects.

    We have continued observational programs designed to explore the chemical composition of comets and establishing their potential for delivering prebiotic organic materials and water to the young Earth and other planets. State-of-the-art international facilities are being employed to conduct multi-wavelength simultaneous studies of comets in order to gain more accurate abundances, distributions, temperatures, and other physical parameters of various cometary species. We are also leading an international collaboration to study the organic composition of Titan with the Atacama Large Millimeter Array (ALMA).

    ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 3.2 7.1 7.2
  • 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 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
  • Detection of Biosignatures

    The project is developing methods of interpreting data, detecting novelty, and identifying biosignatures in data at multiple scales (Figure 1). Investigation will improve detection and decrease diagnostic uncertainty in selecting high-probability regions and high-priority samples. In year one, objectives are to develop algorithms for orbital data analysis and feature extraction and to develop algorithms for novelty detection.

    ROADMAP OBJECTIVES: 2.1 2.2 7.1 7.2
  • Project 2B: Cation Content of Carbonate Minerals as a pCO2 Proxy: Inorganic Synthesis Experiments

    Atmospheric CO2 content and temperature control reaction mechanisms and precipitation kinetics for carbonate minerals. As such, these parameters may indirectly influence the geochemistry and isotope composition of carbonate minerals. To better understand the significance of these geochemical fingerprints, a suite of laboratory experiments is being conducted to characterize the effect of PCO2 (<1 to >90% CO2) and aqueous ratios and low mol% MgCO3 (<3). With the completion of upcoming Mg-isotope analyses and the establishment of a unified consensus on Mg isotope fractionation relations in calcite, Mg isotope systematics can be used to better understand the geochemical and environmental information archived in the rock record.

  • Characterization of Habitability and Biosignature Preservation in Cold Springs

    In an increasingly colder Mars where permafrost was thickening, mineralizing cold springs could have provided extant subsurface habitats and a means to transport evidence of subsurface life to the surface. Depending on conditions and geochemistry, these precipitates could have encapsulated a record of past life, and the residual remnants of such spring mounds could still be exposed at the martian surface. On Earth, high latitude spring systems are rare due to the relatively impermeable permafrost. However, several groups of perennial springs are located at Axel Heiberg Island in the Canadian High Arctic (~80°N). With mean annual air temperatures of -17°C and permafrost depths ≥ 600 meters, these springs flow throughout the year despite minimum air temperatures reaching <-50°C during winter. Thick residual icing pastes form as a result of evaporation, sublimation and freeze fractionation, the mineralogy being dominated by halite, hydrohalite, calcite, gypsum, elemental sulfur, thenardite, and mirabilite. These springs provide an environment where prokaryotes thrive despite extreme conditions and their presence suggests that such systems could have been present throughout Mars history, and activated during cyclical climate changes.The primary goal of this investigation is to evaluate the potential of spring deposits in regions with thick, continuous permafrost and define their taphonomic window and biogeological context. Samples of icing pastes, travertine and other mineral precipitates have been sampled to understand the relationships between geochemistry, environment, presence of biosignatures and their potential preservation.

    ROADMAP OBJECTIVES: 2.1 4.1 7.1
  • Project 2C: Investigation of the Role of Polysaccharide in the Dolomite Growth at Low Temperature by Using Atomistic Simulations

    Polysaccharides in microbial EPS can promote dolomite growth at room temperature. Our molecular dynamics modeling results show that adsorbed polysaccharides can lower activation energy for removing surface water molecules next to the polysaccharides and catalyze dolomite crystallization at low temperature. The process can lower the energy barrier by ~ 1 kcal / mole. Low temperature dolomite / sedimentary dolomite is a potential biosignature. The new finding also provides key to solving the “Dolomite Problem” that has puzzled geologists for decades.

  • Lake Sediment Habitats; Lake Habitability and Sediment Biosignatures

    Regions where lakes and ponds existed once existed on Mars martian are among the highest priority environments for exploration. The physicochemical and biological characteristics of the unique of perennially ice-covered lake ecosystems found on earth in Antarctica, the High Arctic, and in high altitude environments (Altiplano and High Andes) serve as important analogs of earily Mars. Active and abundant microbial communities live in these extreme environments, suggesting the presence of habitable conditions on early on Mars. Unlike temperate lakes, these ecosystems are largely dominated and constrained by their physical environment (e.g., mean annual temperatures near or well below 0°C, with arid or hyper-arid conditions year-round). In these environments, lake sediments accumulate organic biosignatures due to relatively low metabolic rates and cold water. Less understood is their preservation potential once the water evaporates, and sediments are exposed to extreme cold and hyper-arid conditions. Perennially ice-covered lakes are rare on Earth. Their dry, paleo-counterparts are even more exotic, and biosignature preservation in such lake deposits remains largely unstudied. Lake Untersee, one of the largest perennially ice-covered surface lakes in East Antarctica hosts a robust microbial ecosystem including the presence of photosynthetic microbial mats that colonize the lake bottom to depths greater than 100m. These mats are primarily composed of filamentous cyanophytes and form two distinct macroscopic structures – cm-scale cuspate pinnacles dominated by Leptolyngbya spp. and laminated, large conical stromatolites that rise up to 0.5 m above the lake floor, dominated by Phormidium spp. (Andersen et al. 2011). Adjacent to Lake Untersee is the Aurkjosen Cirque, a basin that was once inundated by a large lake which has since evaporated. Desiccated, buried microbial mats have been recovered from this paleo- lacustrine site, and they provide material for the identification of biosignatures and their preservation in and extremely cold setting. Our investigations include the studies of the physical and biogeochemical characteristics of the two lakes, deposition and preservation of biomarkers, and in situ analytical techniques (IR reflectance, Raman, XRD/XRF) to identify organic signatures within a mineralogical context while developing synergistic operational concepts for in situ analyses in paleolake analogs.

    ROADMAP OBJECTIVES: 2.1 4.1 7.1
  • 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
  • Environmental and Biological Signatures in Yellowstone National Park Silica Precipitating Hot Springs

    Radiation from the Sun potentially affects solids, liquids, and gases found on the surfaces of planets. Radiation exposure could change the chemical and mineralogical make-up of the surface materials. Sample-return missions aim to collect samples, cache them for a period of time, and then return them to Earth for additional analysis. We have performed field experiments to document environmental radiation levels and exposures and their impact on recently formed materials and associated organic matter.

    ROADMAP OBJECTIVES: 1.1 2.1 6.1 7.1 7.2
  • Solar System Analogs for Exoplanet Observations

    The worlds of our Solar System can provide an important testing ground for ideas and techniques relevant to characterizing exoplanets. In this task, we use observations and simulations of Solar System planets to understand how astronomers and astrobiologists will recognize signs of habitability and life in future observations of rocky exoplanets. Work in this area this past year includes the first-ever direct detection of molecular nitrogen collision-induced absorption in Earth’s whole-disk spectrum, which can be used to indicate atmospheric pressure and, thus, habitability. Also in this task, VPL scientists have proposed techniques for using color to distinguish Earth-like exoplanets from other types of worlds.

    ROADMAP OBJECTIVES: 1.2 2.2 7.1 7.2
  • Rock Sample Biosignature Library and Automated Identification of Biosignatures

    The goals of this project are to: 1) build a Raman spectra and imaging library of rock samples containing biosignatures as no publically available online sample library currently exists; and to: 2) use this library as testing and training sets to develop automated classifiers for identifying biosignatures in rock spectra. Building a sample library and developing automated classifiers would enable field scientists or robotic explorers on the surface of Mars or elsewhere to automatically identify biosignatures in rock samples from Raman spectra out in the field.

    ROADMAP OBJECTIVES: 1.1 2.1 7.1
  • Undergraduate Research Associates in Astrobiology (URAA)

    2015 saw the twelfth session of our summer program for talented science students (Under-graduate Research Associates in Astrobiology), a ten-week residential research program tenured at Goddard Space Flight Center and the University of Maryland, College Park (http://astrobiology.gsfc.nasa.gov/education.html). Competition was again very keen, with an over-subscription ratio of 4.7. Students applied from over 19 Colleges and Universities in the United States, and 4 Interns from 4 institutions were selected. Each Intern carried out a defined research project working directly with a GCA scientist at Goddard Space Flight Center or the University of Maryland. As a group, the Associates met with a different GCA scientist each week, learning about his/her respective area of research, visiting diverse laboratories and gaining a broader view of astrobiology as a whole. At summer’s end, each Associate reported his/her research in a power point presentation projected nation-wide to member Teams in NASA’s Astrobiology Institute, as part of the NAI Forum for Astrobiology Research (FAR) Series.

    ROADMAP OBJECTIVES: 1.1 1.2 2.1 2.2 3.1 6.2 7.1
  • 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
  • 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
  • Project 3E: Genesis of High-δ18O Archean Chert, Pilbara Craton, Australia

    The cherts of the Strelley Pool formation host the oldest generally accepted evidence of life, stromatolites, organic matter and microfossils. Oxygen isotope ratios provide independent evidence to evaluate conditions when quartz formed. These results support habitable conditions during formation of early quartz and late alteration for genesis of late high δ18O-quartz.

    ROADMAP OBJECTIVES: 1.1 4.1 7.1
  • 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 4B: New Standards for Analysis of O and C Isotope Ratios in Ca-Mg-Fe Carbonates

    Stable isotope ratios are a powerful tool for determining the temperature and fluid conditions during formation of carbonates that host evidence for early life on Earth. However, sedimentary carbonates are often zoned at μm-scale and conventional analysis yields average values. We developed a suite of standards for the dolomite-ankerite series that allow us to make the first accurate SIMS (Secondary ion mass spectrometry) analyses oxygen and carbon isotope ratios at 1-10 μm-scale for these important carbonate minerals.

    ROADMAP OBJECTIVES: 1.1 4.1 4.3 7.1