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2014 Annual Science Report

University of Wisconsin Reporting  |  SEP 2013 – DEC 2014

Executive Summary

Our research activities in Year 2 of CAN-6 were focused on four themes, all of which broadly fall within the team’s efforts in pushing new approaches to habitability, life detection, and signatures of life: 1) Analog settings and the biomolecules of life; 2) Experimental studies of paleoenvironmental and biological proxies; 3) Hadean, Archean, and Proterozoic environments and biosphere; and 4) Building the Astrobiology infrastructure. In Year 2 we significantly expanded our research portfolio from 16 projects in Year 1 to 21 projects in Year 2, as student, post-doc, and staff hiring efforts were completed.

Theme 1: Analog settings and the biomolecules of life

Six projects were pursued under this theme. In Project 1A: Field analog Geology and Astrobiology in support of Mars exploration, Co-I Pascale Ehrenfreund obtained preliminary results from a field research campaign in the area around the Mars Desert Research Station (MDRS ... Continue reading.

Field Sites
36 Institutions
21 Project Reports
21 Publications
14 Field Sites

Project Reports

  • Project 1C: Studies of Early-Evolved Enzymes in Modern Organisms May Reveal the History of Earth’s Ambient Temperature Over Geological Time

    By addressing a focused question — “Does the thermal stability of the reconstructed ancient enzymes of modern organisms provide evidence of the temperature of the environment in which the enzymes originated?” — this study asks a much broader question, namely, “can the biochemistry of extant life provide evidence of ancient environments?” In the geological record, there is virtually no mineralogical evidence to determine ambient surface temperature and data from other sources are ambiguous and contradictory. By analyzing the thermal stability of ancient reconstructed enzymes we hope that this work will pave the way to solve this fundamental problem and, by doing so, demonstrate a new way to understand the co-evolution of life and its planetary environment.

    ROADMAP OBJECTIVES: 4.1 5.1 6.1
  • 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 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
  • 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
  • Project 2F: Silicon Isotopes as a Tracer of the Coupled Fe-Si Cycle in the Archean

    Before the appearance of marine Si secreting organisms in the early Phanerozoic, the Precambrian ocean was characterized by high Si concentrations, as demonstrated by unusually abundant Precambrian age chert deposits. The Precambrian oceanic Si cycle was controlled by Si input from continental and hydrothermal sources, Si sorption and precipitation during Fe cycling, and export of Si in chemical precipitates. Reconstruction of the Precambrian Si cycle provides a better understanding of key processes that have governed the Si-rich ocean and associated environment where the earliest life on the Earth originated. Si isotopes are potential tracers for Si cycle where δ30Si values range over 4 ‰ in Precambrian rocks. However, unambiguous interpretation of Precambrian Si isotope data is limited by a lack of knowledge on Si isotope fractionation factors determined for systems applicable to the Precambrian. We have established protocols for high-precision Si isotope analysis, and conducted a series of laboratory experiments to determine Si isotope fractionation factors in simulated systems directly relevant to deposition and preservation of Archean cherts. These experiments represent the first attempt for a mechanistic understanding of Precambrian Si isotope data, and our results highlight the importance of deposition and preservation processes in affecting Si isotopic compositions preserved in Archean sedimentary records.

  • Project 3E: Sulfur-Cycling Fossil Bacteria From the 1.8 Ga Duck Creek Formation Provide Promising Evidence of Evolution’s Null Hypothesis

    In the absence of change in the physical-biological environment, evolution of the fundamental aspects of a well-adapted ecosystem — “the form, function and metabolic requirements” of its components — should not occur. Indeed, documentation of evolution in the absence of such changes would show that current understanding of Darwinian evolution is seriously flawed. The mid-Precambrian 2.3 and 1.8 Ga microbial sulfur-cycling assemblages here studied, the first two fossil communities described from quiescent, deep sea, anoxic subsurface mud, are indistinguishable from their modern counterpart. We regard it likely that other essentially identical ancient sub-seafloor microbial biocoenoses will be discovered and think it probable that this initial work will be regarded as having confirmed the linchpin of Darwinian evolution, its logically required null hypothesis.

    ROADMAP OBJECTIVES: 4.1 5.1 6.1
  • Project 4A: New in Situ Techniques (CLSM and Raman) Solve the Problem Presented by the Disaggregation of Acid-Macerated Organic-Walled Microfossils

    The search for evidence of past life in rocks to be returned from Mars seems likely to hinge on the use of non-intrusive, non-destructive techniques that can establish the biogenicity of any detected fossil-like objects by analyses both of their cellular morphology and molecular composition. The most promising rock types to preserve such evidence are chemically precipitated sediments such as cherts, gypsums, carbonates and phosphates — examples of all of which on Earth have been shown to be richly fossiliferous. The organic-walled microbes in such rocks are typically not amenable to investigation by the commonly used but rock-destroying technique of acid maceration. This study shows that the combined use of optical microscopy, confocal laser scanning microscopy, and Raman spectroscopy solves this problem, documenting effective means for the investigation of Mars rocks.

  • Project 1D: Iron Biogeochemistry in Chocolate Pots Hot Spring, Yellowstone National Park

    Small cores were collected from six locations along a transect following the main fluid flow path at Chocolate Pots (CP) hot spring, Yellowstone National Park. The cores were sectioned at 1 cm intervals, and the solids subjected to sequential extraction to isolate different Fe pools. The results showed that cores proximal to the vent outlet contained significant quantities of dissolved/colloidal and HCl-extractable reduced (ferrous) iron [Fe(II)]. Fe recovered from the other cores was present entirely as Fe(III). The most likely explanation for these observations is that internal generation of Fe(II) via microbial reduction is taking place in deposits proximal to the vent. This interpretation is consistent with rapid Fe(II) production during anaerobic incubation of near-vent deposits. Our results provide direct evidence of Fe(III) oxide reduction in deposits proximal to the main vent at CP, and to our knowledge represent the first demonstration of in situ Fe(III) reduction in a circumneutral-pH geothermal environment analogous to those which may have been present on the ancient Earth and Mars. Preliminary stable Fe isotope measurements on the dissolved/colloidal and 0.5M HCl-extractable Fe fractions in the CP cores suggests that Fe(III) reduction influences the isotopic composition of Fe phases proximal to the vent. A comprehensive analysis of all Fe phases in the cores is underway and will be used to develop conceptual models of controls on the stable Fe isotope composition preserved in the hot spring deposits.

    ROADMAP OBJECTIVES: 2.1 4.1 5.3 7.1
  • Project 1E: Microbial Communities in Chocolate Pots Hot Spring, Yellowstone National Park

    DNA was extracted from samples obtained from cores collected at six locations along a transect following the main fluid flow path at at Chocolate Pots (CP) hot spring, Yellowstone National Park. 454 pyrosequencing of 16S rRNA gene amplicons was performed on the extracts, resulting in the generation more than 70 amplicon libraries, each containing a between ca. 2500 and 7500 ca. 300 base pair-long reads. The raw reads were processed and analyzed for their phylogenetic affiliation and other comparisons using the QIIME pipeline. The results indicate that microbial communities in the upper few cm of the Fe/Si-rich CP deposits varied significantly along the sampling transect. Communities at two sites most proximal to the vent source differed substantially from one another and from communities at downstream sites. Although communities at downstream sites were not identical, they were more similar to one another than to the vent-proximal sites. A wide diversity of prokaryotic taxa, including both Bacteria and Archaea, were identified in the libraries, many of which are only distantly (e.g. <90% similarity in 16S rRNA gene sequence) related to known taxa. Communities in cores close to the vent were dominated by anaerobic taxa, many of which have the potential to function as Fe(III) reducers. This result is consistent with the relatively high abundance of reduced (ferrous) iron [Fe(II)] and the rapid rate of Fe(II) production observed in in vitro Fe(III) reduction experiments with material from sites near the vent. Abundant taxa at downstream sites included organisms related to the known Fe(II)-oxidizing organism Sideroxydans paludicola. These results are consistent with Fe geochemical data, which indicate that Fe(II) oxidation is likely the dominant Fe redox cycling pathway in deposits more than 1-2 meters from the vent source. A detailed metagenomic analysis of communities in the upper 1 cm at three sites is underway, with the goal of confirming the function of recognized taxa, and revealing the identity and function of potentially novel Fe redox cycling taxa.

    ROADMAP OBJECTIVES: 2.1 4.1 5.1 5.3 7.1
  • Project 2B: Modeling the Role of Adsorbed Hydrogen Sulfide in Weakening Mg-Water Complex on Dolomite (104) Surface

    Hydrogen sulfide is a major product of sulfate-reducing bacteria (SRB) in marine environment. To characterize the role of dissolved hydrogen sulfide and SRB in promoting dolomite crystallization, ab initio simulations based on density functional theory (DFT) were carried out to study the thermodynamics of competitive adsorption of hydrogen sulfide and water on dolomite (104) surfaces from solution. The results indicate that hydrogen sulfide adsorbed on the (104) surface increases the Mg2+-H2O distances on surrounding surface sites and thus weakens the electrostatic interactions between surface Mg[2^+^] and water molecules. The adsorbed hydrogen sulfide will promote surface water removal and anhydrous Ca-Mg-carbonate and dolomite crystallization at low temperature.

  • Project 2E: Carbonate-Associated Sulfate (CAS) as a Tracer of Ancient Microbial Ecosystems

    The chemical compound sulfate is present in ocean water and ratios of its stable isotopes of sulfur and oxygen have varied over geological time and are indicators of global geochemical processes. Other researchers have extracted trace amounts of sulfate from carbonate minerals of various ages as a glimpse into the Earth’s geological past. We are, however, applying this approach to carbonate minerals formed by microbial processes during burial of sedimentary rocks, which we hoped would give information on the microbial ecosystems. We needed to modify and develop existing methods for extracting the trace amounts of sulfate because our samples would be mineralogically much more complex. Initially, just to test the method we tried it on material from the local Monterey Formation rocks, which are of Miocene age (approx. 13 My old) and were delighted to find that the results enabled us to see the workings of a very complex microbial ecosystem with at least three different sorts of metabolism operating.

    ROADMAP OBJECTIVES: 5.2 6.1 7.1
  • 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 3A: Searching for Ancient Impact Events Through Detrital Shocked Zircons

    Understanding how quickly planetary surface environments evolve on newly accreted worlds is critical for predicting when habitable conditions are established. The meteorite impact history of the inner solar system strongly indicates that the Earth was subject to a global impact bombardment during the first few hundred million years after accretion. The scope, timing, and consequences of this profound process are hotly debated. This project investigated populations of detrital zircons in Archean sedimentary rocks to search for tell-tale signs of impact processes in the form of shock-induced microstructures that are diagnostic of impact. Such features have been shown to survive in detrital shocked zircons eroded from known impact structures on Earth, including the Vredefort, Sudbury, and Santa Fe craters. We have investigated populations of 1,000 zircons per sample using backscattered electron imaging of grain exteriors with a scanning electron microscope. Thus far we have surveyed zircons separated from rocks collected from the Yilgarn craton (Australia), North China craton (China), Wyoming craton (USA), and the Superior craton (Canada). While intriguing microstructures have been observed, thus far no confirmed shock microstructures have been encountered. Our inability the identify shocked grains in populations of 1,000 zircons (per sample) does not necessarily mean shocked grains are absent; our results provide constraints that if they are present, they are in abundances of <0.1% in the detrital population of the rocks investigated. Our detailed search continues…

    ROADMAP OBJECTIVES: 1.1 4.1 4.3
  • 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.

  • 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
  • Project 1A: Field Analog Geology and Astrobiology in Support of Mars Exploration

    We report on preliminary results obtained from the field research campaign exploring the area around the Mars Desert Research Station (MDRS) in Utah (Canyonlands area) in February/March 2012. This region has been previously investigated and characterized as geomorphological and geochemical similar to Mars. Soil and rock samples were collected within two formations of a single geological units, the Brushy Basin and Tununk Shale Member. The objective of this research was to characterize samples from plain, cliff and canyon locations using different analysis techniques including Fourier Transform Infra-Red Spectroscopy (FTIR), X-ray diffraction studies (XRD) and elemental composition surface and morphology (SEM-EDX) in order to determine the sample mineralogy and its variability within the geological unit. The analysis of the organic content of the collected samples (extraction of amino acids) is currently underway. Our aim is to compare data from different formations, topographical units, and specific locations in this Utah desert region in order to determine the variations in chemical and physical properties.

  • Project 1B: Photostability of Pigments and Amino Acids in Space Environment on the International Space Station

    Radiation plays a fundamental role in space environments, planetary systems and on the young Earth where life has emerged ~ 3.6 billion years ago. In order to measure the photostability and photochemical alteration of organic compounds in actual space environments, experiments in Low Earth Orbit (LEO) are crucial to our understanding of potentially destructive effects, particularly from the VUV (vacuum ultraviolet) spectral region. Space-based experiments are conducted in part due to the difficulty of accurately simulating the entire space environment in the laboratory (such as UV radiation, galactic cosmic ray irradiation, microgravity, temperature etc.). In preparation for the EXPOSE-R2 space exposure facility on the International Space Station (ISS) we prepared and investigated thin films of key pigments as well as mineral-associated amino acids for the experiments BIOMEX and Photochemistry on the Space Station that investigate a range of chemical compounds relevant for astrochemistry and astrobiology. The EXPOSE-R2 facility was launched on July 24th, 2014 to the ISS and was activated in November 2014. EXPOSE-R2 will remain in Low Earth Orbit (LEO) for 12-18 months. After retrieval non-destructive as well as destructive analyses will be performed in Earth laboratories to understand the effects of space exposure. We report on the flight preparation of samples and discuss the characteristics of the biomolecule thin-films measured by spectroscopy.

  • 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.

  • 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
  • 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