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Project Reports

• Project 5A: Improvement in the Accuracy of Stable Isotope Analysis by Laser Ablation

  In-situ isotopic analyses are critical for documenting spatial heterogeneities that can be related to the petrography of a sample. In the last decade, recognition of the power of in-situ analysis has spurred development of instrumentation that has improved the precision of in-situ isotopic analysis to unprecedented levels. With this improved precision, it is necessary to critically re-evaluate accuracy in order to identify true heterogeneities form analytical artifacts. We have evaluated the accuracy of in-situ Fe isotope analyses by femto second laser ablation (fs-LA) by evaluating the size and Fe isotope composition of aerosol particles generated by fs-LA, and to evaluate if fs-LA isotope analysis is free of matrix effects. Aerosols produced by fs-LA are small with ~70% of the particles, by mass of Fe, less than 100 nm in aerodynamic diameter, highlighting that the fs-LA particles can be effectively ionized by the plasma. By isotopic mass balance, the aerosols are a stoichiometric sample of the substrate, however, the smallest sized particles have light 56Fe/54Fe isotope compositions and the larger sized particles have heavy 56Fe/54Fe isotope compositions, which highlights the importance of quantitative transport of the aerosol by the ICP source. Matrix studies that include introduction of elements into the fs-LA aerosol by a desolvating nebulizer coupled with isotope analysis of iron oxide standards with variable chemical compositions suggest that matrix effects are driven by space charge processes where elements with low atomic Z relative to Fe such as Mg, and Si have no effects on the accuracy of the analysis but elements with a similar or higher Z such as Mn or U can produce accuracy issues on the order of +0.5 ‰ in δ56Fe.

  ROADMAP OBJECTIVES: 2.1 4.1 7.1 7.2

• Project 4E: Preliminary Studies of Fe Isotope Biogeochemistry in Fe-Rich Yellowstone National Park Hot Springs

  This preliminary project provided background information for future studies of the structure, function, and signatures (living and non-living) of Fe redox-based microbial life in the volcanic terrain of Yellowstone National Park (YNP). The focus on Fe redox-based systems stems from our expanding knowledge of the wide range of microbial energy metabolisms that are known to be associated with Fe redox transformations on Earth and potentially on other planets. Moreover, Fe redox transformations provide the potential for generation of mineralogical, isotopic, and organic biosignatures of past and present microbial life, which represent premier targets for testing the hypothesis that life currently exists or existed in the past on Mars. Preliminary data on Fe geochemistry and isotopic composition, and microbial community composition, was obtained for two contrasting Fe-rich springs in YNP: Chocolate Pots (CP), a warm, circumneutral environment that has formed on top of the Pleistocene-age Lava Creek Tuff, where a mixture of Fe-rich acid-sulfate geothermal fluids and neutral-pH groundwater from the Gibbon River catchment emerge to the surface; and The Gap site, a hot, acid-sulfate spring in the Norris Basin which supports active chemolithotrophic Fe(II) oxidation, analogous to other hot spring environments in YNP. The geochemical data demonstrated significant changes in aqueous Fe abundance and/or speciation along the flow paths at both sites, leading to accumulation of abundant Fe(III) oxides as well as aqueous Fe(III) at the acidic Gap site. A distinct separation in Fe isotope composition between aqueous Fe and deposited Fe(III) oxides (mainly amorphous Fe-Si coprecipitates) was also detected, with the oxide enriched in ⁵⁶Fe relative to ⁵⁴Fe as expected for redox-driven Fe isotope fractionation. However, the degree of fractionation was less the value of ca. 3 ‰ expected in closed system at isotope equilibrium. We suggest that internal regeneration of Fe(II) via dissimilatory Fe(III) reduction could enrich the aqueous Fe(II) pool in the heavy isotope, leading a much lower degree of Fe isotope fractionation – and hence a fundamentally different pattern of Fe isotope fractionation – than would occur in a strictly Fe(II) oxidation-driven reaction system. In support of this argument, an initial set of culturing experiments designed to recovery thermophilic Fe(III)-reducing organisms from CP and Gap materials resulted in the recovery of active Fe(III) reducers from both sites. In addition, preliminary pyrosequencing of ¹⁶S rRNA genes recovered from Gap solids provide evidence for Fe(III) reduction potential by the resident microflora. Particularly in the case of the Gap, sequences related to known Archaeal fermenters and elemental S/Fe(III) oxide reducers were abundant.

  ROADMAP OBJECTIVES: 2.1 5.1 5.3

• Project 4D: Understanding Conditions of Formation of Mars Evaporite Materials by Quantitative Interpretation of Isotope Compositions of Salts

  The variation in the ratios of the naturally occurring (non-radioactive) isotopes of salts dissolved in evaporating water and of the water itself give unparalleled, detailed information on the climate and environment. The existence of hydrated sulfate minerals on Mars and in Terrestrial Martian analog sites indicates that some ancient Martian surface deposits not only precipitated from evaporating surface water but may retain some of that water as part of the crystal structure of the minerals. However, we cannot just analyze the water and use the information because the isotope values are shifted to a small but systematic amount when the water is incorporated in the mineral. We have performed careful laboratory experiments to measure the amount by which the isotope values are shifted for two important mineral types, magnesium sulfate and iron sulfate at a large range of relevant temperatures. In another investigation we have developed a new analytical technique to measure the isotopic compositions of the trace element bromine, similar to the much more common chlorine, present in common salt, sodium chloride. Although these isotopic elements hold a wealth of information progress in using them has been very slow because of the very arduous and lengthily analytical procedures necessary. Our new method allows analysis of samples very much smaller than before and in only a small fraction of the time. These are essential steps in unraveling the climatic and environmental history of Mars.

  ROADMAP OBJECTIVES: 7.1

• Project 4A: Field Analog Geology and Astrobiology in Support of Mars Science Laboratory and Future Mars Surface Missions

  In 2011 we have characterized the mineralogy, organic compounds and microbiology of selected sample sites from desert areas of Utah in the vicinity of MDRS in Hanksville (Foing et al. 2011). The samples were partly analyzed in situ and later distributed to the various laboratories for post-analysis. Among the important findings of this field research campaign in the Utah desert are the diversity in the mineralogical composition of soil samples even when collected in close proximity, the low abundances of detectable polycyclic aromatic hydrocarbons (PAHs) and amino acids, and the presence of biota of all three domains of life with significant heterogeneity (Ehrenfreund et al., 2011). As a follow up study EuroMoonMars campaigns in February-March 2012 collected new samples from the area around the Mars Desert Research Station (MDRS) in Utah, (Canyonlands area), a region known for its geomorphological and geochemical similarity to Mars.

  ROADMAP OBJECTIVES: 2.1 5.1

• Project 3C: In Situ Fe Isotope Analysis of Iron Formations

  The Fe isotope composition of magnetite from the oldest (~3.8 Ga) sedimentary banded iron formations of Isua Greenland provide important constraints on the amount of Fe oxidation and its possible pathways. Iron isotope compositions of individual magnetite layers have been measured at the millimeter scale by micromilling and conventional mass spectrometry analysis and at the micrometer scale using femtosecond laser ablation (fs-LA). There is limited variability in the iron isotope composition of magnetite within a layer as would be expected for these amphibolites grade rocks. Within an individual hand sample there is at most a 0.3 ‰ difference in δ⁵⁶Fe values between different layers. Over a scale of tens of kilometers, the δ⁵⁶Fe values between magnetite layers in different samples range from +1.1 to +0.4 ‰. These high positive δ⁵⁶Fe values are noteworthy, and as a whole, Isua iron formations have higher and less variable δ⁵⁶Fe values as compared to the more massive 2.5 Ga iron formations from the Hamersley basin in Australia and the Transvaal basin in South Africa. This contrast in measured Fe isotope composition is best interpreted as having been produced by differing pathways of Fe cycling. The Isua BIFs most likely formed by small amounts of Fe oxidation from a water column caused by anoxygenic phototrophs with limited diagenetic alteration, whereas the younger 2.5 Ga Australian and South African BIFs were most likely formed by higher proportions of Fe oxidation and considerable diagenetic reactions that took place between pore fluids and iron oxide gels

  ROADMAP OBJECTIVES: 4.1

• Project 3D: Constraints on Oxygen Contents in Earth’s Early Atmosphere and Implications for Evolution of Photosynthesis

  The oxidation state of the atmosphere and oceans on the early Earth remains controversial. Although it is accepted by many workers that the Archean atmosphere and ocean were anoxic, hematite in the 3.46 billion-year-old (Ga) Marble Bar Chert (MBC) from Pilbara Craton, NW Australia has figured prominently in arguments that the Paleoarchean atmosphere and ocean was fully oxygenated. In this study, we report the Fe isotope compositions and U concentrations of the MBC, and show that the samples have extreme heavy Fe isotope enrichment. Collectively, the Fe and U data indicate a reduced, Fe(II)-rich, U-poor environment in the Archean oceans at 3.46 billion years ago. Given the evidence for photosynthetic communities provided by broadly coeval stromatolites, these results suggests that an important photosynthetic pathway in the Paleoarchean oceans may have been anoxygenic photosynthetic Fe(II) oxidation.

  ROADMAP OBJECTIVES: 4.1 6.1 7.1 7.2

• Project 3A: Stable Isotope and Mineralogical Studies of Banded Iron Formations – O Isotopes by SIMS

  During the past year, we have made advances in technique development for analysis of mineral chemistry and stable isotope ratios in minerals. Applications to magnetite in Banded Iron Formation (BIF) have lead to the proposal that silician magnetite forms only in low oxygen fugacity conditions and are thus a signature for the former presence of reduced organic matter. Petrography and in situ analysis of δ¹⁸O by SIMS has shown that the earliest quartz cements in 1.85 Ga Granular Iron formation (GIF) consistently have high δ¹⁸O showing that earlier reports of more variable compositions included altered material.

  ROADMAP OBJECTIVES: 4.1 4.2 7.2

• Project 2D: Catalytic Role of Adsorbed Hydrogen Sulfide in Dolomite Crystallization: Density Functional Theory Study

  The key kinetic barrier in dolomite crystal formation is believed to be the surface Mg²⁺-H₂O complex which hinder the accessibility of surface Mg²⁺ ions to the CO₃²⁺ ions in the solution. Our recent experiments demonstrated that hydrogen sulfide acting as a catalyst can overcome the barrier and promote dolomite nucleation and growth. Our results from ab initio simulations based on density functional theory (DFT) show that hydrogen sulfide can be adsorbed on (104) surface of dolomite from solution. Aqueous hydrogen sulfide produced by sulfate-reducing bacteria adsorbed on the surface can also increase the surrounding surface Mg²⁺-H₂O distances and thus weaken the electrostatic interactions between surface Mg²⁺ and water molecules.

  ROADMAP OBJECTIVES: 7.1 7.2

• Project 2A: Inorganic Growth of Mg-Calcite From Dilute Solutions: Understanding Temperature, Composition and pCO2 Effects

  The magnesium content of calcite has been successfully used in the past as a paleotemperature indicator for both inorganic and biological systems. More recently, the magnesium isotope ratio of Mg-bearing calcite has been suggested to display a temperature dependence, lending itself as an additional potential proxy for temperature. While these systems provide a valuable function to place geological materials within an environmental context, it is important to understand the physicochemical factors that control the incorporation of magnesium in calcite. Toward this end, a series of laboratory experiments were conducted to better understand the effect of solution chemistry and precipitation kinetics on the temperature dependence of the incorporation of magnesium isotopes in calcite. The results suggest that solution Mg/Ca ratio plays a subtle but important role in the use of magnesium as a paleotemperature indicator for calcite.

  ROADMAP OBJECTIVES: 4.1 7.1

• Project 1E: The ORGANIC Experiment on EXPOSE-R: Space Exposure on the International Space Station ISS

  In March of 2009, the Organic experiment integrated into the European multi-user facility EXPOSE-R, containing experiments dedicated to Astrobiology, was mounted through Extra Vehicular Activity (EVA) externally on the International Space Station (ISS). The experiment exposed organic samples of astronomical interest for a duration of 97 weeks (~22 months) to the space environment. The samples that were returned to Earth in spring 2011, received a total UV radiation dose during their exposure including direct solar irradiation of >2500h (>42.1 kJ per sample, based on ASTM E-490 AM0 standard solar spectrum between 119 and 400 nm). The Organics experiment on EXPOSE-R exposed 11 polycyclic aromatic hydrocarbons (PAHs) and 3 fullerene molecules in the form of ultra-thin films to solar UV under vacuum or controlled atmosphere. Ground control experiments of EXPOSE-R were performed at the DLR MUSC Center. A large fraction of the 210 samples (flight, flight dark, ground dark control, and the simulated ground control) have been measured by UV and IR spectroscopy in the last view months. Preliminary data of returned flight samples are shown.

  ROADMAP OBJECTIVES: 3.1

• Project 1D: Establishing Biogenicity and Environmental Setting of Precambrian Kerogen and Microfossils

  This study demonstrates new abilities to use in situ measurements of carbon isotope ratios in microfossil kerogen as a biosignature and to establish taxonomic and micro-structural correlations.

  ROADMAP OBJECTIVES: 2.1 4.1 5.1 5.2 6.1 7.1

• Project 1C: Absorption of Amino Acids on Minerals

  The role of mineral surfaces in extraterrestrial organic synthesis, pre-biotic chemistry, and the early evolution of life remains an open question. Mineral surfaces could promote synthesis, preservation, or degradation of chiral excesses of organic small molecules, polymers, and cells. Different minerals, crystal faces of a mineral, or defects on a face may selectively interact with specific organics, providing an enormous range of chemical possibilities. It has also been suggested in the literature that amino acids may have been delivered to early Earth by meteorite impacts. We focused here on amino-acid adsorption and conformation on model mineral, γ-Al₂O₃.

  We measured adsorption of the acidic amino-acids, glutamate and aspartate, on model nanparticulate oxide mineral, γ-Al₂O₃. Our results should help provide an estimate of the amount of amino-acids delivered. Using bulk adsorption isotherms our results showed similar amounts of adsorption of both amino-acids and FTIR spectroscopy revealed similar bonding configurations for the adsorbed species, over a range of pHs and concentrations.

  The project addresses NASA Astrobiology Institute’s (NAI) Roadmap Goal 3 of understanding how life emerges from cosmic and planetary precursors, and Goal 4 of understanding organic and biosignature preservation mechanisms. The work is relevant to NASA’s Strategic Goal of advancing scientific knowledge on the origin and evolution life on Earth and potentially elsewhere, and of planning future Missions by helping to identify promising targets for the discovery of organics.

  ROADMAP OBJECTIVES: 3.1 3.2 4.1

• Project 1B: Extracellular Polymeric Substances (EPS) and Bacterial Toxicity of Oxides

  Our interdisciplinary project examined the hypotheses that (1) bacterial cell membranes are ruptured in contact with specific mineral surfaces, (2) biofilm-forming extra-cellular polymeric substances (EPS) may have evolved to shield against membrane rupture (cell lysis), (3) differences in cell-wall structure of Gram-negative and Gram-positive bacteria may influence the susceptibility of cells to toxic minerals and (4) mineral toxicity depends on its surface chemistry and nanoparticle size.

  We have confirmed that the viability of wild-type bacterial cells which make EPS and biofilm is higher than that of mutant-type bacteria when exposed to oxide minerals. The effect is seen for both Gram negative and Gram positive bacteria, where the latter are less susceptible to the toxicity of minerals (Xu et al., 2012, Astrobiology; Zhu et al., in prep.). Thus, the thicker peptidoglycan outermost layer of the Gram positive cell surface provides an additional layer of protection compared to the less rigid, phospholipid outer membrane of the Gram negative bacteria (Zhu et al., in prep.). Most interestingly, EPS production could be induced by exposure to toxic minerals. The toxicity of the minerals depends on their surface chemistry (surface charge, ability to generate photocatalytic reactive oxygen species (ROS)) and size (Xu et al., in review).

  By understanding the mechanisms for membranolysis, especially under the extreme conditions of high radiation and heavy impacts during early planetary history, the project addresses the NASA Astrobiology Institute’s (NAI) Roadmap goals of understanding the origins of cellularity, the evolution of mechanisms for survival at environmental limits, and preservation of biosignatures, and NASA’s Strategic Goal of advancing scientific knowledge of the origin and evolution of the Earth’s biosphere and the potential for life elsewhere.

  ROADMAP OBJECTIVES: 3.4 5.1

• Project 1A: Interaction Between Lipid Membranes and Mineral Surfaces

  The goal of our work was to determine whether the surface chemistry or physical properties of mineral surfaces in contact with model “protocells” may have controlled the rupture/integrity of the protocell membranes. We hypothesized that mineral surface/lipid head group interface chemistry may have acted as a Darwinian selection force for the types of protocells which survived. We used a variety of experimental techniques including fluorimetric analysis of vesicle rupture in contact with mineral particles, bulk adsorption isotherms for lipids on oxide particles, Atomic Force Micropscopy and Neutron Reflectivity studies of lipid bilayer formation on planar oxide surfaces. The results could be explained by a modified version of the Deraguin-Landau-Verwey-Ovebeek (DLVO) theory for colloidal stability. Results indicated that lipid vesicles and bilayers are more stable at the positively-charged corundum surface in the low and mid-pH range than at the negatively-charged surface at high pH. Thus, protocells which came in contact with mineral surfaces having a positive surface charge would have maintained their integrity while those contacting negatively-charged surfaces would have been ruptured. Our results may suggest that mineral surface chemistry and lipid head group chemistry may have acted as a Darwinian “evolutionary stress” to select the most robust types of vesicles which “survived.”

  Our project addresses NASA Astrobiology Institute’s (NAI) Roadmap goals of understanding the origins of cellularity and the evolution of mechanisms for survival at environmental limits, and NASA’s Strategic Goal of advancing scientific knowledge of the origin and evolution of the Earth’s biosphere and the potential for life elsewhere.

  ROADMAP OBJECTIVES: 3.4

• Project 2B: The Influence of Temperature, Composition and pCO2 on the Fractionation of Iron Isotopes in the Calcite-Siderite System

  While siderite is a relatively common constituent of the sedimentary rock record, little is known about how solution composition and precipitation kinetics affect the trace element and Fe-isotope composition of siderite that forms at temperatures conducive to life (< 100°C). With this knowledge, siderite deposits may be placed within a more meaningful environmental context and the origin and diagenetic history of siderite can be better understood. In this study, inorganic siderite was precipitated under tightly controlled physicochemical conditions using the chemo-stat technique to better understand the factors that influence Fe-isotope fractionation in aqueous systems that contain siderite. Preliminary results suggest that siderite may be grown heterogeneously on pre-existing calcite surfaces but the resulting solids are highly susceptible to oxidation. These factors need to be better understood before inorganic precipitation experiments can be used with confidence to assess factors that influence the Fe-isotope composition of Fe-bearing carbonates.

  ROADMAP OBJECTIVES: 4.1 7.1

• Project 2C: Roles of EPS Excreted From Anaerobic Microorganism in Governing Dolomite Composition and Crystallization

  EPS from anaerobic microorganisms of sulfate-reducing bacteria, fermentation bacteria, and methanogen can catalyze dolomite nucleation and growth. Compositions of dolomite and Ca-Mg-carbonates is related to the amount of dissolved EPS. Polysaccharide in the EPS is the key to the dehydration of surface water and dolomite crystallization at room temperature. Low temperature dolomite / sedimentary dolomite can be a potential biosignature. The discovery also provides key to solving the “Dolomite Problem” that has puzzled geologists for decades.

  ROADMAP OBJECTIVES: 7.1 7.2

• Project 2E: Preferential Dolomitization of Carbonate Microbialites From a Modern Hypersaline Lake and in Ancient Dolomite

  Modern stromatolite from a hypersaline lake displays micro-laminated layers of calcite and protodolomite high-Mg calcite. The oscillatory layers indicate variations of microbial activity. The dolomite layers with micro-crystals are rich in organic. Extracellular polymeric substance (EPS) from photosynthetic microbes enhance precipitation of high-Mg calcite, and EPS from anaerobic bacteria catalyzes the transformation from high-Mg calcite into protodolomite. Atomic resolution Z-contrast images indicate that protodolomite is consisted of very weakly ordered dolomite domains ranging from 3 to 10 nm and disordered dolomite.

  ROADMAP OBJECTIVES: 7.1 7.2

• Project 2F: Potential for Lithotrophic Microbial Oxidation of Fe(II) in Basalt Glass

  Ferrous iron (Fe(II)) can serve as an energy source for a wide variety of chemolithotrophic microorganisms (organisms that gain energy from metabolism of inorganic compounds). Fe(II) oxidation may have played a role in past (and possibly, present) life on Mars, whose crust is rich in primary Fe(II)-bearing silicate minerals, as well as Fe-bearing clay minerals formed during weathering of primary silicates. This project examined the potential for microbial oxidation of Fe(II) in basaltic glass. Recent research suggests that near‐surface hydrothermal venting may have occurred during past periods of active volcanic/tectonic activity on Mars. Such activities could have produced basalt glass phases that might have served as energy sources for chemolithotrophic microbial activity. Previous and ongoing NAI‐supported studies have shown that an established chemolithoautotrophic Fe(II)‐oxidizing, nitrate‐reducing culture can grow by oxidation of Fe(II) insoluble Fe(II)‐bearing phyllosilicate phases such as biotite and smectite. The initial goal of this project was to determine whether or not this culture is capable of oxidizing Fe(II) in basalt glass. In addition we tested basaltic glass oxidation by a culture of Desulfitobacterium frappieri, as previous studies demonstrated that D. frappieri is capable of nitrate-dependent oxidation of structural Fe(II) in smectite. Finally, in situ and enrichment culturing experiments were conducted to determine whether indigenous Fe(II)-oxidizing organisms in a groundwater iron seep were capable of colonization and oxidation of basaltic glass. The results of these experiments showed that while the various cultures were readily capable of smectite oxidation with nitrate, none were able to carry-out significant oxidation of Fe(II) in basalt glass. We speculate that Fe(II) atoms in the amorphous glass are somehow occluded and therefore not accessible to outer membrane cytochrome systems thought to be involved in extracellular Fe(II) oxidation.

  ROADMAP OBJECTIVES: 2.1 5.1 5.3

• Project 3B: In Situ S Isotope Studies in Archean-Proterozoic Sulfides

  Studies of sulfur isotopes constrain atmospheric and marine conditions in the Paleoproterozoic and Archean. We have developed capabilities for analysis of all four sulfur isotopes, including the rarest isotope (36-S) in situ by ion microprobe. In general sulfur 4 isotope data from Archean sulfides fall on the reference array for mass independent fractionation that was established by earlier bulk measurements. Small deviations from the array are resolved and likely result from biological or environmental forcings.

  ROADMAP OBJECTIVES: 2.1 4.1 5.2 6.1 7.1

• Project 4B: Detection of Biosignatures in Extreme Environments, Analogs for Mars

  The chemical species sulfate, comprised of sulfur and oxygen atoms, is a constituent of minerals on Earth and on Mars. The small variations in the proportions of the isotopes of oxygen found in sulfate have been used to identify whether and inorganic process or microbiological oxidation of sulfide was responsible for sulfate formation. An intermediate product during the oxidation of sulfide to sulfate is sulfite, which also contains sulfur and oxygen. The work described here shows for the first time the relationship between the oxygen isotope compositions of sulfite and water, which is seen to be a significant control of the oxygen isotope composition of sulfate.

  ROADMAP OBJECTIVES: 7.1

• Project 4C: New Ways for Exploring Mars for Environmental History and Biosignatures

  In situ analyses on Mars may take many different forms. We have focused on developing an instrument mounted on a Rover that can make wet chemical analysis of Martian soils. Samples are taken by the Rover’s arm into a scoop which delivers them to a hopper. They are fed from there to one of a number of “test tubes” containing water where they are mixed to extract chemicals for analysis. The analytical process uses a probe, with a number of analysis electrodes attached to it, which dips into the tube. We tested the instrument on a Rover in the JPL Mars Yard, the in-house test field, and were able to demonstrate a successful, complete operational sequence using synthetic soil as the test material.

  ROADMAP OBJECTIVES: 7.1

• Project 5B: A Rover-Based Miniature Mass-Spectrometer – Breakthroughs in Laser Ablation Analysis and Geochronology

  We have made great progress towards a technique to measure absolute ages of rocks using laser sampling methods and mass spectrometry. A laser is used to release potassium and argon from rocks containing feldspar minerals, and after measuring the amount of potassium and argon released we can calculate how old the rock is. Last year, we demonstrated that the potassium and argon are released from the rock using lasers. This year, we modified our instrument so that both the potassium and argon measurements can be made during the same experiment.

  ROADMAP OBJECTIVES: 7.1