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Executive Summary

Our activities in Year 1 were focused on five themes, all of which broadly fall within the team’s efforts in pushing new approaches to “life detection”: i) Analog settings and the biomolecules of life; ii) Experimental studies of paleoenvironmental and biological proxies; iii) Hadean, Archean, and Proterozoic environments and biosphere; iv) Building the Astrobiology infrastructure; and v) Education and public outreach.

Theme 1: Analog Settings and the Biomolecules of Life

Six projects were pursued under the theme of analog setting and biomolecules in Year 1. In Project 1A: Detection of Biosignatures in Extreme Environments and Analogs for Mars, Co-I Max Coleman continued prior work on characterizing the isotopic equilibria between sulfite and water, which is relevant to understanding part of the microbial sulfate reduction system, as well as sulfite oxidation; these isotopic effects may potentially help understand sulfur redox cycling on early Mars. In Year 1, Coleman focused on the key role of sulfite oxidation in defining the oxygen isotope compositions of the resultant sulfate. Coleman showed that the oxygen isotope fractionation between sulfate and water is fundamentally defined during anoxic oxidation of pyrite by ferric iron.

In Project 1B: The extraction of spiked amino acids from a set of (clay-rich) minerals, Co-I Pascale Ehrenfreund began work on the critical issue of extraction of amino acids from rocky substrates, which previous work has shown may severely limit life detection strategies on other planetary bodies. Amino acids are among the most widespread biomolecules on Earth and play an important role in terrestrial biology by being, among other things, the building blocks of proteins. Mineral substrates, in particular clays such as montmorillonite, strongly adsorb organic compounds; although such properties may bear on the evolution of life, strong adsorption of amino acids by clay-rich minerals may inhibit extraction, and hence life detection. In Year 1, Ehrenfreund used amino acid spikes to determine the extraction efficiency of several distinctive (clay-rich) minerals. In this report, Ehrenfreund discusses preliminary results of adsorption properties of four amino acids: Arginine, Serine, Aspartic- and Glutamic acid.

Co-I Huifang Xu led Project 1C: Compositional and structural variations in dolomite and Ca-bearing magnesite from modern and ancient carbonate sediments, which investigated formation pathways of protodolomite, disordered dolomite, and Ca-bearing magnesite from the Great Barrier Reef (Australia). Because the studied Ca-Mg-carbonates were produced by organisms of coralline algae, this work provides a clear evaluation of the role of polysaccharides in producing carbonates that contain Mg. Magnesium incorporation into carbonates is of great interest as a biosignature because its very tightly held hydration sphere may require a role for biological ligands in dehydration and carbonate formation. Work in Year 1 showed that certain polysaccharides can inhibit aragonite precipitation and promote Ca-Mg-carbonate (even magnesite) crystallization. Z-contrast images of the Ca-rich dolomite show two types of Ca-rich precipitates in the host dolomite. The first are nano-precipitates of Mg-calcite, and the second, an ordered nano-phase with an ordering sequence of Ca-Ca-Mg along the c-axis. The new ordered nano-phase has hexagonal structure with compositions between those of calcite and stoichiometric dolomite. The results indicate that carbonate muds rich in extracellular polymeric substances (EPS) were preferentially dolomitized into Ca-rich protodolomite. These results indicate that low-temperature non-stoichiometry dolomite with the observed nano-precipitates may be used as a biosignature.

Iron biogeochemical cycling in circumneutral pH hot spring systems is an increasingly important astrobiological target, given recent discoveries on Mars by Curiosity, and in Year 1 Co-I Eric Roden and Co-I Eric Boyd began work on Project 1D: Integration of iron redox geochemistry and genomics in Chocolate Pots hot springs, Yellowstone National Park. This study explored the potential for microbial reduction of Fe(III) in the warm (ca. 40-60 °C), circumneutral pH (ca. 6.0-6.5) Chocolate Pots (CP) hot springs in Yellowstone National Park. Endogenous microbial communities were able to reduce native CP Fe(III) oxides, as documented in most probable number (MPN) enumerations and ongoing enrichment culture studies. Microbial communities in the enrichments have been analyzed by high-throughput pyrosequencing of 16S rRNA gene amplicons. The sequencing revealed an abundance of the well-known Fe(III)-reducing bacterial species, Geobacter metallireducens, as well several other novel organisms with the potential to contribute to Fe(III) reduction. A shotgun metagenomic (paired-end Illumina sequencing) analysis of the enrichment cultures is in progress to explore the identity and function of G. metallireducens as well as other less well-characterized organisms in the cultures. Of particular interest are the likely presence of thermotolerance genes in the G. metallireducens metagenome, as well as outer membrane cytochrome genes that may be indicative of other Fe(III)-reducing organisms and provide evidence for pathways of electron flow in these cultures.

In Project 1E: Metagenomic analysis of novel chemolithoautotrophic bacterial cultures, Co-I Eric Roden obtained metagenomic sequence information from two novel chemolithoautotrophic cultures: (1) an iron-oxidizing, nitrate-reducing culture that is capable of growth with either soluble or insoluble mineral-bound Fe(II) (biotite, smectite) as the sole energy source; and (2) an aerobic iron/sulfur-oxidizing culture that grows with framboidal pyrite as the sole energy source. Both of these cultures represent novel neutral-pH lithotrophic microbial pathways, the discovery of which broadens our view of potential Fe/S based life on Earth (past and present) and other planets. Roden hypothesizes that genetic components of Fe/S oxidation identified in the metagenome of the cultures will bear resemblance to analogous components to be identified in the pure cultures currently being sequenced, together with existing published and unpublished information from other chemolithoautotrophic microorganisms.

The OREOcube (ORganics Exposure in Orbit cube satellite) experiment on the International Space Station (ISS) investigates the effects of solar and cosmic radiation on organic thin films. In Project 1F: Organics Exposure in Orbit (OREOcube): A next-generation space exposure platform, Co-I Pascale Ehrenfreund is studying organic samples that have been deposited onto inorganic substrates, and monitoring structural changes and photo-modulated organic-inorganic interactions to better understand the role that solid mineral surfaces play in the (photo-)chemical evolution, transport, and distribution of organics. The results of these experiments in low Earth orbit (LEO) allow extrapolation to different solar system and interstellar/interplanetary environments. Organic molecules appropriate for study in thin-film form include biomarkers such as amino acids and nucleobases, as well as polyaromatic hydrocarbons (PAHs), redox molecules, and organosulfur compounds. Inorganic substrates include silicates, metal oxides, iron sulfides, nano-phase iron, and iron-nickel alloys. By measuring in situ changes in the UV-vis-NIR spectra of samples as a function of time on the ISS, OREOcube will provide data sets that capture critical kinetic and mechanistic details of sample reactions that cannot be obtained with current exposure facilities in LEO. Combining in situ real-time kinetic measurements with post-flight sample analysis will provide time-course studies as well as in-depth chemical analysis, enabling characterization and modeling of the chemistry of organic species associated with mineral surfaces in an astrobiological context.

Theme 2: Experimental Studies of Paleoenvironmental and Biological Proxies

Five laboratory-based experimental studies were pursued under this theme in Year 1. In Project 2A: Magnesium isotope fractionation between brucite [Mg(OH)₂] and Mg aqueous species, Co-I Brian Beard led a stable Mg isotope study of brucite, which is ultimately designed to constrain the paleoenvironmental conditions of Naochian martian terranes that contain clay produced through silicate weathering. In Mg-bearing phyllosilicates, octahedrally coordinated Mg²⁺ cations occur in a sheeted structure that is the same as brucite. Determination of Mg isotope fractionation between brucite and aqueous solution, therefore, may provide insight into the origin of Mg isotope variations during weathering and alteration of silicate rocks. Low temperature (4-55 °C) synthesis and exchange experiments determined that the fractionation factor between brucite and aqueous Mg (Δ²⁶Mg_brucite-Mg2+) is -0.18±0.07 ‰. Results of MgO hydrolysis experiments in EDTA-bearing solutions suggest that the Δ²⁶Mg_{brucite-Mg-EDTA} fractionation is ≥ +2.0 ‰ at 22 °C. These findings highlight the importance of ligand bond strength in controlling Mg isotope fractionation, especially organic ligands. Importantly, it raises the possibility that unusually fractionated Mg isotopes in clay-rich terranes, in the absence of carbonate, may indicate a role for biological ligands during weathering.

Interest in the fractionation of stable Mg isotopes in carbonates has grown considerably in recent years, yet few experimental studies have constrained the equilibrium and kinetic effects of Mg isotope fractionation upon formation of Mg-bearing carbonates. Co-I Christopher Romanek, in Project 2B: Origin of carbonates: Environmental proxies and formation pathways, has been exploring the effects of various experimental parameters on isotopic fractionation, including aqueous Mg and Ca contents, pCO₂, temperature, and precipitation rates. A matrix of 34 chemostat experiments was conducted between 4 and 45 °C, over a range of PCO₂ from 0.3 to 3 % and solution composition (Ca: 3 to 15 mmol/L; Mg: 3 to 300 mmol/L) that allows for the factors described above to be evaluated independently for their contribution to Mg isotope fractionation in this system. Mg-calcite was precipitated with up to 12 mol % MgCO₃ at precipitation rates that span the entire range of rates reported in the literature for synthetic Mg-calcite. Preliminary results suggest that equilibrium Mg isotope fractionation factors may only be attained at exceedingly low precipitation rates, less than ~10^-9 mol/m²⋅s, and that kinetic isotope effects at higher (although still very low) precipitation rates, can be on the order of several per mil, which is quite significant. Such extreme sensitivity in stable Mg isotope fractionation factors may reflect the very high dehydration energies of aqueous Mg.

In Project 2C: Calibrating the ¹³C-¹⁸O (“clumped”) isotope temperature scale, PI Clark Johnson has begun an effort to calibrate the stable isotope fractionations that occur among rare C and O isotopes, specifically the ¹³C-¹⁸O bond pair (so called “clumped” isotopes). The non-stochastic distribution of ¹³C-¹⁸O bonds in carbonates has been shown to be a function of temperature, and this approach promises to provide a paleothermometer for ancient oceans or fluids that does not require an assumed fluid isotopic composition. The ¹³C-¹⁸O fractionations for carbonates, however, have not been quantified as a function of precipitation conditions including CO₂-H₂O chemistry, system pH, and precipitation rate. This project explores probable causes of discrepancies among clumped isotope signals found in biogenic, inorganic, and synthetic carbonates and aims to decouple simultaneous physiochemical, thermodynamic, and kinetic processes that can all act on systematic partitioning of isotopes during carbonate formation. In Year 1, a CO₂-H₂O equilibration system was constructed to use in conjunction with carbonate precipitation experiments. The paring is designed to dynamically mix a constant stream of gas-phase CO₂ with liquid phase H₂O in order to fully exchange oxygen atoms and bring CO₂ into isotope as well as thermal equilibrium with the water used to form solid carbonate minerals. The equilibration system will circumvent CO₂-H₂O reactions suspected to impart non-equilibrium isotope and thermodynamic offsets observed in kinetically controlled inorganic precipitations as well as some types of biogenic “vital” effects.

The evidence that biomolecules may play a role in incorporation of Mg into carbonates noted above in Project 1C forms the basis for a laboratory-based investigation by Co-I Huifang Xu,
Project 2D: Project Catalytic roles of microbes in dolomite crystallization in a modern hypersaline lake. Experimental work used Halorhabdus and Halobacteroides biomass obtained from Deep Springs Lake in California, where microbial mediation of dolomite precipitation is documented. The experimental results demonstrate that disordered dolomite can be synthesized at low temperature using the lake biomass. A working hypothesis is that bacterially derived EPS might play a crucial role in dolomite precipitation. It is proposed that polysaccharides can be adsorbed onto Ca-Mg carbonate surfaces through hydrogen bonding, weakening the chemical bonding between Mg and water molecules. This in turn enhances Mg dehydration and incorporation into carbonate, therefore contributing to the growth of disordered dolomite. Robust demonstration of Mg-carbonates as an intrinsic biosignature would greatly enhance life detection strategies on other planetary bodies, given the relative ease with which rover-based chemical composition determinations may be made.

The abundance of sulfate on Earth and Mars provides a measure of surface redox conditions, but direct quantification of ancient sulfate contents from the rock record is due to the high solubility of sulfate minerals. One approach that has been used in terrestrial studies is carbonate-associate sulfate. In Project 2E: Carbonate-associated sulfate (CAS) as a tracer of ancient microbial ecosystems, Co-I Max Coleman is critically evaluating the use of CAS as a sulfate proxy, particularly in systems that contain co-existing sulfide and sulfate. Initial work in Year 1 has focused on developing analytical protocols that effectively isolate sulfate produced by oxidation of pyrite in sulfide-bearing samples, from sulfate that is bound in carbonate. Preliminary work has looked at young sediments, including the Miocene age Monterey Formation, where a sequence of pyrite-rich samples that include both carbonate concretions and phosphate-rich sediments have been collected. This work forms the necessary tests before application of the CAS proxy to the Precambrian rock record.

Theme 3: Hadean, Archean, and Proterozoic Environments and Biosphere

Five projects were pursued under the theme of ancient environments and biosphere in Year 1. In Project 3A: Hadean and Paleoarchean impact events and implications for early life, Co-I Aaron Cavosie began the search for detrital shocked minerals from the early Earth by examining populations of detrital zircons from Archean sedimentary rocks. Earlier work by Cavosie has shown that shocked detrital zircon populations can survive in the sedimentary cycle for ~2 b.y. The sites chosen in Year 1 were based on the criteria of (1) the rocks were deposited in the Archean, and (2) they were from regions where Hadean zircons had been previously reported. SEM work on detrital populations from the Yilgarn craton (Australia), the North China craton (China), and the Wyoming craton (USA) involved a population of >1000 grains each for two of these sites, and ~500 zircons from the third. So far, SEM analysis has not identified shocked zircons from these three regions, but much more extensive stratigraphic coverage is planned in subsequent years.

The chemical and isotopic compositions of Banded Iron Formations (BIFs) have been used as proxies for ancient seawater or paleoenvironments. In Project 3B: Banded iron formation deposition across the Archean-Proterozoic boundary, PI Clark Johnson led an investigation of several BIFs that were deposited just prior to the Great Oxidation Event (GOE). In situ O and Fe isotope measurements of magnetite and hematite in banded iron formations (BIFs) from the 2.5 Ga Dales Gorge member of the Brockman Iron Formation, Western Australia, document distinct fine-scale isotopic zonation, highlighting the distinct behavior of O and Fe isotopes during interaction with post-deposition diagenetic or metamorphic fluids. Stable Fe isotope variations are found to reflect photic zone or early diagenetic processes, whereas stable O isotope variations largely record later metamorphic fluid histories. The question of use of BIFs as paleoceanographic proxies has been independently evaluated using isotopic systems not affected by biology, precipitation, or temperature, such as ⁸⁷Sr/⁸⁶Sr, and in many cases BIFs are strongly out of equilibrium with expected compositions of Precambrian seawater. These results suggest that BIFs may be better recorders of Fe-based microbial processes, rather than proxies for ancient seawater.

In situ carbon isotope analysis of individual microfossils has been a major initiative of Co-I John Valley. In Project 3C: Carbon isotope analysis of Archean microfossils, Valley reports on a study of petrography, Raman microspectroscopy, and in situ analyses of carbon isotope and H/C ratios using secondary ion mass spectrometry (SIMS) of diverse organic microstructures, including possible microfossils, from two localities of the 3.4-billion-year-old Strelley Pool Formation (Western Australia). For the first time, they show that the wide range of carbon isotope ratios recorded at the micrometer scale correlates with specific OM-texture types. In a related effort, in Project 3D: Carbon isotope analysis of Proterozoic microfossils, Co-I John Valley reports on procedures they have developed for accurate in situ analysis of carbon isotope ratios by SIMS for individual Precambrian microfossils of unquestioned biogenicity. Data for three Proterozoic localities show a consistent fractionation of 19 ‰ between organic matter and coexisting carbonates, in spite of over 6 ‰ variability from rock to rock, consistent with fractionations seen for modern cyanobacteria. In one sample, a phytoplanktonic protistan acritarch, found within the same mm-scale domains, are 6 ‰ more fractionated, consistent with photosynthetic eukaryotes. These findings show, for the first time, the possibility of using in situ isotopic microanalysis of fossil microbial mats and ancient sediments in order to distinguish metabolic fingerprints within complex microbial ecosystems and consortia. This work also demonstrates the importance of developing high precision in situ analytical methods in preparation for sample return missions, where returned samples are likely to be quite small.

Co-I Bill Schopf led investigations on the microbial ecology of several Proterozoic sedimentary sequences via Project 3E: Microfossil insights into Proterozoic microbial ecology. In a study of the chert-permineralized 1.8 Ga Duck Creek Dolomite, and underlying units, Western Australia, Schopf found that in sequences of 2.3 to 1.8 Ga age that indicate little environmental change, there has been no evolution of the form, function, or metabolic requirements of its biotic components; this demonstrates, for evidently the first time, the null hypothesis required of Darwinian evolution that stability in environment should result in little evolutionary pressure for change. In a second study of sulfur-cycling bacteria from the 775 Ma chert-permineralized Bambui Group of Brazil, Schopf showed that pyritized microbes of this age were anaerobic sulfur-cyclers. This work, in addition to previous studies, forms the basis for ongoing studies of the biotic response to the Great Oxidation Event, following four lines of evidence: (1) the anaerobic to aerobic transition of metabolic and biosynthetic pathways; (2) rRNA phylogeny-correlated fossil evidence of O₂-protection in immediately post-GOE-preserved cyanobacteria; (3) the earliest fossil occurrences of obligately aerobic eukaryotes; and (4) recent discoveries of mid-Precambrian anaerobic microbial sulfuretums dependent on the GOE-promoted increase of required nutrients.

Theme 4: Building the Astrobiology Infrastructure

Commensurate with the charge that NAI teams contribute to building the astrobiology infrastructure, we report on two projects that were pursued in Year 1. In Project 4A: Teaming with Minority Institutions – Creation of a Summer Research Internship in Astrobiology with the University of Puerto Rico, Co-I Aaron Cavosie reports on the successful implementation of the first cohort of University of Puerto Rico-Mayaguez (UPRM) astrobiology summer interns at the University of Wisconsin-Madison in summer 2013. Four UPRM undergraduate students were chosen who (1) were junior-to-senior level students in good academic standing, (2) expressed an interest in learning more about astrobiology research, (3) were at the critical stage of considering different graduate school opportunities. The goals of the summer internship were to (i) provide the students with an in-depth exposure to astrobiology research at UW, (ii) engage daily in active research projects, (iii) explore and evaluate graduate opportunities at UW, (iv) go on field trips, and (v) enjoy cultural activities in Madison, WI. The 2013 cohort was a smashing success – the students were immersed in mini-research projects on a daily basis, received laboratory tours, interacted with students and faculty at UW-Madison, and enjoyed the Madison culture. In addition, two field trips to visit impact structures in Wisconsin were run, one to the Rock Elm impact structure in western Wisconsin, and a second to the putative Glover Bluff impact structure in south-central Wisconsin. These planetary-geology related field trips provided an opportunity for training students in field methods and observations at unique impact structures where shocked minerals have been documented.

 
In Project 4B: Better, faster, smaller Fe isotope analysis on iron oxides and sulfides by femtosecond laser ablation: aerosol characterization and the influence of ablation cells, Co-I Brian Beard describes new methods that are being developed for in situ stable isotope analysis via laser ablation that increase the precision and/or decrease the volume sampled during the analysis, while maintaining an external precision of ±0.2 ‰ in ⁵⁶Fe/⁵⁴Fe using femtosecond Laser Ablation (fs-LA) with isotopic analysis by MC-ICP-MS. As in Project 3D above, these efforts are aimed at developing the infrastructure for analysis of the very small samples that would characterize sample return missions, and specific to LA analysis, bears on future use of lasers in rover-based analysis. Improvements in spatial resolution have been accomplished through use of a two volume cell that has a rapid (0.2 s) washout time and produces more aerosol particles with smaller aerodynamic diameters as compared to prior generation ablation cells. The smaller aerodynamic diameter particles result in more stable ion signals which produce higher precision isotope ratio analyses. Improvements in ablation cells, as well as mass spectrometer electronics, has allowed a decrease in the volume needed for an Fe isotope analysis to ~600 µm³ with an external precision of ±0.2 ‰ in ⁵⁶Fe/⁵⁴Fe. This volume is an order of magnitude smaller than previous LA systems, and is similar to Fe isotope studies that have been done by SIMS.

Theme 5: Education and Public Outreach (E/PO)

Details of our E/PO activities are reported separately, but we briefly summarize Year 1 activities here. At UW-Madison, Co-I Brooke Norsted led four initiatives. The first was the opening of a Permanent Biosignatures Museum Exhibit in the Geology Museum at UW-Madison. This exhibit features Earth’s oldest rocks and fossils, the “Aromas of Astrobiology”, a 3-foot high Winogradsky column, and a 27 g piece of the Tissint Martian meteorite. It will be seen by ~50,000 visitors annually, 14,000 of whom are school children on one-hour-long guided tours. The second was distribution of Life in the Extreme Trading Cards. This pack of nine extremophile trading cards has been distributed to 5,000 people in the past year, via K-16 teachers. They have also been used to create two classroom products, one for undergraduates, and another for 4-8^th graders. The third was development of the Madison Public Library Summer Reading Club. Planning was done for an astrobiology-themed summer reading program that will impact 6,000+ children and their families in Madison, WI, to be run in summer 2014. The fourth was the Aromas of Astrobiology Booth, which was a prototype of the interactive component of the Biosignatures Exhibit. This booth was used at two outreach events reaching 500+ people in June and September, 2013. The smells were used to engage learners to explore astrobiology, by recreating the scents of early Earth, deep-sea vents, and Titan. Our E/PO activities at NASA-JPL in Year 1 have had numerous challenges due to changing guidelines from NASA HQ regarding NASA E/PO activities. Co-I Kay Ferrari worked on the NASA Nationwide Partnership, which provides professional development training to NASA volunteers in astrobiology so they can carry that message to their communities; this is done through presentation of talks and hosting events across the U.S. Planned new work on Nationwide Education Workshops was delayed in Year 1 due to the restructuring of the Solar System Ambassadors (SSA) and Solar System Educator (SSE) programs, although Ferrari continued to oversee the volunteers in the SSA and SSE programs in Year 1, coordinating activities using existing materials.