Mineralogical Traces of Early Habitable Environments
Tori Hoehler, Lead Co-Investigator
Co-Investigators: Richard Morris, Allan Treiman, David Blake, Linda Jahnke, David Des Marais
Researcher: Michael Kubo
Ames Post Docs: Niki Parenteau, Jennifer Kyle, Tom Bristow, Sanjoy Som
Collaborators: Roger Summons, Bo Barker Jorgensen, Kenneth Stedman, Sherry Cady,
OBJECTIVE 4: Develop and evaluate a capability with which to characterize prior physicochemical environments and availability of energy and raw materials, and map that data into a quantitative assessment of prior habitability. Place particular emphasis on evaluating the early habitability of Mars via landed science investigations.
Objectives, Expected Significance,
and Extending the State of Knowledge
A key thrust of our work is to integrate mechanistic, predictive, and probabilistic models with data provided by the unique observational capabilities of space missions. Planetary missions offer the potential to collect direct evidence of early habitable conditions within our solar system. Mars is a particularly compelling target in this regard, because it may be the only body in the solar system to have preserved accessible evidence of its earliest habitable environments. The habitability of early Earth can be inferred, with timing constrained, by the fact that life proliferated here. However, the rock record of Earth's earliest history is both sparse and profoundly reworked by metamorphism, such that evidence concerning the physical and chemical environment is extremely limited. In contrast, the Martian crust may contain a pristine record of its earliest history – one that is accessible to a systematic program of study using highly capable orbital and landed analytical instruments. As a result, the recent decades of Mars exploration have had a strong focus on characterizing habitability. These efforts have, to date, focused almost exclusively on life's requirement for a solvent - water.
Geomorphological, chemical, mineralogical, and sedimentological evidence suggest that much of the Martian surface was exposed to water at some point during the past (Carr, 2006; Squyres et al., 2004). However, a sole focus on water does not provide a complete or quantitative metric of habitability (Hoehler, 2007). As presently applied, water is a "plus" or "minus" indicator of habitability: the presence of liquid water indicates life-supporting potential; the absence of water prohibits life. Yet, clearly, a spectrum of habitability exists in water-containing systems – from vibrantly to scarcely inhabited, to completely uninhabitable (among inhabited microbial systems, for example, volume-normalize biomass abundance spans a range occupying at least nine orders of magnitude). To move beyond this binary view of habitability – to resolve and quantify the relative degree of habitability in a collection of water-bearing systems – requires that we consider the additional constraints of physicochemical environment and the availability of energy and raw materials. Recent results from both landed and orbital assets have begun to assess these parameters, but their applicability in a quantitative sense has thus far been limited – in part by the analytical limitations of remotely deployed instruments and in part because our understanding of these factors in reference to habitability is still largely, as with water, binary (e.g., life is possible if the temperature is between -20 and 130°C and if energy is "present", and otherwise not). The forthcoming Mars Science Laboratory (MSL) mission will bring to bear a significantly enhanced analytical capability, with a stated goal of characterizing the habitability of Martian surface environments. Optimal progress toward this goal requires that we integrate the results of previous missions (e.g., the 2003 Mars Exploration Rover Mission and the upcoming 2007 Phoenix Scout Mission) and that we match MSL's enhanced analytical capability with an intellectual framework in which to map spacecraft data into quantitative assessments of habitability.
The goal of the present work is to develop and evaluate a more quantitative methodology for assessing the early habitability of Mars via sampling and analytical capabilities that will be, or could conceivably be, deployed in situ. Several factors challenge our ability to be more quantitative in assessing the early habitability of Mars. First, the physical and chemical parameters that constrain habitability must be inferred based on information recorded and preserved in the rock record for three billion years or more. Second, this information must be accessed using a (limited) suite of analytical and sampling capabilities that can be deployed in situ. Third, we presently lack the integrative framework required to weigh and quantify the compound effects of the various environmental controls on habitability.
We plan to develop a framework for mapping mineralogical data (the lasting evidence of physicochemical environment) to habitability (Figure 1). Working across a series of Mars-relevant terrestrial environments, we will assess the capability of this approach with reference to each of the challenges described above (the fidelity of the rock record, the fidelity of the measured data, and the formulation of habitability). More specifically, our approach is formulated in terms of three coupled investigations that correspond directly to these challenges:
Determine the extent to which bulk and spatially-resolved mineralogical analysis can be used to infer prior physicochemical environment with specific emphasis on the main factors that constrain habitability: water activity and chemical composition, energy availability and delivery rate, temperature, and pH.
Develop an integrative energy balance model that quantifies "biomass density potential" as a complex function of the above parameters. Evaluate and calibrate this model by application to actively inhabited systems representing a range of environmental conditions.
Characterize the extent to which different sampling and analytical capabilities result in differential capability to quantify habitability via the above-described approach.
Technical Approach and Methodology
Mineralogical Assessment of Factors Affecting Habitability (Investigation 4.1)
Assessment of early habitability on Mars depends on accessing and interpreting the information contained in the lasting record of early environmental conditions – the rocks and soils of the modern Martian surface environment. Characterization of mineral assemblages in bulk and spatially resolved samples from this record offers the potential to constrain each of the major determinants of habitability. Minerals can 'encode' and preserve information on the physical, chemical, and energetic conditions in their environment of formation, and this code can be read via chemical equilibria, reaction sequences, and reaction rates (e.g., Bethke, 1996). For example, equilibrium assemblages of minerals can be predicted as a function of, e.g., temperature (Figure 2), water-rock ratio (Figure 3), pH, and fluid composition. Identifying and characterizing the relative proportions of minerals in a sample thus provides a way of inferring prior physicochemical environments.
In this way, mineralogy has been used to decipher and reconstruct the physical and chemical conditions associated with hydrothermal and low temperature aqueous alteration of mafic and ultramafic rocks, which are a major focus of this work (e.g., Treiman and Wallendahl, 1998; Palandri and Reed, 2004; Schulte et al., 2006; McCollom, 2007; Navarre-Sitchler and Brantley, 2007; Schwenzer and Kring, 2008). Mineralogical analysis has been similarly used to reconstruct the general environments of earliest and more recent Mars (e.g., King et al., 2004; Hurowitz and McLennan, 2007), and the specific environments of the MER Meridiani and Gusev sites (e.g., Hurowitz et al., 2006; McAdam et al., 2006; Tosca and McLennan, 2006; Ming et al., 2006; Morris et al., 2006). Of most recent interest are geological p-T-X estimates afforded by the discovery of amorphous silica near Home Plate in the Columbia Hills, Gusev Crater (McAdam et al., 2008; Morris et al., 2008; Ruff et al., 2008). Importantly, however, the capability to infer prior physicochemical conditions at such sites based on mineral stability fields has thus far been limited to the small subset of minerals that can be characterized by infrared or Mossbauer spectroscopy. The deployment on MSL of CheMin, which can provide comprehensive and definitive mineralogy via x-ray diffraction and supporting x-ray fluorescence, will dramatically enhance the capability for mineralogical analysis on the surface of Mars.
This work will characterize the potential of comprehensive mineralogical analysis to infer and constrain physical and chemical conditions, and to thereby quantify habitability, across a suite of Mars-relevant settings. The particular focus of this work is to understand how this potential to constrain and quantify habitability varies as a function of environment and sampling/analytical capability:
1. A given environmental parameter (e.g., temperature) may be constrained narrowly, broadly, or not at all, depending on the nature of the mineral assemblage present and the extent to which its components can be resolved and quantified. The level of uncertainty associated with the measured parameter translates directly into uncertainty in quantifying habitability. Different environments are expected to host different (but characteristic) mineral assemblages, which may constrain individual parameters more narrowly or broadly. Indeed, some environments may selectively preserve or erase evidence concerning a particular parameter. Our work will characterize the differential capability for quantifying habitability that results from such environmental variability.
2. Bulk analysis of equilibrium mineral assemblages provides a "snapshot" view of the physical and chemical conditions in which they formed. However, spatial patterns in these assemblages may reveal deeper layers of information concerning the temporal or spatial variability of conditions within a given environment, and may serve to constrain environmental parameters more tightly. For example, alteration of mafic and ultramafic rocks commonly yields veins of alteration material (Figure 4), with mineralogical zones away from the vein indicating, for example, successively lower temperatures (Figure 2) or water/rock ratios (Figure 3). Such zoning can, in theory, be resolved into estimates of temperature, pH, fluid composition, and water/rock ratios. Destruction of this spatial information, for example by powdering, may yield a blurred average of temporal and spatial variability in the conditions of formation (e.g., Figure 4). MSL/CheMin represents a capability to perform comprehensive mineralogical analysis of Mars surface materials in bulk, but spatial resolution of such information will not be possible on scales smaller than the drill cross-section. Our work will assess, as a function of environment type, the differential capability for assessing habitability that results from the potential to preserve and examine spatial patterns in mineralogical information at micron-scale resolution.
Energy Balance Modeling of Factors Affecting Habitability (Investigation 4.2)
It is clear that habitability depends on a variety of environmental factors, and also that inhabited environments reflect a continuum of biomass abundance – from plentiful, to scarce, to non-existent – as a result of the interplay of these factors. However, we largely lack the means to predict the degree of habitability in a system as a function of environmental variables, for two reasons:
1. We have an insufficient understanding of how variations in individual environmental parameters map to quantitative changes in habitability (for example, how biomass abundance may change as a function of temperature, with all other factors held constant).
2. We have an insufficient understanding of how variations in one environmental parameter compare, quantitatively, to variations in another parameter, and how such effects may interact (for example, how a temperature change from 10 to 30 degrees compares to a pH change from 4 to 7, in affecting biomass abundance).
The first challenge is conceivably accessible to experimentation. One means for addressing the second derives from the complexity-based conception of habitability, as follows: A basic tenet of thermodynamics is that complexity can only arise and persist by virtue of the dissipation of free energy. This tenet underlies life's requirement for energy (Schrodinger, 1944) and establishes a quantitative link between habitability and energy availability (Hoehler, 2004; Hoehler, 2007). Specifically, the quantity of biomass (the amount of complex material) that can be supported in a system scales with the energy dissipated therein (Harder, 1997; Tijhuis et al., 1993). Each environmental factor influences habitability by supporting or placing pressure on complexity. In so doing, each alters the rate of energy consumption required to support a unit biomass. For example, increasing temperature increasingly favors disorder (destruction of complexity), and increases the rates of reactions that bring about that destruction. This increased pressure on complexity can be (and is, in biological systems) offset by additional expenditure of energy. In this way, each of the factors that influence habitability can be weighed in relation to the change it incurs in biological energy demand.
As part of our previous NAI work, we developed a conceptual model that casts habitability as a balance between the biomass-normalized demand for energy and the corresponding capability to meet that demand by transduction (harvesting, storage, and reapplication) of energy from the surrounding environment (Hoehler, 2007). The supply and demand terms are both functions of physicochemical environment and resource availability. We will modify this energy balance model in order to calculate "biomass density potential" (a volume-normalized prediction of how much biomass a particular environment may support). A critical requirement for this model is to identify the functions that describe the effects of individual parameters on biological energy demand. Ideally, such a model should incorporate functions for each of the factors that influence habitability. In the present work, we will focus on temperature, pH, and water activity as the parameters most likely to vary widely across the environments considered. Experimental determination of the relation between these parameters and biological energy demand does not lie within the scope of this project. Rather, we will base our model on the results of published work and ongoing collaborative projects:
Experimental work with a range of microbial cultures has demonstrated an exponential relationship (with empirically determined activation energy) between temperature and maintenance energy, a biomass-normalized measure of energy consumption (Harder, 1997; Tijhuis et al., 1993). In our initial model construct, we will assume this relationship. The relationship between pH and energy demand is not fully explored in the literature, but the energy-expending basis by which cells maintain clement intracellular conditions in acidic or basic environments is well understood (Krulwich, 1995; Krulwich et al., 1996; Krulwich and Ivey, 1990). Our model will initially incorporate a pH dependence based on this mechanistic consideration. Experimental work is also underway in a collaborative project (led by Hoehler) to quantify the effects of pH on maintenance energy in microbial cultures, and the model construct will be updated as dictated by results from these experiments. The energy-expending mechanisms associated with decreasing water activity are well characterized when ionic salts are the principal agents affecting that activity (Oren, 1999), as we expect for the sites we will study. Although two basic mechanisms – "salt out" and "salt in" – have been identified, "salt in" strategists typically occupy the upper reaches of the salinity scale (Oren, 1999). Our model will incorporate energetic considerations consistent with "salt out" strategies, both because the energy dependence is better defined and because the range of salinities we expect to encounter are generally more consistent with "salt out" strategists.
We will "calibrate" the energy balance modeling approach, and evaluate its utility in resolving "degree" of habitability, through application to natural systems in which the model inputs (physicochemical environmental data) and output (biomass density) will be characterized. Although the central focus of this work will be a suite of Mars-analog sites (see following section), it is anticipated that the validation/calibration activity will benefit by application to a broader range of systems, in which environmental conditions and energy availability vary widely. To this end, we will apply the model to additional systems for which the necessary parameters are being measured through collaborative projects. Specifically: (i) Hydrothermal and lake environments in Yellowstone National Park (representing a broad array of temperature, pH, and energy availability) that are being characterized by Jahnke and (ii) an array of marine sedimentary systems (typically representing a wide range in energy availability but relatively narrow ranges of temperature, pH, and salinity) that are being similarly characterized by Jørgensen.
Field Program and "Pair-wise" Approach to Information Content Affecting Habitability (Investigation 4.3)
We will conduct a program of field research assessing habitability in a suite of Mars-relevant systems through application of the mineralogy/ energy balance approach. More specifically, we will focus on basalt-hosted or basalt-dominated features, as are expected to dominate Martian surface geology. Working within such environments, we will characterize habitability in multiple examples of each the three main environment types that MEPAG's Next Decade Science Advisory Group (ND-SAG) identified as having highest priority in reference to Mars astrobiology science goals:
Sedimentary Materials Rock Suite
Such materials can reflect a variety of inputs, ranging from transported clasts to chemical precipitates formed in situ. Lithified fine-grained sedimentary materials represent the principal repository of Earth's early microfossil record.
Hydrothermal Rock Suite
Hydrothermal structures provide attractive targets because they provide a rich source of chemical energy that can potentially support local "oases" of high biomass. Because most terrestrial examples also exhibit active and rapid mineralization, they also have potential to record evidence of conditions at the time of formation, and to entomb/preserve any associated microbiology or microbially-templated mineral formations.
Low Temperature Altered Rock Suite
Low temperature alteration of igneous rocks appears to be widespread on Mars. Such processes have potential to deliver energy in sustained fashion to any associated life, and represent one of the most viable environments for the potential widespread and long-term habitability of the Martian crust. Through formation of alteration mineralogy, they may, like hydrothermal vents, record evidence of past habitable conditions and entomb or template evidence of life itself.
A diverse array of basalt-hosted sedimentary, hydrothermal, and low-temperature alteration features are represented among our two principal field locales (altered basalts of the Mauna Kea and Kilauea Volcanic fields, Hawaii, and ophiolite complexes in the Klamath mountains, southern Oregon, as described in a following section).
Both the balance of factors that constrains habitability and the type and abundance of associated biomass are anticipated to differ markedly across the range of studied systems. Similarly, for inactive remnants of such systems, the ability to access information needed to characterize this balance is expected to vary significantly, as a function of both (a) qualitative and quantitative differences in the degree to which different environments preserve evidence of their conditions of formation and (b) the capabilities of various sampling and analytical approaches to resolve and characterize that evidence (an effect that may also vary with environment type). To address each of these considerations, we will employ a "pair-wise" approach to both field sites and methodology.
Active and Remnant Systems
As a system transitions from an active/habitable to an inactive / remnant state, the availability and quality of information required for quantifying habitability are expected to decrease. The most lasting record of such information is that captured in the form of resilient mineral signatures. These signatures may selectively preserve certain types of environmental information over others and may vary in the quantitative extent to which they constrain a given parameter. The information content thus captured will also, expectedly, vary significantly with environment type. Working across the spectrum of systems represented in our field sites, we will examine both active and remnant versions of a particular type of feature (e.g., active and remnant versions of a hot spring).
In active systems, defined here as those having sufficient water activity to sustain life, we will characterize aqueous geochemistry and physical environment (the parameters that directly determine habitability) and, in parallel, will quantify and characterize any associated biomass, on both a total and metabolism-specific basis. Collectively, these factors represent both the inputs (environmental parameters) and output (biomass density) of the integrative energy balance model for habitability. Thus, full characterization of active systems affords the mechanism by which we will validate and "calibrate" that model.
In parallel with the aqueous geochemical, physical, and biomass measurements, we will characterize the associated (and, in particular, actively forming) mineralogy. Such mineralogy represents the potentially lasting recorder of habitable conditions within the studied environment. Because the mineralogical composition of actively-forming minerals is sensitive to environmental conditions, we will determine mineralogy both in the laboratory (with collected samples) and in situ using field instrumentation similar to those used for Mars robotic exploration (e.g., MER Mossbauer MIMOS II, MRO-CRISM VNIR, and MSL ChemMin XRD). Mineralogical characterization in active systems allows comparison with the direct measurements of physical and chemical properties in the system. In so doing, we will characterize, on an environment-specific basis, the qualitative and quantitative extent to which mineralogy records information about each of the factors that constrain habitability.
Remnant versions of formerly active/habitable systems are stripped of directly measurable information concerning the physical and chemical environment that constrains habitability, and likewise of active biomass that may be supported by this environment. In such systems, as on the present surface of Mars, the requisite information must be inferred based on evidence recorded by mineralogical or other markers. We will attempt to constrain and quantify the past habitability of such systems using the coupled mineralogy-energy balance approach described above. Factors such as temperature, pH, and the like will be constrained to ranges by this analysis, rather than exact values (as can be directly measured in active systems), and some pieces of information may be absent altogether. A principal focus of this activity will be to determine the extent to which such uncertainty impacts the quantitative estimation of habitability, on a parameter-specific and environment-specific basis.
In parallel with the mineralogical and chemical characterization of these remnant systems, we will quantify and characterize any biomass residuals (in the total and metabolism-specific sense, as for active systems), in order to understand better the styles of preservation/degradation of organic carbon associated with range of environment types under study.
In seeking to map mineralogy to habitability for inactive/remnant systems, this activity is directly preparatory for the mission that will be undertaken by MSL, in environments that are clear analogs for those likely to be encountered on Mars. Further, this activity will directly assess the utility of an energy balance integrative model for quantifying habitability on Mars to a greater extent than has been possible. The team that will undertake this investigation includes the PI (Blake) and three Co-Is (Des Marais, Morris, Treiman) of the MSL CheMin team, and one Co-I (Morris) of the MSL SAM team.
MSL-Like and Ground-Based Sampling and Analytical Suites
A potentially significant challenge in characterizing the past habitability of Martian environments using in situ science platforms is the limited analytical and sampling capability that can be deployed on the Martian surface. In particular, although a platform such as MSL will deliver a broad range of capabilities for characterizing chemical and mineralogical information at bulk scales, it lacks the potential to preserve spatial integrity within a sample, to apply other than surface-based imaging techniques, or to collect such imagery at micron and sub-micron resolution. The extent to which such added capabilities (as could be brought to bear in a ground-based laboratory) would enhance the quantitative assessment of habitability is uncertain. Although most factors that directly affect habitability are, arguably, bulk properties of the system (that is, relatively invariant over micron scales), additional information concerning the long-term evolution of conditions within the system may be accessible by, e.g., examining water-rock reaction fronts or mineral accretion sequences at micron scales. We will characterize this potential difference by assessing habitability using a suite of analytical and sampling capabilities comparable to that of MSL and, in parallel, using an enhanced capability that allows for precision sampling, extensive sample preparation, and application of high resolution imaging techniques. The specific capabilities to be deployed are described in the following sections.
The principal focus of this investigation is to understand how mineralogical data map to habitability. As such, the centerpiece of this investigation will be a clone of the MSL CheMin instrument (to be provided by Blake) that provides definitive mineralogy data by X-ray diffraction and supporting X-ray fluorescence (note: while there is no longer a requirement for the MSL-CheMin instrument to provide quantitative XRF data, calibrated raw XRF data will nevertheless be transmitted to Earth along with XRD data). In order to understand better how this capability may be enhanced through the application of complementary analytical techniques, we will also characterize samples using analogs or commercial equivalents of the ChemCam and SAM instruments that will fly on MSL, the Mossbauer spectrometer that is still active on the Mars Exploration Rovers, and the VNIR spectrometer on MRO-CRISM. All are, or will be, available in the laboratory of Morris. The CheMin and Mossbauer instruments can be deployed in the field. Provision of samples to these instruments will be limited to the capabilities available on MSL. Samples for the laboratory instruments, CheMin and SAM, will be provided as powder obtained from percussion drilling of targeted samples. Contact and remote instruments will be applied to brushed or untreated surfaces, but not to rock interiors except as powder derived from MSL-like sampling.
To provide as complete an assessment of habitability as possible, and to document the differential capability of a limited MSL-like sampling and analytical suite vs. that assessment, we will also apply an expanded range of state of the art capabilities, as described below.
Enhanced sampling and analytical capabilities will be applied to the same (when possible) or comparable samples as for the MSL-like analyses, with a focus on understanding the importance of spatial information and resolution. Expanded sampling capabilities will include precision sub-sampling, preparation of petrographic thin sections, and other instrument-specific preparations. We will again characterize mineralogy on powdered samples, using a state-of-the-art laboratory XRD instrument (Blake) and laboratory Mossbauer and VNIR instruments (Morris) to assess the importance of instrument-specific limitations in, e.g., 2-theta resolution for XRD. XRF data will likewise be collected in a CheMin-specific geometry using an Amptek™ diode and MSL-style sample cell to compare to XRF data returned by the field instrument and from Mars. Mineralogy will be further characterized, with micron-scale resolution and preservation of spatial information, via ion microprobe (Treiman). As appropriate, samples will also be characterized at micron- and sub-micron resolution via scanning electron microscopy and spectroscopy (available through Blake) and, as required, by secondary ion mass spectrometry (to be arranged with outside laboratories by Treiman). A subset of samples will also be analyzed by Pyrolysis-GC/MS (Vogel in the laboratory of Collaborator Summons) to provide as comprehensive a characterization of organic carbon as possible (thus providing a "ground-based" laboratory counterpart to the capability of SAM).
A key feature of the comparison of MSL-like and ground-based sampling and analytical capabilities will be to determine which expansions of current flight capabilities would yield the greatest enhancement in quantifying habitability. Such a determination would expectedly aid in prioritizing investments in development of new sampling or analytical capabilities for missions, for specific application to astrobiology science objectives.
Mauna Kea and Kilauea, Hawaii
The Island of Hawaii is a well-recognized site for studying the alteration of basaltic precursors by a variety of pathways that are process analogues for alteration of basaltic precursors on Mars. The summit region of Mauna Kea volcano (3000 m to 4200 m) is considered to be semi-arid, barren, alpine desert tundra (e.g., Ugolini, 1974; Wolfe et al., 1997). Under these conditions, palagonitic tephra with no detectable phyllosilicates is a common alteration product of precursor glassy basaltic tephra (e.g., Morris et al., 2000, 2001). Several of the summit cones have undergone different styles of hydrothermal alteration subsequent to their formation. Cone Puu Waiau has undergone hydrothermal alteration by vapors and fluids under near neutral to alkaline conditions, as evidenced by the preponderance of phyllosilicate alteration products (e.g., smectite) (Ugolini, 1974; Wolfe et al., 1997). In contrast, cone Puu Poliahu has undergone hydrothermal alteration under acid sulfate conditions, as evidenced by sulfate alteration products (e.g., alunite and jarosite) (e.g., Wolfe et al., 1997; Morris et al., 1996, 2000). Other sulfate-bearing phases may originally have been present at the time of acid-sulfate conditions (65-4 ka (Wolfe et al., 1997)), but are now absent because of subsequent aqueous leaching. These and other locations for hydrothermal alteration have been mapped by aircraft overflights of Mauna Kea (e.g., Swayze et al., 2002; Guinness et al., 2007).
Kilauea volcano, because it is currently active (Puu Oo cone), provides an analogue site where modern and even current alteration products of basaltic material can be obtained. Hydrothermal alteration is currently active at fumaroles and steam vents at Sulfur Bank, the edge Halemaumau crater, and sulfateras in the Kau Desert (e.g., Morris et al., 2000). Alteration by acid fog/rain occurs along the Southwestern Rift near Halemaumau crater and into the Kau Desert (e.g., Minitti et al., 2007). The Kau Desert is in the rain shadow of Kilauea volcano, permitting the fog/rain to interact with volcanic SO2 emanations. An additional site for the acid fog/rain style of alteration is the saddle road between Mauna Kea and Mauna Loa volcanoes, where there are a number of Muana Loa flows having a range of ages (e.g., Kahle et al., 1988).
Morris has worked extensively on these and other sites and will lead the Hawaii fieldwork.
Klamath Mountains, Oregon and California
A principal focus of this NAI proposal is recognition and interpretation of low-temperature abiotic and biotic effects in basaltic and ultramafic rocks, such as are known on Mars and as are expected on differentiated rocky planets. For this focus, we choose several ophiolite complexes – slabs of oceanic crust thrust onto dry land. Ophiolite sections can include (bottom to top): mantle peridotite, plutonic peridotites and gabbros, sheeted dike systems (remnants of spreading ridges), pillow basalts, and deep-ocean sediments (including clastics and cherts). The Klamath Mountains (SW Oregon and NW California) expose several ophiolite complexes, notably the Josephine and Coast Range (Orr and Orr, 2000; Harper, 2003), which provide opportunities for understanding the recognition and interpretation of low-temperature effects in a range of geochemical settings.
Ultramafic rocks of these Klamath ophiolites are being serpentinized today (Barnes and O'Neil, 1969), so they provide for understanding interaction of cold groundwater with basaltic and ultramafic material. Co-Is in this proposal have started this work, focusing on serpentinization as an energy source as a matrix for preservation of biosignatures (Schulte et al., 2006). Here we would continue that effort to refine the understanding of energy sources, and to examine how biosignatures might/are/could be preserved in aqueous systems that involve serpentinization of olivine (yielding alkaline waters), sulfide-rich systems (yielding acid sulfate waters), and mixed olivine-sulfide systems (yielding mixed but poorly defined waters).
The Klamath ophiolites also afford superb opportunities for exploring spacecraft / instrument-based recognition and interpretation of hydrothermal and sulfidic alteration of basaltic, ultramafic, and volcaniclastic rocks. Among the ocean-floor rocks of the Josephine and Coast-Range ophiolites are remnants of many mid-ocean-ridge hydrothermal systems, including relict 'black smoker' deposits of sulfide. One, the Turner-Albright sulfide deposit, is developed on and in basaltic rocks (flows and hyaloclastites), and sulfide-poor (hydrothermal) and by sulfide-rich (black smoker) fluids (Kuhn and Baitis, 1987; Zierenberg et al., 1988). Temperature estimates for the sulfide alteration assemblages range up to 350°C. Another, the Almeda mine area, along the Rogue River, is a massive sulfide exhalative and stockwork deposit developed mostly in silicic volcaniclastic sediments; it includes rocks altered at hydrothermal and near-ambient temperatures. Yet a third, for example, is developed in ultramafic rocks of the plutonic sequence (Foose, 1986). Beyond the original hydrothermal and sulfidic alteration of the host rocks, these occurrences are also ideal for exploring groundwater (and oxidative) alteration of sulfide minerals to acid solutions. It will be especially interesting to explore how acid sulfate alteration interacts with mafic silicates, which by themselves would produce alkaline solutions.
Characterization of Field Sites
Geological Context and Sampling and Characterization of Rock Suites
Investigations of the inorganic aspects of our Earth analog samples will follow standard field methods and petrologic analyses. In the field, samples will be collected in situ from known geological settings and units. Samples will be chosen to show the ranges of alteration and deposition processes, and documented photographically and in field notes. Oriented samples will be taken as required. In situ measurements (XRD, Mossbauer, and perhaps Raman) of samples in their pristine state and as-prepared in the field using a percussion drill will validate the collection of representative samples and allow the team to determination whether mineralogical changes occurred between sample collection in the field and sample analysis in the laboratory.
Upon return to the lab, samples will be split and prepared as appropriate. Powders will be prepared to mimic RAT or drill products from a spacecraft lander. Petrographic thin sections will be prepared (by Treiman and co-workers) to permit optical identification of minerals and rock textures, and chemical analyses of the minerals by electron microprobe (Treiman). For extended investigations, petrographic thin sections also permit additional analyses, such as trace elements or oxygen isotopes by secondary ion mass spectrometry (SIMS), which will be arranged external to this proposal as needed.
Aqueous Geochemistry and Physical Conditions
For active systems, measurements will be made in situ of the principal physicochemical environmental parameters that factor into the energy balance model (temperature, pH, and salinity), using standard techniques. To quantify energy availability and flux, the aqueous chemical environment will be characterized for a wide range of potential metabolites as follows: ionic species by ion chromatography, dissolved H2, CH4, and atmospheric fixed gases by gas chromatography, short-chain organic acids by high-performance liquid chromatography (Albert and Martens, 1997), total carbonate species by flow injection analysis (Hall and Aller, 1992), and total sulfide species by colorimetry (Fonselius, 1983).
Biomass Characterization and Quantification
We will quantify biomass (active systems) or examine environment-specific effects on biomass/biomarker preservation (remnant systems) by quantifying and characterizing, on a compound-specific basis, microbial membrane lipids and lipid derivatives. For active systems, a snapshot of total and, in some cases, taxonomically specific estimates of microbial biomass abundance will be obtained by membrane lipid analysis. Biomass abundance will be estimated by analysis of polar core lipids (PCL). The PCL are readily degraded by lipases after cell death (Harvey et al., 1986; Vance and Vance, 1985), so that PCL measurement provides a standard whereby microbial cell numbers or total microbial biomass can be estimated (White et al., 1997). Quantification and characterization of molecular structural variation within the acyl, alkyl and isoprenyl chains of the PCL will be pursued to quantify the relative contributions of various taxa (representing different metabolic capabilities) to the total biomass (White et al. 1997; Jahnke et al. 2008).
Lipid analysis will also be applied in characterization of remnant systems, but with qualitatively different purpose. Most membrane lipids, along with the majority of other biomass components, do not recognizably survive diagenetic processing, so that quantification of former biomass abundance is problematic. Nonetheless, because the potential for quantification and characterization of the organic carbon fraction in Martian surface materials is a critical element of the MSL instrument suite, we will seek to evaluate the environmental variation in patterns of carbon preservation as characterized by MSL-like and ground based instrument suites. In addition to the general quantification and characterization of the carbon fraction in remnant systems, a specific focus of this work will be on the characterization and quantification lipids that contain ring structures or are highly branched, which typically survive into the geologic record (Summons and Walter, 1990; Brocks and Summons 2004; Peters et al. 2005 and references therein).
Lipid analyses will be conducted on extracts of powdered rock (remnant and active systems) on sediments, visually obvious biological material (e.g., microbial mats or filaments), or filtrate from fluids present in the system (active systems):
Analytical methods for PCL lipids. As part of our previous NAI-support work, we developed a lipid extraction and analysis protocol for characterizing the bacterial and archaeal populations in a hypersaline microbial mat and the underlying sediment (Jahnke et al., 2008). This protocol is effective for the detection and structural characterization of small amounts of bacterial and archaeal lipids and, with minor modifications, will allow for the general survey of microbial biomass associated with these samples. Analyses will be conducted using both standard gas chromatographic techniques with mass selective detection (for lipid extracts) and pyrolysis GC-MS. The latter technique allows structural characterization of complex macromolecular material in sediments and organic matrices through high temperature (~610 degrees C) cleavage of low molecular weight moieties. This will allow direct comparison of extractible free and functionalized lipids with those bound in high molecular weight matrix and support pyrolysis measurements of fossil analogs, and it provides a method (and data stream) closely analogous to that employed by the MSL/SAM instrument.
Key Applications of this Work
This portion of this work will yield a methodology for better quantifying the habitability of early Martian environments, based on the data stream from the Mars Science Laboratory. This methodology will be developed and evaluated through application to a series of Mars-relevant environments, in advance of and in parallel with the MSL mission. Our proposal team includes several members of the MSL CheMin team and one member of the MSL SAM team, so that the methodology to be developed as part of this work has potential for direct and timely application in interpreting MSL results.
AMES TEAM RESEARCH
Early Habitable Environments and the Evolution of Complexity
---David J. Des Marais, Principal Investigator
Cosmic Distribution of Chemical Complexity
---Lou Allamandola, Lead Co-Investigator
Disks and the Origins of Planetary Systems
---Sanford Davis, Lead Co-Investigator
Mineralogical Traces of Early Habitable Environments
---Tori Hoehler, Lead Co-Investigator
Origins of Functional Proteins and the Early Evolution of Metabolism
---Andrew Pohorille, Lead Co-Investigator