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Project Reports

• ALTERNATIVE EARTH 1 – Atmospheric Traces of Oxygenic Photosynthesis

  The precise timing of the onset of oxygenic photosynthesis is a matter of intense debate. Current estimates span over a billion years of Earth history, ranging from prior to 3.7 billion years ago (Ga), the age of the oldest sedimentary rocks, to 2.4—2.3 Ga, coincident with the first permanent rise of atmospheric oxygen at the so-called “Great Oxidation Event” (GOE). Even without consensus on when biological oxygen production emerged, pinpointing the evolution of this process is essential for understanding Earth’s planetary evolution. If oxygenic photosynthesis evolved early, well before the permanent rise of atmospheric oxygen, the transition to a more oxidizing world in the Proterozoic is likely to be a reflection of Earth’s tectonic history, such as the emergence and stabilization of continents and related shifts in the temporal patterns of volcanism and associated fluxes of reduced gas. Alternatively, biological evolution (specifically, the emergence of oxygenic photosynthesizers) may have directly triggered this switch in Earth states. We are exploring these alternative models and their implications for the systematics of planetary oxygenation on Earth from a combined experimental, empirical and theoretical perspective.

  ROADMAP OBJECTIVES: 4.1 7.2

• Project 1: The Origin of Homochirality

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

  ROADMAP OBJECTIVES: 1.2 3.2 3.4 4.1 4.2 7.1 7.2

• Life Underground

  Our multi-disciplinary team from the University of Southern California, California Institute of Technology, Jet Propulsion Lab, Desert Research Institute, Rensselaer Polytechnic Institute, and Northwestern University is developing and employing field, laboratory, and modeling approaches aimed at detecting and characterizing microbial life in the subsurface—the intraterrestrials. We posit that if life exists, or ever existed, on Mars or other planetary body in our solar system, evidence thereof would most likely be found in the subsurface. This study takes advantage of unique opportunities to explore the subsurface ecosystems on Earth through boreholes, mine shafts, sediment coring, marine vents and seeps, and deeply-sourced springs. Access to the subsurface—both continental and marine—and broad characterization of the rocks, fluids, and microbial inhabitants is central to this study. Our focused research themes require subsurface samples for laboratory and in situ experiments. Specifically, we are carrying out in situ life detection, culturing and isolation of heretofore unknown intraterrestrial archaea and bacteria using numerous novel and traditional techniques, and incorporating new and existing data into regional and global metabolic energy models.

  ROADMAP OBJECTIVES: 2.1 2.2 3.1 3.2 3.3 4.1 5.1 5.2 5.3 6.1 6.2 7.2

• Field Activities at the Coast Range Ophiolite Microbial Observatory (CROMO)

  CROMO provides ongoing excellent exposure to samples of ophiolite-hosted serpentinites and associated rocks, access to monitoring wells important for observing serpentinization-related groundwater flow regimes, and serves as a community-building platform that fosters new scientific collaboration. CROMO has served as a test-bed for refining new experimental approaches, and progressing from basic observations to more complex, multi-disciplinary science.

  Within the past year, studies at CROMO have focused on the subsurface hydrogeochemical dynamics, by monitoring groundwater hydrology, measuring the concentrations and composition dissolved iron, sulfur, dissolved inorganic carbon, major inorganic anions and cations, dissolved hydrogen, carbon monoxide and methane gases, and organic compounds, in addition to time-series analyses.

  CROMO datasets are being incorporated into an exploratory database project aimed at addressing NASA’s public data requirements. Once developed, this database will help to address data sharing plans for collaborators and serve as a valuable tool for CROMO data management across collaborating labs.

  In 2015, project members Dawn Cardace, Masako Tominaga, Michael Kubo, Lauren Seyler, Mary Sabuda, Abigail Johnson, Ken Wilkinson, & Cameron Hearne participated in a field trip to CROMO from August 21-27, to continue seasonal bio/geo/chemical monitoring of the wells, as well as assessing the site for future geophysical measurements.

  ROADMAP OBJECTIVES: 5.1 5.2 5.3 6.1 6.2 7.1 7.2

• ALTERNATIVE EARTH 2 – Dramatic Oxygen Fluctuations

  Our studies of the middle portion of the Paleoproterozoic (2.2 to 2.0 Ga) are focused on whether Earth’s surface experienced a unidirectional oxygen rise or instead rose to high levels (potentially near-modern) and then crashed dramatically. More specifically, we are rigorously testing the idea that the middle Paleoproterozoic Earth was marked by high oxygen levels—in strong contrast to traditional arguments for far lower values. The resolution of this question is perhaps one of the most important issues in Earth history, as it points to the likelihood that the much later development of complex life was not solely contingent on high levels of oxygen at Earth’s surface. Work to date has focused on trying to place empirical constraints on ocean-atmosphere O₂ levels during the Paleoproterozoic and developing quantitative theoretical tools for understanding the dynamics of large shifts in ocean-atmosphere oxygen levels.

  ROADMAP OBJECTIVES: 4.1 7.2

• Inv 3 – Planetary Disequilibria: Characterizing Ocean Worlds and Implications for Habitability

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

  ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 4.2 6.2 7.1 7.2

• Astronomical Biosignatures, False Positives for Life, and Implications for Future Space Telescopes

  In this task, we identify novel biosignatures and also identify “false positives” for life, which are ways for non-biological processes to mimic proposed biosignatures. Of primary concern are false positives that could mimic easier to detect biosignatures like O₂, which we plan to search for with future space-based telescopes. This is a growing area of research that VPL’s past work has motivated, leading to multiple research teams across the planet following our example. Our work continues to be at the forefront of this area of work, as we have identified new non-biological mechanisms for mimicking signs of life. Further, we explained the ways in which these non-biological mechanisms could be identified, and “true positives” from biology confirmed with secondary measurements. Finally, we communicated these lessons to various teams that are studying concepts for future missions that would search for these signs of life. This connection to missions will ensure that our research is incorporated into those missions, so that they will not be “tricked” by these false positives.

  ROADMAP OBJECTIVES: 1.1 1.2 4.1 4.3 5.2 5.3 7.2

• ALTERNATIVE EARTH 3 – Oxygen Stasis and the Rise of Eukaryotes

  The importance of a full understanding of the controls on ocean-atmosphere O₂ levels during the mid-Proterozoic is difficult to overstate. The evolution of O₂ levels in the mid-Proterozoic ocean-atmosphere system forms the backdrop for the initial emergence and subsequent evolutionary stasis of eukaryotic life. Furthermore, it provides the possibility of a remarkably long period of Earth’s history during which many of the links among tectonics, climate, and life may have been short-circuited and/or amplified in unusual ways. Finally, it provides the preface that is essential reading for any story about the proximate causes of the subsequent emergence of complex life in the late Neoproterozoic. The central question in this regard is whether ocean-atmosphere O₂ levels were low enough to inhibit the evolution and ecological emergence of complex multicellular life, or must we seek mechanisms strictly associated with internal biology to explain this event—or both? Our developing framework for very low oxygen levels during the mid-Proterozoic in the deep ocean, shallow ocean, and atmosphere is the baseline against which the dramatic environmental, climatic, and biotic events and triggers of the later Proterozoic should be assessed.

  ROADMAP OBJECTIVES: 4.1 4.2 7.2

• ALTERNATIVE EARTH 4 – the Rise of Complexity Amid Environmental Turmoil

  Climatic turmoil and major upheavals in global biogeochemical cycles characterize the latter part of the Proterozoic Eon, during the so-called Neoproterozoic (1,000–541 million years ago). The Neoproterozoic was marked by pronounced shifts in atmospheric composition—especially increased oxygen levels. This environmental instability provided the backdrop for the rise of complex life, including animals; however, limited empirical constraints have hindered attempts to untangle the cause-and-effect relationships among biological innovations, shifts in ecosystem complexity, and biogeochemical evolution. Likewise, still sparse coupled geochemical and paleontological records make it difficult to gauge whether the Neoproterozoic unfolded as a unidirectional march toward greater organismal complexity and higher oxygen levels, as traditionally envisioned, or whether dramatic swings in surface oxygen levels accompanied non-unidirectional ecological shifts. To resolve this debate, we are producing extensive, high-resolution records of oxygen levels and tracking the distribution, abundance, and impact of eukaryotic phytoplankton over this critical interval. Our central goal is to work synergistically with the Origins of Complexity NAI Team to better understand how the rise of complex life shaped planetary-scale biosignatures.

  ROADMAP OBJECTIVES: 4.1 4.2 7.2

• Subsurface Serpentinization Processes and In-Situ Microbial Life in Oman

  The Rock-Powered Life team has initiated several field-based efforts in Oman focused on characterizing the geochemistry and microbial community structure and activity within massive exposures of peridotites undergoing low-temperature serpentinization. In this project, we are using deep wells drilled hundreds of meters into peridotite catchments to access waters stored in the deep subsurface, and to capture the mineralogical and biological processes that give rise to hyperalkaline fluids rich in dissolved H₂ and CH₄. In particular we extract biomass from the fluids for genetic sequencing in order to identify the types of life that can live within the extreme conditions of low energy and carbon availability, and to infer the metabolisms that sustain in-situ life activity. These analyses are paired with mineralogical analyses of the subsurface rocks and isotopic analyses of the dissolved gases in order to quantify the water/rock reactions occurring in the modern system that give rise to energy transfer from the rocks to living ecosystems.

  ROADMAP OBJECTIVES: 3.1 4.1 5.3 7.2

• Evolution of Protoplanetary Disks and Preparations for Future Observations of Habitable Worlds

  The evolution of protoplanetary disks tells the story of the birth of planets and the formation of habitable environments. Microscopic interstellar materials are built up into larger and larger bodies, eventually forming planetesimals that are the building blocks of terrestrial planets and their atmospheres. With the advent of ALMA and continuing use of the Hubble Space Telescope, we are poised to break open the study of young exo-planetesimals, probing their organic content with detailed observations comparable to those obtained for Solar System bodies. Furthermore, studies of planetesimal debris around nearby mature stars are paving the way for future NASA missions to directly observe potentially habitable exoplanets.

  ROADMAP OBJECTIVES: 1.1 1.2 3.1 7.2

• Exoplanet Detection and Characterization: Observations, Techniques and Retrieval

  In this task, VPL team members use observations and theory to better understand how to detect and characterize extrasolar planets. Techniques to improve the detection of extrasolar planets, and in particular smaller, potentially Earth-like planets are developed, along with techniques to probe the physical and chemical properties of exoplanet atmospheres. These latter techniques require analysis of spectra to best understand how it might be possible to identify whether an extrasolar planet is able to support life, or already has life on it.

  ROADMAP OBJECTIVES: 1.1 2.2 7.2

• Mars Analogs: Habitability and Biosignatures in the Atacama Deser

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

  ROADMAP OBJECTIVES: 2.1 5.1 5.3 6.1 6.2 7.1 7.2

• RPL and Expedition 357: Serpentinization and Life at the Atlantis Massif

  Circulating hydrothermal fluids associated with mid-ocean ridges represent some of the most prominent examples of the intersection between chemical energy and the biosphere. The Lost City Hydrothermal Field, which sits atop the Atlantis Massif near the Mid Atlantic Ridge hosts a microbial ecosystem which feeds off the products of serpentinization. IODP Expedition 357, which sailed in Fall 2015, obtained rock cores and fluids from the Atlantis Massif, which are being used for the coordinated investigation of serpentinization processes and life. Lost City is known to sustain abiogenic organosynthesis reactions and as such has been suggested to be an analogue to prebiotic early Earth environments and potential extraterrestrial habitats.

  ROADMAP OBJECTIVES: 3.1 3.4 5.1 5.2 5.3 7.2

• Exploring the Structure and Composition of Exoplanets With Current and Future Telescopes

  This project addresses a major frontier of planetary science and astrobiology, namely the identification and characterization of habitable (and inhabited) exoplanets. Measurements of molecular absorption in the atmospheres of these planets offer the chance to explore several outstanding questions regarding the atmospheric structure and composition of hot Jupiters. Targeted questions include the possibility of bulk compositional variations among planets, and the presence or absence of a stratospheric temperature inversion on individual planets. In this reporting period, we emphasized four areas:
  1. We improved our modeling and analysis of exoplanet transit and eclipse measurements obtained with the Hubble Space Telescope (HST) and the Spitzer Space Telescope on highly irradiated, Jupiter-mass planets.
  2. We improved our data analysis methods to better understand aspects of measuring the chemical composition of the planet’s atmosphere, and we advanced the chemical and thermal modeling of the planet’s hot dayside.
  3. We developed simulations of future observations with the James Webb Space Telescope (JWST), and we provided science leadership for a future balloon-borne telescope that can perform transit spectroscopy of hot exoplanet atmospheres.
  4. We estimated the discovery yield of future Earth-like exoplanet imaging missions as part of the planning process for the next Astrophysics Decadal Survey, and we are now expanding this effort to estimate the science yield from spectroscopic characterization of them.

  ROADMAP OBJECTIVES: 1.1 1.2 7.2

• Interstellar and Nebular Chemistry: Theory and Observations

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

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

  ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 3.2 7.1 7.2

• Subglacial Environments as Water‐Rock Hosted Microbial Ecosystems

  Glaciers, ice sheets and ice caps cover ~11% of the earth’s surface, and likely covered up to 100% during Neoproterozoic glaciations. The beds of these ice masses can have significant sectors at the pressure melting point. The resulting water lubricates ice sliding and accelerates erosion, provides habitat for subglacial microbial ecosystems, and may have acted as refugia during past global glaciations on Earth. Such environments may also act as habitats for life on other planetary bodies.

  Grinding of bedrock by glaciers exposes fresh mineral surfaces capable of sustaining microbial metabolism. The foci of RPL investigations on subglacial environments are categorized into two key areas of relevance to habitability studies: i) determine the extent to which minerals support chemotrophic metabolism and the production of biosignatures (e.g., weathering products), and ii) quantifying the influence of water-rock interactions in supplying substrates to support energy metabolism. Through these interdisciplinary and collaborative studies, we aim to characterize the active microbial processes in subglacial environments and to define the sources of energy that sustains this microbial life.

  ROADMAP OBJECTIVES: 2.1 5.1 5.2 5.3 6.1 6.2 7.2

• Global Surface Biosignatures: Reflectance Spectra of Anoxygenic Phototrophs and Cyanobacteria

  This project investigates the spectral reflectance signature of anoxygenic photosynthetic bacteria, as an alternative to the “biosignature” of the vegetation “red-edge.” The vegetation red-edge is so called due to the sharp contrast in visible light absorbance by light harvesting pigments in plant leaves versus their high reflectance in the near-infrared (NIR). This contrast occurs around 700 nm in the red/far-red. This signature is ubiquitous among plants, which all utilize chlorophyll a. However, anoxygenic phototrophs contain a diverse array primary photopigments, including bacterichlorophylls (Bchl) a, b, d, e, and g. These Bchl pigments display different absorption maxima with peaks primarily in the NIR. There is an abundance of data on plant spectral reflectance thanks to the Earth remote sensing field. However, there is a dearth of data on anoxygenic phototrophs and cyanobacteria. For this project, we measured the reflectance spectra of pure cultures as well as environmental samples of laminated microbial mats to characterize their detectable biosignature features. This work will help inform the search for life on exoplanets at a similar stage of evolution or biogeochemical state as the pre-oxic Earth.

  ROADMAP OBJECTIVES: 4.1 5.2 7.2

• Detection of Biosignatures

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

  ROADMAP OBJECTIVES: 2.1 2.2 7.1 7.2

• Advances in Gene Sequencing From Low-Biomass Water-Rock Hosted Ecosystems

  One of the approaches our team is taking to explore rock-powered life is to study microorganisms hosted within rocks that are undergoing potentially life-supporting reactions with water. The chemistry of the rock microenvironments shapes the abundance, diversity and distribution of microbial life. In turn, that microbial life locally affects the in-situ geochemistry. This project is currently focusing on the successful extraction and sequencing of the exceedingly small amounts of DNA that accumulates within rocks, in order to successfully detect and characterize the rock-hosted life. Ultimately our improved approaches will support the application of next-generation DNA sequencing technology in the study of natural microbial ecosystems that are key for understanding the mechanisms of rock-powered life.

  ROADMAP OBJECTIVES: 3.2 4.1 5.1 5.2 5.3 6.1 7.2

• The Long Wavelength Limit of Oxygenic Photosynthesis

  Oxygenic photosynthesis (OP) produces the strongest known biosignatures at the planetary scale on Earth: atmospheric oxygen and the spectral reflectance of vegetation. The pigment chlorophyll a was long considered the unique controller of both of these biosignatures, in its capability to enable water splitting to obtain electrons and thus produce oxygen as a biogenic gas, through spectral absorbance of light from the blue to 680 nm in the red. Then the discovery in 1996 of the cyanobacterium Acaryochloris marina shattered this conventional wisdom. A. marina was found to have replaced 93-97% of Chl a with Chl d, which enables it to perform oxygenic photosynthesis with much lower energy photons in the far-red/near-infrared. Since that first discovery in 1996, more far-red oxygenic phototrophs have been discovered, revealing a previously unsuspected diversity in the photosystems of oxygenic phototrophs. We seek to determine the long wavelength limit at which OP might remain viable and what factors affect the selection of that wavelength limit. This would clarify whether and how to look for OP adapted to the light from stars with a difference radiance spectrum from our Sun.

  Under this project in previous years and with other co-investigators, we spectrally quantified the thermodynamic efficiency of photon energy use in Acaryochloris marina str. MBIC11017, determined that its water-splitting wavelength is in the range 710-723 nm, and that it is more efficient than a Chl a cyanobacterium. The current focus of the project is to understand the adaptations of far-red/near-infrared (NIR) oxygenic photosynthetic organisms in general: in which environments they are competitive against chlorophyll a organisms, and what energetic shifts have been made in their photosynthetic reactions centers to enable their use of far-red/NIR photons. We are conducting field sampling and measurements to isolate new strains of far-red-utilizing oxygenic photosynthetic organisms, to quantify the spectral and temporal light regime in which they (and previously discovered strains) live in nature, and to use these light measurements to drive kinetic models of photon energy use to determine efficiency thresholds of survival.

  ROADMAP OBJECTIVES: 3.2 4.2 5.1 5.3 6.2 7.2

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

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

  ROADMAP OBJECTIVES: 7.1 7.2

• Global Surface Biosignatures: Circular Polarization Spectra of Anoxygenic Phototrophs and Cyanobacteria

  This new project focuses on characterizing the chiral signature of biological molecules. The phenomenon of chirality is a powerful biosignature and, in principle, can be remotely observed on planetary scales using circular polarization spectroscopy. Molecules such as photosynthetic pigments are optically active and have several chiral centers, and influence the polarization of light. This can be measured using full Stokes spectropolarimetry. The goal of this interdisciplinary project is to characterize the circular polarization spectra of chiral photosynthetic pigments in anoxygenic phototrophs and cyanobacteria as global surface biosignatures.

  ROADMAP OBJECTIVES: 4.1 5.2 7.2

• Environmental and Biological Signatures in Yellowstone National Park Silica Precipitating Hot Springs

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

  ROADMAP OBJECTIVES: 1.1 2.1 6.1 7.1 7.2

• Solar System Analogs for Exoplanet Observations

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

  ROADMAP OBJECTIVES: 1.2 2.2 7.1 7.2

• Biogenic Gases From Anoxygenic Photosynthesis in Microbial Mats

  This lab and field project aims to measure biogenic gas fluxes in engineered and natural microbial mats composed of anoxygenic phototrophs and anaerobic chemotrophs, such as may have existed on the early Earth prior to the advent of oxygenic photosynthesis. The goal is to characterize the biogeochemical cycling of S, H, and C in an effort to constrain the sources and sinks of gaseous biosignatures that may be relevant to the detection of life in anoxic biospheres on habitable exoplanets.

  ROADMAP OBJECTIVES: 4.1 5.2 6.1 7.2

• Taphonomy of Microbial Ecosystems

  We perform experiments to understand shapes, molecules and isotopic signals of microbial processes in modern and old sediments. Experimental studies of microbial interactions with sediments, ions in the solution and the flow help us elucidate mechanisms that may have shaped sandy surfaces and preserved fossils on these surfaces at the dawn of animal life. Culture-based studies of isotopic fractionations produced by microbial processes and microbial membrane lipids help us interpret corresponding signals in the rock record and modern environments.

  ROADMAP OBJECTIVES: 2.1 4.1 4.2 5.1 5.2 6.1 7.1 7.2

• Project 3G: A 3,400 Ma-Old Shallow Water Anaerobic Sulfuretum Evidences the Anoxic Archean Atmosphere

  Carbonaceous cherts of the ~3430 Ma Strelley Pool Formation contain innumerable “swirls” of fossilized sulfuretum bacteria encompassing quartz-replaced anhydrite nodules intermixed with layered assemblages of phototrophic filamentous fossil microbes. The geologic setting of the fossil-hosting unit, the preservation of the sulfuretum swirls adpressed to quartz pseudomorphs of precipitated anhydrite or gypsum, and the lack of physical disruption of the assemblage document its near-surface quiescent marine environment. The anaerobic physiology of the sulfuretum microbes indicates that Earth’s surface was anoxic. This exceedingly ancient biota is therefore interpreted to be composed of anaerobic H2S-producing sulfuretum microbes and H₂S-using anoxygenic phototrophic bacteria. As such, this first-identified fossil microbial consortium provides firm evidence of the anoxia of Earth’s early environment.

  ROADMAP OBJECTIVES: 4.1 5.2 6.2 7.2

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

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

  ROADMAP OBJECTIVES: 7.2