2014 Annual Science Report

Astrobiology Roadmap Objective 4.1 Reports Reporting  |  SEP 2013 – DEC 2014

Project Reports

  • 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 5.3 6.1 6.2 7.2
  • Life Underground

    Our multi-disciplinary team from USC, Caltech, JPL, DRI, RPI, and now also Northwestern 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 3.3 4.1 5.1 5.2 5.3 6.1 6.2 7.2
  • Astrobiology of Icy Worlds

    Our goal in the Astrobiology of the Icy Worlds Investigation is to advance our understanding of the role of ice in the broad context of astrobiology through a combined laboratory, numerical, analytical, and field investigations. Icy Worlds team pursues this goal through four major investigations namely, the habitability, survivability, and detectability of life of icy worlds coupled with “Path to Flight” Technology demonstrations. A search for life linked to the search for water should naturally “follow the ice”. Can life emerge and thrive in a cold, lightless world beneath hundreds of kilometers of ice? And if so, do the icy shells hold clues to life in the subsurface? These questions are the primary motivation of our science investigations

    ROADMAP OBJECTIVES: 1.1 2.1 2.2 3.1 3.2 4.1 5.1 5.2 5.3 6.2 7.1
  • Project 1: Dynamics of Self-Programming Systems

    This project is a theoretical attempt to understand how evolution can arise from inanimate physical systems. The key idea is that matter can organize into structures that not only replicate and carry information, but are able to program and reprogram themselves functionally. We have already been able to construct simple computer programs that can increase their complexity in an open-ended way, but in this grant period we have been building a mathematical formulation of how this arises using recursive function theory. We have also been trying to develop cellular automata meta-programming pairs that can co-evolve complexity.

    ROADMAP OBJECTIVES: 3.2 4.1 4.2 5.3 6.2
  • Biosignatures in Ancient Rocks – Kasting Group

    We have been working on two things: 1) the question of whether there are plausible “false positives” for life on extrasolar planets, i.e., high abiotic O2 and/or O3 levels that might be confused with evidence for photosynthesis, and 2) hydrodynamic escape of hydrogen from H2- or H2O-rich primitive atmospheres. We are developing a two-component model to describe this process. Old single-component models evidently do not obey the diffusion limit, so are are trying to remedy that.

    ROADMAP OBJECTIVES: 1.1 2.1 4.1 7.2
  • Disks and the Origins of Planetary Systems

    This task is concerned with the evolution of complex habitable environments. The planet formation process begins with fragmentation of large molecular clouds into flattened disks. This disk is in many ways an astrochemical “primeval soup” in which cosmically abundant elements are assembled into increasingly complex hydrocarbons and mixed in the dust and gas within the disk. Gravitational attraction among the myriad small bodies leads to planet formation. If the newly formed planet is a suitable distance from its star to support liquid water at the surface, it is in the so-called “habitable zone.” The formation process and identification of such life-supporting bodies is the goal of this project.

    ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 4.1 4.3
  • Biosignatures in Ancient Rocks – Kump Group

    We are analyzing FAR-DEEP cores that span the putative “oxygen overshoot” associated with the termination of the Great Oxidation Event, 2.0 billion years ago. The volcanic rocks in question are highly oxidized. Our hypothesis is that oxygen-enriched groundwaters altered these rocks during a time interval when atmospheric oxygen concentrations approached modern levels, falling subsequently to lower values characteristic of the ensuing billion years. Kump has also proposed a new explanation for the “second rise of atmospheric oxygen” in the Neoproterozoic (ca. 850 Ma).

    ROADMAP OBJECTIVES: 1.1 4.1 4.2 4.3 5.2 6.1
  • Early Animals: Lipid Biomarkers as the Earliest Evidence of Metazoans

    A complex hydrocarbon, 24-isopropylcholestane, has been proposed as a biomarker for a particular group of sponges—the earliest-branching animals—and found in Neoproterozoic rocks. However, a particular group of marine algae, the pelagophytes, can also produce the precursor to this compound, and it has not been known whether this ability is more widespread within the eukaryotes. We have used genomic data combined with time-calibrated phylogenies to approach this question and find that pelagophytes did not evolve this ability until the Paleozoic, while in sponges it evolved in the Neoproterozoic. This work supports the conclusion that this sterane is a true sponge biomarker.

  • Charnay NAI NPP PostDoc Report

    My project focuses on the modeling of clouds and photochemical haze in the atmospheres of the early Earth and exoplanets. I use a 3D model, developed to simulate any kind of atmospheres, to study the formation, dynamics, climatic impact and observational features of clouds/haze. My first object of interest is GJ1214b, a mini-Neptune whose observations by HST revealed a cloudy/hazy atmosphere. The formation of such high and thick clouds is not understood. My second object of interest is the Archean Earth for periods with a methane-rich atmosphere leading to the formation of organic haze.

  • Biosignatures in Ancient Rocks – Ohmoto Group

    This project has been aimed at understanding the chemical and biological natures of the ocean-atmosphere-lithosphere systems during the Archean. A second objective is testing a hypothesis that the MIF-S isotope signatures, which characterize some Archean and younger sedimentary rocks, were generated during reactions between hydrothermal fluids and organic-rich sediments, rather than through atmospheric reactions.

    ROADMAP OBJECTIVES: 1.1 4.1 6.1
  • Project 1C: Studies of Early-Evolved Enzymes in Modern Organisms May Reveal the History of Earth’s Ambient Temperature Over Geological Time

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

    ROADMAP OBJECTIVES: 4.1 5.1 6.1
  • Project 3: The Origin of Homochirality

    A universal aspect of living systems on Earth is their homochirality: Life uses dextrorotary sugars and levorotary amino acids. The reasons for this are hotly debated and not close to being settled. However, the leading idea is that autocatalytic reactions grew exponentially fast at the origin of life, and whatever chiral symmetry breaking was accidentally present became amplified subsequently. We are calculating the way in which this can take place using statistical mechanics, and also trying to see how a uniform homochirality could be stable to spatial fluctuations.

    ROADMAP OBJECTIVES: 3.2 3.4 4.1 4.2 5.1 5.2 7.1 7.2
  • Early Animals: Modeling the Biotic-Abiotic Interface in the Early Evolution of Multicellular Form

    The size of early multicellular organisms was sufficint to modify their local environment. Our initial work modeling of Neoproterozoic frond-like forms in the earliest-known communities of multicellular organisms demonstrates they were of sufficient scale and density to generate a distinctive canopy flow-regime. This modified environment yielded a selective advantage towards large eukaryotic forms that evolved at this time. This result is a function of limits imposed by diffusion at the surface of organisms, and how height and attendant velocity exposure escape these limits. Building on these results, we are now developing additional models of abiotic/biotic interactions at organismal surfaces, which are implicit in the morphology, development and orientation of other Neoproterozoic fossils. Ultimately, this work will help illuminate how forms initialy dependent on passive diffusion became more trophically complex, yielding a transition to the animal radiation.

    ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1
  • Project 4: Rapid Evolution in Stressed Populations: Theory

    Evolution is typically thought of as occurring over millions of years. But recently it has become clear that we have grossly over-estimated this time scale. Perhaps the most famous example of this is the rapid evolution of resistance of bacteria, worldwide, to modern antibiotics. Similarly, early life has an evolution time scale problem: given the age of the Earth and the known age of the Last Universal Common Ancestor, life must have arisen and evolved the majority of the complexity of the modern cell in less than a billion years. This project is a theoretical attempt to understand how a fluctuating environment can accelerate evolution rate, and lead to evolution on ecosystem time scales. Eventually, this work will join up with the experimental work being done by our team, using the GeoBioCell, in Project 8.

    ROADMAP OBJECTIVES: 4.1 4.2 5.1 5.2 5.3 6.1
  • Early Animals: Predation, Oxygen and Preservation in Early Animal Evolution

    Research in the Knoll lab has focused on three major issues relevant to early animal evolution. First, Knoll and colleagues developed a hypothesis to explain the mid-Neoproterozoic diversification of eukaryotes by invoking the evolution of eukaryote-eating protists (analogous to the evolution of carnivores driving the Cambrian diversification of animals). Second, work to integrate ecological data from modern oxygen-minimum zones with paleontological and geochemical data has yielded insights on early animal evolution. Finally, collaborations with other groups have focused on a variety of topics including the preservation of tiny animals in phosphate in the earliest Cambrian, a new Neoproterozoic record of vase-shaped protists.

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

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

    ROADMAP OBJECTIVES: 2.1 4.1 5.3 7.1
  • Biosignatures in Extraterrestrial Settings

    The Biosignatures in Extraterrestrial Environments group works on finding and characterizing exoplanets, in particular through very high resolution spectroscopy; and developing new techniques for finding exoplanets and characterizing their properties. It also works on understanding the evolution and dynamics of planetary systems, including the solar system, and the role of astrophysical processes in establishing and sustaining life in extraterrestrial environments.

    ROADMAP OBJECTIVES: 1.1 1.2 2.1 2.2 3.1 4.1 4.3 6.2 7.1 7.2
  • Project 5: The Environment of the Early Earth

    This project involves the development of capabilities that will allow scientists to obtain information about the conditions on early Earth (3.0 to 4.5 billion years ago) by performing chemical analyzes of crystals (minerals) that have survived since that time. When they grow, minerals incorporate trace concentrations of ions and gaseous molecules from the local environment. We are conducting experiments to calibrate the uptake of these “impurities” that we expect to serve as indicators of temperature, moisture, oxidation state and atmosphere composition. To date, our focus has been mainly on zircon (ZrSiO4), but we have recently turned our attention to quartz as well.

  • Early Animals: Sensory Systems and Combinatorial Codes

    Understanding the evolution of integrated sensory organs—such as the eyes, ears and nose that develop in concert on our heads—is fundamental to understanding animal complexity. These are the features that permit movement and the environmental responses that characterize animals. We examine understudied early branches of the animal family tree, with a focus on the jellyfish Aurelia, to understand how the genetic regulation of sensory organs is conserved in some cases and evolves in others. Comparison of developmental regulation reveals how similar gene networks can be differentially modified and deployed, permitting the evolution of complex sensory systems. Jellyfish provide an ideal study system for the examination of the evolution of such sensory systems in animal evolution, as they are the most basal branch the animal tree with multiple sensory modes, and these develop at multiple stages in a complex life history. This provides us the ability to compare and contrast within the broader cnidarian group to which jellyfish belong, and to the bilaterians, the broad group containing humans and most other animals. The application of genomic methods greatly enhances our ability to pursue these questions.

  • Biosignatures of Ancient Rocks – Hedges Group

    Our work involves the design, assembly, and release to the public of a tree of life calibrated to geologic time (timetree). It is needed by astrobiologists to help determine the source of biomarkers for the presence of life in the geologic record.

    ROADMAP OBJECTIVES: 3.3 3.4 4.1 4.2 7.1 7.2
  • Project 1E: Microbial Communities in Chocolate Pots Hot Spring, Yellowstone National Park

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

    ROADMAP OBJECTIVES: 2.1 4.1 5.1 5.3 7.1
  • Project 5: The Origins of Life’s Diversity

    The huge diversity of life poses a major challenge to ecological theory and a major source of optimism for astrobiology. Ecological theory argues that a single environmental niche should be colonized by a single species of organism, or perhaps a small community, and so the diversity of life should be essentially a measure of the number of niches present. The huge diversity of life does suggest, however, that the ability of life to explore, colonize and especially create environmental niches has been drastically underestimated. Accordingly, the likelihood of extraterrestrial life arising is also underestimated, or at least inadequately estimated, by our present understanding of biological evolution. This project attempts to solve this problem by developing a new theory for niche diversity.

    ROADMAP OBJECTIVES: 3.4 4.1 4.2 5.1 5.2 5.3 6.1 6.2
  • Biosignatures of Life in Ancient Stratified Ocean Analogs

    Instigated by Macalady and Kump in 2010, this project investigates biosignatures of life in modern analogs for stratified ancient and/or extraterrestrial oceans. The primary field site is a sinkhole in Florida. Other field site include stratified ocean analogs in the Bahamas, New York State, and the Dominican Republic. A website monitoring the activities of an informal working group on Early Earth Photosynthesis is maintained by Macalady (http://www.geosc.psu.edu/~jlm80/EEP.html).

    ROADMAP OBJECTIVES: 2.1 3.3 3.4 4.1 5.2 5.3 6.1 7.1 7.2
  • Early Animals: Taphonomic Controls on the Early Animal Fossil Record

    We have been carrying out a number of studies in support of our objective to investigate the controls on the preservation of complex life on earth, with the ultimate aim of allowing the fossil evidence for the succession of events to be constrained and interpreted. These studies include investigating the connections between taphonomy and ecology of the Ediacara Biota based on the collection of fossil specimens and their careful examination, laboratory experiments designed to better understand how these fossils became preserved in different settings, and investigations of how Proterozoic eukaryotic microfossils are preserved, again from studying both new fossil material through a variety of approaches, and performing analog experiments in the laboratory.

  • Project 6. Mining Archaeal Genomes for Signatures of Early Life: Comparison of Metabolic Genes in Methanogens

    Methanogenic archaea derive energy from simple starting materials, producing methane and carbon dioxide in the process. The chemical simplicity of the growth substrates and versatility of the organisms in extreme environments provide for a possibility that they could exist on other planets. By characterizing the evolution of methanogens from the most simple to most complex organism as well as their growth characteristics under controlled environments, we hope to address the question as to whether they could exist on planets such as Mars, where bursts of methane have been seen, yet no source has yet been identified.

    ROADMAP OBJECTIVES: 1.1 2.1 3.1 3.2 3.3 3.4 4.1 4.2 5.1 5.2 5.3 6.1 6.2 7.1 7.2
  • Early Animals: The Genomic Origins of Morphological Complexity

    The Peterson lab has continued its focus on micro-RNAs (miRNA) in order to better understand the relationship between genetic and phenotypic diversity. Toward this goal, they have established a new database of miRNA genes (as opposed to sequences) assembled under strict quality control and an entirely novel nomenclature, bridging the different names previously given to the same gene across taxa. This database allows the evolution of miRNA genes to be studied across the animal kingdom. Such study shows that miRNA evolution is not correlated to the duplication of genetic material, but shaped by periods of intense miRNA innovation.

  • Titan as a Prebiotic Chemical System – Benner

    In 2007, NASA sponsored a committed of the National Academies of Science to explore whether life might exist in environments outside of the traditional habitable zone, defined as positions in a solar system where liquid surface water might be found. Alternative solvents which have analogous “habitable zones” farther away from their star include hydrocarbons, ammonia, and dinitrogen. The core question asked whether life having genetic biopolymers might exist in these solvents, which are in many cases (including methane) characterized by the need for “cold” (temperatures < 100K in the case of methane).

    These “weird” solvents would require “weird” genetic molecules, “weird” metabolic processes, and “weird” bio-structures. In pursuit of this “big picture” question, we turned to Titan, which has exotic solvents both on its surface (methane-hydrocarbon) and sub-surface (perhaps super-cooled ammonia-rich water). This work sought genetic molecules that might support Darwinian evolution in both environments, including non-ionic polyether molecules in the first and biopolymers linked by exotic oxyanions (such as phosphite, arsenate, arsenite, germanate) in the second.

    In the current year, we completed our studies that identified biopolymers that might work in hydrocarbon solvents. These studies have essentially ruled out biological processes in true cryosolvents. However, a series of hydrocarbons containing different numbers of carbon atoms (one, two, three, and four, for example, in methane, ethane, propane, and butane) cease to be cryosolvents as their chain lengths increase. These might be found on “warm Titans”. Further, they might exist deep in Titan’s hydrocarbon oceans, where heating from below would lead to warm hydrocarbon oceans.

    These studies showed that polyethers are insufficiently soluble in hydrocarbons at very low temperatures, such as the 90-100 K found on Titan’s surface where methane is a liquid at ambient pressures. However, we did show that “warm Titans” could exploit propane (and, of course, higher hydrocarbons) as a biosolvent for certain of these “weird” alternative genetic biopolymers; propane has a huge liquid range (far larger than water). Further, we integrated this work with mineralogy-based work that allows reduced molecules to appear as precursors for less “weird” genetic biomolecules, especially through interaction with various mineral species, including borates, molybdates, and sulfates.

    ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 3.2 3.4 4.1 5.3 6.2 7.1 7.2
  • Biosignatures of Life in Extremely Energy-Limited Environments

    The terrestrial subsurface is the least explored habitat on earth and is characterized by darkness and reducing conditions that limit how fast microbes can obtain energy (low energy fluxes). The diversity and metabolic strategies of microbes in this environment are the subject of our investigation.

    ROADMAP OBJECTIVES: 4.1 4.3 5.1 5.3 7.1
  • Early Animals: The Origins of Biological Complexity

    The focus of the Erwin group remained on the origins of novelty and innovation, particularly associated with the origin and early diversification of animals during the Cryogenian, Ediacaran and early Cambrian. A field campaign in Namibia yielded new specimens, new fossil localities, and a potential new organism from the Ediacaran. Work on the phylogeny of early Cambrian lobopods was carried out to the hypothesis that arthropods evolved from this enigmatic group of organisms.

  • Planetary Surface and Interior Models and SuperEarths

    We use computer models to simulate the evolution of the interior and the surface of real and hypothetical planets around other stars. Our goal is to determine the initial characteristics that are most likely to contribute to making a planet habitable in the long run. Observations in our own Solar System show us that water and other essential materials are continuously consumed via weathering (and other processes: e.g., subduction, sediment burial) and must be replenished from the planet’s interior via volcanic activity to maintain a biosphere. The surface models we are developing will be used to predict how gases and other materials will be trapped through weathering and biological processes over time. Our interior models are designed to predict tidal effects, heat flow, and how much and what sort of materials will come to a planet’s surface through resurfacing and volcanic activity throughout its history.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1 5.2 6.1
  • Project 2C: Developing the 13C-18O Clumped Isotope Thermometer

    One of the critical parameters in understanding the evolution of the Earth is the temperature of the oceans. Proposals, for example, that early life was hyperthermophilic would be supported if there was evidence for a “hot early ocean”, which some stable isotope data support. However, arguments against a “hot early ocean” include lower solar luminosity early in Earth history, and evidence for widespread glaciations. A new geothermometer is based on the enhanced thermodynamic stability of “clumped isotopes” (e.g., 13C-18O bonds) in carbonate minerals, which exhibits a temperature dependence. However, attempts to calibrate this temperature dependence have identified kinetic isotope effects that can give apparently anomalous results. In this project, experiments were designed to systematically probe formation rate effects on 13C-18O bonding during calcite mineral lattice assembly from aqueous solutions. Preliminary results do not show a correlation between precipitation rate and 13C-18O bonding over the range investigated but do provide evidence that is being used to deconvolute and identify physiochemical conditions and processes that lead to disequilibrium in 13C-18O bonding during carbonate mineral formation.

    ROADMAP OBJECTIVES: 4.1 6.1 7.1 7.2
  • Project 2D: Magnesium Isotopes in Carbonates as a Tracer of Marine Conditions in the Early Earth

    Massive dolomitization events affect seawater Mg concentration and have a profound influence on the carbonate cycle in seawater that ultimately controls seawater chemistry and atmospheric carbon dioxide levels. The Mg isotope fractionation factor between dolomite and aqueous Mg has been experimentally constrained at 130, 160, and 220 degrees C to derive a temperature-dependent fractionation factor. This Mg isotope fractionation function has been determined to allow evaluation of the Mg isotope composition of fluids that have produced dolomite. Based on these new data it is now possible to infer secular changes in seawater Mg isotope compositions based on the analysis of sedimentary dolomites. This information can be used to infer changes in the intensity of dolomitization which removes Mg from seawater and tectonism which controls mid ocean ridge hydrothermal circulation that largely removes Mg from seawater as well as impacts weathering.

    ROADMAP OBJECTIVES: 4.1 7.1 7.2
  • Molecular Biosignatures of Redox-Sensitive Bacteria and Hyperthermophiles

    The Summons lab has been researching a range of molecular and isotopic phenomena aimed at shedding light on what controls Neoproterozoic ocean redox, evolutionary trends in the abundances of molecular fossils (biomarkers) and the enigmatic natural variability carbon isotopic compositions of organic and inorganic carbon at this time. Our studies of carotenoid pigment biomarkers for green and purple sulfur bacteria have revealed that they are ubiquitous in rock extracts of Proterozoic to Paleozoic age—implying that the shallow oceans became sulfidic more frequently than previously thought. Other projects focused on the biosynthesis of another important biomaker, the hopanoids, vesicles released from marine bacteria for interaction between cells and their environment, and the molecular signatures of microbial communities in hot springs in Yellowstone National Park.

    ROADMAP OBJECTIVES: 4.1 4.2 5.1 5.2 7.1
  • Stellar Effects on Planetary Habitability and the Limits of the Habitable Zone

    In this task, VPL team members studied the interaction between stellar radiation (including light) and planetary atmospheres to better understand the limits of planetary habitability and the effects of stellar radiation on planetary evolution. Work this year included using climate models to recalculate the boundaries of the surface liquid water habitable zone planets of different masses, an exploration of the effect of a star’s spectrum on the rate at which a planet can exit a snowball state, and calculation of water loss from terrestrial planets with different fractions of atmospheric carbon dioxide. Atmospheric escape models were also used to illustrate how the pre-main sequence evolution of M-dwarf stars could strip the gaseous envelopes from mini-Neptune planets, transforming them into potentially-habitable, Earth-sized rocky bodies. In pioneering work, VPL researchers also showed that the pre-main sequence phase of an M-dwarf can lead to strong atmospheric escape of water on otherwise potentially habitable worlds, potentially rendering them uninhabitable. Observational work was also undertaken to characterize the frequency and characteristics of stellar flares on M dwarf stars from Kepler data, as input to future work on characterizing the effect of stellar flares on habitability.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1
  • Paleontological, Sedimentological, and Geochemical Investigations of the Mesoproterozoic-Neoproterozoic Transition

    As we learn more about the earliest evolutionary history of animals and other complex multicellular organisms, it becomes clearer that a satisfactory understanding of these events have to be set within the broader context of late Mesoproterozoic and early Neoproterozoic biological and environmental change. To this end, several labs within our team have focused research effort of Mesoproterozoic and Neoproterozoic sedimentary successions. Over the reporting period, this has included stratigraphic and sedimentological fieldwork on rocks of this age in northwestern Canada, Death Valley, Mongolia, and anaylsis of drill cores from Russia, Congo and Zambia. Progress has also been made in new techniques for the discovery and description of Proterozoic microfossils, the processes forming ooids and wrinkle structures, severalfold improvements in the precision of oxygen-17 measurements, which can record the balance of atmospheric oxygen and carbon dioxide, and in measurements of nitrogen isotopes in ancient pigments, a potential redox tracer for the Proterozoic.

  • Project 2F: Silicon Isotopes as a Tracer of the Coupled Fe-Si Cycle in the Archean

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

  • Understanding Past Earth Environments

    This year, this interdisciplinary effort continued on two major fronts. First, we furthered the development and use of new techniques that help us characterize environmental conditions on ancient Earth. This included progress on our development of a technique for estimating the atmospheric pressure on Archean Earth, and the development and use other techniques for analyzing the chemistry of Archean lakes. We also used our existing models of ancient Earth to simulate other conditions consistent with the conclusions reached from these laboratory analyses.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1 4.2 5.1 5.2 6.1
  • Remote Sensing of Organic Volatiles on Mars and Modeling of Cometary Atmospheres

    During this period, Dr. Villanueva mainly worked on processing high-resolution (spectral and spatial) data of Mars acquired in January/2014 and in the observational campaigns of 2008, 2009 and 2010, using the recently developed new analytical and modeling capabilities. Unprecedented maps of the D/H ratio in water were extracted from these data, and a paper was recently accepted by Science (see below). In addition, he participated in several international conferences and collaborated on several Titan and cometary projects.

    ROADMAP OBJECTIVES: 1.1 2.1 3.1 3.2 4.1 7.1
  • Taphonomy, Curiosity and Missions to Mars

    Members of our team continue to be involved in both the MER and MSL missions on Mars. On the latter mission, team members have recently documented a long-lived, habitable environment in Gale Crater dominated by rivers and lakes. Research on the mineralogy and geochemistry of rocks at the base of Mt Sharp has improved our understanding of their complex diagenetic history. Progress has also been made in linking orbital observations with those made by the rovers; this has been advanced particularly by field research at Rio Tinto and detailed laboratory experiments that constrain the relationship between mineral combinations and their signatures in infrared reflectance spectroscopy—and their effect on our ability to detect organics.

    ROADMAP OBJECTIVES: 2.1 4.1 4.2 6.1 7.1
  • Stoichiometry of Life – Task 2c – Field Studies – Other

    We performed biogeochemical and microbiological studies of novel aquatic habitats, floating pumice in lakes of northern Patagonia that were derived from the 2011 eruption of the Puyehue / Cordon Caulle volcano in Chile.

    ROADMAP OBJECTIVES: 4.1 5.2 5.3 6.1
  • Project 3A: Searching for Ancient Impact Events Through Detrital Shocked Zircons

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

    ROADMAP OBJECTIVES: 1.1 4.1 4.3
  • Task: 3a: Ancient Records – Geologic

    Among the fundamental questions in Earth history is when and where O2 first accumulated in the shallow ocean. These settings could have been ideal local ‘oases’ for initial O2 accumulation and for early eukaryotic life. Iodine geochemistry has emerged as an exciting possibility for exploring such settings characterized by carbonate deposition, but the proxy remains only rudimentarily known because of the lack of validation and calibration in modern shallow carbonate environments. Our work over the past year sought to remedy that situation while simultaneously exploring the proxy’s potential in deep time.

  • Project 3B: Genesis of High-δ18O Archean Chert, Pilbara Craton, Australia

    This investigation centers on the 3.43 – 3.35 Ga Strelley Pool Formation in the Pilbara craton of western Australia, which harbors some of the oldest convincing evidence for life. The research has three major components – 1) detection and characterization of habitable Paleoarchean environments to apply to the search for life-bearing extraterrestrial environments; 2) creating an isotopic guide to the sedimentary environments and relative timing and origin of these formation’s textures; 3) constrain paleoenvironmental evidence for the putative stromatolitic microfossils in the region. We are comparing conventional bulk analytical techniques vs. SIMS in-situ microanalysis to unravel the δ18O and δ13C isotopic and geochemical variation of the micro-textural, and generational quartz, dolomite, ankerite, and calcite varieties in these stromatolitic rocks. Understanding paleoenvironments supporting ancient biospheres aids in the understanding of the necessary conditions for life’s persistence, providing further basis for locating and identifying extraterrestrial life.

  • Project 3C: The Role of Early Continental Weathering in Providing a Habitable Planet

    Recent studies of biogeochemical cycles recorded in Archean sedimentary rocks suggest an early diverse microbial ecology that may have required extensive continentally-sourced nutrients (i.e., phosphorus) early in Earth history. Widespread continental weathering is at odds, however, with studies that suggest a majority of continental crust was submerged and seawater chemistry was largely controlled by oceanic hydrothermal fluids. Here, we present new Sr and O isotope results from stratiform barite deposits from the 3.23 Ga Fig Tree Group, South Africa. The Sr and O isotope data indicate the barite was formed from a mixture of hydrothermal fluids and seawater, and that seawater was more radiogenic then previously predicted. The only appreciable source of radiogenic Sr is from continental weathering, and thus we propose that continental weathering was more extensive throughout the Archean than previously thought. This in turn has important implications for the availability of continentally-sourced nutrients to early marine environments on Earth.

    ROADMAP OBJECTIVES: 1.1 4.1 6.1 7.1 7.2
  • Task 4: Biogeochemical Impacts on Planetary Atmospheres

    Oxygenation of Earth’s early atmosphere must have involved an efficient mode of carbon burial. In the modern ocean, carbon export of primary production is dominated by fecal pellets and aggregates produced by the animal grazer community. But during most of Earth’s history the oceans were dominated by unicellular, bacteria-like organisms (prokaryotes) causing a substantially altered biogeochemistry. In this task we experiment with the marine cyanobacterium Synechococcus sp. as a model organism and test its aggregation and sinking speed as a function of nutrient (nitrogen, phosphorus, iron) limitation. We have found that these minute cyanobacteria form aggregates in conditions that mimic the open ocean and can sink gravitationally in the water column. Experiments with added clay minerals (bentonite and kaolinite) that might have been present in the Proterozoic ocean, show that these can accelerate aggregate sinking. In addition we find that Synechococcus could potentially export carbon 2–3 times of that contained in their cells via aggregation, likely due to the scavenging of transparent exopolymer particles and dissolved organic matter. Thus, aggregation and sinking by these small cyanobacteria could have constituted an important mode of carbon export in the Proterozoic ocean.

    ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1 7.2
  • Project 3D: A Microbial Iron Shuttle in Early Earth Marine Basins

    Iron-based metabolisms are deeply rooted in the tree of life, and yet comparatively little attention has been paid to searching for Fe-based biosignatures as compared, for example, photosynthetically-based metabolisms. Dissimilatory Iron Reduction (DIR) is found in both Archaea and Bacteria domains of life, its electron acceptors and donors are widespread in the solar system. This project focuses on determining the basin-scale footprint of DIR in well preserved samples of Mesoarchean age (~3 Ga) in the Witwatersrand Supergroup of South Africa. Preliminary results show a trend of iron enrichment that correlates with δ56Fe depletion from the proximal shelf to the deep distal basin, which is interpreted to indicate a DIR-driven “iron pump” or “shuttle”, where microbially-produced aqueous Fe(II) on continental shelves was pumped to the deep basin and trapped as Fe-bearing sulfides or oxides. These results not only confirm that Fe-based metabolisms were important on the early Earth ~3 b.y. ago, but that it had a substantial “footprint” in the biosphere on a basin-wide scale.

    ROADMAP OBJECTIVES: 4.1 5.2 6.1 7.1 7.2
  • Project 3E: Sulfur-Cycling Fossil Bacteria From the 1.8 Ga Duck Creek Formation Provide Promising Evidence of Evolution’s Null Hypothesis

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

    ROADMAP OBJECTIVES: 4.1 5.1 6.1
  • Project 3F — Apatitic Latest Precambrian and Early Cambrian Fossils Provide Direct Evidence of Concentrations of Environmental Oxygen

    Means are not currently available to asses either quantitatively or semi-quantitatively the concentration of oxygen in Earth’s atmosphere over geological time. Despite this, the environmental availability of O2 has been repeatedly postulated to be a cause of major changes in Earth’s biota, most particularly at the Precambrian-Cambrian boundary-defining “Cambrian Explosion of Life,” a time in Earth history when large deposits of phosphate-rich apatite were deposited in shallow basins worldwide. This study shows that substitution of Sm+3 in the Ca I and Ca II sites of fossil-permineralizing, -infilling, and -encrusting apatite can differentiate between oxic, dysoxic, an anoxic settings of apatite formation. Further studies are to be undertaken to establish such REE-substitution as a quantitative O2 paleobarometer.

    ROADMAP OBJECTIVES: 4.1 4.2 6.1 6.2 7.2
  • Project 4A: New in Situ Techniques (CLSM and Raman) Solve the Problem Presented by the Disaggregation of Acid-Macerated Organic-Walled Microfossils

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

  • Project 4B: New SIMS Procedures for in Situ Analysis of Mass-Independent Fractionation of S Isotopes

    An in situ sulfur four-isotope analysis technique with multiple Faraday cup detectors by ion microprobe was developed and applied to detrital pyrite grains in ~2.4 Ga glaciogenic sandstone from the Meteorite Bore Member of the Turee Creek Group, Western Australia.

    ROADMAP OBJECTIVES: 4.1 7.1 7.2