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Project Reports

• Biosignatures in Ancient Rocks – Kasting Group

  The work by Ramirez concerned updating the absorption coefficients in our 1-D climate model. Harman’s work consisted of developing a 1-D code for modeling hydrodynamic escape of hydrogen from rocky planets.

  ROADMAP OBJECTIVES: 1.1 3.2 4.1 4.2 4.3 5.1 5.2 5.3 6.1 6.2 7.1 7.2

• Investigation 1: Habitability of Icy Worlds

  Habitability of Icy Worlds investigates the habitability of liquid water environments in icy worlds, with a focus on what processes may give rise to life, what processes may sustain life, and what processes may deliver that life to the surface. Habitability of Icy Worlds investigation has three major objectives. Objective 1, Seafloor Processes, explores conditions that might be conducive to originating and supporting life in icy world interiors. Objective 2, Ocean Processes, investigates the formation of prebiotic cell membranes under simulated deep-ocean conditions, and Objective 3, Ice Shell Processes, investigates astrobiological aspects of ice shell evolution.

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

• Life Underground

  Our multidisciplinary team from USC, Caltech, JPL, DRI, and RPI 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, 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 seek to carry out in situ life detection and characterization experiments, employ numerous novel and traditional techniques to culture heretofore unknown intraterrestrial archaea and bacteria, and incorporate 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

• 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, as these are the features that permit movement and the environmental responses that characterize animals. We are looking at understudied early branches of the animal family tree—including the jellyfish Aurelia and the annelid worm Neanthes—to understand how the genetic regulation of sensory organs is conserved in some cases and evolves in others. Comparisons of developmental regulation in different clades reveal how similar gene networks can be differentially modified and deployed, permitting the evolution of complex sensory systems. The application of genomic methods greatly enhances our ability to pursue these questions.

  ROADMAP OBJECTIVES: 4.1 4.2

• Deconstruction of the Ribosome

  In this Project we are investigating the folding and interactions of a fragment of rRNA with a fragment of a ribosomal protein (rProtein), both derived from T. thermophilus. The goal is to examine the granularity of rRNA-rProtein recognition, to determine if small RNA and protein components of the ribosome can recapitulate interactions observed in the native ribosome. We have assayed the in vitro and in vivo folding and interactions of an isolated subdomain of rRNA with an rProtein and with a peptide fragment of the rProtein. Chemical mapping shows that a 199-nucleotide fragment of Domain III of the 23S rRNA (defined here as Domain IIIcore) folds to a near-native state. This rRNA fragment binds to ribosomal protein L23 in a yeast three-hybrid assay, as predicted from interactions in the native ribosome. A peptide was designed based on the segment of the rProtein that penetrates deep into the core of the native ribosome and associates primarily with Domain IIIcore. A spectroscopic assay shows that the peptide forms a 1:1 complex with both Domain III and Domain IIIcore. The results indicate that rRNA-rProtein recognition is fine-grained, and can be directed by specific interactions between small rRNA and rProtein fragments.

  ROADMAP OBJECTIVES: 3.2 4.1 4.2

• 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

• Habitability, Biosignatures, and Intelligence

  Understanding the nature and distribution of habitable environments in the Universe is one of the primary goals of astrobiology. Based on the only example of life we know, we have devel-oped various concepts to predict, detect, and investigate habitability, biosignatures and intelli-gence occurrence in the near-solar environment. In particular, we are searching for water vapor in atmospheres of extrasolar planets and protoplanets, developing techniques for remote detec-tion of photosynthetic organisms on other planets, have detected a possible bio-chemistry sig-nature in Martian clays contemporary with early life on Earth, developed a comprehensive methodology and an interactive website for calculating habitable zones in binary stellar systems, expanded on definitions of habitable zones in the Milky way Galaxy, and proposed a novel ap-proach for searching extraterrestrial intelligence.

  ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 3.2 4.1 4.2 6.2 7.1 7.2

• Early Animals: Taphonomic Controls on the Early Animal Fossil Record

  Our objectives are to investigate the controls on the preservation of complex life on earth to allow the fossil evidence for the succession of events to be constrained and interpreted. We are concerned with how changing diversity correlates to specific environmental events during the late Neoproterozoic and earliest Phanerozoic. Are the correlations we draw between evolutionary patterns and environmental events real or an artifact of changing preservation potential, that is, taphonomy?

  ROADMAP OBJECTIVES: 4.1 4.2

• Culturing Microbial Communities in Controlled Stress Micro-Environments

  In NAI Theme 4B, our goal in Year 1 has been to initiate our understanding of how cells structure their genomes in response to specific environmental stresses and to determine whether or not such mechanisms have been a major force in directing the evolution of cells in natural environments over evolutionary time. Natural environments are typically rather heterogeneous at small scales, as established by sampling from geothermal hot spring communities, and so it is important to understand the generic impact on the evolution and structure of microbial communities. Our first step towards probing this phenomenon has been to culture living bacterial populations within a small specially constructed microfluidic device (called the GeoBioCell), where strong physical, chemical and biological gradients can be imposed under carefully controlled conditions.

  ROADMAP OBJECTIVES: 3.2 3.4 4.1 4.2 5.1 5.2 5.3 6.1

• Early Animals: The Genomic Origins of Morphological Complexity

  Understanding the origins of life’s complexity here on Earth is paramount to finding it elsewhere in the universe. The fossil record indicates that complexity on Earth arose in a near geological moment—the famous Cambrian explosion—about 525 million years ago. However, molecular sequence analyses indicate that complex animals actually arose nearly 200 million years before they make their first appearance in the fossil record (Erwin et al. 2011). This disparity between the advent of morphological complexity and its appearance in the fossil record motivates an interesting question: why is it that we cannot detect complex life here on Earth for nearly 200 million years? And if we cannot detect it on Earth, what hope would we have on another distant Earth-like planet? Our research is focused on addressing this question by trying to obtain a better understanding of what encodes morphological complexity in the genome. Our research (Heimberg et al. 2008; Philippe et al. 2001; Tarver et al. 2013) suggests that a group of non-coding RNA genes—microRNAs—might be instrumental for the advent and maintenance of complexity in animals, and therefore sequencing the genomes and the transcriptomes (the expressed component of the genome) from carefully chosen taxa might allow us to better understand the biology of animals that predated the Cambrian explosion.

  ROADMAP OBJECTIVES: 4.1 4.2

• Experimental Evolution and Genomic Analysis of an E. Coli Containing a Resurrected Ancestral Gene

  In order to study the historical pathways and modern mechanisms of protein evolution in a complex cellular environment, we combined ancestral sequence reconstruction with experimental evolution. Our first goal was to identify how ancestral states of a protein effect cellular behavior by directly engineering an ancient gene inside a modern genome. We could then identify the evolutionary steps of this organism harboring the ancient gene by subjecting it to laboratory evolution, and directly monitoring the resulting changes within the integrated ancient gene as well as the rest of the host genome.

  ROADMAP OBJECTIVES: 3.4 4.1 5.1 5.2 6.1 6.2

• Project 3: The Origin, Evolution, and Volatile Inventories of Terrestrial Planets

  We study the origin and evolution of the terrestrial planets with a special emphasis on CHON volatiles, their delivery and retention in the deep interiors of terrestrial planets. We will experimentally investigate how CHON volatiles may be retained even during magma ocean phases of terrestrial evolution. We investigate the early Earth’s recycling processes studying the isotopic composition of diamonds, diamond inclusions, and associated lithologies. We continue to integrate new information from the NASA Messenger Mission to Mercury into the broader context of understanding the inner Solar System planets.

  ROADMAP OBJECTIVES: 1.1 3.1 4.1

• Dynamics of Self-Programming Systems

  Living systems are unique in that they have the capacity to evolve. Evolving systems can reprogram themselves and so they are able to respond to perturbations by creating new functionality. This feature is something very different from physical systems, which obey a fixed or predetermined equation of motion. This project is a theoretical attempt to describe this state of affairs mathematically, and to construct computer programs that have the capacity to evolve and thus become more complex without this being “built in” by the original programmer.

  ROADMAP OBJECTIVES: 3.2 4.1 4.2 5.3 6.2

• Project 4: Survival of Sugars in Ice/Mineral Mixtures on High Velocity Impact

  Understanding the delivery and preservation of organic molecules in meteoritic material is important to understanding the origin of life on Earth. Though we know that organic molecules are abundant in meteorites, comets, and interplanetary dust particles, few studies have examined how impact processes affect their chemistry and survivability under extreme temperatures and pressures. We are investigating how impact events may change the structure of simple sugars, both alone and when combined with ice mixtures. The experiments will allow us to understand how sugar chemistry is affected by high pressure events and to contrast the survival probabilities of sugars in meteorite and comet impacts. This will lead to a better understanding of how organic molecules are affected during their delivery to Earth. This project leverages expertise in two different NAI nodes, increasing collaborative interaction among NAI investigators.

  ROADMAP OBJECTIVES: 1.1 3.1 4.1 4.3

• Origin of Earth’s Water

  Understanding the sources and delivery mechanisms of water to the Earth and the other terrestrial planets allows for the validation of planetary accretion models. This information can help us establish at what time the Earth contained sufficient water for the development of life. A key parameter in determining the source(s) of terrestrial planetary water is the hydrogen isotope composition of this water. However, hydrogen fractionation during surface and atmospheric processes on terrestrial planets such as Earth and Mars may have significantly changed the Deuterium/Hydrogen (D/H) ratio in the various water reservoirs. Therefore, to determine the primordial D/H ratio of these planets water we must find reservoirs that has been unaffected by surface processes. Plate tectonics is known to drag surface water down into the crust and the upper mantle, but the transition zone and lower mantle are thought to be uncontaminated by surface water. Therefore, we aimed to sample terrestrial hydrous minerals and melt inclusions sourced from these uncontaminated regions, such as deep mantle plume samples from Iceland and Baffin Island, along with possible deep mantle diamond inclusions. As plate tectonics never developed on Mars, the primary igneous hydrous minerals in martian meteroites were assumed to be isolated from martian surface processes. We analyzed the D/H ratio of these samples using the Cameca ims 1280 ionmicroprobe at the University of Hawaii to produce a dataset that establishes the primordial D/H ratio of Earth and Mars.

  To gain insights into the amount of water present in terrestrial planetary mantle material we synthesized samples of high-pressure mineral phases that are likely hosts for H, and thus water, in planetary interiors. We measured the physical properties of these minerals, including crystal structure, density, elasticity, and electrical conductivity, to investigate the degree to which water may be incorporated into these minerals in the Earth’s mantle.

  Models of terrestrial planet formation have been successful in producing terrestrial-class planets with sizes in the range of Venus and Earth. However, these models have generally failed to produce Mars-sized objects. The body that is usually formed around Mars’ semimajor axis is, in general, much more massive than Mars. We have developed new model for the formation of Mars in which a local depletion in the density of the protosolar nebula results in a non-uniform formation of embryos and ultimately the formation of Mars-sized planets.

  ROADMAP OBJECTIVES: 1.1 4.1

• Early Animals: The Origins of Biological Complexity

  The fossil record provides the best evidence for the emergence of complex life and its relationship to changes in the environment. But this record is increasing supplemented by comparative studies of the development of living animals. Our group has been working on both the fossil record of some of the oldest fossil evidence of animals, as well as applying studies of the development of modern animals to interpret these fossils. The goal is to understand the interactions between changes in the physical environment, ecological interactions and in developmental mechanisms in evolutionary innovations leading to greater biological complexity.

  ROADMAP OBJECTIVES: 4.1 4.2 4.3

• Biosignatures in Extraterrestrial Settings

  We are working on finding potentially habitable extrasolar planets, using a variety of search techniques, and developing some of the technology necessary to find and characterize low mass extrasolar planets. We also work on modeling and numerical techniques relevant to the problem of identifying extrasolar sites for life, and on some aspects of the prospects for life in the Solar System outside the Earth. The ultimate goal is to find signatures of life on nearby extrasolar planets.

  ROADMAP OBJECTIVES: 1.1 1.2 2.1 2.2 3.1 4.1 4.3 6.2 7.1 7.2

• Project 5: Geological-Biological Interactions

  We continue to study the intersection between geology and biology. We continue to explore how sub-seafloor interactions support deep ocean hydrothermal ecosystems. We study life’s adaption to extremes of pressure, cold, and salinity. We adapt and apply multiple isotopic sulfur geochemistry towards the understanding of microbial metabolism and as a means of detecting ancient metabolisms recorded in the rock record through characteristic sulfur isotopic signatures. We apply state-of-the-art methods to derive chemical and isotopic biosignatures of life in the Earth’s most ancient rocks.

  ROADMAP OBJECTIVES: 4.1 5.1 6.1 6.2 7.1

• Early Animals: What Made “fronds” Grow in Neoproterozoic Deep Seas?

  Rangeomorph fossils look superficially like plants, however, some lived in aphotic deep water and their nutrition is inferred to involve direct uptake of dissolved resources. We employ models of flow in the rangeomorph community and uptake at the organismal surface to demonstrate how these larger organisms had an advantage over bacteria, despite sharing a similar ecological niche. Through these reconstructions we demonstrate that height provides access to higher velocities in these communities, and under these low-flow conditions, velocity dictates nutrient uptake. Thus we demonstrate the nature of adaptive advantage for larger eukaryotic life forms in the first communities of large organisms in the late Precambrian, just prior to the radiation of animals.

  ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1

• The Nature of the Last Archaeal and Eukaryal Ancestor

  The evolutionary history of the eukaryotic cell is intimately linked evolution of atmospheric oxygen and with the endosymbiosis of bacterial symbionts to become the mitochondrial organelles. This project seeks to understand the evolutionary history of the eukaryotic cell using contemporary analogs of ancestral anaerobic eukaryotes (rumen ciliates), which are often associated with endosymbiotic archaea and bacteria in tightly associated communities. We study the evolution of this association using state-of-the-art metagenomic and ecological methods to gain a better understanding of the evolution of these types of associations and thus of eukaryotic evolutionary history.

  ROADMAP OBJECTIVES: 3.4 4.1 4.2 5.2 6.1

• Biosignatures in Relevant Microbial Ecosystems

  PSARC is investigating microbial life in some of Earth’s most mission-relevant modern ecosystems. These environments include the Dead Sea, the Chesapeake Bay impact structure, methane seeps, ice sheets, and redox-stratified Precambrian ocean analogs. We target environments that, when studied, provide fundamental information that can serve as the basis for future solar system exploration. Combining our expertise in molecular biology, geochemistry, microbiology, and metagenomics, and in collaboration with some of the planet’s most extreme explorers, we are deciphering the microbiology, fossilization processes, and recoverable biosignatures from these mission-relevant environments.

  PSARC Ph.D. (now postdoctoral researcher at Caltech) Katherine Dawson published a new paper documenting the anaerobic biodegradation of organic biosignature compounds pristane and phytane. PSARC Ph.D. Daniel Jones (now postdoctoral researcher at U. Minnesota) published a new paper that uses metagenomic data to show how sulfur oxidation in the deep subsurface environments may contribute to the formation of caves and the maintenence of deep subsurface microbial ecosystems. PSARC Ph.D. student Khadouja Harouaka published a new paper that represents some of the first available information about possible Ca isotope biosignatures. Lastly, the Macalady group published a paper showing how ecological models based on available energy resources can be used to predict the distribution of microbial populations in space and time.

  ROADMAP OBJECTIVES: 4.1 4.3 5.1 5.2 5.3 6.1 7.1 7.2

• Ironing Out the RNA World

  We have proposed hypothesize that Fe²⁺ was an RNA cofactor on the ancient earth when iron was benign and abundant, and that Fe²⁺ was replaced by Mg²⁺ during the great oxidation. Our hypothesis is supported by our observations (1,2) that (i) RNA folding is conserved between complexes with Fe²⁺ and Mg²⁺ and (ii) at least some phosphoryl transfer ribozymes are more active in the presence of Fe²⁺ than Mg²⁺. We have shown that reversing the putative metal substitution in an anoxic environment, by removing Mg²⁺ and adding Fe²⁺, expands the catalytic repertoire of some RNAs. Fe²⁺ can confer on RNA a previously uncharacterized ability to catalyze single electron transfer. Catalysis is specific, in that it is dependent on the type of RNA. The 23S rRNA and tRNA, some of the most abundant and ancient RNAs (3), are found to be efficient electron transfer ribozymes in the presence of Fe²⁺. Therefore, the catalytic competence of ancient RNAs may have been greater in early earth conditions than in extant conditions, and the experiments described here may be reviving latent function. The Center is currently testing the hypothesis that replacement of Fe²⁺ by Mg²⁺ in RNA assemblies has not been universal.

  ROADMAP OBJECTIVES: 4.1 4.2

• Project 6: 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 conducting chemical analyzes of crystals (minerals) that have survived since that time. 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. Our focus has been mainly on zircon, quartz, and apatite.

  ROADMAP OBJECTIVES: 1.1 4.1 4.3

• Life and Environments: Fossils of the Late Meso- and Early Neoproterozoic

  Any understanding of the major biological, biogeochemical and climatic events that characterized the late Neoproterozoic Era (ca. 750-541 million years ago) requires that we understand the state of Earth biota and environment as the critical interval began. Members of the Knoll lab have discovered and analyzed a series of fossil assemblages deposited between 1100 and 800 million years ago and continued to show the relationship between evolution and environmental change on the early Earth.

  ROADMAP OBJECTIVES: 4.1 4.2

• Genetic Evolution and the Origin of Life

  In this task biologists and chemists use field and laboratory work to better understand the environmental effects on growth rates for freshwater stromatolites and the mechanisms that govern their adaptation to their environment. Stromatolites are microbial mat communities that have the ability to calcify under certain conditions. They are believed to be an ancient form of life, that may have dominated the planet’s biosphere more than 2 billion years ago. Our work focuses on understanding these communities as a means of understanding environmental impacts on evolution, and characterizing their metabolisms and gas outputs, for use in planetary models of ancient environments. This year we also started a new project looking at the chemical affinities of the building blocks of life, as a way to understand how life might have initially formed from these chemical precursors.

  ROADMAP OBJECTIVES: 3.2 3.4 4.1 4.2 5.2 5.3 6.1 6.2

• Subsurface Exploration for Astrobiology: Oceanic Basaltic Basement Biosphere

  While extraterrestrial life is likely to exist within the subsurface of water-occupied objects such as Enceladus and Europa, the continued investigation of the subsurface biosphere on the earth provides important insight and implications for astrobiology. This research investigates a deep sub-seafloor basement biosphere. At the ocean floor, lying underneath an often times thick layer of sediment is hard basaltic rock, or basement. Seawater enters the basement and circulates within. It is now known that low temperature hydrothermal fluids (<100oC) circulate everywhere within the porous and permeable volcanic rocks of the upper ocean basement, providing temperature and chemical gradients that host extensive alteration of basement rocks and fluids and form plausible habitats for microbial life. While microbial activity has been observed in deeply buried sediments and exposed basement rock, few direct tests have been carried out in deep subseafloor basement rocks or fluids. A majority of the crustal hydrothermal flow and seawater-crustal fluid exchange, and the corresponding advective heat and mass output, occurs on the flanks of the mid-ocean ridge with basement ages of >1 million years old. This low-temperature ridge flank flow rivals the discharge of all rivers to the ocean and is about three orders of magnitude greater than the high temperature discharge at mid-ocean ridges. The resulting ridge flank chemical flux impacts ocean biogeochemical cycles and may sustain deep basement microbial communities. Access to uncontaminated fluids from subseafloor basement is problematic, especially where ridge flanks and ocean basins are buried under thick, impermeable layers of sediment (i.e., thick enough to act as a barrier to rapid exchange of fluids). We rely on custom designed instrumentation to collect large volume high integrity basement fluids, where the concentrations of microorganisms are often very low (e.g. about 1/10 of bottom seawater concentrations). By studying the chemical composition of crustal fluids, we have learned that several important energy sources, such as dissolved methane and hydrogen, are available. In addition, the isotopic signature of dissolved methane suggests that microbial production and consumption occurs in the basement environment. By filtering microbial biomass from the fluids and investigating their nucleic acids, we are investigating the evolutionary and functional characteristics of the diverse bacterial, archaeal, and viral communities that inhabit the deep subsurface of Earth. Our on-going research includes the investigation of temporal (at hourly-resolution) and spatial (at a few hundred meter scale) biogeochemical and biological variability in order to more effectively constrain our measured parameters. We are also characterizing the dissolved organic carbon pool in basement fluids to investigate the role that basement environment plays in the global carbon cycle.

  ROADMAP OBJECTIVES: 4.1 5.1 5.2 5.3 6.1 6.2

• Life and Environments: Geochemistry of Late Precambrian Oxygenation

  The first year of work marked a successful transition from the goals and projects defining our last NAI node and the initiation of new, exciting research lines. Recently, our work on the Ediacaran transition in the Earth system culminated in an integrated geochemical study that both covers the state of the late Precambrian world, but also serves as a critical tie point for our upcoming work on Cryogenian ocean and atmospheric chemistry. This entails the extension of similar tools to those we applied in the Ediacaran, as well as the development of a new ¹⁷O system in the Johnston Lab that will serve as a central measurement for the upcoming projects.

  ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1

• Developing New Biosignatures

  The development and experimental testing of potential indicators of life is essential for providing a critical scientific basis for the exploration of life in the cosmos. In microbial cultures, potential new biosignatures can be found among isotopic ratios, elemental compositions, and chemical changes to the growth media. Additionally, life can be detected and investigated in natural systems by directing cutting-edge instrumentation towards the investigation of microbial cells, microbial fossils, and microbial geochemical products. Over the next five years, we will combine our geomicrobiological expertise and on-going field-based environmental investigations with a new generation of instruments capable of revealing diagnostic biosignatures. Our efforts will focus on creating innovative approaches for the analyses of cells and other organic material, finding ways in which metal abundances and isotope systems reflect life, and developing creative approaches for using environmental DNA to study present and past life.

  ROADMAP OBJECTIVES: 2.1 3.1 4.1 5.1 7.1

• Project 2B: Origin of Carbonates: Environmental Proxies and Formation Pathways

  Magnesium isotopes can provide insights into past environmental conditions including formation temperatures and sources of Mg for carbonates, including dolomite, which is a common sedimentary carbonate of the geologic rock record. For Mg isotopes to be a useful proxy, the factors that control isotope fractionation during formation of carbonates must be known. Previous experimental studies have provided conflicting results on potential kinetics effects during the inorganic synthesis of Mg-calcite from solution. To resolve these differences, a matrix of 34 laboratory experiments were conducted to independently determine the effects of temperature, precipitation kinetics, and solution composition (e.g.,pCO₂, aqueous Mg/Ca ratio) on Mg- isotope fractionation in the Mg-calcite-aqueous Mg system. Preliminary results suggest that factors in addition to precipitation rate (e.g., aqueous Mg/Ca ratio, pCO₂) may play a role in the fractionation of Mg isotopes in the Mg-calcite-aqueous Mg system.

  ROADMAP OBJECTIVES: 4.1 7.1

• 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 work out what sorts of initial characteristics 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

• Life and Environments: Proterozoic Geology, Geochemistry and Paleontology

  The search for life on other planets, including Mars, is inevitably a comparative exercise with Earth as the only known planet that carries confirmed biosignatures (chemical or morphological). Often, these pursuits bridge multiple disciplines from sedimentology/stratigraphy, classic paleontology, inorganic and isotope geochemistry to the study and distribution of specific organic compounds that are considered good proxies for particular sorts of organisms (i.e. biomarkers). The Ediacaran Period (635 – 542 Ma) sees the first direct evidence for the rise of multicellularity, which is arguably one of the most critical biological transitions in the rock record. Equally intriguing is the immediately pre-ceding interval, the Cryogenian Period (850 – 635 Ma) with global glaciations, massive perturbations in geochemical cycles, a probable rise of atmospheric oxygen, and an apparent evolutionary radiation within the eukaryotic domain. In contrast to the canonical view, emerging research on Neoproterozoic sedimentary successions by the MIT-NAI team now suggests that much of the apparently sudden rise of animal life that is manifested in the Ediacaran sedimentary record was initiated by events that happened earlier, during the late Mesoproterozoic Era and through the Cryogenian Period (1200 – 650 Ma). Our work seeks to illuminate this time period by documenting the stratigraphy, isotopic records, fossil assemblages, and biomarker contents of critical Meso- to Neoproterozoic transitions in well-preserved Proterozoic sections from Canada and Russia. We especially seek to understand the genetic links and time relationships (which inform rates) among tectonic, geochemical and biological changes.

  ROADMAP OBJECTIVES: 4.1 4.2

• Project 2C: Calibrating the ¹³C-¹⁸O (“clumped”) Isotope Temperature Scale

  Determining paleotemperatures in ancient fluid-mineral systems is key to determining ancient habitability. Stable oxygen isotope studies of carbonates have long used changes in ¹⁸O/¹⁶O ratios to infer the temperature from which carbonate precipitated, using a laboratory-calibrated temperature conversion, but this requires knowledge of the ¹⁸O/¹⁶O ratios of the fluid. This is often not known. A relatively new approach is to use the non-random variations in rare C and O isotopes, specifically the preferential enhancement of ¹³C-¹⁸O bonds, which has been shown to be related to temperature and independent of the fluid isotopic composition. Experimental calibrations, however, have been inconsistent, and goal of this project is to reconcile these discrepancies.

  ROADMAP OBJECTIVES: 2.1 4.1 7.1 7.2

• Molecular Biosignatures: Fossil Record of Animal Biopolymers

  We contributed to a study of the diagenetic products of the animal pigment eumelanin and learned how to recognize melanin-derived products in the fossil record.

  ROADMAP OBJECTIVES: 4.1 4.2 7.1

• Stellar Effects on Planetary Habitability and the Limits of the Habitable Zone

  In this task VPL Team members explore the interactions between a planet and its parent star and how these interactions affect whether or not the planet can support life. These interactions can be radiative, with light from the star affecting the planet’s climate, or UV from stellar flares affecting the radiation environment at the planet’s surface. Or they interactions can be gravitational, with the star periodically deforming planets on elliptical orbits and thereby transferring energy into the planet. Both radiative and gravitational effects can input too much heat into a planet’s environment and cause it to lose the ability to maintain liquid water at the surface. Research this year included looking at the limits of the habitable zone with new calculations, exploring how gravitational tidal energy could cause a planet to lose its ocean, and understanding the effects that tidal deformation and incoming stellar radiation would have on the habitability of exomoons.

  ROADMAP OBJECTIVES: 1.1 1.2 4.1

• The Nature and Detectability of Astronomical Biosignatures

  In this project VPL team members explore the nature and detectability of biosignatures, global signs of life in the atmosphere or on the surface of a planet. This year we completed comprehensive modeling work that explores the potential for non-biological generation of oxygen and ozone in early Earth-like atmospheres, which could result in a “false positives” for photosynthetic life. We also explored the detectability of molecular dimers, especially O₂-O₂ as potentially easier to detect biosignature gases for transit transmission observations.

  We also calculated maximum methane fluxes from the geological process of serpentinization, as a potential false positive for life, and looked at the nature and detectability of non-photosynthetic pigments as potential biosignatures for life on exoplanets. We also started work to develop new, more generalized biosignatures via measurement of thermodyamic and kinetic anomalies in planetary atmospheric compositions that are associated with life. We complemented this theoretical work with field work in caves dominated by sulfur-bacteria, to understand isotopic processing of sulfur by life, as a potential biosignature for life on Mars, or for planets with sulfur-domianted biospheres.

  ROADMAP OBJECTIVES: 1.1 1.2 4.1 7.2

• Understanding Past Earth Environments

  For much of the history Earth, life on the planet existed in an environment very different than that of modern-day Earth. Thus, the ancient Earth represents a planet with a biosphere that is both dramatically different than the one in which we live, but that is also accessible to detailed study. As such, it serves as a model for what types of biospheres we may find on other planets. A particular focus of our work was on the “Early Earth” (formation through to about 500 million years ago), a timeframe poorly represented in the geological and fossil records but comprises the majority of Earth’s history. We have studied the composition, pressure and climate of the ancient atmosphere; the delivery of biologically available phosphorus; studied the sulfur, oxygen and nitrogen cycles; and explored atmospheric formation of molecules that were likely important to the origins of life on Earth.

  ROADMAP OBJECTIVES: 1.1 1.2 4.1 4.2 5.1 5.2 6.1

• Project 3A: Banded Iron Formation Deposition Across the Archean-Proterozoic Boundary

  Prior to widespread oxygenic photosynthesis, reduced iron, Fe(II), was the dominant form of soluble iron in surface environments on the early Earth, and likely Mars. On Earth, extensive iron deposits, Banded Iron Formations (BIFs), which currently supply the majority of the iron used in our society, largely formed prior to the Great Oxidation Event of ~2.4 Ga age, and yet contain substantial quantities of oxidized iron, Fe(III). The pathways by which these different oxidation states arose remains unclear. In addition, the chemical and isotopic compositions of BIFs have been used as proxies for ancient seawater or paleoenvironments. In competition with this proposal, however, has been use of BIFs as a tracer of microbial iron cycling. To test the use of BIFs as ambient paleoenvironmental proxies or proxies of microbial process, BIFs from South Africa and Australia were examined from the micron scale to the 100’s of meter scales. We find that BIFs tend to record specific pathways of oxidation of Fe(II), as well as reduction of Fe(III), and extensive post-depositional changes, and it may be quite difficult to infer ambient paleoenvironmental conditions form such deposits.

  ROADMAP OBJECTIVES: 2.1 4.1 5.2 6.1 7.1 7.2

• Molecular Biosignatures: Reconstructing Events by Comparative Genomics

  Reconstructing ancient events in genome evolution provides a valuable narrative for planetary history. Phylogenetic analysis of protein families within microbial lineages can be used to detect horizontal gene transfers and the evolution of new metabolic pathways and physiologies, many of which are significant in reconstructing ancient ecologies and biogeochemical events. These gene transfers can also be used to constrain molecular clock models for early life evolution, applying principles of stratigraphy and date calibration. A better understanding of gene evolution, including partial horizontal gene transfer, is needed to improve these inferences and avoid systematic errors.

  ROADMAP OBJECTIVES: 3.2 3.4 4.1 4.2 4.3 5.1 5.2 6.1

• Project 3B: Carbon Isotope Analysis of Archean Microfossils

  We have completed a study of petrography, Raman microspectroscopy, and in situ analyses of carbon isotope and H/C ratios using secondary ion mass spectrometry (SIMS) of diverse organic microstructures, including possible microfossils. This work has focussed on two localities of the 3.4-billion-year-old Strelley Pool Formation (Western Australia). For the first time, we show that the wide range of carbon isotope ratios recorded at the micrometer scale correlates with specific types of texture for organic matter (OM), arguing against abiotic processes to produce the textural and isotopic relations. These results support the biogenicity of OM in the Strelley Pool Formation.

  ROADMAP OBJECTIVES: 1.1 2.1 4.1 4.2 5.2 6.2 7.2

• Task 3.5.1: Titan as a Prebiotic Chemical System

  Six years ago, NASA sponsored a National Academies report that asked whether life might exist in environments outside of the traditional habitable zone, where “weird” genetic molecules, metabolic processes, and bio‐structures might avoid the water‐based biochemistry that is found across the terran biosphere. 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. Further, we asked about the possibility that Titan might inform our understanding of prebiotic chemical processes, including those on “warm Titans”. Our experimental activities found few possibilities for non‐phosphate-based genetics in subsurface aqueous environments, even if they are rich in ammonia at very low temperatures. Further, we showed that polyethers are insufficiently soluble in hydrocarbons at very low temperatures, such as the 90‐100 K found on Titan’s surface. However, we did show that “warm Titans” could exploit propane 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 other work that allows reduced molecules to appear as precursors for more standard genetic biomolecules, especially through interaction with various mineral species.

  ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 3.2 4.1 4.2 5.3 6.2 7.1 7.2

• Remote Sensing of Organic Volatiles on Mars and Modeling of Cometary Atmospheres

  Using our newly developed analytical routines, Villanueva reported the most comprehensive search for trace species on Mars (Villanueva et al. 2013b, Icarus) and described in detail the chemical taxonomy of comets C/2001 Q4 and C/2002 T7 (de Val-Borro et al. 2013). He expanded our already comprehensive high-resolution spectroscopic database to include billions of spectral lines of ammonia (NH3, Villanueva et al. 2013a), hydrogen cyanide (HCN, Villanueva et al. 2013a, Lippi et al. 2013), hydrogen isocyanide (HNC, Villanueva et al. 2013a), cyanoacetylene (HC3N, Villanueva et al. 2013a), monodeuterated methane (CH3D, Gibb et al. 2013), and methanol (CH3OH, DiSanti et al. 2013). For each species, he developed improved or new fluorescence models using the new spectral models. These permit unprecedented improvement in models of absorption spectra in planetary atmospheres (Earth, Mars), and in computing fluorescence cascades for emission spectra of cometary gases pumped by solar radiation. Villanueva utilized these new models in analyzing spectra of comets that enabled record observations of CO in comet 29P/Schwassmann-Wachmann-1 (see report by Paganini), revealed the unusual organic composition of comet 2P/Encke (see report by Mumma), developed new fluorescence models for the ν2 band of methanol and for the ν3 band of CH3D in comets (see reports by DiSanti and by Bonev), and discovered two modes of water release in comet 103P/Hartley-2 (see report by Bonev).

  ROADMAP OBJECTIVES: 1.1 2.1 3.1 3.2 4.1 7.1

• Neoproterozoic Aerobic Transition

  The Proterozoic carbon isotopic record contains evidence of a series of large perturbations to the global carbon cycle, some or all of which may be associated with changes in atmospheric O₂. Our team is formulating a theoretical model to explain not only these disruptions but also the permanent increase in O₂ levels that occurred by the end of the Proterozoic.

  ROADMAP OBJECTIVES: 1.1 4.1 4.2 5.2 6.1

• 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

• Preparation of Review Articles

  We prepared a number of astrobiologically-related review articles during the reporting period.

  ROADMAP OBJECTIVES: 4.1 7.1

• Project 3C: Carbon Isotope Analysis of Proterozoic Microfossils

  We have developed procedures for accurate in situ analysis of carbon isotope ratios by SIMS for individual Precambrian microfossils of unquestioned biogenicity. Data for three Proterozoic localities show a consistent fractionation of 19 per mil between organic matter and coexisting carbonates, in spite of over 6 per mil variability from rock to rock, consistent with fractionations seen for modern cyanobacteria. In one sample, a phytoplanktonic protistan acritarch, found within the same mm-scale domains, are 6 per mil more fractionated, consistent with photosynthetic eukaryotes. These findings show for the first time the possibility of using in situ isotopic microanalysis of fossil microbial mats and ancient sediments in order to distinguish metabolic fingerprints within complex microbial ecosystems and consortia.

  ROADMAP OBJECTIVES: 2.1 4.1 4.2 5.2 7.2

• Project 3D: Microfossil Insights Into Proterozoic Microbial Ecology

  In a study of the chert-permineralized 1.8 Ga Duck Creek Dolomite, and underlying units, Western Australia, Schopf found that in sequences of 2.3 to 1.8 Ga age that indicate little environmental change, there has been no evolution of the form, function, or metabolic requirements of its biotic components. In a second study of sulfur-cycling bacteria from the 775 Ma chert-permineralized Bambui Group of Brazil, Schopf showed that pyritized microbes of this age were anaerobic sulfur-cyclers. This work, in addition to previous studies, forms the basis for ongoing studies of the biotic response to the Great Oxidation Event.

  ROADMAP OBJECTIVES: 4.1 5.1 5.2 6.1 7.2

• Stoichiometry of Life – 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 cyano-bacterium Synechococcus sp. as a model organism and test its aggregation and sinking speed as a function of nutrient (nitrogen, phosphorus, iron) limitation. So far, 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.

  ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1 7.2

• Taphonomy, Curiosity and Missions to Mars

  MIT team members are actively involved in both the continuing MER and new MSL missions to Mars. Team members are also collaborating on research designed to provide ground truth for remotely sensed clay mineral identifications on Mars, exploring, as well, the relationship between clay mineralogy and organic carbon preservation in sedimentary rocks. For example, our team has been exploring the use of reflectance spectroscopy, which is a rapid, non-destructive technique, for assessing the presence and abundance of organic materials preserved in ancient rocks. Sumner chairs the Gale Mapping Working Group, which is producing geomorphic and geologic maps of the landing area and lower slopes of Mt. Sharp in Gale Crater. This map is being used for long-term planning of science campaigns for Curiosity as well as to put observations into a regional context.

  ROADMAP OBJECTIVES: 2.1 4.1 4.2 6.1 7.1

• Stoichiometry of Life, Task 3a: Ancient Records – Geologic

  Fossil and chemical fingerprints of animal life first appear in the geologic record around 600 million years ago. The four billion years of Earth history before this milestone were marked by dramatic changes that we take for granted today but that set the stage for our existence. Our work is exploring the evolving compositions of the early atmosphere and ocean and their cause-and-effect relationships with the evolution of life—spanning the middle 50% of Earth history from the first production of oxygen via photosynthesis to the first appearance of animals—using established and novel geochemical tracers. This work is changing our view of the early environmental conditions that facilitated, and just as often throttled, the rise of life.

  Our efforts over the last year included continued analysis of mid-Proterozoic samples from Australia—emphasizing sulfur isotope systematics, trace metal geochemistry, and organic biomarkers.

  ROADMAP OBJECTIVES: 4.1 4.2

• The Astrobiology Walk

  The Goddard Center for Astrobiology (GCA) has completed the development and installation of a permanent outdoor exhibit at the Goddard Space Flight Center (GSFC) Visitor Center as a major public outreach effort. The “Astrobiology Walk” is designed to showcase the latest scientific discoveries from the GCA research theme “Search for the Origin and Evolution of Organics” in the context of a timeline for the evolution of the Universe and the Solar System. The exhibit consists of ten outdoor stations situated on the circular pathway around the Visi-tor Center’s “Rocket Garden”, each with a memorable iconic 3D object to convey the main scientific message. QR codes link each placard to web sites relevant to that topic.

  ROADMAP OBJECTIVES: 1.1 1.2 2.1 2.2 3.1 3.2 4.1 4.3 7.1 7.2