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2015 Annual Science Report

Massachusetts Institute of Technology Reporting  |  JAN 2015 – DEC 2015

Executive Summary

Neoproterozoic Environments and Environmental Change
Members of the Johnston and Macdonald teams worked to further articulate the environmental changes associated with the late Proterozoic. These studies have taken two clear directions that are complementary, yet independent. First, and published in Nature, they presented the first reconstruction of ocean chemistry – as viewed through the iron speciation and trace metal proxy records – whereby true statistical tests are available (testing for bias, the symmetry of data distribution, etc). These results, which include contributions from team members Macdonald, Knoll and Sperling, illustrated the persistence of deep ocean anoxia well into the Paleozoic (Sperling et al 2015). In parallel, and along with NAI funded post-doc Ben Cowie, they built a custom fluorination line for extracting O2 from barite for high precision δ17O isotope analyses. These data place constraints on the collapse of the post Marinoan ... Continue reading.

Field Sites
47 Institutions
20 Project Reports
89 Publications
19 Field Sites

Project Reports

  • The MER Mission to Mars

    NAI team member Andrew Knoll continued to work as part of the science team for the MER mission to Mars. Exploration continues along the clay-rich lip of Endeavor crater. Publications in 2015 include a synthesis of recent research in the Endeavour region and a analysis of Mn-bearing surface features exposed along Murray Ridge.

  • The MSL Mission to Mars

    The overall scientific goal of the Mars Science Laboratory (MSL) mission is to explore and quantitatively assess a local region on Mars’ surface as a potential habitat for life, past or present. The MSL rover carries ten scientific instruments and a sample acquisition, processing, and distribution system. The various payload elements work together to detect and study potential sampling targets with remote and in situ measurements; acquires samples of rock, soil, and atmosphere and analyze them in onboard analytical instruments; and to observe the environment around the rover. MSL has been investigating a site that shows clear evidence for ancient aqueous processes based on orbital and ground-based data and has been undertaking a search for past and present habitable environments.

  • Taphonomy of Microbial Ecosystems

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

    ROADMAP OBJECTIVES: 2.1 4.1 4.2 5.1 5.2 6.1 7.1 7.2
  • Mars Analog Studies: Mineral Assemblages in Terrestrial Settings

    It is now widely recognized that hydrated minerals, including clays, sulfates, chlorides and other salts, are important components of the martian crust. Such minerals and assemblages of minerals have the potential to record important information about past interactions between sediment, surface and groundwaters, and the atmosphere. The overarching theme of this project is to examine terrestrial analog sites to better understand how martian mineral assemblages may be used to infer these processes. Current sites include Rio Tinto, Spain and Lake Towuti, Indonesia. We have studied samples from the former and have determined that it may provide an appropriate mineralogical analog for enigmatic hydrous mineral-bearing terrains observed in Valles Marineris, Mars by orbiting spacecraft. Over the past year we have also begun to study mafic and ultramafic sediments in Lake Towuti to examine stratigraphic variations in Fe and Si-bearing mineral phases. Current results indicate these sediments and this lake system may be an appropriate mineralogical and/or chemical analog for ancient lacustrine sediments observed by the Curiosity rover in Gale Crater.

    ROADMAP OBJECTIVES: 2.1 4.1 4.3 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 else-where 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. 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 an-other 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 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 ex-pressed component of the genome) from carefully chosen taxa might allow us to better under-stand the biology of animals that predated the Cambrian explosion.

  • 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 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, Peru, and anaylsis of drill cores from Russia, Congo and Zambia. Progress has also been made in new techniques for the discovery, description, and interpretation of Proterozoic microfossils, and several-fold improvements in the precision of oxygen-17 measurements, which can record the balance of atmospheric oxygen and carbon dioxide.

    ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1
  • Earth’s Evolving Nitrogen Cycle – Implications for Community Complexity and Stability

    This project examines nitrogen isotope patterns in Proterozoic and Paleozoic rocks, as part of a broader effort to understand the co-evolution of Earth’s redox cycles and marine ecosystems. The results are being incorporated into a growing framework of data and models that have as their primary objective to show how planetary geochemical cycles evolve with and/or help to record signatures of living systems – both microbial and complex. The project aims to yield a better understanding of the transition from primarily anoxic to primarily oxic deep oceans, and how that transition is mirrored in nutrient budgets (i.e., nitrogen) and the marine ecosystems that depend on the stability of these cycles. Understanding N-cycling throughout Earth’s history has critical implications for the evolution of complex marine ecosystems on geologic timescales.

    ROADMAP OBJECTIVES: 4.1 4.2 5.2 5.3 6.1
  • Early Animals: The Origins of Biological Complexity

    We seek to understand the interactions of ecological, environmental and developmental processes that generate biological novelty and innovation, with particular emphasis on the events associated with the origin and early evolution of animals. The larger goal is to develop a general model of novelty (the origin of new organismal characters) and innovation (the ecological and evolutionary success of these novelties) and determine whether it applies through the history of life. Alternatively episodes of novelty and innovation may be dominated by historical contingency so that no general model can be developed.

  • 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 of 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.

  • Early Animals: Modeling the Biotic-Abiotic Interface in the Early Evolution of Multicellular Form

    Multicellular organisms in the sea modify their local hydraulic environment. Modeling of the earliest-known multicellular communities of frond-like forms demonstrated that they were large enough and closely spaced enough to generate a distinctive canopy flow-regime. In this context diffusion at the surface of organism was limiting and height and attendant velocity exposure permitted escape from these limits (Ghisalberti et al. 2014). Building on these results, we are developing models of abiotic/biotic interactions at organismal surfaces, relevant to the morphology, development and orientation of other Neoproterozoic fossils. A subset of these are flat-lying forms such as Dickinsonia. These may interact with the sediment modifying redox gradients. Ultimately, this work will help illuminate how forms initially dependent on passive diffusion became more trophically, morphologically and behaviorally complex, during the diversification of animals.

    ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1
  • Progress in the Elucidation of Microbial Biosignatures

    A number of discrete individual investigations have contributed to improved knowledge about the occurrence and interpretation of microbial molecular biosignatures across all geological timescales.

    A new analytical approach enabled a revised geologic distributions of fossilized biomarkers for anoxygenic sulfur bacteria. The prevalence of okenane and chlorobactane suggests that marine photic zone euxinia (PZE) was more intense and frequent in the geologic past. However, the presence of these compounds in some sediments and oils may also be a signature for basin restriction rather than one indicating more widespread marine anoxia.

    In a related work, pervasive photic zone euxinia and disruption of biogeochemical cycles was demonstrated for a sequence of rocks deposited on the northeastern Panthalassic Ocean during the end-Triassic extinction.

    A study of lipids and their isotopic compositions, combined with stable isotope probing experiments, demonstrated that streamer biofilm communities, which are a present in the high temperature zones of hydrothermal features of the Lower Geyser Basin of Yelowstone National Park, can alternate their metabolism between autotrophy and heterotrophy depending on substrate availability.

    Other collaborations with numerous colleagues resulted in documentation of lipid and isotopic biosignatures in cultured bacteria.

    ROADMAP OBJECTIVES: 3.2 4.2 5.1 5.2 5.3 6.1
  • Fullerenes and Mass Extinctions?

    A re-examination of past reports of the occurrence of fullerenes at mass extinction horizons, using proven extraction and analysis approaches, has failed to detect them. We conclude that fullerene cannot be used as a proxy for bolide impacts or mass extinction events.

  • Mars Analog Studies: Ice Covered Lakes on Earth and Mars

    Ice-covered lakes in Antarctica provide models for sedimentary processes on ancient Mars and microbial ecosystems for early Earth. Ice affects sedimentation because sand grains can be blown onto the ice, where they can eventually go through the ice into the lake below. Understanding the details of these processes and resulting sediments will allow us to better reconstruct details of lake environments and their implications for climate on early Mars. Early Earth ecosystems, and those on early Mars if life ever existed there, consist exclusively of microorganisms, which is also true for many Antarctic lakes. Thus, these lakes provide the opportunities to investigate ecological principles for early ecosystems. Data from the microbial mats in these lakes are providing insights into the growth of stromatolite, the geochemical impacts of oxygen-producing photosynthesis, and environments that may have promoted the early diversification of animals.

    ROADMAP OBJECTIVES: 2.1 4.1 4.2 5.1 5.2 6.1
  • Early Animals: Taphonomic Controls on Fossil Record

    This project has focused on Neoproterozoic life with an emphasis on factors influencing fossil preservation. A combination of field and experimental approaches has been used to study preservation of Ediacara-type fossils and to test the prevailing ‘death-mask’ hypothesis that considers iron sulfides to have been a primary agent. Results so far indicate that ferruginization was a late-stage process and not consistent with this model suggesting an important role for early silicification. Initial experimental results show that microbial mats are prone to silicification and that their presence in association with invertebrate carcasses inhibits decay and enhances the preservation of soft-bodied organisms. An investigation of factors controlling the preservation of eukaryotic microfossils in Proterozoic rocks is also underway. Experimental data indicate that certain clays inhibit the growth of decay bacteria such as Pseudoaltermonas.

    New fossil assemblages from grey shales and cherts have been discovered from this same interval – a significant development because very few fossils have been described from rocks between the two Snowball Earth ice ages. The preponderance of exceptional preservations in the Cambrian and subsequent early Paleozoic may be explained in part by a delay in intense mixing of marine shelf sediments by bioturbators, which did not develop until the Devonian. This slow onset of thorough mixing may also have contributed to the late rise of sulfate in the oceans and a mid-Paleozoic drop in oxygen levels.

  • Biosphere-Geosphere Stability and the Evolution of Complex Life

    Five times in the past 500 million years, mass extinctions have resulted in the loss of greater than three-fourths of living species. Each of these events is associated with a significant perturbation of Earth’s carbon cycle. But there are also many such environmental events in the geologic record that are not associated with mass extinctions. What makes them different? We hypothesize that mass extinctions are associated with an instability in the carbon cycle. This project attempts to specify, both theoretically and empirically,the conditions that result in such an instability.

    ROADMAP OBJECTIVES: 4.3 5.1 5.2 6.1
  • Early Animals: Evolution of Complex Multicellularity

    Oxygen availability has long been viewed as a principal deriver of Ediacaran-Cambrian animal diversification, yet quantitative constraints on oxygen history and physiological constraints on animal function at low pO2 have been limited. New statistical analyses of iron-sepciation data for Proterozoic and Paleozoic shales indicate that end-Proterozoic oxygen increase was limited, but physiologial insights from present day oxygen minimum zones indicate that oxygen levels may well have crossed the theshold reuqired from large diverse animals that include carnivores.

  • Evolution of Precambrian Life and Primary Producers

    Life on Earth is sustained by photosynthesis, both on land and in the sea. New research provides novel perspectives on the evolution of diatoms, responsible for 25% of all photosynthesis in today’s oceans. Also, new fossils from Russia strengthen the relationship between early eukaryotes and environmental conditions in Proterozoic oceans.

    ROADMAP OBJECTIVES: 4.1 4.2 6.1
  • Early Animals: Lipid Biosignatures

    We established the structures of two unusual steroid-related molecules that appear to be characteristic of Neoproterozoic ecosystems.

    We responded to an 2013 critique of the sponge biomarker hypothesis with a detailed rebutal. Currently, the most parsimonious interpretation of the presence of the unusual steroid, 24-isopropylcholestane, in Neoproterozoic sediments is that represents a molecular fossil of demosponges.

    We devolped a new approach to evaluating the diets of early hominins based on analyese of fecal sterols. We studied the fecal sterols of great apes and determined that they were distinct from the fecal sterols of Neandethals and modern humans (Sistiaga et al., 2015).

  • Ancient Gene Families and HGT

    We have identified a subset of genes that appear to have been horizontally transferred from very ancient lineages that diverged earlier than the ancestor of the 3 known Domains of life.

  • Mars Analog Studies: Reflectance Spectroscopy of Organics in Ancient Rocks and Meteorites

    Aside from laboratory analyses of meteorites and in situ measurements by mass spectrometers on rover and lander platforms, the search for extraterrestrial organic material on Mars, carbonaceous© chondrite parent bodies, and other planetary surfaces is primarily limited to remote sensing techniques. Our team has been exploring the use of visible and near-infrared reflectance spectros-copy for assessing the presence and abundance of organic materials preserved in ancient terrestrial rocks and C chondrite meteorites. We have continued a series of controlled laboratory experiments to analyze (1) a suite of isolated kerogens and ancient terrestrial sedimentary rocks from various depositional environments and (2) several suites of synthetic clay-organic mixtures. Our goal is to better characterize the potential of reflectance spectroscopy as a method for organic detection and quantification in planetary environments, with the benefits that this technique is rapid, non-destructive, and applicable at laboratory, rover and orbital scales. The spectral models we are de-veloping will provide a foundation for quantifying organics that may be observed in spectroscopic data returned by the Hayabusa2 and OSIRIS-REx missions, laboratory spectra of C chondrites, and future Mars missions equipped with imaging spectrometers.

    ROADMAP OBJECTIVES: 2.1 4.1 4.3 6.1