2012 Annual Science Report

Massachusetts Institute of Technology Reporting  |  SEP 2011 – AUG 2012

Executive Summary

The Neoproterozoic Environment
Tanja Bosak and her collaborators investigated 1) how microbial processes shape some sedimentary rocks, 2) how microbial processes influence the isotopic composition of sulfur-rich minerals that are used to understand the evolution of oxygen and the cycling of carbon in the past, 3) searched for fossils of organisms that lived between 716 and 635 million years ago, surviving times when ice covered entire oceans, even at the equator and 4) used these fossils, recovered from limestone rocks, to understand the cycling of carbon during this unusual time.

In their investigations of the dynamics of the rise of oxygen during the Neoproterozoic Rothman and Bosak have been testing the predictions of the “anti-priming” hypothesis: if more easily degradable organic matter was degraded in oxic environments, this may have slowed down the degradation of organic matter in anaerobic environments and the overall degradation of ... Continue reading.

Field Sites
21 Institutions
18 Project Reports
59 Publications
10 Field Sites

Project Reports

  • Atmospheric Oxygen and Complex Life

    Our team is working to understand what the world looked like just before and just after the evolution of animals. This encompasses field geology (identifying rocks of that age), chemical analysis of those rocks, and close examination of the small, enigmatic fossilized forms within those same geologic units. To synthesize these interdisciplinary approaches, our team also works to contribute overview/review papers that speak to the contribution from each field.

    ROADMAP OBJECTIVES: 4.1 4.2 6.1 6.2
  • Bacterial Steroids and Triterpenoids

    Methylococcus capsulatus is one of a handful of bacteria that are capable of producing both sterols and the sterol-like hopanoid lipids. In this project, we are studying the biosynthesis and function of both sterols and hopanoids of M. capsulatus in order to gain insight into the evolutionary and functional significance of these molecules in the bacterial domain.

    ROADMAP OBJECTIVES: 5.1 5.3
  • Reconstruction of Ancient Proteins

    The genetic code is one of the most ancient and universal aspects of biology on Earth, and determines how specific DNA sequences get interpreted as peptide sequences, which then fold into all the proteins necessary for the growth and function of living cells. To a large extent, this code is determined by a class of proteins that specify which RNA adaptor molecules (tRNA) become attached to which amino acids, aminoacyl-tRNA synthetases. Therefore, reconstructing the amino acid sequences of the ancestors of these synthetases, existing ~4 billion years ago, can tell us the mechanisms by which the genetic code arose, and how it evolved to the modern form inherited by all known living organisms.

    ROADMAP OBJECTIVES: 3.2 3.4 4.1 4.2
  • Micro-RNAs as Phylogenetic Markers

    Since the beginning of 2011, we have published 12 peer-reviewed papers centered on three themes. First, we have pioneered the use of microRNAs (miRNAs) – small 22 nucleotide non-coding RNAs – as phylogenetic characters, and have recently gained new insights into the relationships of vertebrates, arthropods, brachiopods, and flies. Second, we have noted that the number of miRNAs an organism possesses seems related to their relative morphological complexity such that more complex animals have many more miRNAs than simple animals. Third, in a recent Science paper (Erwin et al.2012) we summarized all of our molecular-clock work to date which strongly suggests that bilaterians have a fairly extensive cryptic Precambrian history, which when coupled with our miRNA work makes this missing record even more enigmatic, and the resolution of this paradox is the focus of our current and much of our future NASA-sponsored work.

    ROADMAP OBJECTIVES: 4.2
  • Biomechanics of Rangeomorph Fauna

    The oldest evidence of complex communities of lifeforms come from Newfoundland, Canada. The fossil beds discovered there are dominated by rangeomorphs, which look superficially like underwater plants, but probably got their nutrition by direct uptake of dissolved resources in the water. Here, we use models of water flow in the community to see how these complex organisms could have competed with bacteria for organic matter or reduced compounds in the water. Ultimately, we have determined that by sticking up off the sea floor, rangeomorphs could take advantage of sheer forces created by moving water, and gain an advantage over bacteria in competition for nutrients. The benefits of sticking up into water flow may have driven the early evolution of complex life on earth. Ongoing work seeks to clarify the transitions between flow regimes across stages of community succession from prokaryotic mats to eukaryotic communities

    ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1
  • Ediacaran-Cambrian Diversification of Animals

    We have continued our focus on the record of the early origin of animals, focusing on the fossil record of the Ediacaran and Early Cambrian. Our comprehensive analysis of the Ediacaran-Cambrian diversification of animals, using a new database of first occurrences combined with new molecular clock results (in collaboration with Peterson’s group), was published last year in Science. Erwin and Valentine completed the first comprehensive book on the Cambrian explosion, which is in press and due for release in late 2012 or early 2013.

    ROADMAP OBJECTIVES: 4.2
  • Geochemical Signatures of Multicellular Life

    Sterols are essential membrane components of eukaryotes but their structural diversity varies across different eukaryotic lineages. Our research aimed to determine if are any systematic variations in sterol structures between Metazoa and their immediate unicellular relatives. We found that there is a stepwise reduction in production of 24-alkyl sterol on the path toward eumetazoa suggesting an evolutionary preference for C27 sterols among animals and their kin. A major exception to this finding are the Demosponges which produce a structurally diverse array of sterols.
    We also completed a study of sediments and oils in the South Oman Salt Basin that reported an array of unusual hydrocarbon patterns that are likely to be biosignatures for early metazoa.

    ROADMAP OBJECTIVES: 4.2 5.1
  • Habitability of Extrasolar Planets

    We model if and under what conditions some of the recently detected Super-Earths – small, Earth-sized planets that have been discovered in in the classical Habitable Zone Sun-like stars – could be habitable. These models explore the underlying physics of planetary atmospheres and their remotely detectable features.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1 4.2 6.2 7.2
  • Paleontological Investigations of the Advent and Maintenance of Multicellular Life

    Cohen and Knoll (2012) published a monograph on scale microfossils in the ca. 800 million year old Fifteen Mile group, northwestern Canada. These fossils, document defenses against protistan predation and are the most diverse eukaryotic fossils known from pre-Ediacaran rocks. Justin Strauss discovered a rich new assemblage of testate microfossils in Neoproterozoic strata from northwestern Canada and undergraduate student Ross Anderson completed a senior thesis on testate protists from shales from the Neoproterozoic Dalradian succession in Scotland.

    ROADMAP OBJECTIVES: 4.2
  • The Development of Sensory and Nervous Systems in the Basal Branches of the Animal Tree

    Animals interact with the world through complex sensory structures (eyes, ears, antennas, etc.), which are coordinated by collections of neurons. While the nervous and sensory systems of animals are incredibly diverse, a growing body of evidence suggests that many of these systems are controlled by similar sets of genes. We are looking at early branching and understudied lineages of the animal family tree (using the jellyfish Aurelia and the worm Neanthes respectively) to see if these animals use similar genes during neurosensory development as the better-studied fruit fly and mouse. This research is critical for determining which structures are shared between animals because of common ancestry (known as homologous structures) and those that evolved independently in different lineages. Ultimately, such research informs how morphologically and behaviorally complex animals evolve.

    ROADMAP OBJECTIVES: 4.1 4.2
  • Understanding the Shuram Excursion

    The Shuram carbon isotopic excursion – one of the largest deviations in Earth history- was first discovered in Oman before being found in deposits across the planet. While the causes of this isotopic excursion are as yet unknown, one hypothesis implicates major changes in Ediacaran carbon cycling that occurred simultaneously with the advent of complex life. Alternative hypotheses posit that it is simply a diagenetic anomaly. This research demonstrated that the Shuram Formation carbonates were formed in equilibrium with a fluid with the same oxygen isotopic composition as seawater and at ~50C.

    ROADMAP OBJECTIVES: 4.1 4.2
  • Unicellular Protists of the Neoproterozoic

    We investigated 1) how microbial processes shape some sedimentary rocks, 2) how microbial processes influence the isotopic composition of sulfur-rich minerals that are used to understand the evolution of oxygen and the cycling of carbon in the past, 3) searched for fossils of organisms that lived between 716 and 635 million years ago, surviving times when ice covered entire oceans, even at the equator and 4) used these fossils, recovered from limestone rocks, to understand the cycling of carbon during this unusual time.

    ROADMAP OBJECTIVES: 4.1 4.2 5.1 6.1 7.1
  • Timescales of Events in the Evolution and Maintenance of Complex Life

    We are using natural occurring isotopes produced by long-lived radioactive decay to: provide high-precision dates on geological and biological processes and to trace the geochemical evolution of the oceans during key times in Earth history.

    ROADMAP OBJECTIVES: 4.1 5.3 6.1
  • Geochemical Signals for Low Oxygen Worlds

    We are studying the physiology of sulfate reducing bacteria, organisms that perform a key microbial metabolism in anoxic worlds. By calibrating microbial sulfur isotope effects, we can infer the redox level of paleoenvironments in the geologic past by studying sedimentary records. The sulfur cycle is intimately linked to the redox budget of the Earth’s surface, such that this study will help inform us about the evolution of aerobic environments, a key process that set the stage for animal evolution. Similarly, we also are studying the role of oxygen in controlling the budget and transformations of nitrogen in the ocean. Nitrogen is a critical nutrient limiting marine production, and the balance of its redox cycling controls how much nitrogen is added or removed from the ocean by redox-sensitive processes.

    ROADMAP OBJECTIVES: 1.1 4.1 4.2 5.1 7.1
  • The Neoproterozoic Carbon Cycle

    We are studying the dynamics of the rise of oxygen during the Neoproterozoic (1 billion years ago to 543 million years ago) through culturing experiments, models and observations (see the progress report on the Unicellular Protists). We are testing the predictions of the following “anti-priming” hypothesis: if more easily degradable organic matter was degraded in oxic environments, this may have slowed down the degradation of organic matter in anaerobic environments and the overall degradation of organic matter, increasing the concentration of oxygen in the atmosphere and the surface ocean. We are currently developing theoretical predictions and testing these ideas by laboratory enrichment cultures of anaerobic microbes that degrade complex substrates in the presence and absence of labile organic compounds.

    ROADMAP OBJECTIVES: 1.1 4.1 4.2 5.2 6.1 6.2
  • Molecular Basis for Complexity Development

    Cadherins are large, multi-domain proteins that are also cell surface receptors which function in cell adhesion, cell polarity, and tissue morphogenesis. They are considered essential to the appearance of animal life. We found cadherin genes in Capsaspora owczarzaki and the choanoflagellate Salpingoeca rosetta suggesting that this protein family predates the divergence of the C. owczarzaki, choanoflagellate, and metazoan lineages.

    ROADMAP OBJECTIVES: 4.2
  • Metabolic Networks From Cells to Ecosystems

    Members of the Segre’ group use systems biology approaches to study the complex network of metabolic reactions that allow microbial cells to survive and reproduce under varying environmental conditions. The resource allocation problem that underlies these fundamental processes changes dramatically when multiple cells can compete or cooperate with each other, for example through metabolic cross-feeding. Through mathematical models of microbial ecosystems and computer simulations of spatially structured cell populations, the Segre’ team aims at understanding the environmental conditions and evolutionary processes that favor the emergence of multicellular organization in living systems.

    ROADMAP OBJECTIVES: 3.4 4.2 5.2 6.1
  • Astrobiological Exploration of Mars

    MIT Team member John Grotzinger is the Project Scientist of the MSL mission currently underway at Gale Crater on Mars. John, and his team at Caltech, led a major study of potential landing sites which resulted in the selection of Gale Crater. Since then, they have been involved in the Gale Imaging Working Group, which has been identifying key HiRISE and CRISM data products, which will enhance the science mission. Several members of the Grotzinger group have also been involved in creating a geologic map of the landing site. This involves mapping 1.5° square quads in the landing ellipse and nearby areas. Since landing, the mapping focus has shifted from compiling a regional map to understanding the details of the units and geological relationships in the immediate vicinity of Curiosity.

    ROADMAP OBJECTIVES: 1.1 2.1