2013 Annual Science Report

Massachusetts Institute of Technology Reporting  |  SEP 2012 – AUG 2013

Executive Summary

Members of the MIT Team have been working on some of the oldest fossil evidence of animals and applying studies of modern animal development to interpret these fossils. The goal is to understand how the interactions between changes in the physical environment, ecological interactions and in developmental mechanisms in evolutionary innovations lead to greater biological complexity.

Environmental change and evolutionary innovation:
In January 2013 The Cambrian Explosion: The Construction of Animal Biodiversity by Douglas Erwin and Jim Valentine was published (Roberts Publishing). The book argues that the origin and early diversification of animals can only be understood through integrating our understanding of changes in the physical environment (principally changes in ocean redox), the construction of networks of ecological interactions, and the growth of regulatory interactions in gene networks that control development.

Graduate Student Sarah Tweedt (University of Maryland ... Continue reading.

Field Sites
47 Institutions
15 Project Reports
68 Publications
10 Field Sites

Project Reports

  • 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
  • Molecular Biosignatures: Preservation in Mineral-Forming Ecosystems

    Molecular biosignatures are an important and informative means to reconstruct ancient ecosys-tems, especially, in the case of those dominated by microbes. Most microbes leave only fragmentary chemical records and fossilized hard-parts confined to those taxa with mineralized tests. Preservation can be significantly enhanced when these molecular biosignatures are encapsulated in minerals which are actively forming where the microbes are living and where they may be sequestered from the deleterious effects of oxygen and radiation. We studied several such organo-mineral associations comprising carbonate, silica and gypsum and document a diverse range of molecular biosignatures some of which would be preservable over long timescales. These results are relevant for the study of sediments on the ancient earth, but are also useful in predictive sense for the study of minerals on other planets.

    ROADMAP OBJECTIVES: 5.1 5.3 7.1
  • 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
  • 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?

  • 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
  • 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
  • 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
  • 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.

  • 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
  • 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.

  • 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.

  • 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
  • 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.

  • Molecular Biosignatures: Hopanoid Sources in Modern Systems

    Molecular fossils preserved in sedimentary rocks provide a record of Earth’s early biosphere and its associated carbon cycle. Among the earliest and most abundant molecular fossils are the hopanoids. Derived primarily from bacteria, their diagenetic products, the hopanes, are detectable over timescales of billions of years and have been proposed to be among the most abundantly preserved molecules on Earth. However, an overall picture of their environmental, physiological, and taxonomic origins remains elusive. Are they primarily remnants of primary producers or of heterotrophic consumers? Do they primarily come from free-living marine communities, or from shallow mats, tidal zone communities, or even terrigenous runoff? Here we aim to obtain compound-specific carbon isotope data for hopanoids to infer their sources in modern systems, as proxies for understanding ancient environments.

    ROADMAP OBJECTIVES: 3.2 5.1 5.3 6.1
  • Preparation of Review Articles

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