nai

Project Reports

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• Mining Archaeal Genomes for Signatures of Very Early Life

  Carl Woese proposed that life started as semi-autonomous subcellular forms named progenotes. The progenotes lacked cell membranes and readily exchanged information, suggesting that aspects of information processing had already been developed. Woese further hypothesized that certain early life processes crossed a Darwinian threshold, where incorporation of new components of a processes was not tolerated. We aim at determining whether translation, transcription, and replication have crossed the Darwinian threshold. To determine whether DNA replication has crossed the Darwinian Threshold, interchangeability of the DNA replication processivity factor known as the sliding clamp is being examined. It is only in the presence of the sliding clamp that DNA polymerases in extant organisms can gain the speed required to replicate their genomes. In Bacteria, the sliding clamp is the b-subunit of Pol-III and in Archaea and Eukarya the functional homolog is proliferating cell nuclear anti-gen (PCNA). We have, therefore, expressed and purified a sliding clamp from each of the three domains of life (E. coli beta-subunit, M. acetivorans PCNA, and human PCNA). Sliding clamps are loaded in a clamp loader dependent manner; therefore, we have cloned, expressed and purified an archaeal clamp loader from M. acetivorans. Our next step is to determine whether an archaeal clamp loader can interact with each of the sliding clamps from the three domains of life and whether any of the interactions leads to loading of the sliding clamps onto DNA to orchestrate processive DNA synthesis.

  ROADMAP OBJECTIVES: 3.2 3.4 4.2

• Extremophile Ribosomes

  Many animals share a common response to environmental stresses. The responses include reorganization of cellular organelles and proteins. Similar stress responses between divergent species suggest that these protective mechanisms may have evolved early and been retained from the earliest eukaryotic ancestors. Many eukaryotic cells have the capacity to sequester proteins and mRNAs into transient stress granules (SGs) that protect most cellular mRNAs. Our observations extend the phylogenetic range of SGs from trypanosomatids, insects, yeast and mammalian cells, where they were first described, to a species of the lophotrochozoan animal phylum Rotifera. We focus on the distribution of three proteins known to be associated with both ribosomes and SG formation: eukaryotic initiation factors eIF3B, eIF4E and T-cell-restricted intracellular antigen 1. We found that these three proteins co-localize to SGs in rotifers in response to temperature stress, osmotic stress and nutrient deprivation as has been described in other eukaryotes. We have also found that the large ribosomal subunit fails to localize to the SGs in rotifers. Furthermore, the SGs in rotifers disperse once the environmental stress is removed as demonstrated in yeast and mammalian cells. These results are consistent with SG formation in trypanosomatids, insects, yeast and mammalian cells, further supporting the presence of this protective mechanism early in the evolution of eukaryotes.

  ROADMAP OBJECTIVES: 3.2 4.2 5.3

• 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

• 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

• 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

• Thermodynamics of Life

  Although thermodynamics dictates that all spontaneous processes must be purely dissipative and “destructive” (the notoriously ungenerous face of the “2nd law”), under particular circumstances a spontaneous process can be a compound of two mechanistically coupled sub-processes only one of which (necessarily the larger one), is dissipative while its coupled, lesser partner is literally “driven” to be creative and generative – that is, a process that can “do work”, “build stuff”, and “make things happen”. A system functioning in this way is technically an engine and all living systems are necessarily, examples of such thermodynamically compound and creative “engine” systems – while at the same time operating internally via a complex, interlinked clockwork of such engines.
  Moreover, living systems inherently belong to a special thermodynamic subclass of such engines, namely those that are “autocatalytic” (self-growing and self-stabilizing) in their operation. Arguably, in fact, it is the property of being autocatalytic thermodynamic engines which at root underlies the potency and magic of living systems and which at the same time constitutes life’s most assuredly universal, fundamental, and primitive property. However, as of yet, we understand the implications of these thermodynamic facts quite poorly – notwithstanding that they seem certain to materially impact questions regarding the origin of life, evolutionary dynamics, and community, trophic, and ecology-level organization.
  The present project undertakes to redress this situation to some extent by investigating the formal dynamical behavior of model systems made up of interacting, thermodynamically driven, autocatalytic engines.

  ROADMAP OBJECTIVES: 3.3 3.4 4.2 5.1 5.2

• 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

• Resurrection of an Ancestral Peptidyl Transferase

  Ancient components of the ribosome, inferred from a consensus of previous work, were constructed in silico, in vitro, and in vivo. The resulting model of the ancestral ribosome incorporates about 20% of the extant 23S rRNA and fragments of four ribosomal proteins. We confirmed that the ancestral rRNA can: (i) assume canonical 23S rRNA-like secondary structure, (ii) assume canonical tertiary structure, and (iii) form native complexes with ribosomal protein fragments. We call the assembled a-RNA and rPeptide fragments the aPTC. We are currently focusing on characterizing the catalytic activity of the a-PTC.

  ROADMAP OBJECTIVES: 3.2 4.2

• 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

• RiboVision: Visualization and Analysis of Ribosomes

  Ribosomes present special problems and opportunities related to visualization and analysis because they are exceeding complex and information-rich. Many structures have determined at near-atomic resolution, a large number of rRNAs have been sequenced, and each is a large macromolecular assembly with many components and highly complex function. We are devising visualization and analysis methods in analogy with Google Maps, but applied to the ribosome. We have used these tools to make important discoveries relevant to ribosomal structure, function and origins.

  ROADMAP OBJECTIVES: 3.2 4.2

• 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

• 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

• The Long Wavelength Limit of Oxygenic Photosynthesis

  Oxygenic photosynthesis (OP) produces the strongest biosignatures at the planetary scale on Earth: atmospheric oxygen and the spectral reflectance of vegetation. Both are controlled by the properties of Chlorophyll a, its ability to perform the water-splitting to produce oxygen, and its spectral absorbance that is limited to red and shorter wavelength photons. We seek to answer what is the long wavelength limit at which OP might remain viable, and how. This would clarify whether and how to look for OP adapted to the light from red dwarfs or M stars, which emit little visible light but abundant far-red and near-infrared. Very recently discovered cyanobacteria have been found to harbor alternative chlorophylls adapted to spectral light environments very much like that of M stars. This projects uses field, lab, and modeling studies to study these far-red adapted cyanobacteria as analogues for extrasolar oxygenic photosynthesis pushing the long wavelength limit.

  ROADMAP OBJECTIVES: 3.2 4.2 5.1 5.3 6.2 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

• 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 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

• 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

• 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

• 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

• 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