2009 Annual Science Report
Carnegie Institution of Washington Reporting | JUL 2008 – AUG 2009
Project 5: Geological-Biological Interactions
This project focuses on a wide range of questions spanning understanding microbial diversity in extreme environments to the identification of biosignatures in modern and ancient rocks. In terms of environments, research in this project focuses on research at deep sea hydrothermal vents, desert sulfate deposits, arctic hydrothermal fields, as well as Paleoproterozoic terrains of Australia, Canada, and India. By learning more how life adapts to extreme environments on Earth, we hope to gain a better understanding of the limits of life on other worlds. By understanding better the signature of life recorded in ancient rocks, we hope to better refine our search stategies for the presence of life on other worlds.
Task 5.1 Life in extreme environments
Over the past year CoIs Baross and Schrenk have focused on the physiology and phylogeny of microbial communities in the extreme environments associated with deep-sea hydrothermal systems. The emphasis is on magma-hosted and peridotite-hosted hydrothermal systems and subseafloor rock-hosted ecosystems affected by hydrothermal activity. These hydrothermal systems can support life without input from photosynthesis; furthermore, they may have been one of the important settings for crucial steps in the origin of life and for the earliest microbial ecosystems. One of the hypotheses addressed is that the predominant groups of Bacteria and Archaea encountered in the extreme hydrothermal vent environments have metabolic pathways and other physiological characteristics that are ancient. In particular the characteristics of hydrogen and methane metabolizing microbial biofilms in extreme vent environments may be analogues to the earliest microbial communities and thus could provide insight into the nature of the last-universal-common ancestor (LUCA). Their research can be divided into three components: 1) molecular and physiological characterization of hydrogen and methane cycling biofilms associated with peridotite and magma-hosted hydrothermal systems, 2) geochemical and physical parameters that effect the physiological and phylogenetic diversity of subseafloor microbial communities and particularly those that use hydrogen as the primary energy source, and 3) the characterization of the virus communities associated with hydrothermal vent environments and their possible role in horizontal gene transfer.
Research at the Lost City Hydrothermal Field continues to focus on the role of serpentinization reactions in producing carbon and energy sources that support microbial ecosystems. The Lost City Hydrothermal Field is driven by the interaction of water with ultramafic rock such as olivine, which results in the production of high temperature (>90°C) and high pH fluids (10 to 11), a combination of extreme conditions never before seen in the marine environment. Moreover, this water/rock interaction produces high concentrations of hydrogen, methane, hydrocarbons, formate and possibly acetate. CoI Baross along with CIW-NAI supported graduate student Brazelton have shown that approximately 85% of all detectable cells in the Lost City biofilms collected from high-temperature, high-pH chimneys belong to a single, novel phylotype of archaea affiliated to the order Methanosarcinales, a group that includes both methane producing and methane consuming species. We have also demonstrated in microcosm incubations with isotopically labeled substrates, that both methanogenesis and methanotrophy can occur in Lost City chimney biofilms. Recently, further evidence for multiple physiologies and substantial genetic diversity within the Lost City Methanosarcinales biofilm was obtained from sequencing of the intergenic transcribed spacer (ITS) region and high-sensitivity pyrosequencing of 16S rRNA in Lost City chimneys. The vast majority of sequence tags matched the dominant archaeal phylotype, highlighting the extremely low diversity of the Lost City archaeal community. The deep sequencing effort also revealed an unexpected cluster of rare sequences with that were similar to the dominant archaeal phylotype. Other clusters of rare sequences were found associated with all major archaeal and bacterial taxa from this environment. Interestingly, many sequences that are rare in some chimneys become dominant in other chimneys. Such shifts within a cluster can occur in less than 10 years, suggesting that species or strains pre-adapted to very specialized geochemical regimes are able to quickly increase in abundance from rare to dominant when conditions allow. These data show that archaeal species which are favorably selected by new conditions already existed at low levels before the environmental change occurred, the genomes of the favorably selected organisms must have already encoded the necessary adaptations prior to the change. In short, they were pre-adapted to the new conditions. The most parsimonious explanation of the many species shifts detected in this study where a rare organism increased its relative abundance on the order of years is that these organisms had been pre-adapted for hundreds or thousands of years to the particular niche created by the environmental change. Therefore, the rare biosphere of the Lost City microbial community represents a large repository of genetic memory created by a long history of past environmental changes selecting for new species within a small pool of organisms that originally colonized the extreme environment. The rare organisms are able to quickly exploit new niches as they arise because they or their ancestors had been previously selected for the same conditions in the past. Further support for this conclusion comes from metagenomic analyses of Lost City biofilms which revealed remarkably high abundance and diversity of genes involved in lateral gene transfer. It is very likely that lateral gene transfer may be the source of the physiological diversity in the Lost City biofilm. Finally, our studies of microbial biofilms supported by serpentinization reactions could lead to a better understanding of how water and ulftamafic rock interactions sustain life and by implications sustain life on the ancient Earth and on other planetary bodies.
CoI Baross and students also continue to focus on the microbial diversity and physiology at diffuse-flow vents at active hydrothermal vent environments. We view sub-seafloor microbial ecosystems not only as analogues to ancient ecosystems, capable of being sustained in the absence of input from photosynthesis, but also as potential analogue environments that might exist on Mars and other planets/moons. Moreover, subseafloor microbial communities that are dependent on CO2 as the primary source of carbon, and hydrogen, sulfur and metals as the energy sources may also be important in global primary production and biogeochemical cycling. We have thus far examined the subseafloor microbial community diversity from 5 geographically distinct diffuse-flow hydrothermal vent sites over the course of 10 years following the 1998 eruption at Axial Seamount and a similar suite of samples from the Main Endeavour Vent Field, Juan de Fuca Ridge since between 2005 and 2009. Our focus has been to ascertain if there is spatial variation in the microbial community structure associated with different vents and if so, whether or not that variation is linked to differences in vent fluid chemistry and temperature. Statistical analysis of vent fluid temperature and chemical composition showed that there were significant differences between vents in any year, but that the composition of vents changed over time such that no vent maintained a chemical composition completely distinct from the others. In contrast, the subseafloor microbial communities associated with individual vents also changed from year to year but each location maintained a distinct community structure (based on molecular diversity measurements) that was significantly different from all other vents included in this study. Potential isolating or stabilizing mechanisms to explain our observed distribution patterns, include biogeographic barriers preventing dispersal of microbes among vents, or to environmental selection of ubiquitous, rare phylotypes that proliferate in response to specific environmental conditions. This is one of very few studies to combine temporal and spatial information to compare multiple vents within a single large hydrothermal area.
Over the past year CoI Schrenk and colleagues at East Carolina University studied a number of aspects of life in extreme environments using microscopic, molecular, and geochemical tools; including both high and low pH, high pressures, and high temperatures. Alkaline seeps of pH >11 fluids were sampled from the Tablelands Ophiolite (Newfoundland, Canada) with Penny Morrill (collaborator; Memorial University) and Dina Bower (NAI-ORAU post doc) in July 2009. A graduate student in Dr. Schrenk’s lab at East Carolina University (Quinn Woodruff) also participated in the field expedition. The seep ecosystem was systematically sampled and environmental conditions including fluid and gas chemistry, temperature, and local geography were documented. Samples were collected for ribosomal RNA analyses of microbial phylogenetic and functional diversity; with particular focus upon quantifying genes expected to be abundant in this volatile-rich, anaerobic habitat. Additionally, samples were collected for microscopic analyses of biofilms associated with the catalytic peridotite mineral surfaces in the serpentinite ecosystem.
At the low pH end of the spectrum, CoI Schrenk is continuing to analyze organic polymers in microbial biofilms from the Iron Mountain mine in northern California in collaboration with Dr. J. Banfield (NAI alumnus) and colleagues at UC Berkeley. The acid mine drainage at this site is amongst the lowest ever recorded in a natural environment, and supports the growth of prolific biofilms in what is essentially concentrated sulfuric acid. While the genomic and proteomic content of the biofilms has been extensively studied, the “glue” the holds the biofilms together is less well known. Schrenk and colleagues (including PI Cody) are applying a range of extraction and preparatory methods to disrupt and concentrate the extracellular polymers for detailed downstream analyses using spectrophotometry, GC-MS, and NMR spectroscopy.
Also during the past year CoI Schrenk has initiated studies of the physiological effects of high hydrostatic pressure were conducted using iron oxide rich microbial mat samples obtained from 5,000 meters water depth near Loihi Seamount, Hawaii in Oct. 2008 in collaboration with Dr. K. Edwards (USC; NAI alumnus with UH). These experiments evaluated the impact of using in situ hydrostatic pressures or 50 MPa upon the growth rates and microbial diversity of enrichment cultures in a variety of environmentally relevant growth media (lithoautotrophic, oligotrophic, and heterotrophic). The enrichment cultures, which were prepared and analyzed by an undergraduate student working in the Schrenk Lab at ECU, yielded essentially pure cultures related to a known piezophilic deep-sea bacterium (Photobacterium profundum str. SS9) at high pressures, whereas the incubations at 0.1 MPa (1 atm) yielded complex microbial assemblages. This work replicates some of the earliest work in deep-sea microbiology by Zobell and colleagues in the 1950’s, while applying modern molecular tools to phylogenetically characterize the enrichment cultures. This work will be presented in an oral presentation at the Fall 2009 American Geophysical Union meeting in San Francisco, CA.
CoI Schrenk lab is also continuing research into documenting the abundance and diversity of microbial communities in high temperature hydrothermal ecosystems including shallow marine sediments of the Aeolian Islands (Sicily), as well as deep-sea hydrothermal vent chimneys from the Northeast Pacific Ocean. These efforts are directed at relating the distribution of microbial communities to the thermal and chemical characteristics of these hydrothermal gradient ecosystems, and to provide observational data related to the upper temperature limits of life.
CoI Schrenk and colleagues also continue to develop and implement novel culturing techniques to uncover the physiological and functional diversity of microorganisms in both laboratory and natural settings. Laboratory experiments included applying in situ hydrostatic pressures to enrich for new groups of piezophilic microorganisms from iron oxide rich microbial mats from Loihi Seamount, near Hawaii. Additionally, alkaliphilic enrichment cultures were initiated using samples from the Tablelands Ophiolite in media containing natural mineral substrata and either filtered seep fluids or artificial mineral water as liquid media. Both of these research projects were conducted by undergraduate students at ECU as part of their senior theses in Biology. Another line of research involved developing novel strategies for the in situ enrichment of microorganisms in their natural habitats. During the field expedition to the Tablelands Ophiolite in situ colonization experiments containing natural mineral assemblages were deployed in the alkaline serpentinite seeps. These experiments are being used to evaluate colonization kinetics and succession of microbial communities as they relate to changes in mineralogy (e.g. serpentinization). Through careful analysis of the microbe-mineral interactions, we hope to gain insight into the linkages between serpentinization, fluids, and life. Second, various configurations of in situ colonization experiments, and their surface chemistries are being tested and validated in the lab at a proof-of-concept stage, with the ultimate goal of being deployed in natural hydrothermal settings.
CoI Schrenk and colleagues continue efforts to document the microbial communities of both shallow marine and deep-sea hydrothermal gradients ecosystems using co-registered molecular, microscopic, and geochemical tools. Sediment cores obtained from shallow marine hydrothermal ecosystems of the Aeolian Islands near Sicily have been sub-sectioned into strata representing distinct thermal and chemical conditions. Microbial cell densities and distributions have been determined with the sedimentary ecosystems and related to total organic carbon content, temperature, and end-member fluid chemistry. Additionally, DNA has been extracted from the sediment layers and is being screened using terminal restriction fragment length polymorphism (T-RFLP) analysis for differences in microbial phylogenetic diversity, and for the presence of genes involved in autotrophy (biological assimilation of inorganic carbon). This work is being undertaken by two undergraduates as part of a senior thesis project in the Department of Biology at ECU, and will be continued by a graduate student with a follow on field expedition during the upcoming year.
Over the past year CoI Schenk has also initiated studies of microbial distribution and function in deep-sea 'black smoker’ hydrothermal vent chimneys in collaboration with a colleague (Dr. J. Holden) from U. Mass.Amherst. Most past attempts to quantify microbial distributions in these structures have relied upon the homogenization, extraction, and purification of microbial cells thus eliminating important contextual data. Efforts are being made to optimize procedures for the in situ imaging and quantification of microbial distribution within pore space of the sulfide structures using a technique called fluorescently-labeled embedded coring (FLEC). Thus far, the technique has worked well with general DNA stains, but will eventually be integrated with phylogenetic staining techniques to target specific groups of microorganisms.
Finally, CoI Schrenk contributed to a review paper for Annual Reviews in Marine Science compiled with colleagues from the Marine Biological Lab (Dr. J. Huber; CIW node) and the U. of Southern California (Dr. K. Edwards). The paper is a synthesis of existing literature and knowledge of life in the subseafloor, with the purpose of defining distinct microbial biomes in this hard-to-study habitat. The review paper will serve as a template to guide future explorations of the seafloor. Iterations of the manuscript have been presented at INVEST (an international workshop intended to guide the next decade of ocean drilling research) and the AGU Ocean Sciences Meeting.
Over the past year CoI Steele and colleagues has been studying the adaptation mechanisms of microorganisms, especially cyanobacteria, to changing environmental conditions in arctic geothermal springs. Microorganisms are frequently exposed to changing environmental conditions. Cold can be a stress that modifies physical and chemical parameters and therefore cells need to adapt to temperature changing conditions. Geothermal springs are warm and active all year around, but experience extreme variations in temperature, and long periods of continuous daylight and darkness. Given the nature of the springs, it is important to understand how the microorganism that live there adapt to these varying conditions. To gain an overview of the microbial/eukaryotic diversity across the various environments within the spring we started to analyze the community using molecular fingerprinting methods. We extracted DNA from filters (planktonic cells), of biofilms in water, biofilms that appear to be in the process of being trapped in calcite, and endoliths that are probably trapped biofilms in various stages of becoming lithified. We are currently in the process of analyzing DNA for diversity by using 454 parallel-tagged pyrosequencing for partial 16S analyses.
Collaborators Kish and Glamoclija along with CoI Steele have been studying microbial diversity in modern sulfate deposits During the past funding period. Sulfates are a constitutive part of rocks and regolith exposed to the surface of Mars. The White Sands National Monument (WSNM) (New Mexico) with its gypsum desert is an excellent terrestrial analog to sulfate deposits on Mars and a unique natural laboratory for studying arid evaporitic ecosystems and their relations to microbial life, as well as the potential of such environments for preservation of organics through geologic time. Gypsum-rich sand, and gypsum- and halite-rich sediments, and crusts with contribution of different types of carbonates, clay, and different types of sulfo-salts were collected from the dunes, interdunes, Alkali Flats, and the surface of dried Lake Lucero. DNA extractions with PCR amplification revealed the presence of Eubacteria, Archaea and Eukaryota in samples from 400 yr old paleodunes and in samples from the Lake Lucero. Most of the analyzed samples showed presence of Eubacteria and Archaea, including the samples of large selenite crystals. The desert environments at the WSNM appear to be inhabited by diverse microbial communities well adapted to arid conditions. Extracted DNA was probed using universal PCR primers for all three domains of life prior to sequencing the small subunit ribosomal DNA to obtain species-specific identification of all microorganisms found in each pigmented layer of the samples. These samples were cross-compared to similarly pigmented samples obtained from a hypersaline environment in Canada on field expeditions undertaken by Dr Adrienne Kish and Dr Dina Bower under the supervision of CoI Steele.
Task 5.2 Microbial Adaptations to Chemistry and Pressure at Life’s Extremes
It is estimated that more life resides below the surface of Earth than on or above it. Because of this, understanding the effects of high pressure (HP) on microorganisms is necessary for fully understanding life in a planetary context. The limitations presented by HP inform our notions of habitability not only on Earth but also its potential existence in elsewhere in the solar system. HP treatment is also employed by food processors to limit microbial growth. All of these applications necessitate detailed investigation into the effects of HP on microbial systems.
Significant strides have been made by collaborator Kish and CoI Steele at the Geophysical Laboratory over the past 12 months in the effort to better understand the effects of HP (up to 400 MPa) on cellular macromolecules. Using model organisms from all three domains of life, they have analyzed comparative survival assays under a range of HP conditions. They have also been able to analyze the effects of alterations in experimental parameters on HP survival in a given model organism, enabling comparison of previously published and future works using a range of different experimental apparatus based on an understanding of the roles of the experimental variables. Particular attention was paid to the role of the intracellular milieu using extremely halophilic micro-organisms that feature high concentrations of either intracellular salts or compatible solutes used to balance the hypersaline external environment in which they are cultured. These results were compared to those obtained from mesophilic micro-organisms to determine the role of small molecules in the cytosol in overall HP survival.
The role of protein damage in cell death under HP conditions was examined in greater detail to determine the types of molecular level damages produced by HP and the effect of those damages on cellular function. HP sensitive and HP resistant organisms were compared using molecular level techniques ranging from SDS-PAGE and Western Blots using antibodies specific for various types of macromolecular damages to the use of microscopy to document changes in cellular morphology after exposure to HP conditions. Detailed analysis of changes in protein abundances and molecular weight due to chemical alterations under HP conditions were undertaken using a highly sensitive SELDI-TOF mass spectrophotometer.The results from these studies are currently being prepared for publication.
Task 5.3: Biosignatures
During the 2008-2009 research period CoI Farquhar has focused on the role of microorganisms in the sulfur cycle. This research included (1) designing and undertaking experiments with sulfur and oxygen isotopes to characterize the way that sulfur is transferred through microbial metabolisms, and (2) coupled field and laboratory studies of modern ecosystems (Lago di Cadagno, Switzerland) where sulfur is cycled in order to characterize the isotopic variability of all four sulfur isotopes. This work was part of an ongoing collaboration with Don Canfield at the University of Southern Denmark and partially supported by funds from the Guggenheim Foundation and the Danish Grundforskningsfond, in addition to involvement of the NAI. This collaboration brings together analytical capabilities of my group with the microbiological expertise of the Danish group: the combination of these two has extended beyond what each could expect to achieve in isolation. A series of experiments were undertaken that involved culturing of Desulfobacterium autotrophicum using a variety of growth conditions (sulfate concentration, electron donors and temperature) and with sulfate that was synthesized to have a 17O isotopic label. This experiment is still underway and the run products have not been analyzed (yet) for the four naturally occurring sulfur isotopes (32S, 33S, 34S, & 36S) or for their oxygen isotopes (16O, 17O, & 18O). The isotopic label will allow us to monitor isotopic exchange that occurs with sulfur intermediates produced by the metabolism and provides a way to constrain the mass-flow of sulfur via reoxidative pathways. These isotopic analyses will be undertaken in the next year, and the data will be evaluated in an effort to obtain new insights into the isotope effects associated with the sulfur transformations that occur at the cellular level and will involve graduate student Brian Harms. Further work was undertaken at a field site in Switzerland (Lago Di Cadagno), a meromictic (permanently stratified) sulfidic lake and a paper describing these results is presently in review with the journal Geology (Canfield, Farquhar, Zerkle). The focus of this manuscript is the observation that incubation with natural populations of sulfate reducers from Lago di Cadagno produced isotope fractionations of greater than 70 ‰ for δ34S. The lake is lake with relatively low sulfate concentrations (2mM) and yields in-situ fractionations of approximately 30 to 40 ‰ for δ34S depending on the season at which it is samples. These changes, and the high fractionations are used to obtain insight into low sulfate systems and this lake is thought to be in some respects, an analog for the Proterozoic oceans. Other work related to the NAI involved a collaboration with the Penn-State group to help with analyses of products from abiological thermochemical sulfate reduction experiments. A mass-independent signal was observed and may be either a magnetic isotope effect or an effect such as the one advocated by the Penn state group in a study by Lasaga et al. (2008). These results are described in a study by Watanabe et al. (2009).
Over the past year Collaborator Papineau and CoI Hauri have been involved in method development because the nanoSIMS (Secondary Ion Mass Specrometer) has not been used before to measure three stable isotopes of sulfur simultaneously. Most tests to date have been performed on conductive Fe-bearing sulfides mouted in indium and polished with near-zero relief. With Cs, a routine primary beam diameter of 100 nm is obtained with 1-2pA of current, sufficient to yield 1MHz of 32S from pyrite at >6000 MRP. A 2.5 nA Cs beam with a diameter of 700 nm yields 90 pA of 32S from pyrite at >6000 MRP, sufficient to analyze 32S-33S-34S on Faraday cups and 36S in EM @ >10,000 cps. Specification tests immediately after installation in 2005 demonstrated a reproducibility of <0.3 permil (1-sigma) in 10 analyses within a single sputter crater on Balmat pyrite, and this was subsequently improved to 0.15 permil (1-sigma) in 2006. Further tests showed that reproducibility on separate craters of a single grain, and separate craters in separate Balmat pyrite grains located in different holes of the sample holder, were improved to better than 0.2 permil (1-sigma) through careful attention to reproducibility of sample height (Z-axis control) and centering of the secondary ion beam in the entrance slit of the mass spectrometer. Using a beamsize of 15x15 microns, the 2-sigma reproducibility on standards was +/- 1.0 and +/- 0.3 permil for d34S and D33S values, respectively, and we obtained mass dependent fractionation slopes of 0.5167 and 0.5172. So far, our survey of 2.7 Ga Abitibi and Bababudan/Sandur BIF and chert sulfides has revealed a range of about 15 permil in d34S (between +6 and -9 permil) and mostly positive D33S values up to +2.9 permil (Figure 3). These data are consistent with a generally anoxic Neoarchean atmosphere and possibly with some microbial sulfur processing in the original depositional environment.
Also during the previous funding period Collaborator Papineau, working with a number of CoI’s, on this grant has been performing detailed petrographic surveys of apatite grains in association with CM in several Paleoproterozoic, Neoarchean and Eoarchean banded iron formations (BIFs) in the highly debated Akilia Qp rock. Petrographic and Raman spectroscopic surveys of Paleoproterozoic BIFs show that apatite grains typically occur as bands parallel to bedding and are often associated with CM that likely represents diagenetically alterated biomass. Carbonaceous material in the Vichadero BIF from Uruguay occurs in concentrations below 0.15 wt% and has d13C values between -30.0 and -31.7‰, whereas that from the Bijiki BIF from Michigan is up to 8.35 wt% with d13C values between -19.4 and -26.6‰. Isotope compositions of CM in micro-drilled powders from the Akilia Qp rock have d13Cgr values between -21.1 to -25.7‰ and d13Ccarb values of carbonate in whole rock powders range between -3.3 to -5.5 ‰. Micron-scale carbon isotope analyses of graphite associated with apatite and other minerals in the Akilia Qp rock by NanoSIMS reveals a larger range of d13Cgr values between -4.1 and -22.8‰ indicating the presence of isotopically heterogeneous sub-domains within the graphite. Papineau and collaborators data on Paleoproterozoic BIFs provide a useful petrographic context to trace the diagenetic alteration and subsequent metamorphic crystallization of organic matter in BIFs. A paper detailing this work has been submitted for publication.
Collaborator Papineau along with CoI’s Cody, Fogel, Steele, and Stroud has also been applying a cooridinated analytical approach to better understand the nature of carbon in BIFs from the Eoarchean Nuvvuagittuq Supracrustal Belt (NSB) in northern Québec. Preliminary analyses of organic carbon in microdrilled powders from NSB BIFs revealed d13Corg values down to -35‰ and there are hints that values may be even more 13C-depleted. In a quartz+amphibole+magnetite BIF from the NSB, apatite grains are mostly in the quartz matrix and these are occasionally associated with carbonaceous material (CM). Laser scanning Raman analyses of these mineral associations revealed that the CM has strong G- and D-band peaks (at ~1575 cm-1 and ~1345 cm-1, respectively) characterized by low full widths at half maximums (FWHM) consistent with partly disordered graphite that likely crystallized at high temperature. One such particle of graphite associated with apatite was found to host curled graphite structures identified by an unusually strong D*-band (at ~2700 cm-1). This apatite-associated graphite particle was extracted with a focused ion beam (FIB) extraction technique in preparation for transmission electron microscopy (TEM) and synchrotron-based scanning transmission X-ray microscopy (STXM). These new results can now be compared with similar microscopic mineral associations from BIFs from the quartz-pyroxene rock from the Island of Akilia as shown in Figure 2.
During this same period Collaborator Papineau and CoI Fogel have been focusing on the C-N-P-S cycle during the Paleoproterozoic. The accumulation of atmospheric oxygen in the Paleoproterozoic atmosphere occurred over several hundred millions of years. Sulfur isotopes indicate that this began around 2.5 Ga and continued during the interglacial and post-glacial period between about 2.4 and 2.2 Ga. Higher levels of seawater sulfate have been inferred from Paleoproterozoic sedimentary sulfides and this was likely the result of increased oxidative weathering that caused higher riverine delivery of sulfate to seawater. Carbon isotope excursions in Paleoproterozoic interglacial carbonates from the Transvaal Supergroup in South Africa and in post-glacial carbonates on most continents indicate a relative increase in burial rates of organic carbon and suggest a significant production of atmospheric oxygen. Because atmospheric oxygen is primarily produced by oxygenic photosynthesis, these observations lead to the suggestion that the cause of atmospheric oxygenation may have been high productivity by cyanobacteria due to the concomitant increased delivery of riverine phosphate. This hypothesis was investigated in the Lower Aravalli Group in Rajasthan. Papineau finds that carbonaceous shales in the Jhamarkotra Fm. of the Lower Aravalli Group have distinct geochemical characteristics depending on their association with phosphorites in the Udaipur Epicontinental Sea (phosphate domain – PD) or in the Aravalli Epeiric Sea (non-phosphate domain – NPD). Lithostratigraphic correlations suggest that these domains of the Jhamarkotra Fm. are co-eval, but that they may have developed in succession with the syn-kinematic opening of the Aravalli rift. Black shales from the PD have high levels of organic matter (up to 14%wt) and generally homogeneous d13Corg values, whereas those from the NPD have less than 3%wt of organic carbon and occasionally high d13Corg values. These results were interpreted to indicate different signatures of high primary productivity as a result of high nutrient availability depending on the depositional environment. New carbon isotope data from stratigraphically underlying dolomite in the Jhamarkotra Fm. also preserve distinct geochemical characteristics according to their occurrences in the PD or NPD. Dolomite from the NPD often has high d13Ccarb values, whereas stromatolitic phosphorites from the PD often have high d13Corg values and this is shown in Figure 1. The chemical composition (H/C and O/C ratios), Raman spectral characteristics, and synchrotron-based STXM spectra of organic matter extracted from a large selection of these various samples indicate some degree of graphitization, but insignificant alteration of geochemical compositions by metamorphism. Collectively, carbon isotope data for organic matter and carbonate throughout the Jhamarkotra Fm. show different geochemical signatures for high levels of primary productivity that are intimately related depositional environments. We suggest that high weathering rates and the consequent increased delivery of phosphate to seawater along this Paleoproterozoic rifted margins stimulated blooms of oxygenic photosynthesis. This scenario may have been a widespread phenomenon during the Paleoproterozoic and may have been responsible for atmospheric oxygenation at that time.
CoI Steele has continued using Raman spectroscopy peak mapping of microfossils in cherts to elucidate the biological nature of these features. Of particular relevance to this study is the emphasis placed on whether features in the Apex chert of the Pilbara, Australia constitute evidence of 3.5 billion year old filamentous organisms. In these studies, confocal Raman peak mapping has been used for the first time to analyse microfossils from a range of samples (including Apex) and it is evident that the ordered and disordered (D and G bands respectively) peaks of macromolecular carbon exist in all types and ages of fossils and features analyzed. CoI Steele has undertaken 2-D microRaman imaging using instrumentation that has a spatial and spectral resolution that are much higher than used in the previous studies in an attempt to prove or disprove the biogenicity of the purposed ancient fossil Eoleptenema apex. He has also undertaken studies on Apex and Strelley pool cherts, which show in some cases, the presence of fossilized younger presumably contaminant organisms.
Finally CoIs Hazen and Sverjensky and coworkers continue to investigate the co-evolution of minerals and life. The central premise of “mineral evolution” is that the geo- and biospheres have coevolved through a sequence of deterministic and stochastic events that result in the diversification of the mineral kingdom through Earth history. Important implications of this model are (1) that different terrestrial planets and moons achieve different stages of mineral evolution, and (2) the majority of the >4400 known mineral species on Earth are the indirect consequence of biologically mediated changes to ocean and atmospheric chemistry, most notably the Great Oxidation Event (GOE). Hazen conclude that perhaps 1500 mineral species can arise abiotically – some of which may be essential to life’s origins. On Earth the additional ~2900 species arose from oxidative alteration and weathering after the rise in atmospheric oxygen. An important unanswered question is whether some of these minerals, which are biologically mediated on Earth, can form abiotically, or if they represent robust biosignatures.
PROJECT INVESTIGATORS:John Baross
PROJECT MEMBERS:George Cody
RELATED OBJECTIVES:Objective 4.1
Earth's early biosphere.
Environment-dependent, molecular evolution in microorganisms
Effects of environmental changes on microbial ecosystems
Adaptation and evolution of life beyond Earth
Biosignatures to be sought in Solar System materials