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Shaelyn N Silverman, Sebastian H Kopf, Brad M Bebout, Richard Gordon, Sanjoy M Som
Earth's atmospheric composition has changed significantly over geologic time. Many redox active atmospheric constituents have left evidence of their presence, while inert constituents such as dinitrogen gas (N2 ) are more elusive. In this study, we examine two potential biological indicators of atmospheric N2 : the morphological and isotopic signatures of heterocystous cyanobacteria. Biological nitrogen fixation constitutes the primary source of fixed nitrogen to the global biosphere and is catalyzed by the oxygen-sensitive enzyme nitrogenase...
October 5, 2018: Geobiology
Martina Sollai, Laura Villanueva, Ellen C Hopmans, Gert-Jan Reichart, Jaap S Sinninghe Damsté
Archaea are important players in marine biogeochemical cycles, and their membrane lipids are useful biomarkers in environmental and geobiological studies. However, many archaeal groups remain uncultured and their lipid composition unknown. Here, we aim to expand the knowledge on archaeal lipid biomarkers and determine the potential sources of those lipids in the water column of the euxinic Black Sea. The archaeal community was evaluated by 16S rRNA gene amplicon sequencing and by quantitative PCR. The archaeal intact polar lipids (IPLs) were investigated by ultra-high-pressure liquid chromatography coupled to high-resolution mass spectrometry...
October 3, 2018: Geobiology
Kazumi Ozaki, Christopher T Reinhard, Eiichi Tajika
The possibility of low but nontrivial atmospheric oxygen (O2 ) levels during the mid-Proterozoic (between 1.8 and 0.8 billion years ago, Ga) has important ramifications for understanding Earth's O2 cycle, the evolution of complex life and evolving climate stability. However, the regulatory mechanisms and redox fluxes required to stabilize these O2 levels in the face of continued biological oxygen production remain uncertain. Here, we develop a biogeochemical model of the C-N-P-O2 -S cycles and use it to constrain global redox balance in the mid-Proterozoic ocean-atmosphere system...
October 3, 2018: Geobiology
Emma U Hammarlund, M Paul Smith, Jan A Rasmussen, Arne T Nielsen, Donald E Canfield, David A T Harper
The early Cambrian Sirius Passet fauna of northernmost Greenland (Cambrian Series 2, Stage 3) contains exceptionally preserved soft tissues that provide an important window to early animal evolution, while the surrounding sediment holds critical data on the palaeodepositional water-column chemistry. The present study combines palaeontological data with a multiproxy geochemical approach based on samples collected in situ at high stratigraphic resolution from Sirius Passet. After careful consideration of chemical alterations during burial, our results demonstrate that fossil preservation and biodiversity show significant correlation with iron enrichments (FeHR /FeT ), trace metal behaviour (V/Al), and changes in nitrogen cycling (δ15 N)...
September 27, 2018: Geobiology
James A Bradley, Jan P Amend, Douglas E LaRowe
Microorganisms buried in marine sediments are known to endure starvation over geologic timescales. However, the mechanisms of how these microorganisms cope with prolonged energy limitation is unknown and therefore yet to be captured in a quantitative framework. Here, we present a novel mathematical model that considers (a) the physiological transitions between the active and dormant states of microorganisms, (b) the varying requirement for maintenance power between these phases, and (c) flexibility in the provenance (i...
September 24, 2018: Geobiology
Aaron M Martinez, Diana L Boyer, Mary L Droser, Craig Barrie, Gordon D Love
The end-Devonian Hangenberg Crisis constituted one of the greatest ecological and environmental perturbations of the Paleozoic Era. To date, however, it has been difficult to precisely constrain the occurrence of the Hangenberg Crisis in the Appalachian Basin of the United States and thus to directly assess the effects of this crisis on marine microbial communities and paleoenvironmental conditions. Here, we integrate organic and inorganic chemostratigraphic records compiled from two discrete outcrop locations to characterize the onset and paleoenvironmental transitions associated with the Hangenberg Crisis within the Cleveland Shale member of the Ohio Shale...
September 24, 2018: Geobiology
Chloe L Stanton, Christopher T Reinhard, James F Kasting, Nathaniel E Ostrom, Joshua A Haslun, Timothy W Lyons, Jennifer B Glass
The potent greenhouse gas nitrous oxide (N2 O) may have been an important constituent of Earth's atmosphere during Proterozoic (~2.5-0.5 Ga). Here, we tested the hypothesis that chemodenitrification, the rapid reduction of nitric oxide by ferrous iron, would have enhanced the flux of N2 O from ferruginous Proterozoic seas. We empirically derived a rate law, dN2Odt=7.2×10-5[Fe2+]0.3[NO]1 , and measured an isotopic site preference of +16‰ for the reaction. Using this empirical rate law, and integrating across an oceanwide oxycline, we found that low nM NO and μM-low mM Fe2+ concentrations could have sustained a sea-air flux of 100-200 Tg N2 O-N year-1 , if N2 fixation rates were near-modern and all fixed N2 was emitted as N2 O...
August 22, 2018: Geobiology
Dave Keighley, Suporn Boonsue, Douglas Hall
Microscopic globular structures have been observed in some beds of oil shale from eastern Utah. These beds comprise carbonate-dominated mud that is interlaminated with variably thick and continuous organic-rich layers. Collectively they are enriched in phosphorus, REEs, and actinides. The beds are considered of lacustrine origin and assigned to the Eocene Green River Formation. The globules themselves are of microcrystalline carbonate fluorapatite (μCFA), often contain concentric internal structures, and usually group together in clusters of up to 80, possibly more...
August 13, 2018: Geobiology
Kaarel Mänd, Kalle Kirsimäe, Aivo Lepland, Chris H Crosby, Jake V Bailey, Kurt O Konhauser, Richard Wirth, Anja Schreiber, Kaarel Lumiste
Sedimentary phosphorites comprise a major phosphorus (P) ore, yet their formation remains poorly understood. Extant polyphosphate-metabolizing bacterial communities are known to act as bacterial phosphate-pumps, leading to episodically high dissolved phosphate concentrations in pore waters of organic-rich sediment. These conditions can promote the precipitation of amorphous precursor phases that are quickly converted to apatite-usually in carbonate fluorapatite form [Ca10 (PO4 ,CO3 )6 F2-3 ]. To assess the mechanisms underpinning the nucleation and growth of sedimentary apatite, we sampled P-rich sediments from the Namibian shelf, a modern environment where phosphogenesis presently occurs...
July 30, 2018: Geobiology
Veljo Kisand, Liisi Talas, Anu Kisand, Normunds Stivrins, Triin Reitalu, Tiiu Alliksaar, Jüri Vassiljev, Merlin Liiv, Atko Heinsalu, Heikki Seppä, Siim Veski
Most studies that utilize ancient DNA have focused on specific groups of organisms or even single species. Instead, the whole biodiversity of eukaryotes can be described using universal phylogenetic marker genes found within well-preserved sediment cores that cover the post-glacial period. Sedimentary ancient DNA samples from Lake Lielais Svētiņu, eastern Latvia, at a core depth of 1,050 cm in ~150 year intervals were used to determine phylotaxonomy in domain Eukaryota. Phylotaxonomic affiliation of >1,200 eukaryotic phylotypes revealed high richness in all major eukaryotic groups-Alveolata, Stramenopiles, Cercozoa, Chlorophyta, Charophyta, Nucletmycea, and Holozoa...
July 23, 2018: Geobiology
Melody R Lindsay, Maximiliano J Amenabar, Kristopher M Fecteau, Randal V Debes, Maria C Fernandes Martins, Kirsten E Fristad, Huifang Xu, Tori M Hoehler, Everett L Shock, Eric S Boyd
The geochemistry of hot springs and the availability of oxidants capable of supporting microbial metabolisms are influenced by subsurface processes including the separation of hydrothermal fluids into vapor and liquid phases. Here, we characterized the influence of geochemical variation and oxidant availability on the abundance, composition, and activity of hydrogen (H2 )-dependent chemoautotrophs along the outflow channels of two-paired hot springs in Yellowstone National Park. The hydrothermal fluid at Roadside East (RSE; 82...
July 23, 2018: Geobiology
Erica Victoria Barlow, Martin Julian Van Kranendonk
Eighteen microfossil morphotypes from two distinct facies of black chert from a deep-water setting of the c. 2.4 Ga Turee Creek Group, Western Australia, are reported here. A primarily in situ, deep-water benthic community preserved in nodular black chert occurs as a tangled network of a variety of long filamentous microfossils, unicells of one size distribution and fine filamentous rosettes, together with relatively large spherical aggregates of cells interpreted as in-fallen, likely planktonic, forms. Bedded black cherts, in contrast, preserve microfossils primarily within, but also between, rounded clasts of organic material that are coated by thin, convoluted carbonaceous films interpreted as preserved extracellular polymeric substance (EPS)...
September 2018: Geobiology
Henrik Drake, Martin J Whitehouse, Christine Heim, Peter W Reiners, Mikael Tillberg, K Johan Hogmalm, Mark Dopson, Curt Broman, Mats E Åström
In the deep biosphere, microbial sulfate reduction (MSR) is exploited for energy. Here, we show that, in fractured continental crystalline bedrock in three areas in Sweden, this process produced sulfide that reacted with iron to form pyrite extremely enriched in 34 S relative to 32 S. As documented by secondary ion mass spectrometry (SIMS) microanalyses, the δ34 Spyrite values are up to +132‰V-CDT and with a total range of 186‰. The lightest δ34 Spyrite values (-54‰) suggest very large fractionation during MSR from an initial sulfate with δ34 S values (δ34 Ssulfate,0 ) of +14 to +28‰...
September 2018: Geobiology
Jérémie Aubineau, Abderrazak El Albani, Ernest Chi Fru, Murray Gingras, Yann Batonneau, Luis A Buatois, Claude Geffroy, Jérôme Labanowski, Claude Laforest, Laurent Lemée, Maria G Mángano, Alain Meunier, Anne-Catherine Pierson-Wickmann, Philippe Recourt, Armelle Riboulleau, Alain Trentesaux, Kurt O Konhauser
The 2.1-billion-year-old (Ga) Francevillian series in Gabon hosts some of the oldest reported macroscopic fossils of various sizes and shapes, stimulating new debates on the origin, evolution and organization of early complex life. Here, we document ten representative types of exceptionally well-preserved mat-related structures, comprising "elephant-skin" textures, putative macro-tufted microbial mats, domal buildups, flat pyritized structures, discoidal microbial colonies, horizontal mat growth patterns, wrinkle structures, "kinneyia" structures, linear patterns and nodule-like structures...
September 2018: Geobiology
Anne E Otwell, Stephen J Callister, Robert W Sherwood, Sheng Zhang, Abby R Goldman, Richard D Smith, Ruth E Richardson
We established Fe(III)-reducing co-cultures of two species of metal-reducing bacteria, the Gram-positive Desulfotomaculum reducens MI-1 and the Gram-negative Geobacter sulfurreducens PCA. Co-cultures were given pyruvate, a substrate that D. reducens can ferment and use as electron donor for Fe(III) reduction. G. sulfurreducens relied upon products of pyruvate oxidation by D. reducens (acetate, hydrogen) for use as electron donor in the co-culture. Co-cultures reduced Fe(III) to Fe(II) robustly, and Fe(II) was consistently detected earlier in co-cultures than pure cultures...
September 2018: Geobiology
Alexander Brasier, David Wacey, Mike Rogerson, Paul Guagliardo, Martin Saunders, Siri Kellner, Ramon Mercedes-Martin, Tim Prior, Colin Taylor, Anna Matthews, John Reijmer
Lacustrine carbonate chimneys are striking, metre-scale constructions. If these were bioinfluenced constructions, they could be priority targets in the search for early and extraterrestrial microbial life. However, there are questions over whether such chimneys are built on a geobiological framework or are solely abiotic geomorphological features produced by mixing of lake and spring waters. Here, we use correlative microscopy to show that microbes were living around Pleistocene Mono Lake carbonate chimneys during their growth...
September 2018: Geobiology
Claire R Cousins, Marilyn Fogel, Roxane Bowden, Ian Crawford, Adrian Boyce, Charles Cockell, Matthew Gunn
We investigated bacterial and archaeal communities along an ice-fed surficial hot spring at Kverkfjöll volcano-a partially ice-covered basaltic volcano at Vatnajökull glacier, Iceland, using biomolecular (16S rRNA, apsA, mcrA, amoA, nifH genes) and stable isotope techniques. The hot spring environment is characterized by high temperatures and low dissolved oxygen concentrations at the source (68°C and <1 mg/L (±0.1%)) changing to lower temperatures and higher dissolved oxygen downstream (34.7°C and 5...
September 2018: Geobiology
Mario Giordano, Camilla Olivieri, Simona Ratti, Alessandra Norici, John A Raven, Andrew H Knoll
We report the results of simple experiments which support the hypothesis that changes in ocean chemistry beginning in the Mesozoic Era resulted in an increase in the nutritional quality per mole of C and per cell of planktonic algal biomass compared to earlier phytoplankton. We cultured a cyanobacterium, a diatom, a dinoflagellate, and a green alga in media mimicking aspects of the chemistry of Palaeozoic and Mesozoic-Cenozoic oceans. Substantial differences emerged in the quality of algal biomass between the Palaeozoic and Mesozoic-Cenozoic growth regimes; these differences were strongly affected by interspecific interactions (i...
September 2018: Geobiology
Tyler B Johnson, Collin Mach, Ryan Grove, Robert Kelly, Kevin Van Cott, Paul Blum
Microbes belonging to the genus Metallosphaera oxidize sulfidic minerals. These organisms thrive at temperature extremes and are members of the archaeal phylum Crenarchaeota. Because they can employ a lithoautotrophic metabolism, energy availability likely limits their activity raising questions about how they conduct biogeochemical activity. Vesicles are membrane encapsulated structures produced by all biological lineages but using very different mechanisms. Across the Crenarchaeota, it has been proposed that a eukaryotic-like Endosomal Sorting Complex Required for Transport system promotes formation of these structures but in response to unknown signals and for undefined purposes...
July 17, 2018: Geobiology
Carl A Peters, Simon C George
Research on the early rise of oxygenic photosynthesis and eukaryotes has recently encountered a major pitfall, as some hopane and sterane biomarkers reported in Archaean rocks are the results of contamination. Following an extensive petrological framework in the Pilbara Craton, Western Australia, oil-bearing fluid inclusions and solid bitumens were identified in replacement and hydrothermal carbonate veins cross-cutting Archaean metasedimentary rocks. The 2.55-2.63 billion years old metasedimentary rocks were found to be depleted of indigenous biomarkers...
July 5, 2018: Geobiology
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