| 1. |
- Ivarsson, Magnus, et al.
(författare)
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Anaerobic fungi: a potential source of biological H2 in the oceanic crust.
- 2016
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Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 7:674, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- The recent recognition of fungi in the oceanic igneous crust challenges the understanding of this environment as being exclusively prokaryotic and forces reconsiderations of the ecology of the deep biosphere. Anoxic provinces in the igneous crust are abundant and increase with age and depth of the crust. The presence of anaerobic fungi in deep-sea sediments and on the seafloor introduces a type of organism with attributes of geobiological significance not previously accounted for. Anaerobic fungi are best known from the rumen of herbivores where they produce molecular hydrogen, which in turn stimulates the growth of methanogens. The symbiotic cooperation between anaerobic fungi and methanogens in the rumen enhance the metabolic rate and growth of both. Methanogens and other hydrogen-consuming anaerobic archaea are known from subseafloor basalt; however, the abiotic production of hydrogen is questioned to be sufficient to support such communities. Alternatively, biologically produced hydrogen could serve as a continuous source. Here, we propose anaerobic fungi as a source of bioavailable hydrogen in the oceanic crust, and a close interplay between anaerobic fungi and hydrogen-driven prokaryotes.
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| 2. |
- Neubeck, Anna, et al.
(författare)
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Effect of Nickel Levels on Hydrogen Partial Pressure and Methane Production in Methanogens
- 2016
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 11:12
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrogen (H-2) consumption and methane (CH4) production in pure cultures of three different methanogens were investigated during cultivation with 0, 0.2 and 4.21 mu M added nickel (Ni). The results showed that the level of dissolved Ni in the anaerobic growth medium did not notably affect CH4 production in the cytochrome-free methanogenic species Methanobacterium bryantii and Methanoculleus bourgensis MAB1, but affected CH4 formation rate in the cytochrome-containing Methanosarcina barkeri grown on H-2 and CO2. Methanosarcina barkeri also had the highest amounts of Ni in its cells, indicating that more Ni is needed by cytochrome-containing than by cytochrome-free methanogenic species. The concentration of Ni affected threshold values of H-2 partial pressure (pH(2)) for all three methanogen species studied, with M. bourgensis MAB1 reaching pH(2) values as low as 0.1 Pa when Ni was available in amounts used in normal anaerobic growth medium. To our knowledge, this is the lowest pH(2) threshold recorded to date in pure methanogen culture, which suggests that M. bourgensis MAB1 have a competitive advantage over other species through its ability to grow at low H-2 concentrations. Our study has implications for research on the H-2-driven deep subsurface biosphere and biogas reactor performance.
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| 3. |
- Neubeck, Anna, et al.
(författare)
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Microbial community structure of a serpentine-hosted abiotic gas seepage at the Chimaera ophiolite,Turkey
- 2017
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Ingår i: Applied and Environmental Microbiology. - Washington. - 0099-2240 .- 1098-5336. ; 83:12
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Tidskriftsartikel (refereegranskat)abstract
- The surface waters at the ultramafic ophiolitic outcrop in Chimaera, Turkey, are characterized by high pH values and high metal levels due to the percolation of fluids through areas of active serpentinization. We describe the influence of the liquid chemistry, mineralogy, and H2 and CH4 levels on the bacterial community structure in a semidry, exposed, ultramafic environment. The bacterial and archaeal community structures were monitored using Illumina sequencing targeting the 16S rRNA gene. At all sampling points, four phyla, Proteobacteria, Actinobacteria, Chloroflexi, and Acidobacteria, accounted for the majority of taxa. Members of the Chloroflexi phylum dominated low-diversity sites, whereas Proteobacteria dominated high-diversity sites. Methane, nitrogen, iron, and hydrogen oxidizers were detected as well as archaea and metal-resistant bacteria. IMPORTANCE Our study is a comprehensive microbial investigation of the Chimaera ophiolite. DNA has been extracted from 16 sites in the area and has been studied from microbial and geochemical points of view. We describe a microbial community structure that is dependent on terrestrial, serpentinization-driven abiotic H2, which is poorly studied due to the rarity of these environments on Earth.
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| 4. |
- Carlsson, Diana, et al.
(författare)
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Fossilized endolithic microorganisms in pillowlavas from the Troodos ophiolite, Cyprus
- 2019
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Ingår i: Geosciences. - Basel : MDPI. - 2076-3263. ; 9:11
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Tidskriftsartikel (refereegranskat)abstract
- The last decade has revealed the igneous oceanic crust to host a more abundant and diverse biota than previously expected. These underexplored rock-hosted deep ecosystems dominated Earth’s biosphere prior to plants colonized land in the Ordovician, thus the fossil record of deep endoliths holds invaluable clues to early life and the work to decrypt them needs to be intensified. Here, we present fossilized microorganisms found in open and sealed pore spaces in pillow lavas from the Troodos Ophiolite (91 Ma) on Cyprus. A fungal interpretation is inferred upon the microorganisms based on characteristic morphological features. Geochemical conditions are reconstructed using data from mineralogy, fluid inclusions and the fossils themselves. Mineralogy indicates at least three hydrothermal events and a continuous increase of temperature and pH. Precipitation of 1) celadonite and saponite together with the microbial introduction was followed by 2) Na and Ca zeolites resulting in clay adherence on the microorganisms as protection, and finally 3) Ca carbonates resulted in final fossilization and preservation of the organisms in-situ. Deciphering the fossil record of the deep subseafloor biosphere is a challenging task, but when successful, can unlock doors to life’s cryptic past.
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| 5. |
- Cataldi, Gianni, et al.
(författare)
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Searching for Biosignatures in Exoplanetary Impact Ejecta
- 2017
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Ingår i: Astrobiology. - : Mary Ann Liebert Inc. - 1531-1074 .- 1557-8070. ; 17:8, s. 721-746
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Tidskriftsartikel (refereegranskat)abstract
- With the number of confirmed rocky exoplanets increasing steadily, their characterization and the search for exoplanetary biospheres are becoming increasingly urgent issues in astrobiology. To date, most efforts have concentrated on the study of exoplanetary atmospheres. Instead, we aim to investigate the possibility of characterizing an exoplanet (in terms of habitability, geology, presence of life, etc.) by studying material ejected from the surface during an impact event. For a number of impact scenarios, we estimate the escaping mass and assess its subsequent collisional evolution in a circumstellar orbit, assuming a Sun-like host star. We calculate the fractional luminosity of the dust as a function of time after the impact event and study its detectability with current and future instrumentation. We consider the possibility to constrain the dust composition, giving information on the geology or the presence of a biosphere. As examples, we investigate whether calcite, silica, or ejected microorganisms could be detected. For a 20km diameter impactor, we find that the dust mass escaping the exoplanet is roughly comparable to the zodiacal dust, depending on the exoplanet's size. The collisional evolution is best modeled by considering two independent dust populations, a spalled population consisting of nonmelted ejecta evolving on timescales of millions of years, and dust recondensed from melt or vapor evolving on much shorter timescales. While the presence of dust can potentially be inferred with current telescopes, studying its composition requires advanced instrumentation not yet available. The direct detection of biological matter turns out to be extremely challenging. Despite considerable difficulties (small dust masses, noise such as exozodiacal dust, etc.), studying dusty material ejected from an exoplanetary surface might become an interesting complement to atmospheric studies in the future.
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| 6. |
- Einarsson, Torbjörn, et al.
(författare)
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En studie av betydelsen av den nationella överenskommelsen för civilsamhällets organisationer på det nationella planet
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- På hösten 2008 undertecknades Överenskommelsen mellan regeringen, idéburna organisationer inom det sociala området och Sveriges Kommuner och Landsting. Under de tio år som denna nationella Överenskommelse har funnits på plats så har åtminstone ett 20-tal lokala (kommunala) och regionala överenskommelser med likartad inriktning och lydelse tecknats. Baserat på tidigare forskning utgår vi i rapporten ifrån tanken att Överenskommelsen är en central komponent i den ’omförhandling av samhällskontraktet’ som vi menar pågår. I denna studie undersöker vi därmed frågan om hur den svenska Överenskommelsen på nationell nivå har påverkat förutsättningarna för det civila samhällets organisationer i det lokala. Studien är i huvudsak kvantitativ och försöker primärt besvara följande frågor om de lokala överenskommelser som har undertecknats på det sociala området under perioden 2009–2017: • Vad karakteriserar samverkan mellan civilsamhälle och ofentlig sektor inom ramen för de lokala överenskommelserna? • Vilka delar av den ideella sektorn är det som deltar i dessa lokala överenskommelser? • Leder överenskommelser på det lokala planet till någon ekonomisk eller organisatorisk tillväxt för det redan existerande civilsamhället? • Startas det fer nya ideella organisationer i samband med de lokala överenskommelserna?Sammanfattningsvis framträder några viktiga resultat både vad gäller civilsamhället inom Överenskommelsekommuner samt för de organisationer som själva anger att de deltar i lokala eller regionala överenskommelser.
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| 7. |
- Ivarsson, Magnus, et al.
(författare)
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Exceptional Preservation of Fungi as H2-Bearing Fluid Inclusions in an Early Quaternary Paleo-Hydrothermal System at Cape Vani, Milos, Greece
- 2019
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Ingår i: Minerals. - : MDPI. - 2075-163X. ; 9:12, s. 1-33
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Tidskriftsartikel (refereegranskat)abstract
- The production of H-2 in hydrothermal systems and subsurface settings is almost exclusively assumed a result of abiotic processes, particularly serpentinization of ultramafic rocks. The origin of H-2 in environments not hosted in ultramafic rocks is, as a rule, unjustifiably linked to abiotic processes. Additionally, multiple microbiological processes among both prokaryotes and eukaryotes are known to involve H-2-production, of which anaerobic fungi have been put forward as a potential source of H-2 in subsurface environments, which is still unconfirmed. Here, we report fungal remains exceptionally preserved as fluid inclusions in hydrothermal quartz from feeder quartz-barite veins from the Cape Vani Fe-Ba-Mn ore on the Greek island of Milos. The inclusions possess filamentous or near-spheroidal morphologies interpreted as remains of fungal hyphae and spores, respectively. They were characterized by microthermometry, Raman spectroscopy, and staining of exposed inclusions with WGA-FITC under fluorescence microscopy. The spheroidal aqueous inclusions interpreted as fungal spores are unique by their coating of Mn-oxide birnessite, and gas phase H-2. A biological origin of the H-2 resulting from anaerobic fungal respiration is suggested. We propose that biologically produced H-2 by micro-eukaryotes is an unrecognized source of H-2 in hydrothermal systems that may support communities of H-2-dependent prokaryotes.
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| 8. |
- Ivarsson, M., et al.
(författare)
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Fossilized Life in Subseafloor Ultramafic Rocks
- 2018
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Ingår i: Geomicrobiology Journal. - : Informa UK Limited. - 0149-0451 .- 1521-0529. ; 35:6, s. 460-467
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Tidskriftsartikel (refereegranskat)abstract
- Ultramafic rocks are hypothesized to support a subseafloor hydrogen-driven biosphere because of extensive production of bioavailable energy sources like H-2 or CH4 from fluid-rock interactions. Hence, the apparent lack of microbial remains in subseafloor ultramafic rocks, in contrast to their frequent observation in subseafloor basalts, is somewhat of a paradox. Here we report fossilized microbial remains in aragonite veins in ultramafic rocks from the 15 degrees 20N Fracture Zone area on the Mid-Atlantic Ridge (MAR), collected during Ocean Drilling Program (ODP) Leg 209. The microbial remains consist of filamentous structures associated with biofilms. The young age (<1 Myr) and absence of diagenesis result in fossilized microbial communities with a pristine composition characterized by carbonaceous matter (CM) and the enrichment in trace elements such as Ni, Co, Mo and Mn. Our study confirms the presence of the hypothesized deep subseafloor biosphere hosted in ultramafic rocks. We further show that host rock composition may influence the microbial elemental composition, which is recorded during the fossilization.
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| 9. |
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| 10. |
- Ivarsson, Magnus, et al.
(författare)
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The igneous oceanic crust – Earth’s largest fungal habitat?
- 2016
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Ingår i: Fungal ecology. - : Elsevier BV. - 1754-5048 .- 1878-0083. ; 20, s. 249-255
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Tidskriftsartikel (refereegranskat)abstract
- In recent years the igneous oceanic crust has been recognized as a substantial microbial habitat and a scientific frontier within Geology, Biology, and Oceanography. A few successful metagenomic investigations have indicated the presence of Archaea and Bacteria, but also fungi in the subseafloor igneous crust. A comprehensive fossil record supports the presence of fungi in these deep environments and provides means of investigating the fungal presence that complements metagenomic methods. Considering the vast volume of the oceanic crust and that it is the largest aquifer on Earth, we put forward that it is the largest fungal habitat on the planet. This review aims to introduce a yet unexplored fungal habitat in an environment considered extreme from a biological perspective. We present the current knowledge of fungal abundance and diversity and discuss the ecological role of fungi in the igneous oceanic crust.
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| 11. |
- Neubeck, Anna, 1974-, et al.
(författare)
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Low-temperature dunite hydration : evaluating CH4 and H2 production from H2O and CO2
- 2016
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Ingår i: Geofluids. - : Wiley. - 1468-8115 .- 1468-8123. ; 16:3, s. 408-420
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Tidskriftsartikel (refereegranskat)abstract
- Abiotic methane (CH4) and hydrogen (H2) produced after hydration of mafic/ultramafic rocks represent energy sources for microbes that may thrive in the deep subsurface regions of Earth and possibly on other planets. While H2 is a direct product of serpentinization, CH4 can form via Fischer–Tropsch Type (FTT) reactions (carbon reduction) that, due to potential H2 migration, can be spatially and temporally detached from serpentinization. We tested an alternative process hypothesized by some scholars, in which CO2 can be reduced through dunite hydration without initially added H2, implying that CH4 can form in the same serpentinized fluid–rock system. The experiment used natural dunite sand (Forsterite 92), CO2 with δ13C ~ −25‰ (VPDB), and a 1 mm dissolved SiO2 solution mixed in 30 glass bottles (118 mL) stored for up to 8 months at low temperature (50°C) to simulate land-based serpentinization systems. In addition, 30 control bottles without olivine were used as blanks. Trivial amounts of CH4 (orders of 0.2–0.9 ppmv) were detected in both samples and blanks, likely representing analytical noise; essentially, no significant amount of CH4 formed under the experimental conditions used in this work. Low amounts of H2 (~2.55 ± 1.39 ppmv) were generated, with production yields that were one order of magnitude lower than in previously published experiments. Moderate concentrations of SiO2 appeared to hinder low-temperature H2 production. Our experiment confirms that the low-temperature reduction of CO2 into CH4 through direct olivine hydration, without initial H2, is sluggish and not straightforward, which is consistent with previous studies. The presence of substantial amounts of H2, as well as suitable metal catalysts, appears to be essential in the low-temperature production of abiotic CH4, as observed in published FTT experiments.
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| 12. |
- Neubeck, Anna, et al.
(författare)
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Mineralogical determination in situ of a highly heterogeneous material using a miniaturized laser ablation mass spectrometer with high spatial resolution
- 2016
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Ingår i: International Journal of Astrobiology. - 1473-5504 .- 1475-3006. ; 15:2, s. 133-146
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Tidskriftsartikel (refereegranskat)abstract
- Techniques enabling in situ elemental and mineralogical analysis on extraterrestrial planets are strongly required for upcoming missions and are being continuously developed. There is ample need for quantitative and high-sensitivity analysis of elemental as well as isotopic composition of heterogeneous materials. Here we present in situ spatial and depth elemental profiles of a heterogeneous rock sample on a depth-scale of nanometres using a miniaturized laser ablation mass spectrometer (LMS) designed for planetary space missions. We show that the LMS spectra alone could provide highly detailed compositional, three-dimensional information and oxidation properties of a natural, heterogeneous rock sample. We also show that a combination of the LMS and Raman spectroscopy provide comprehensive mineralogical details of the investigated sample. These findings are of great importance for future space missions where quick, in situ determination of the mineralogy could play a role in the process of selecting a suitable spot for drilling.
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| 13. |
- Onstott, T.C., et al.
(författare)
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Paleo-rock-hosted life on Earth and the search on Mars: a review and strategy for exploration
- 2019
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Ingår i: Astrobiology. - : Mary Ann Liebert Inc, Publishers. - 1531-1074 .- 1557-8070. ; 19:10, s. 1230-1262
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Tidskriftsartikel (refereegranskat)abstract
- Here we review published studies on the abundance and diversity of terrestrial rock-hosted life, the environments it inhabits, the evolution of its metabolisms, and its fossil biomarkers to provide guidance in the search for life on Mars. Key findings are (1) much terrestrial deep subsurface metabolic activity relies on abiotic energy-yielding fluxes and in situ abiotic and biotic recycling of metabolic waste products rather than on buried organic products of photosynthesis; (2) subsurface microbial cell concentrations are highest at interfaces with pronounced chemical redox gradients or permeability variations and do not correlate with bulk host rock organic carbon; (3) metabolic pathways for chemolithoautotrophic microorganisms evolved earlier in Earth's history than those of surface-dwelling phototrophic microorganisms; (4) the emergence of the former occurred at a time when Mars was habitable, whereas the emergence of the latter occurred at a time when the martian surface was not continually habitable; (5) the terrestrial rock record has biomarkers of subsurface life at least back hundreds of millions of years and likely to 3.45 Ga with several examples of excellent preservation in rock types that are quite different from those preserving the photosphere-supported biosphere. These findings suggest that rock-hosted life would have been more likely to emerge and be preserved in a martian context. Consequently, we outline a Mars exploration strategy that targets subsurface life and scales spatially, focusing initially on identifying rocks with evidence for groundwater flow and low-temperature mineralization, then identifying redox and permeability interfaces preserved within rock outcrops, and finally focusing on finding minerals associated with redox reactions and associated traces of carbon and diagnostic chemical and isotopic biosignatures. Using this strategy on Earth yields ancient rock-hosted life, preserved in the fossil record and confirmable via a suite of morphologic, organic, mineralogical, and isotopic fingerprints at micrometer scale. We expect an emphasis on rock-hosted life and this scale-dependent strategy to be crucial in the search for life on Mars.
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| 14. |
- Preiner, Martina, et al.
(författare)
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Serpentinization : Connecting Geochemistry, Ancient Metabolism and Industrial Hydrogenation
- 2018
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Ingår i: Life. - : MDPI AG. - 2075-1729.
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Forskningsöversikt (refereegranskat)abstract
- Rock-water-carbon interactions germane to serpentinization in hydrothermal vents have occurred for over 4 billion years, ever since there was liquid water on Earth. Serpentinization converts iron(II) containing minerals and water to magnetite (Fe3O4) plus H-2. The hydrogen can generate native metals such as awaruite (Ni3Fe), a common serpentinization product. Awaruite catalyzes the synthesis of methane from H-2 and CO2 under hydrothermal conditions. Native iron and nickel catalyze the synthesis of formate, methanol, acetate, and pyruvate-intermediates of the acetyl-CoA pathway, the most ancient pathway of CO2 fixation. Carbon monoxide dehydrogenase (CODH) is central to the pathway and employs Ni-0 in its catalytic mechanism. CODH has been conserved during 4 billion years of evolution as a relic of the natural CO2-reducing catalyst at the onset of biochemistry. The carbide-containing active site of nitrogenase-the only enzyme on Earth that reduces N(2)is probably also a relic, a biological reconstruction of the naturally occurring inorganic catalyst that generated primordial organic nitrogen. Serpentinization generates Fe3O4 and H-2, the catalyst and reductant for industrial CO2 hydrogenation and for N-2 reduction via the Haber-Bosch process. In both industrial processes, an Fe3O4 catalyst is matured via H-2-dependent reduction to generate Fe5C2 and Fe2N respectively. Whether serpentinization entails similar catalyst maturation is not known. We suggest that at the onset of life, essential reactions leading to reduced carbon and reduced nitrogen occurred with catalysts that were synthesized during the serpentinization process, connecting the chemistry of life and Earth to industrial chemistry in unexpected ways.
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| 15. |
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| 16. |
- Tulej, Marek, et al.
(författare)
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Chemical Composition of Micrometer-Sized Filaments in an Aragonite Host by a Miniature Laser Ablation/Ionization Mass Spectrometer
- 2015
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Ingår i: Astrobiology. - : Mary Ann Liebert Inc. - 1531-1074 .- 1557-8070. ; 15:8, s. 669-682
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Tidskriftsartikel (refereegranskat)abstract
- Detection of extraterrestrial life is an ongoing goal in space exploration, and there is a need for advanced instruments and methods for the detection of signatures of life based on chemical and isotopic composition. Here, we present the first investigation of chemical composition of putative microfossils in natural samples using a miniature laser ablation/ionization time-of-flight mass spectrometer (LMS). The studies were conducted with high lateral (similar to 15 mu m) and vertical (similar to 20-200 nm) resolution. The primary aim of the study was to investigate the instrument performance on micrometer-sized samples both in terms of isotope abundance and element composition. The following objectives had to be achieved: (1) Consider the detection and calculation of single stable isotope ratios in natural rock samples with techniques compatible with their employment of space instrumentation for biomarker detection in future planetary missions. (2) Achieve a highly accurate chemical compositional map of rock samples with embedded structures at the micrometer scale in which the rock matrix is easily distinguished from the micrometer structures. Our results indicate that chemical mapping of strongly heterogeneous rock samples can be obtained with a high accuracy, whereas the requirements for isotope ratios need to be improved to reach sufficiently large signal-to-noise ratio (SNR). Key Words: Biogenicity-Biomarkers-Biosignatures-Filaments-Fossilization. Astrobiology 15, 669-682.
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| 17. |
- Wiesendanger, Reto, et al.
(författare)
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Chemical and Optical Identification of Micrometer-Sized 1.9 Billion-Year-Old Fossils by Combining a Miniature Laser Ablation Ionization Mass Spectrometry System with an Optical Microscope
- 2018
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Ingår i: Astrobiology. - : Mary Ann Liebert Inc. - 1531-1074 .- 1557-8070. ; 18:8, s. 1071-1080
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Tidskriftsartikel (refereegranskat)abstract
- The recognition of biosignatures on planetary bodies requires the analysis of the putative microfossil with a set of complementary analytical techniques. This includes localized elemental and isotopic analysis of both, the putative microfossil and its surrounding host matrix. If the analysis can be performed with spatial resolution at the micrometer level and ppm detection sensitivities, valuable information on the (bio)chemical and physical processes that influenced the sample material can be gained. Our miniaturized laser ablation ionization mass spectrometry (LIMS)-time-of-flight mass spectrometer instrument is a valid candidate for performing the required chemical analysis in situ. However, up until now it was limited by the spatial accuracy of the sampling. In this contribution, we introduce a newly developed microscope system with micrometer accuracy for Ultra High Vacuum application, which allows a significant increase in the measurement capabilities of our miniature LIMS system. The new enhancement allows identification and efficient and accurate sampling of features of micrometer-sized fossils in a host matrix. The performance of our system is demonstrated by the identification and chemical analysis of signatures of micrometer-sized fossil structures in the 1.9 billion-year-old Gunflint chert.
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| 18. |
- Wiesendanger, Reto, et al.
(författare)
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Chemical and optical identification of micrometer sized 1.9 Ga old fossils with a miniature LIMS system combined with an optical microscope
- 2018
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Ingår i: Astrobiology. - USA : Mary Ann Liebert Inc. - 1531-1074 .- 1557-8070. ; 18:8, s. 1071-1080
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Tidskriftsartikel (refereegranskat)abstract
- The recognition of biosignatures on planetary bodies requires the analysis of the putative microfossil with a set of complementary analytical techniques. This includes localized elemental and isotopic analysis of both the putative microfossil and its surrounding host matrix. If the analysis can be performed with spatial resolution at the micrometer level and part-per-million detection sensitivities, valuable information on the (bio)chemical and physical processes that influenced the sample material can be gained. Our miniaturized laser ablation ionization mass spectrometry (LIMS)-time-of-flight mass spectrometer instrument is a valid candidate for performing the required chemical analysis in situ. However, up until now it was limited by the spatial accuracy of the sampling. In this contribution, we introduce a newly developed microscope system with micrometer accuracy for ultra high vacuum application, which allows a significant increase in the measurement capabilities of our miniature LIMS system. The new enhancement allows identification and efficient and accurate sampling of features of micrometer-sized fossils in a host matrix. The performance of our system is demonstrated by the identification and chemical analysis of signatures of micrometer-sized fossil structures in the 1.9 billion-year-old Gunflint chert.
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| 19. |
- Young, E. D., et al.
(författare)
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The relative abundances of resolved (CH2D2)-C-12 and (CH3D)-C-13 and mechanisms controlling isotopic bond ordering in abiotic and biotic methane gases
- 2017
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 203, s. 235-264
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Tidskriftsartikel (refereegranskat)abstract
- We report measurements of resolved (CH2D2)-C-12 and (CH3D)-C-13 at natural abundances in a variety of methane gases produced naturally and in the laboratory. The ability to resolve (CH2D2)-C-12 from (CH3D)-C-13 provides unprecedented insights into the origin and evolution of CH4. The results identify conditions under which either isotopic bond order disequilibrium or equilibrium are expected. Where equilibrium obtains, concordant Delta (CH2D2)-C-12 and Delta (CH3D)-C-13 temperatures can be used reliably for thermometry. We find that concordant temperatures do not always match previous hypotheses based on indirect estimates of temperature of formation nor temperatures derived from CH4/H-2 D/H exchange, underscoring the importance of reliable thermometry based on the CH4 molecules themselves. Where Delta (CH2D2)-C-12 and Delta (CH3D)-C-13 values are inconsistent with thermodynamic equilibrium, temperatures of formation derived from these species are spurious. In such situations, while formation temperatures are unavailable, disequilibrium isotopologue ratios nonetheless provide novel information about the formation mechanism of the gas and the presence or absence of multiple sources or sinks. In particular, disequilibrium isotopologue ratios may provide the means for differentiating between methane produced by abiotic synthesis vs. biological processes. Deficits in (CH2D2)-C-12 compared with equilibrium values in CH4 gas made by surface-catalyzed abiotic reactions are so large as to point towards a quantum tunneling origin. Tunneling also accounts for the more moderate depletions in (CH3D)-C-13 that accompany the low (CH2D2)-C-12 abundances produced by abiotic reactions. The tunneling signature may prove to be an important tracer of abiotic methane formation, especially where it is preserved by dissolution of gas in cool hydrothermal systems (e.g., Mars). Isotopologue signatures of abiotic methane production can be erased by infiltration of microbial communities, and Delta (CH2D2)-C-12 values are a key tracer of microbial recycling.
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