Geobiology最新文献

{"title":"Living to Lithified: Construction and Preservation of Silicified Biomarkers","authors":"Kalen L. Rasmussen,&nbsp;Patrick H. Thieringer,&nbsp;Sophia Nevadomski,&nbsp;Aaron M. Martinez,&nbsp;Katherine S. Dawson,&nbsp;Frank A. Corsetti,&nbsp;Xin-Yuan Zheng,&nbsp;Yiwen Lv,&nbsp;Xinyang Chen,&nbsp;Aaron J. Celestian,&nbsp;William M. Berelson,&nbsp;Nick E. Rollins,&nbsp;John R. Spear","doi":"10.1111/gbi.12620","DOIUrl":"https://doi.org/10.1111/gbi.12620","url":null,"abstract":"<div>\u0000 \u0000 <p>Whole microorganisms are rarely preserved in the fossil record but actively silicifying environments like hot springs provide an opportunity for microbial preservation, making silicifying environments critical for the study of microbial life through time on Earth and possibly other planetary bodies. Yet, the changes that biosignatures may undergo through lithification and burial remain unconstrained. At Steep Cone Geyser in Yellowstone National Park, we collected microbial material from (1) the living system across the active outflows, (2) the silicified areas adjacent to flows, and (3) lithified and buried material to assess the preservation of biosignatures and their changes across the lithification transect. Five biofabrics, built predominantly by <i>Cyanobacteria</i> <i>Geitlerinema</i>, <i>Pseudanabaenaceae</i>, and <i>Leptolyngbya</i> with some filamentous anoxygenic phototrophs contributions, were identified and tracked from the living system through the process of silicification/lithification. In the living systems, δ³⁰Si values decrease from +0.13‰ in surficial waters to −2‰ in biomat samples, indicating a kinetic isotope effect potentially induced by increased association with actively growing biofabrics. The fatty acids C_16:1 and <i>iso</i>-C_14:0 and the hydrocarbon C_17:0 were disentangled from confounding signals and determined to be reliable lipid biosignatures for living biofabric builders and tenant microorganisms. Builder and tenant microbial biosignatures were linked to specific <i>Cyanobacteria</i>, anoxygenic phototrophs, and heterotrophs, which are prominent members of the living communities. Upon lithification and burial, silicon isotopes of silicified biomass began to re-equilibrate, increasing from δ³⁰Si −2‰ in living biomats to −0.55‰ in lithified samples. Active endolithic microbial communities were identified in lithified samples and were dominated by <i>Cyanobacteria</i>, heterotrophic bacteria, and fungi. Results indicate that distinct microbial communities build and inhabit silicified biofabrics through time and that microbial biosignatures shift over the course of lithification. These findings improve our understanding of how microbial communities silicify, the biomarkers they retain, and transitionary impacts that may occur through lithification and burial.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 5","pages":"1-30"},"PeriodicalIF":2.7,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142320705","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fossil Geyserite and Testate Amoebae in Geothermal Spring Vent Pools: Paleoecology and Variable Preservation Quality in Jurassic Sinter of Patagonia (Deseado Massif, Argentina)","authors":"Ana Julia Sagasti,&nbsp;Kathleen A. Campbell,&nbsp;Juan L. García Massini,&nbsp;Amanda Galar,&nbsp;Diego M. Guido,&nbsp;Pascale Gautret","doi":"10.1111/gbi.12621","DOIUrl":"https://doi.org/10.1111/gbi.12621","url":null,"abstract":"<p>Geyserite is a type of terrestrial siliceous hot spring deposit (sinter) formed subaerially in proximal vent areas, with near-neutral pH, alkali chloride discharge fluids characterized by initial high temperatures (~73°C to up to 100°C) that fluctuate rapidly in relation to dynamic hydrology, seasonality, wind, and other environmental parameters. We analyzed sinters at the Claudia paleogeothermal field from the Late Jurassic (~150 Ma) Deseado Massif geological province, Argentinean Patagonia. The geyserite samples—with spicular to columnar to nodular morphologies—contain abundant microfossils in monotypic assemblages that occur in three diagenetic states of preservation. The best-preserved microfossils consist of vesicle-like structures with radial heteropolar symmetry (~35 μm average diameter), circular apertures, smooth walls lacking ornamentation, and disk- or beret-like shapes. Comparisons with extant, morphologically similar organisms suggest an affinity with the testate amoebae of the <i>Arcella hemisphaerica–Arcella rotundata</i> complex and <i>Centropyxis aculeata</i> strain <i>discoides</i>. These species occur in active geothermal pools between 22°C and 45°C, inconsistent with the temperature of formation of modern geyserites. We propose that the testate amoebae may have colonized the geyserite during cooler phases in between spring-vent eruptive cycles to prey on biofilms. Silica precipitation through intermittent bathing and splashing of fluctuating thermal fluid discharge could have led to their entrapment and fossilization. Petrographic analysis supports cyclicity in paleovent water eruptions and later diagenesis that transformed the opal into quartz. Spatially patchy degradation and modification of the silicified microorganisms resulted in variable preservation quality of the microfossils. This contribution illustrates the importance of microscale analysis to locate early silicification and identify high-quality preservation of fossil remains in siliceous hot spring deposits, which are important in early life studies on Earth and potentially Mars.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 5","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.12621","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142320701","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Morphological and Microbial Diversity of Hydromagnesite Microbialites in Lake Salda: A Mars Analog Alkaline Lake","authors":"Yagmur Gunes,&nbsp;Fatih Sekerci,&nbsp;Burak Avcı,&nbsp;Thijs J. G. Ettema,&nbsp;Nurgul Balci","doi":"10.1111/gbi.12619","DOIUrl":"10.1111/gbi.12619","url":null,"abstract":"<div>\u0000 \u0000 <p>Lake Salda, a terrestrial analog for the paleolake in Jezero Crater on Mars, hosts active, subfossil, and fossil hydromagnesite microbialites, making it an ideal location to study microbialite formation and subsequent processes. Our understanding of this record is still limited by an incomplete knowledge of the macro- and mesoscale morphotypes of microbialites, along with their spatial distribution and correlation with microbial and geochemical processes that influence microbialite formation. In this study, we investigated the spatial distribution, morphotypes, mineralogy, geochemistry, and microbial diversity of the microbialites and identified six distinct zones (Zone I to Zone VI) with major microbialite build-ups in Lake Salda. Newly identified microbialites were classified based on the macro- and mesostructures. Our work shows that the lake contains stromatolites, thrombolites, stromatolitic thrombolites, dendrolites, and microbially induced sedimentary structures. At macroscale, Lake Salda microbialites exhibit hemispheres, stacked domes, and laterally linked columnar structures while minicolumns, knobs, mesoclots, laminae, and botryoidal structures are common at mesoscale. The macro- and mesoscale distribution of different microbialite types spatially correlates with microbial community composition and water depth. Deep-growing microbialites with a low abundance of Cyanobacteria (∼1%–4%) and high abundance of Firmicutes (28%–93%) exhibit steeply convex lamination, producing finger-like minicolumnar mesostructures. In contrast, shallow-growing microbialites with a low abundance of Firmicutes (0%–5%) and high abundance of Cyanobacteria (11%–37%) have well-preserved gently convex millimeter-scale lamination, resulting in cauliflower mesostructures. Palygorskite ((Mg, Al)₂Si₄O₁₀(OH)) is identified in the diatom-rich microbial layer of the deep-growing microbialites. Regardless of the microbialite types, hydromagnesite and aragonite are present in the extracellular polymeric substance (EPS)-rich zone of the shallow and deep-growing microbialites. Overall, environmental changes (e.g., water depth and, accommodation space) play a major role in the formation and spatial distribution of different microbialite morphologies at the macro- and mesoscale. Differences in the relative abundance of dominant microorganisms between mesostructured types suggest that mesomorphology may be influenced by changes in microbial diversity. Spatial variations in the microbialite morphotypes, along with the abundant presence of entombed biomass (e.g., mineralized filaments), may indicate areas that have a high potential for the preservation of biosignatures.</p>\u0000 </div>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 5","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142277636","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Oceanic and Sedimentary Microbial Sulfur Cycling Controlled by Local Organic Matter Flux During the Ediacaran Shuram Excursion in the Three Gorges Area, South China","authors":"Fumihiro Matsu'ura,&nbsp;Yusuke Sawaki,&nbsp;Tsuyoshi Komiya,&nbsp;Jian Han,&nbsp;Shigenori Maruyama,&nbsp;Takayuki Ushikubo,&nbsp;Kenji Shimizu,&nbsp;Yuichiro Ueno","doi":"10.1111/gbi.12617","DOIUrl":"10.1111/gbi.12617","url":null,"abstract":"&lt;div&gt;\u0000 \u0000 &lt;p&gt;The increased difference in the sulfur isotopic compositions of sedimentary sulfate (carbonate-associated sulfate: CAS) and sulfide (chromium-reducible sulfur: CRS) during the Ediacaran Shuram excursion is attributed to increased oceanic sulfate concentration in association with the oxidation of the global ocean and atmosphere. However, recent studies on the isotopic composition of pyrites have revealed that CRS in sediments has diverse origins of pyrites. These pyrites are formed either in the water column/shallow sediments, where the system is open with respect to sulfate, or in deep sediments, where the system is closed with respect to sulfate. The δ&lt;sup&gt;34&lt;/sup&gt;S value of sulfate in the open system is equal to that of seawater; on the contrary, the δ&lt;sup&gt;34&lt;/sup&gt;S value of sulfate in the closed system is higher than that of seawater. Therefore, obtaining the isotopic composition of pyrites formed in an open system, which most likely retain microbial sulfur isotope fractionation, is essential to reconstruct the paleo-oceanic sulfur cycle. In this study, we carried out multiple sulfur isotope analyses of CRS and mechanically separated pyrite grains (&gt;100 μm) using a fluorination method, in addition to secondary ion mass spectrometry (SIMS) analyses of in situ δ&lt;sup&gt;34&lt;/sup&gt;S values of pyrite grains in drill core samples of Member 3 of the Ediacaran Doushantuo Formation in the Three Gorges area, South China. The isotope fractionation of microbial sulfate reduction (MSR) in the limestone layers of the upper part of Member 3 was calculated to be &lt;sup&gt;34&lt;/sup&gt;&lt;i&gt;ε&lt;/i&gt; = 55.7‰ and &lt;sup&gt;33&lt;/sup&gt;&lt;i&gt;λ&lt;/i&gt; = 0.5129 from the δ&lt;sup&gt;34&lt;/sup&gt;S and Δ&lt;sup&gt;33&lt;/sup&gt;S' values of medium-sized pyrite grains ranging from 100 to 300 μm and the average δ&lt;sup&gt;34&lt;/sup&gt;S and Δ&lt;sup&gt;33&lt;/sup&gt;S' values of CAS. Model calculations revealed that the influence of sulfur disproportionation on the δ&lt;sup&gt;34&lt;/sup&gt;S values of these medium-sized pyrite grains was insignificant. In contrast, within the dolostone layers of the middle part of Member 3, isotope fractionation was determined to be &lt;sup&gt;34&lt;/sup&gt;&lt;i&gt;ε&lt;/i&gt; = 47.5‰. The &lt;sup&gt;34&lt;/sup&gt;&lt;i&gt;ε&lt;/i&gt; value in the middle part of Member 3 was calculated from the average δ&lt;sup&gt;34&lt;/sup&gt;S values of the rim of medium-sized pyrite grains and the average δ&lt;sup&gt;34&lt;/sup&gt;S values of CAS. This observation revealed an increase in microbial sulfur isotope fractionation during the Shuram excursion at the drill core site. Furthermore, our investigation revealed correlations between δ&lt;sup&gt;34&lt;/sup&gt;S&lt;sub&gt;CRS&lt;/sub&gt; values and CRS concentrations and between CRS and TOC concentrations, implying that organic matter load to sediments controlled the δ&lt;sup&gt;34&lt;/sup&gt;S&lt;sub&gt;CRS&lt;/sub&gt; values rather than oceanic sulfate concentrations. However, these CRS and TOC concentrations are local parameters that can change only at the kilometer scale with local redox conditions and the intensity of primary production. Therefore, the decreasing δ&lt;s","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 5","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142265664","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Spatially Restricted Distribution of Thermophilic Endospores in Laptev Sea Shelf Sediments Suggests a Limited Dispersal by Local Geofluids","authors":"Emelie Ståhl,&nbsp;Anna Linderholm,&nbsp;Volker Brüchert","doi":"10.1111/gbi.12618","DOIUrl":"https://doi.org/10.1111/gbi.12618","url":null,"abstract":"<p>Thermospores, the dormant resting stages of thermophilic bacteria, have been shown to be frequent but enigmatic components of cold marine sediments around the world. Multiple hypotheses have been proposed to explain their distribution, emphasizing their potential as model organisms for studying microbial dispersal via ocean currents. In the Arctic Ocean, the abundance and diversity of thermospores have previously been assumed to be low. However, this assessment has been based on data mainly from the western fjords of Svalbard, thus leaving most of the Arctic unexplored. Here, we expand the knowledge about the distribution of thermospores in the Arctic Ocean by investigating the abundance and diversity of thermospores in heated shelf sediments from three sites in the outer Laptev Sea. Two of the sites are located in an area with methane-emitting cold seeps with a thermogenic source signature suggestive of an origin in a deep hydrocarbon reservoir, while the third site is a reference site not known to be impacted by seepage. We found that activity of viable thermospore populations was more prominent at one of the investigated seep sites. This finding is supported by both radiotracer growth experiments showing thermophilic, sulfate-reducing activity triggered by heating, as well as 16S gene sequence analyses showing significantly enriched ASVs affiliated to the phylum <i>Firmicutes</i> following high-temperature incubations. An enrichment of the sulfate-reducing, endospore-forming class <i>Desulfotomaculia</i> in heated samples compared to unheated samples was also observed. Furthermore, several ASVs identified at the seep site are closely related to thermospore-producing bacteria associated with the deep biosphere, including hydrocarbon and hydrothermal systems. Based on the combined information from induced activity, estimated abundance, and phylogenetic composition using 16S rRNA gene sequencing, we propose likely source environments and dispersal vectors for thermospores in the Arctic Ocean.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 5","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.12618","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142170201","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Significance of lignin and fungal markers in the Devonian (407 Ma) Rhynie Chert","authors":"Alex I. Holman,&nbsp;Stephen F. Poropat,&nbsp;Paul F. Greenwood,&nbsp;Rajendra Bhandari,&nbsp;Madison Tripp,&nbsp;Peter Hopper,&nbsp;Arndt Schimmelmann,&nbsp;Luke Brosnan,&nbsp;William D. A. Rickard,&nbsp;Klaus Wolkenstein,&nbsp;Kliti Grice","doi":"10.1111/gbi.12616","DOIUrl":"10.1111/gbi.12616","url":null,"abstract":"<p>The Rhynie Chert (Lower Devonian, Scotland) hosts a remarkably well-preserved early terrestrial ecosystem. Organisms including plants, fungi, arthropods, and bacteria were rapidly silicified due to inundation by silica-rich hot spring fluids. Exceptional molecular preservation has been noted by many authors, including some of the oldest evidence of lignin in the fossil record. The evolution of lignin was a critical factor in the diversification of land plants, providing structural support and defense against herbivores and microbes. However, the timing of the evolution of lignin decay processes remains unclear. Studies placing this event near the end of the Carboniferous are contradicted by evidence for fungal pathogenesis in Devonian plant fossils, including from the Rhynie Chert. We conducted organic geochemical analyses on a Rhynie Chert sample, including hydropyrolysis (HyPy) of kerogen and high-resolution mass spectrometric mapping of a thin section, to elucidate the relationship between lignin and the potential fungal marker perylene. HyPy of kerogen showed an increase in relative abundance of perylene supporting its entrapment within the silicate matrix of the chert. Lignin monomers were isolated through an alkaline oxidation process, showing a distribution dominated by H-type monomers. G- and S-type monomers were also detected, preserved by rapid silicification. Polycyclic aromatic hydrocarbons including perylene, a known marker for lignin-degrading fungi, were also concentrated in the kerogen and found to be localized within silicified plant fragments. Our results strongly link perylene in the Rhynie Chert to the activity of phytopathogenic fungi, demonstrating the importance of fungal degradation processes as far back as the Early Devonian.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 4","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.12616","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142003104","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Controls on authigenic mineralization in experimental Ediacara-style preservation","authors":"Silvina Slagter,&nbsp;Kurt O. Konhauser,&nbsp;Derek E. G. Briggs,&nbsp;Lidya G. Tarhan","doi":"10.1111/gbi.12615","DOIUrl":"10.1111/gbi.12615","url":null,"abstract":"<p>The earliest evidence of complex macroscopic life on Earth is preserved in Ediacaran-aged siliciclastic deposits as three-dimensional casts and molds, known as Ediacara-style preservation. The mechanisms that led to this extraordinary preservation of soft-bodied organisms in fine- to medium-grained sandstones have been extensively debated. Ediacara-style fossilization is recorded in a variety of sedimentary facies characterized by clean quartzose sandstones (as in the eponymous Ediacara Member) as well as less compositionally mature, clay-rich sandstones and heterolithic siliciclastic deposits. To investigate this preservational process, we conducted experiments using different mineral substrates (quartzose sand, kaolinite, and iron oxides), a variety of soft-bodied organisms (microalgae, cyanobacteria, marine invertebrates), and a range of estimates for Ediacaran seawater dissolved silica (DSi) levels (0.5–2.0 mM). These experiments collectively yielded extensive amorphous silica and authigenic clay coatings on the surfaces of organisms and in intergranular pore spaces surrounding organic substrates. This was accompanied by a progressive drawdown of the DSi concentration of the experimental solutions. These results provide evidence that soft tissues can be rapidly preserved by silicate minerals precipitated under variable substrate compositions and a wide range of predicted scenarios for Ediacaran seawater DSi concentrations. These observations suggest plausible mechanisms explaining how interactions between sediments, organic substrates, and seawater DSi played a significant role in the fossilization of the first complex ecosystems on Earth.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 4","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141986995","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Lateral redox variability in ca. 1.9 Ga marine environments indicated by organic carbon and nitrogen isotope compositions","authors":"Kento Motomura,&nbsp;Andrey Bekker,&nbsp;Minoru Ikehara,&nbsp;Takashi Sano,&nbsp;Ying Lin,&nbsp;Shoichi Kiyokawa","doi":"10.1111/gbi.12614","DOIUrl":"10.1111/gbi.12614","url":null,"abstract":"<p>The stepwise oxygenation of Earth's surficial environment is thought to have shaped the evolutionary history of life. Microfossil records and molecular clocks suggest eukaryotes appeared during the Paleoproterozoic, perhaps shortly after the Great Oxidation Episode at ca. 2.43 Ga. The mildly oxygenated atmosphere and surface oceans likely contributed to the early evolution of eukaryotes. However, the principal trigger for the eukaryote appearance and a potential factor for their delayed expansion (i.e., intermediate ocean redox conditions until the Neoproterozoic) remain poorly understood, largely owing to a lack of constraints on marine and terrestrial nutrient cycling. Here, we analyzed redox-sensitive element contents and organic carbon and nitrogen isotope compositions of relatively low metamorphic-grade (greenschist facies) black shales preserved in the Flin Flon Belt of central Canada to examine open-marine redox conditions and biological activity around the ca. 1.9 Ga Flin Flon oceanic island arc. The black shale samples were collected from the Reed Lake area in the eastern part of the Flin Flon Belt, and the depositional site was likely distal from the Archean cratons. The black shales have low Al/Ti ratios and are slightly depleted in light rare-earth elements relative to the post-Archean average shale, which is consistent with a limited contribution from felsic igneous rocks in Archean upper continental crust. Redox conditions have likely varied between suboxic and euxinic at the depositional site of the studied section, as suggested by variable U/Al and Mo/Al ratios. Organic carbon and nitrogen isotope compositions of the black shales are approximately −23‰ and +13.7‰, respectively, and these values are systematically higher than those of broadly coeval continental margin deposits (approximately −30‰ for δ¹³C_org and +5‰ for δ¹⁵N_bulk). These elevated values are indicative of high productivity that led to enhanced denitrification (i.e., a high denitrification rate relative to nitrogen influx at the depositional site). Similar geochemical patterns have also been observed in the modern Peruvian oxygen minimum zone where dissolved nitrogen compounds are actively lost from the reservoir via denitrification and anammox, but the large nitrate reservoir of the deep ocean prevents exhaustion of the surface nitrate pool. Nitrogen must have been widely bioavailable in the ca. 1.9 Ga oceans, and its supply to upwelling zones must have supported habitable environments for eukaryotes, even in the middle of oceans around island arcs.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 4","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141915600","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Featured Cover","authors":"","doi":"10.1111/gbi.12613","DOIUrl":"10.1111/gbi.12613","url":null,"abstract":"<p><b>Cover</b></p><p>The cover image is based on the Research Article <i>Pyritic Stromatolites from the Paleoarchean Dresser Formation, Pilbara Craton: Resolving Biogenicity and Hydrothermally Influenced Ecosystem Dynamics</i> by Raphael J. Baumgartner et al., https://doi.org/10.1111/gbi.12610\u0000 \u0000 <figure>\u0000 <div><picture>\u0000 <source></source></picture><p></p>\u0000 </div>\u0000 </figure>\u0000 </p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 4","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.12613","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141883782","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dynamics of the osmotic lysis of mineral protocells and its avoidance at the origins of life","authors":"Yang Ding,&nbsp;Silvana S. S. Cardoso,&nbsp;Julyan H. E. Cartwright","doi":"10.1111/gbi.12611","DOIUrl":"10.1111/gbi.12611","url":null,"abstract":"<p>The osmotic rupture of a cell, its osmotic lysis or cytolysis, is a phenomenon that active biological cell volume regulation mechanisms have evolved in the cell membrane to avoid. How then, at the origin of life, did the first protocells survive prior to such active processes? The pores of alkaline hydrothermal vents in the oceans form natural nanoreactors in which osmosis across a mineral membrane plays a fundamental role. Here, we discuss the dynamics of lysis and its avoidance in an abiotic system without any active mechanisms, reliant upon self-organized behaviour, similar to the first self-organized mineral membranes within which complex chemistry may have begun to evolve into metabolism. We show that such mineral nanoreactors could function as protocells without exploding because their self-organized dynamics have a large regime in parameter space where osmotic lysis does not occur and homeostasis is possible. The beginnings of Darwinian evolution in proto-biochemistry must have involved the survival of protocells that remained within such a safe regime.</p>","PeriodicalId":173,"journal":{"name":"Geobiology","volume":"22 4","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1111/gbi.12611","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141632143","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}