Geobiology最新文献

Impact crater hydrothermal systems, formed after asteroid and comet impacts, have been proposed as promising habitats for life on early Earth and as key targets in the search for life on planetary bodies such as Mars, since they provide liquid water and active geochemical turnover. Because no newly formed impact structures exist on Earth, studies of microbial establishment in impact-crater hydrothermal systems have largely relied on the direct observation of fossil microbial life or its isotopic signatures. To address this limitation, we established simulated microcosm hydrothermal systems in the laboratory using melt-bearing impact breccia (suevite) from the Ries impact structure, Germany, and temperate soils. Within weeks, these systems hosted taxonomically diverse communities, with broad metabolic potential, partitioned among oxidized impact glass, endolithic suevite habitats, and sedimentary environments. Dominant taxa included thermophiles from primarily heterotrophic lineages (e.g., Meiothermus and Aneurinibacillus spp.), as well as lineages with potentially chemolithotrophic metabolisms (e.g., Brockia spp.). Metagenomic annotations identified genes associated with methane, iron, and sulfur cycling, including sulfate-reduction, indicating metabolic potential for biogeochemically relevant processes under hydrothermal conditions. These results show that impact-generated hydrothermal systems can rapidly support diverse thermophilic microbial communities with habitat-specific community structure and metabolic potential, supporting their relevance as analogue environments for studying early microbial establishment and biosignature formation in planetary impact settings.

Chitin is a fundamental structural biopolymer, yet its fossil record is predominantly biased towards marine Lagerstätten or specific stagnant non-marine settings, leaving its stability in dynamic continental environments poorly understood. Here, we report the molecular preservation of indigenous chitin within the shells of the bivalve Nakamuranaia soni from the Lower Cretaceous Kitadani Formation, Japan—a renowned dinosaur-bearing fluvial succession. While Paleozoic and Jurassic records of chitin exist for arthropods and brackish gastropods, our findings represent one of the earliest direct records of chitinous biopolymers within a strictly freshwater fluvial Lophotrochozoan. High-resolution FE-SEM and histochemical staining (Calcofluor White and Congo Red) revealed exceptionally preserved periostracal honeycomb-like templates, morphologically and chemically congruent with extant unionids. FT-IR spectroscopy confirmed diagnostic polysaccharide backbone linkages and amide modes matching reference β-chitin, while host-rock analysis (negative control) established the indigenous nature of these organics. Decalcification experiments yielded a rigid silica–chitin hybrid framework, suggesting that early-stage silicification acted as a ‘taphonomic shield’. We propose that rapid mineralisation, driven by volcaniclastic-rich hydrochemistry, encapsulated the microfibrils, providing both steric hindrance, and chemical stabilisation. This discovery demonstrates that authigenic silicification can mitigate the degradative effects of freshwater diagenesis, significantly expanding the spatial and molecular boundaries of the terrestrial fossil record.

The enigmatic Ediacara biota represents Earth's earliest example of macroscopic, complex life, yet the driving forces promoting their mid-Ediacaran evolution and subsequent extinction across the Ediacaran–Cambrian boundary remain speculative. If these were true animals requiring oxygen for aerobic respiration, their rise has often been linked to dramatic changes in the redox state of seawater. Their disappearance from the fossil record—whether gradual or abrupt—and replacement with Cambrian animals has similarly been linked to redox fluctuations, suggesting an environmental driver, or alternatively to biological factors such as predation of the predominantly soft-bodied organisms and bioturbation that disrupted the microbial mats in which they were intimately associated. Insofar as Ediacara extinction is linked to a major perturbation of the global carbon cycle (the BAsal Cambrian carbon isotope Excursion or BACE), an environmental driver seems likely. On the one hand, their demise might reflect the spread of seawater anoxia if these organisms had aerobic metabolisms, but on the other, widespread ocean oxygenation may have been the proximal cause of their extinction and the BACE event if the biota was tolerant and even thrived under low-oxygen conditions. To test between the two alternative redox scenarios, we present a suite of geochemical data including uranium isotopes (δ²³⁸U) from carbonate and evaporite-rich successions that span the BACE on the Siberian Platform. Like conditions before and after the event, consistently low δ²³⁸U values from both sections (median reconstructed seawater δ²³⁸U = −0.74‰ to −0.79‰) suggest that widespread ocean anoxia persisted across the Ediacaran–Cambrian transition. The integrated data indicate that neither a rise nor fall of seawater oxidation state led to the demise of the Ediacara biota. Lacking evidence for a redox driver, we hypothesize that sea-level regression and the widespread development of evaporative conditions in shallow-water environments negatively impacted the largely immobile, diffusion-dependent, and potentially stenothermal Ediacara biota by subaerial exposure, dehydration through osmosis, and/or large temperature variations in shallow water. Thereafter, normal salinity and subtle rises in shallow ocean O₂ levels in concert with tectonic and ecological factors could have driven the Cambrian radiation in oceans that remained O₂-depleted well into the Paleozoic Era.

Microbialites are rocks formed by microbial communities that influence, promote, and/or control the precipitation of mineral phases. The oldest microbialites date back to the Archean and formed under globally anoxic conditions. Accordingly, modern microbialites developing under oxic conditions are limited analogs of their earliest predecessors. We discovered microbialites in the deep, seasonally anoxic water column of crater lakes Alchichica and Atexcac (Mexico). We studied the prokaryotic communities of plankton and microbialites from oxic and anoxic layers, alongside the temporal dynamics of microbialite communities incubated under strict continuous anoxia. 16S rRNA gene amplicon sequencing showed shifts in the relative abundance of taxa under anoxia, rather than changes in overall diversity. Regardless of their original depth, microbialite-associated communities from oxic and anoxic zones converged after ~25 weeks of laboratory exposure to a N₂-H₂-CO₂ (85:10:5) atmosphere. Sequences assigned to likely anoxygenic photosynthetic taxa, notably within the Alpha- and Gammaproteobacteria, together with phyla associated with sulfate-reduction and other sulfur-cycling bacteria, increased in relative abundance. We isolated seven bacterial strains under anoxia, some of them biomineralizing. Several of these strains were cyanobacteria affiliated with the Leptolyngbyales, suggesting that they either continue to perform oxygenic photosynthesis or, hypothetically, switch to H₂S-dependent anoxygenic photosynthesis. Our results indicate that these microbialite communities adapt to long-term anoxia (more than 70 weeks) under laboratory conditions, likely sustaining photosynthetic alkalinization and carbonate precipitation under such conditions.

Biogenic aragonite is a composite of mineral and biomolecules that exhibits superior material properties compared to its inorganic analog. This superiority underpins the success of the bioaragonite structures which support coral reefs and shell fisheries, yet the mechanisms improving the physical resilience of bioaragonite are not well understood. In this study, aragonite is synthesised under chemical conditions which simulate those of calcification sites in marine organisms. Aspartic acid, glutamic acid, and glycine in solution are incorporated into the aragonite at concentrations typically observed in marine biominerals and are observed to significantly improve aragonite Vickers hardness. Aspartic acid is incorporated more efficiently than glutamic acid or glycine, but for comparable amounts of amino acid incorporation, glycine improves aragonite hardness significantly more than either aspartic or glutamic acid. Glycine and glutamic acid incorporation reduce the aragonite grain size, thereby improving resilience to indentation via energy dissipation along grain boundaries. In contrast, aspartic acid also improves hardness on a smaller scale, possibly due to crystal structure distortions. These results suggest that amino acid incorporation influences biogenic aragonite hardness via multiple mechanisms and provide a prototype for exploring the influence of more complicated biomineral proteins.

The Carri Laufquen Lakes System is a highly alkaline, basalt-hosted lacustrine environment in northern Patagonia, Argentina. Diverse morphologies of Late Pleistocene sub-fossil stromatolites occur along the lakeshores. Using detailed optical and electron microscopy, spectroscopy and organic geochemical analyses, this study shows that stromatolite growth and early diagenetic processes were strongly influenced by microbially controlled organomineralisation. Mineralisation of extracellular polymeric substances and cyanobacterial sheaths promoted early lithification and exceptional preservation of stromatolite fabrics and biosignatures. Organic matter is closely associated with Al–bearing silicate minerals at the micro–nanoscale, enhancing fossilisation potential and preserving biogeochemical signatures. The resulting mineral assemblage in the Carri Laufquen stromatolites, dominated by Mg-carbonate with minor Al-silicates and carbonaceous material, resembles the geochemistry of ancient lacustrine deposits around the margins of Jezero crater, highlighting the propensity of such deposits for biosignature preservation, and providing a framework for detailed characterisation of such materials following Mars Sample Return.

Multiple lines of evidence point to a major diversification of Eukarya in the late Tonian period, ca. 800–720 Ma ago. Regular steranes, lipid biomarkers primarily sourced from eukaryotes, are first unambiguously reported from multiple sites. Here, we present lipid biomarker stratigraphic records from two drill-cores from the Lena-Anabar Basin in northern Siberia, in addition to new biomarker data from the Walcott Member of the Chuar Group, USA. The Siberian drill-cores span the late Tonian (ca. 800–750 Ma) and late Ediacaran-early Cambrian periods (ca. 565–539 Ma), with Cryogenian strata absent. Compositional differences in sedimentary organic matter were assessed using a suite of biomarker hydrocarbon parameters, with seawater redox and phosphorus availability determined using iron speciation, trace metals, and phosphorus phase partitioning. Steranes were consistently detected in Tonian strata in the Siberian drill-cores, with sterane/hopane (S/H) values being uniformly low (< 0.05), consistent with a low-productivity, marine environment in which bacteria outcompeted eukaryotes for limited nutrients. This was confirmed by phosphorus phase partitioning data that suggest that phosphorus was a key limiter of late Tonian marine eukaryote abundance. Unlike Siberia, late Tonian samples from the Chuar Group showed consistently higher S/H values (up to 0.38) and elevated total organic carbon content (1.3–5.6 wt.%) indicative of higher algal productivity in a eutrophic marine setting. Tonian strata primarily yielded cholestane (C₂₇ sterane), indicating red algal dominance with small contributions of cryostane and ergostane (C₂₈ steranes), while Ediacaran strata in both Siberian drill-cores were dominated by stigmastane (C₂₉ sterane), indicating green algal dominance, capturing this global secular shift in a single location. The distinctive C₂₇-sterane dominance commonly found for the late Tonian is captured here for the first time from an oligotrophic marine environment that sustained oxic to weakly reducing redox conditions, supporting the idea that the Tonian rise of algae occurred widely across the oceans.