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.

This study investigates the occurrence of aromatic carotenoids and oxygen-bearing geolipids, namely γ-n-alkyl-γ-butyrolactones, δ-n-alkyl-δ-valerolactones, and γ-isoprenoid-alkyl-γ-butyrolactones, in Miocene sediments from the Valjevo-Mionica Basin (Serbia), from the 360-400 m depth interval. Soluble organic matter was analyzed by gas chromatography-mass spectrometry (GC-MS), and the biomarker data were integrated with previously published geological, mineralogical, and geochemical data to reconstruct the depositional environment. Aromatic carotenoid distributions provide evidence for photic-zone euxinia (PZE) and indicate changes in microbial community composition within the stratified lacustrine system. Isorenieratane and β-isorenieratane predominance in the 360-370 m interval is most consistent with strongly stratified PZE conditions favoring low-light-adapted green sulfur bacteria. In contrast, the 370-380 m interval records a greater contribution from purple sulfur bacteria, as indicated by abundant okenane, whereas the prevalence of renierapurpurane in the 380-400 m interval, together with elevated Li, Mg, and B concentrations and clay minerals, is compatible with a significant cyanobacterial contribution under alkaline, restricted-basin conditions. The occurrence of γ- and δ-lactones is consistent with anoxic, saline depositional environments characterized by limited bioturbation and active microbial transformation of organic matter, with subsequent cyclization and dehydration occurring during early diagenesis. Mass spectral fragmentation patterns indicate the presence of a previously undescribed compound (molecular mass ~568 Da) within the 370-390 m interval, for which intramolecular lactonization of a torularhodin-derived precursor is proposed as one plausible formation pathway. These findings expand the diversity of biomarkers associated with PZE and contribute to paleoenvironmental reconstructions of paleolakes, which represent sensitive archives of global paleoclimate change.

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 (δ[238]U) from carbonate and evaporite-rich successions that span the BACE on the Siberian Platform. Like conditions before and after the event, consistently low δ[238]U values from both sections (median reconstructed seawater δ[238]U = -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.

Biogenic marine carbonate production is a key component of the global carbon cycle, with shelf environments contributing disproportionately to global CaCO3 production. Yet, empirical data remain scarce for many shelf habitats, including globally widespread coralline algal beds (CABs; rhodolith and maerl beds), formed by free-living coralline algae (rhodoliths sensu lato). Moreover, available CAB-associated carbonate production estimates remain poorly integrated across spatial scales, limiting assessments of their broader relevance. Here, we quantified rhodolith growth, through alizarin staining, and carbonate production of three northeastern Atlantic CABs and incorporated those estimates into a global dataset. We then scaled compiled rates by known CAB area to assess total carbonate production rates across spatial scales and compared CABs with other major carbonate producers. Rhodolith growth and carbonate production rates in the study region fell within the range reported for other temperate CABs, while CAB production rates globally varied widely across climatic zones (0.04-2.1 kg CaCO3 m[-2] year[-1]). When scaled to individual CAB areal extents, total carbonate production ranged from 5 t to 0.025 Gt year[-1]. At larger spatial scales, available ecoregion-level estimates, representing ~70% of estimated global CAB area, yielded a total of 0.31-1.85 Gt CaCO3 year[-1]. Although area-based CAB production rates were generally lower than those of coral reefs, their broader distribution resulted in total carbonate production estimates that overlap with those for shallow tropical coral reefs and exceed those for calcareous green algae. Altogether, spatial scaling highlights CABs as local and regional carbonate-production hotspots that may contribute substantially (7%-44%) to global shelf carbonate production. However, while these estimates provide a first larger-scale approximation of CAB-associated carbonate production, it should be considered that they represent gross production and should therefore not be interpreted as net carbonate budgets. Better constraining the contribution of CABs to global carbonate cycling will require quantifying carbonate losses and accumulation, together with expanding the spatial coverage of production data.

Earth's earliest known framework reef, ~1500-million-year-old Yesanpo Mound in the Wumishan Formation, North China, consists of columns and cones built by innumerable conjoined originally aragonitic ministromatolites, each ≤ 2 cm wide. The Mound contains numerous irregular, decimetric, cavities. These are now filled with carbonate mud, giant ooids, and originally aragonitic marine cement. The role of ministromatolites in constructing this modular framework very broadly resembles that of polyps in present-day scleractinian coral colonies. Yesanpo Mound preserves geochemical signatures and traces of organic filaments consistent with suboxic conditions, yet it predates the earliest reported reef-dwelling animals by ~600 Myr. Similar spaces in reef framework may have provided ideal habitats for cryptic biota during the late Proterozoic. These are prime targets in the continued search for early animal life.

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.

Following the largest known Phanerozoic extinction, the end-Permian mass extinction, the Early Triassic is often considered an interval of slow biotic recovery. During this time, the minor Smithian-Spathian extinction occurred, further delaying the biotic recovery of this epoch. One mechanism linked to the slow recovery is widespread marine anoxic conditions, but the spatiotemporal changes to anoxia following the mass extinction remain poorly constrained. Here, we utilized local and global redox-sensitive metal proxies to track variations in (de-)oxygenation at Wallenbergfjellet, a section in Spitsbergen, Arctic Norway. Local proxies (e.g., Fe speciation and trace metal concentrations) indicate basinal anoxia and possibly euxinia prevalent in the Boreal Ocean during this interval. Importantly, thallium isotopes, a global paleoredox proxy sensitive to Mn oxide burial, have not previously been applied to the Early Triassic recovery interval that followed the end-Permian mass extinction, though basinal restriction may limit geographic extent of interpretations. Our results show a shift in ε[205]Tl values from ~ -4.0 in the Smithian to ~ -2.0 at the Smithian-Spathian boundary (SSB), consistent with a rapid expansion of global anoxia coincident with the boundary extinction. A rapid perturbation in thallium isotopes at the SSB (from -4.0 to -2.0 ε-units) indicates this interval experienced an expansion of anoxic conditions that can be linked to the minor extinction event during the recovery interval following the end-Permian mass extinction. This suggests that global anoxia persisted throughout the Early Triassic and contributed to delayed biotic recovery, with the SSB representing a major intensification of reducing conditions.

Microbial dolostones that now form the Arkaroola reef, northern Adelaide Rift Complex, and were deposited during the Cryogenian interglacial period, display a wide range of meso-scale stromatolite morphotypes in outcrop. Microcharacterisation involving optical microscopy, combined scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) and nanoscale secondary ion mass spectroscopy (NanoSIMS), was undertaken to identify microbial textures and relics in stromatolite samples. Microbial textures identified are micritic streaky and micropeloidal (grumous) microstructures as well as microcolumns, micritic threads and micritised tubular outlines resembling the Girvanella calcimicrobe. Within these microbial textures, multiple biotic components are discerned, including intact and flattened tubular bacterial sheaths, smooth and nanogranular non-crystalline extracellular polymeric substances (EPS), filamentous and spherical bacteriomorphs, as well as coccobacilli-like moulds. The biotic-mineralogical interface is characterised by microcrystalline rhombic dolomite, nano-sized pyrite spheroids and nano-sized flaky silicates in direct contact with biotic components. Interpreted as a mixed community of filamentous and coccoidal (cyano)bacteria, these microbes were important contributors to reef building. Preservation of microfossils was likely facilitated by synsedimentary silicification of EPS and bacterial sheaths. Microbial metabolic processes lowered kinetic barriers for authigenic precipitation of clay minerals on bacterial surfaces serving as nucleation sites. These synsedimentary clays strengthened initially soft microfabrics and potentially helped establish chemical conditions that promoted early diagenetic precipitation of protodolomite. The findings of this study show that carbonates may intricately preserve microfossils where associated with synsedimentary authigenic clays and microcrystalline dolomite. These results contribute to a deeper understanding of the formation and growth of microbial reefs during the Cryogenian interglacial period.

Layered microbial communities, called microbial mats, commonly form in the intertidal or shallow subtidal zone, particularly in areas protected from wave action and strong currents. These microbial mats can accrete by growing around sand-sized detrital mineral grains in a two-step process known as trapping and binding. We hypothesized that trapping and binding by microbial mats can promote the stabilization of sand-sized sediment and is therefore a process that should be considered as an important mode of biostabilization for sandy coastlines threatened by sea-level rise and increased storm intensity. To test this hypothesis, we designed a suite of in situ field incubation experiments to assess the amount of sediment microbial mats can trap if given a large sediment supply. These experiments, conducted on Little Ambergris Cay, Turks and Caicos Islands, focused on two of the most common morphologies of microbial mats (i.e., polygonal tufted mats and flat mats). We observed cyanobacterial filaments move around and on top of sand-sized grains within the first 24 h of each experiment, with increased movement related to environmental factors (duration of submergence, protection from tidal advection, and light availability). The results of our experiments show that polygonal tufted mats can stabilize twice the amount of sand-sized sediment than was naturally delivered over multi-month timescales, meaning these mats are sediment supply-limited and are capable of capturing more sediment. Furthermore, microbial mats have the capacity to trap and bind larger grains than seagrasses and mangroves. We recommend that microbial mats should be considered as part of nature-based management solutions for biostabilization of sand-sized sediment.

Throughout Earth's history, shifts in ocean redox influenced the bioavailability of trace metals, shaping the activity of microorganisms. In Proterozoic oceans, the precipitation of copper (Cu) with sulfide was hypothesized to limit the bioavailability of Cu. This limitation may have suppressed microbial reduction of nitrous oxide (N2O), due to the Cu dependency of nitrous oxide reductase (Nos). It is thought that without this critical microbial sink, Proterozoic oceans were a significant net source of N2O. Here, we revisit this paradigm in light of recently derived ~20-fold lower estimates for sulfide in Proterozoic seawater and an empirical evaluation of the potential for microbial N2O reduction under sulfidic conditions. Leveraging publicly available environmental metatranscriptomes, we infer active N2O reduction from the detection of nosZ transcripts in multiple marine and lacustrine systems in which sulfide and Cu concentrations are analogous to those of the Proterozoic. In controlled culture experiments, we demonstrate that the purple non-sulfur bacterium Rhodopseudomonas palustris can reduce N2O at sulfide concentrations up to 50 μM, well above levels predicted for Proterozoic oceans. Based on trace metal speciation modeling, we suggest that Cu remains bioavailable under Proterozoic-like conditions as a dissolved CuHS[0] complex. Collectively, these observations suggest microbial N2O reduction occurs under euxinic conditions, implying that Proterozoic marine N2O emissions were lower than previously proposed. Our conclusions inform our understanding of the microbial ecology in sulfidic waters, the early climate, and the search for extraterrestrial life.

Microbially mediated manganese (Mn) oxidation is a key process in the biogeochemical cycling of Mn. While Shewanella is widely recognized for its metal-reducing capabilities, recent studies have shown that certain terrestrial strains can also oxidize Mn[2+] during aerobic respiration. Nevertheless, the Mn[2+]-oxidizing capacity of marine Shewanella strains, which are ubiquitous in oceanic settings, has remained largely unexplored, and the influence of environmental factors on this capacity has not been systematically evaluated. Here, we investigated the ability of the deep-sea bacterium S. piezotolerans WP3 to oxidize Mn[2+] under aerobic conditions and examined the effects of temperature (4°C-20°C) and hydrostatic pressure (0.1-20 MPa). We found that S. piezotolerans WP3 efficiently oxidizes Mn[2+] to Mn oxides, predominantly forming bixbyite-like minerals and amorphous mixed-valence nanoparticles. This oxidation process was not attributable to a Mn[2+]-specific enzyme but to bacterially generated reactive oxygen species (ROS), with superoxide (O2 [•-]) playing the primary role. Both temperature and hydrostatic pressure significantly affected the final extent of Mn[2+] oxidation by altering the production of O2 [•-]. Transcriptomic analysis revealed that exposure to high hydrostatic pressure induced the upregulation of genes involved in antioxidative stress, which likely accounts for the enhanced ROS-mediated Mn[2+] oxidation observed in cultures incubated at 20 MPa. Under alternating aerobic and anaerobic conditions, strain WP3 mediated successive Mn oxidation and reduction, ultimately forming rhodochrosite as a secondary mineral. These results suggest that S. piezotolerans WP3 has the potential to mediate Mn redox cycling in marine sediments, coupling ROS-dependent oxidation with anaerobic Mn reduction.