Searching for signs of past or present life is a central objective of Mars exploration. The detection of organic molecular biosignatures is highly desirable, as they can provide direct and reliable evidence of biological activity. However, Mars’s intense radiation environment poses a major challenge because it degrades or modifies these molecules, complicating their detection. To assess the stability of organic molecules, researchers have conducted various irradiation simulation experiments. However, the survivability and chemical reactivity of amino acids under Martian-like conditions remain controversial. One possible reason is the inconsistent physical states of amino acids used in these studies. Herein, we investigated the stability of glycine, cysteine, and histidine in three different physical states (i.e., powders, crystals, and solutions) under 60Co γ-ray irradiation. The results show that the stability of amino acids varies with their physical state. For glycine, the powders undergo a polymorphic transformation with a total dose of 2.39 MGy, while its single crystals remain largely intact at the same irradiation dose. In contrast, glycine in aqueous solution shows significant modification involving both decomposition and complex recombination or polymerization. Cysteine and histidine also display physical-state-dependent responses, with their powders being more stable than their aqueous counterparts but less resistant than their crystals. These results suggest that the preservation of organics on Mars may be biased by their physical states. Therefore, future Martian life-detection missions should consider not only the molecular identity but also the physical state of target compounds when interpreting data and designing sampling strategies.

Basalt reservoirs are attractive geologic CO2 storage repositories, as they also promote mineral trapping of injected CO2 in the form of carbonate minerals. In this study, a long-term core flooding experiment was conducted with in situ X-ray computed tomography (XCT) to evaluate CO2-induced basalt dissolution and carbonate precipitation as functions of injectate alkalinity. A saw-cut, heterogeneous basalt core was subjected to a constant flow of CO2-saturated fluids for 62 days, where step increases in the alkalinity of the CO2-saturated fluids (via increasing [NaHCO3]) were introduced to promote conditions favoring mineral carbonation. Despite reaching temperature (100 °C), pressure (10 MPa PCO2), and pore fluid chemistry (0.64 M NaHCO3) conditions that have been demonstrated to promote rapid and extensive carbonate precipitation in prior work, minimal precipitation occurred over the 62-day experimental duration, while net dissolution occurred. The results underscore the complexity of interplay among controls of coupled basalt dissolution and carbonate precipitation reactions, where elevated alkalinity will not definitively ensure or enhance CO2 mineralization across all basalt lithologies.

Glacial isostatic adjustment (GIA) profoundly influences postglacial tectonics, sea-level change, and geothermal systems; however, its role during the deglaciation of the Neoproterozoic Snowball Earth remains poorly constrained. Sheet-crack is one of the diagnostic structures in Marinoan (635 Ma) cap carbonates that overlie glacial tillites. Available geochemical evidence indicates that sheet-crack cements precipitated immediately following crack formation, potentially preserving GIA-driven fluid signatures. This study presents fluid inclusion microthermometric data from sheet-crack quartz and barite cements along shelf-to-slope transects on the Yangtze Block, South China. Fluid inclusion homogenization temperatures (Th) reveal the occurrence of a ubiquitous low-temperature hydrothermal event, with most Th values clustering at ∼145 °C–190 °C and ∼120 °C–180 °C in platform facies and slope facies, respectively. Fluid salinities in platform facies exhibit unimodal distributions and low to moderate (∼2–8 wt % NaCl eq.), while those in slope facies show broadly continuous distributions, with most values concentrated at intermediate-to-high salinities (∼6–15 wt % NaCl eq.) and a subordinate low-salinity tail. These patterns are consistent with varying contributions from recirculated, geothermally heated seawater and basinal brines. We propose a refined model in which GIA-related geothermal anomalies promoted a widespread low-temperature hydrothermal circulation event, responsible for sheet-crack cementation shortly after the Marinoan deglaciation, South China.

Long-term application of phosphorus (P) fertilizers in the intensive croplands has led to the accumulation of residual phosphorus in soils, referred to as legacy phosphorus. Most reported observations on the role of extracellular polymeric substances in enhancing P availability have been based on microbially excreted mixtures, rather than on relatively pure exopolysaccharides, as used in the present study. The objective of this work was to investigate the effects of purified exopolysaccharides (EPS) produced from Rhizobium tropici on the solubility of soil legacy phosphorus and on their interactions with soil, clay minerals, and Fe/Al oxides. A Mississippi River Delta agricultural soil, two clay minerals (montmorillonite and kaolinite), and Fe/Al oxides were spiked with phosphate and treated with the purified EPS and then incubated under laboratory conditions at a field capacity moisture. Results show that EPS strongly interacted with phosphate, enhancing its complexation and promoting the solubilization of legacy soil phosphorus. EPS facilitated P transformation from the soil residual phosphorus fraction and HCl-extractable P (Ca–P) fractions into the water-soluble form, thereby increasing phosphorus bioavailability. Therefore, the current study demonstrates the beneficial role of EPS from Rhizobium tropici in improving the solubility and bioavailability of soil legacy phosphorus in agricultural soils where substantial phosphorus has accumulated, particularly in intensive cultivated crop fields. Application of EPS may therefore increase P fertilizer efficiency, reduce phosphorus losses through runoff, and mitigate water body eutrophication.

Icy grain mantles play a crucial role in the chemistry of star-forming regions, allowing reactions that contribute to the formation of astrophysically complex organic molecules (COMs), including acetaldehyde (CH3CHO) and formamide (NH2CHO). Both compounds are also revealed in cometary comae. Laboratory experiments allowed us to reveal the formation of acetaldehyde and formamide in ices exposed to energetic sources, suggesting that the exposure of icy mantles and surfaces to Galactic cosmic rays (GCR) and solar charged particles triggers the formation of COMs. In this article, we provide data on the relevance of the initial ice composition on the formation and abundance of acetaldehyde and formamide. Furthermore, we aim to understand the time scales required in young star-forming regions to form both compounds through the ion-bombardment of icy grain mantles. We simulated the exposure of icy grain mantles to energetic charged particles in the laboratory. We produced a large set of icy mixtures comprising various molecules detected toward the solid phase of star-forming regions, including H2O, CO, CH3OH, CH4, NH3, and N2, and we exposed them to 200 keV H+ at 17 K simulating low-energy GCR. We followed the chemical evolution of ices by means of infrared spectroscopy. In the spectra, we looked for absorption features attributed to acetaldehyde (7.40 μm) and formamide (7.20 μm). We also provide estimations of their abundance as a function of the dose in the various investigated mixtures. The analysis revealed that the ice composition plays a primary role in both the destruction of the deposited species and the formation of new compounds. Water–methanol–ammonia mixtures are the most efficient in the formation of both COMs. The time scales required for their formation fall in the typical lifetimes of pre- and protostellar phases and strongly depend on the cosmic-ray ionization rate taken into account. We show that ices exposed to energetic ions can form both acetaldehyde and formamide. Abundances are found to be strongly related to the initial ice composition. We thus suggest that the bombardment of icy grain mantles by GCR is a relevant player in the formation of both compounds in the lifetime of pre- and protostellar objects.

In the Middle Jurassic, whether the Bangong-Nujiang Tethys Ocean extended eastward from the central Tibetan Plateau into western Yunnan, China, thereby separating the Tengchong and Baoshan blocks, remains unresolved. Middle Jurassic carbonate rocks of the Liuwan Formation of the Baoshan Block provide essential insights. This study examines the petrography, rare earth element and yttrium (REE+Y) geochemistry, and strontium isotopic composition of the Liuwan Formation limestones to determine their depositional environment and tectonic setting. Results indicate that these carbonate rocks show no significant recrystallization or dissolution. REE+Y patterns show light-REE enrichment, slightly positive La and Ce anomalies, a minimal Eu anomaly, and a Y anomaly, all indicating open marine conditions. The 87Sr/86Sr ratios range from 0.707287 to 0.707554 (averaging 0.707365) and are slightly higher than those of coeval seawater. These geochemical signatures suggest a depositional environment between open marine and restricted settings, influenced by freshwater influx and volcanic activity, indicating an ocean separating the Baoshan and Tengchong blocks. Tectonic proxies suggest a stable passive margin for the Baoshan Block and a subduction-related tectonic/depositional setting for the Tengchong Block. Subduction of the Bangong-Nujiang Ocean beneath the Tengchong Block explains these distinct tectonic settings. Correlations among 87Sr/86Sr values and REE+Y geochemistry of the Liuwan Formation reveal paleoceanographic characteristics of the ancient subducted ocean and the contributions from multiple sources. These findings support the existence of the Bangong-Nujiang Ocean between the Tengchong and Baoshan blocks during the Middle Jurassic, enhancing our understanding of eastern Tethys paleogeography and evolution.

Ferrihydrite (Fh), which plays a critical role in element cycling and contaminant sequestration in the environment, is susceptible to transformation. However, understanding and predicting its transformation process are challenging due to the multitude of influencing factors. Herein, we developed six machine learning (ML) models and selected the best performance model (Random Forest) to predict the transformation and fate of Fh. Key influencing factors for Fh transformation, including the C/Fe ratio and Fe(II)/Fe(III) ratio, were identified. ML further implied a distinct transformation route between biological-induced and chemical-induced Fh transformation; that is, the former one resulted primarily in lepidocrocite (Lp), while the latter tended to more readily yield goethite (Gt) or magnetite (Mt) via intermediate phases. Linking with the fixation capacity of different Fe minerals, our ML model indicated the risk of emerging pollutants (e.g., perfluoroalkyl and polyfluoroalkyl substances, PFAS) and global warming during the Fh transformation under different environmental conditions. The predicted release risk of PFAS and soil organic carbon could reach up to 67.8% in paddy soil and 181.6 Pg globally, respectively. Through a data-driven approach, this study provides new insights into the transformation, fate, and implications of poorly crystalline iron minerals, highlighting their roles in pollutant turnover and carbon cycling.