In order to characterize rhenium transport via infiltration of fluids in the Earth's interior, the solubility and solution mechanisms of ReO2 in aqueous fluids were determined to 900 & DEG;C and about 1710 MPa by using an externally-heated hydrothermal diamond anvil cell. In order to shed light on how Re solubility and solution mechanisms in aqueous fluids can be affected by interaction of Re with other solutes, compositions ranged from the comparatively simple ReO2-H2O system to compositionally more complex Na2O-ReO2-SiO2-H2O fluids. Fluids in the ReO2-SiO2-H2O, SiO2-H2O, Na2O-SiO2-H2O, and Na2O-ReO2-H2O systems also were examined. The presence of Na2O enhances the ReO2 solubility so that in Na2O-ReO2-H2O fluids, for example, Re solubility is increased by a factor of 10-15 compared with the Re solubility in Na2O-free ReO2-H2O fluids. The SiO2 component in ReO2-SiO2-H2O causes reduction of ReO2 solubility compared with ReO2-H2O fluids. The ReO2 solubility in the Na-bearing Na2O-ReO2-SiO2-H2O fluids is greater than that in fluids in both the ReO2-H2O and ReO2-SiO2-H2O systems. Rhenium is dissolved in aqueous fluid as ReO4-complexes with Re in fourfold coordination with oxygen. Some, or all, of the oxygen in these complexes is replaced by OH-groups depending on whether Na2O also is present. It is proposed that during dehydration of hydrated subduction zone mineral assemblages in the upper mantle, the alkali/alkaline earth ratio of the source of the released aqueous fluid affects the extent to which Re (and other HFSE) can be transported into an overlying peridotite mantle wedge. The infiltration of such fluids will, in turn, affect the Re content (and Re/Os ratio) of magma formed by partial melting of this peridotite wedge.

The Maaz formation consists of the first lithologies in Jezero crater analyzed by the Mars 2020 Perseverance rover. This formation, investigated from Sols (Martian days) 1 to 201 and from Sols 343 to 382, overlies the Seitah formation (previously described as an olivine-rich cumulate) and was initially suggested to represent an igneous crater floor unit based on orbital analyses. Using SuperCam data, we conducted a detailed textural, chemical, and mineralogical analyses of the Maaz formation and the Content member of the Seitah formation. We conclude that the Maaz formation and the Content member are igneous and consist of different lava flows and/or possibly pyroclastic flows with complex textures, including vesicular and non-vesicular rocks with different grain sizes. The Maaz formation rocks exhibit some of the lowest Mg# (=molar 100 x MgO/MgO + FeO) of all Martian igneous rocks analyzed so far (including meteorites and surface rocks) and show similar basaltic to basaltic-andesitic compositions. Their mineralogy is dominated by Fe-rich augite to possibly ferrosilite and plagioclase, and minor phases such as Fe-Ti oxides and Si-rich phases. They show a broad diversity of both compositions and textures when compared to Martian meteorites and other surface rocks. The different Maaz and Content lava or pyroclastic flows all originate from the same parental magma and/or the same magmatic system, but are not petrogenetically linked to the Seitah formation. The study of returned Maaz samples in Earth-based laboratories will help constrain the formation of these rocks, calibrate Martian crater counting, and overall, improve our understanding of magmatism on Mars.

Light organs (LO) with symbiotic bioluminescent bacteria are hallmarks of many bobtail squid species. These organs possess structural and functional features to modulate light, analogous to those found in coleoid eyes. Previous studies identified four transcription factors and modulators (SIX, EYA, PAX6, DAC) associated with both eyes and light organ development, suggesting co-option of a highly conserved gene regulatory network. Using available topological, open chromatin, and transcriptomic data, we explore the regulatory landscape around the four transcription factors as well as genes associated with LO and shared LO/eye expression. This analysis revealed several closely associated and putatively co-regulated genes. Comparative genomic analyses identified distinct evolutionary origins of these putative regulatory associations, with the DAC locus showing a unique topological and evolutionarily recent organization. We discuss different scenarios of modifications to genome topology and how these changes may have contributed to the evolutionary emergence of the light organ.

We applied single-crystal x-ray diffraction and Raman spectroscopy in a diamond-anvil cell up to 36 GPa and first-principles theoretical calculations to study the molecular dissociation of solid iodine at high pressure. Unlike previously reported, we find that the familiar Cmce molecular phase transforms to a Cmc21 molecular structure at 16 GPa, and then to an incommensurate polymeric Fmmm(00 & gamma; )s00 structure, which can be viewed as a mixture of molecular I2 and zigzag chains of three iodine atoms, at 20 GPa. The available data are consistent with metallization of iodine at the boundary between the commensurate Cmc21 structure and the incommensurate Fmmm(00 & gamma; )s00 structure at 20 GPa.

The search for definitive biosignatures-unambiguous markers of past or present life-is a central goal of paleobiology and astrobiology. We used pyrolysis-gas chromatography coupled to mass spectrometry to analyze chemically disparate samples, including living cells, geologically processed fossil organic material, carbon-rich meteorites, and laboratory-synthesized organic compounds and mixtures. Data from each sample were employed as training and test subsets for machine-learning methods, which resulted in a model that can identify the biogenicity of both contemporary and ancient geologically processed samples with ~90% accuracy. These machine-learning methods do not rely on precise compound identification: Rather, the relational aspects of chromatographic and mass peaks provide the needed information, which underscores this method's utility for detecting alien biology.

The origin of life on earth requires the synthesis of protobiopolymers in realistic geologic environments along strictly abiotic pathways that rely on inorganic phases (such as minerals) instead of cellular machinery to promote condensation. One such class of polymer central to biochemistry is the polynucleotides, and oligomerization of activated ribonucleotides has been widely studied. Nonetheless, the range of laboratory conditions tested to date is limited and the impact of realistic early Earth conditions on condensation reactions remains unexplored. Here, we investigate the potential for a variety of minerals to enhance oligomerization using ribonucleotide monomers as one example to model condensation under plausible planetary conditions. The results show that several minerals differing in both structure and composition enhance oligomerization. Sulfide minerals yielded oligomers of comparable lengths to those formed in the presence of clays, with galena being the most effective, yielding oligonucleotides up to six bases long. Montmorillonite continues to excel beyond other clays. Chemical pretreatment of the clay was not required, though maximum oligomer lengths decreased from ~11 to 6 bases. These results demonstrate the diversity of mineral phases that can impact condensation reactions and highlight the need for greater consideration of environmental context when assessing prebiotic synthesis and the origin of life.

Metallicity gradients refer to the sloped radial profiles of the metallicities of gas and stars and are commonly seen in disk galaxies. A well-defined metallicity gradient of the Galactic disk is observed particularly well with classical Cepheids, which are good stellar tracers thanks to their period-luminosity relation, allowing precise distance estimation and other advantages. However, the measurement of the inner-disk gradient has been impeded by the incompleteness of previous samples of Cepheids and the limitations of optical spectroscopy in observing highly reddened objects. Here we report the metallicities of 16 Cepheids measured with high-resolution spectra in the near-infrared YJ bands. These Cepheids are located at 3-5.6 kpc in Galactocentric distance, R-GC, and reveal the metallicity gradient in this range for the first time. Their metallicities are mostly between 0.1 and 0.3 dex in [Fe/H] and more or less follow the extrapolation of the metallicity gradient found in the outer part, R-GC > 6.5 kpc. The gradient in the inner disk may be shallower or even flat, but the small sample does not allow the determination of the slope precisely. More extensive spectroscopic observations would also be necessary for studying minor populations, if any, with higher or lower metallicities that were reported in previous literature. In addition, the 3D velocities of our inner-disk Cepheids show a kinematic pattern that indicates noncircular orbits caused by the Galactic bar, which is consistent with the patterns reported in recent studies on high-mass star-forming regions and red giant branch stars.

Stage 55, T3 exposure for 12 hours.

Stage 55, T3 exposure for 48 hours.