Presence of water on exomoons orbiting free-floating planets: a case study

A free-floating planet (FFP) is a planetary-mass object that orbits around a non-stellar massive object (e.g. a brown dwarf) or around the Galactic Centre. The presence of exomoons orbiting FFPs has been theoretically predicted by several models. Under specific conditions, these moons are able to retain an atmosphere capable of ensuring the long-term thermal stability of liquid water on their surface. We model this environment with a one-dimensional radiative-convective code coupled to a gas-phase chemical network including cosmic rays and ion-neutral reactions. We find that, under specific conditions and assuming stable orbital parameters over time, liquid water can be formed on the surface of the exomoon. The final amount of water for an Earth-mass exomoon is smaller than the amount of water in Earth oceans, but enough to host the potential development of primordial life. The chemical equilibrium time-scale is controlled by cosmic rays, the main ionization driver in our model of the exomoon atmosphere.

The physiology and evolution of microbial selenium metabolism

Selenium is an essential trace element whose compounds are widely metabolized by organisms from all three domains of life. Moreover, phylogenetic evidence indicates that selenium species, along with iron, molybdenum, tungsten, and nickel, were metabolized by the last universal common ancestor (LUCA) of all cellular lineages, primarily for the synthesis of the 21st amino acid selenocysteine. Thus, selenium metabolism is both environmentally ubiquitous and a physiological adaptation of primordial life. Selenium metabolic reactions comprise reductive transformations both for assimilation into macromolecules and dissimilatory reduction of selenium oxyanions and elemental selenium during anaerobic respiration. This review offers a comprehensive overview of the physiology and evolution of both assimilatory and dissimilatory selenium metabolism in bacteria and archaea, highlighting mechanisms of selenium respiration. This includes a thorough discussion of our current knowledge of the physiology of selenocysteine synthesis and incorporation into proteins in bacteria obtained from structural biology. Additionally, this is the first comprehensive discussion in a review of the incorporation of selenium into the tRNA nucleoside 5-methylaminomethyl-2-selenouridine and as an inorganic cofactor in certain molybdenum hydroxylase enzymes. Throughout, conserved mechanisms and derived features of selenium metabolism in both domains are emphasized and discussed within the context of the global selenium biogeochemical cycle.

Unique metabolic strategies in Hadean analogues reveal hints for primordial physiology

Primordial microorganisms are postulated to have emerged in H2-rich alkaline Hadean serpentinite-hosted environments with homoacetogenesis as a core metabolism. However, investigation of two modern serpentinization-active analogues of early Earth reveals that conventional H2-/CO2-dependent homoacetogenesis is thermodynamically unfavorable in situ due to picomolar CO2 levels. Through metagenomics and thermodynamics, we discover unique taxa capable of metabolism adapted to the habitat. This included a novel deep-branching phylum, "Ca. Lithoacetigenota", that exclusively inhabits Hadean analogues and harbors genes encoding alternative modes of H2-utilizing lithotrophy. Rather than CO2, these metabolisms utilize reduced carbon compounds detected in situ presumably serpentinization-derived: formate and glycine. The former employs a partial homoacetogenesis pathway and the latter a distinct pathway mediated by a rare selenoprotein - the glycine reductase. A survey of serpentinite-hosted system microbiomes shows that glycine reductases are diverse and nearly ubiquitous in Hadean analogues. "Ca. Lithoacetigenota" glycine reductases represent a basal lineage, suggesting that catabolic glycine reduction is an ancient bacterial innovation for gaining energy from geogenic H2 even under serpentinization-associated hyperalkaline, CO2-poor conditions. This draws remarkable parallels with ancestral archaeal H2-driven methyl-reducing methanogenesis recently proposed. Unique non-CO2-reducing metabolic strategies presented here may provide a new view into metabolisms that supported primordial life and the diversification of LUCA towards Archaea and Bacteria.

A Living Spatial Movement of Relation. Reconceptualising Ricœur’s Oneself as Another and Heidegger’s Being and Time

Beyond the disparate and mainly fleeting references to life in Ricoeur’s Oneself as Another, whether as life as power, living well and with others, or as Ricoeur’s attempt to develop a concept of embodied subjectivity as flesh, which is presumably living flesh, not dead flesh, a further and arguably primordial life principle needs emphasis, namely, living space. Ricoeur’s recognition of the vital significance of space primordiality, as a pivotal dimension that is even prior to language, offers a significant conceptual leap in Ricoeur’s later work, Oneself as Another. Ricoeur’s proposed ontology of the flesh is one dimension towards expression of an authentic phenomenology of spatiality, though not necessarily the only one. Building upon but going beyond Ricoeur, the article explores concentric and diametric spatial interplay in relation to the early Heidegger’s existential spatiality, Angst and care, as candidate living spatial movements. This proposed primordial spatial discourse re-examines Ricoeur’s conatus as power to act, and his quest for a structure of relation to the other that is not closure, separation, or diametric opposition.

Priestesses of Art

This chapter delves into the largely unexplored intersections of gender stereotypes and art-religious rhetoric in music criticism. It introduces case studies on the priestesses of art—and champions of Brahms’s compositions—Clara Schumann and Amalie Joachim, showing how for these performers, repertoire selection and performativity influenced the creation of motherly priestesses. In the context of nineteenth-century discourses on gender and sex roles, intensified by the nascent women’s rights movement, we encounter a paradox of the pure style: Priestesses were invested with a kind of natural sensual authority that was suited only to women as primordial life-givers. This analysis establishes a more nuanced gendered context for understanding the priestly rhetoric and its criticism.

Cyclophosphates, a new class of native phosphorus compounds, and some insights into prebiotic phosphorylation on early Earth

Cyclophosphates are a class of energy-rich compounds whose hydrolytic decomposition (ring opening) liberates energy that is sufficient for initiation of biomimetic phosphorylation reactions. Because of that, cyclophosphates might be considered as a likely source of reactive prebiotic phosphorus on early Earth. A major obstacle toward adoption of this hypothesis is that cyclophosphates have so far not been encountered in nature. We herein report on the discovery of these minerals in the terrestrial environment, at the Dead Sea basin in Israel. Cyclophosphates represent the most condensed phosphate species known in nature. A pathway for cyclophosphate geosynthesis is herein proposed, involving simple pyrolytic oxidation of terrestrial phosphides. Discovery of natural cyclophosphates opens new opportunities for modeling prebiotic phosphorylation reactions that resulted in the emergence of primordial life on our planet.

Nano−porous pyrite and organic matter in 3.5-billion-year-old stromatolites record primordial life

Stromatolites of the ∼3.5 billion-year-old Dresser Formation (Pilbara Craton, Western Australia) are considered to be some of Earth’s earliest convincing evidence of life. However, uniquely biogenic interpretations based on surface outcrops are precluded by weathering, which has altered primary mineralogy and inhibited the preservation of microbial remains. Here, we report on exceptionally preserved, strongly sulfidized stromatolites obtained by diamond drilling from below the weathering profile. These stromatolites lie within undeformed hydrothermal-sedimentary strata and show textural features that are indicative of biogenic origins, including upward-broadening and/or upward-branching digitate forms, wavy to wrinkly laminae, and finely laminated columns that show a thickening of laminae over flexure crests. High-resolution textural, mineralogical, and chemical analysis reveals that the stromatolites are dominated by petrographically earliest, nano-porous pyrite that contains thermally mature, N-bearing organic matter (OM). This nano-porous pyrite is consistent with a formation via sulfidization of an originally OM-dominated matrix. Evidence for its relationship with microbial communities are entombed OM strands and filaments, whose microtexture and chemistry are consistent with an origin as mineralized biofilm remains, and carbon isotope data of extracted OM (δ13COM = −29.6‰ ± 0.3‰ VPDB [Vienna Peedee belemnite]), which lie within the range of biological matter. Collectively, our findings provide exceptional evidence for the biogenicity of some of Earth’s oldest stromatolites through preservation of OM, including microbial remains, by sulfidization.