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The Marathon conduit-type Cu-platinum-group element (PGE) deposit occurs within the Proterozoic Coldwell alkaline complex, Ontario, Canada, and comprises three zones of mineralization that occur at varying distances from the contact with Archean country rocks. Multiple sulfur isotope studies (δ34S, Δ33S, Δ36S) of sulfides from the Marathon deposit show that Δ33S and Δ36S measurements, as well as the relationship between them, are critical in demonstrating crustal S contamination. This is particularly significant for magmatic Cu-PGE deposits in contact with Archean country rocks where the δ34S of sulfides are within the range of typical mantle values (0‰ ± 2‰), as is the case at the Marathon deposit. Although the δ34S values of sulfides from the Marathon deposit did not reflect any evidence of crustal S assimilation, the Δ33S range (-0.91‰ to 0.00‰), and a negative correlation between Δ33S and Δ36S, indicate that S was derived from both the mantle and Archean supracrustal rocks. Given that the country rocks contain insignificant amounts of sulfide, crustal S assimilation must have occurred at depth, prior to magma emplacement. The magnitude of the Δ33S anomaly decreases with increasing distance from the basal contact, suggesting either that S contamination was greatest in the mineralized zone that occurred in close proximity to the contact or that crustal S signatures have been diluted in the mineralized zones further from the contact. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes a comparison of ultraviolet photolysis experiments undertaken with SO2 (oxygen with isotopes at natural abundance levels) and S18O2 (18O-substituted oxygen). Experiments were conducted in a closed photocell using a deuterium lamp (principally 190–235nm) under pressure regimes (5–25Torr) that produced optically thick conditions for 32SO2 and variable optical depths for other isotopologues. The experiments, which were designed to examine the effects of intramolecular isotopic substitution of oxygen atoms on the S-MIF produced during UV photolysis of SO2, reveal generally reduced sulfur fractionation for 18O-rich SO2 as compared to 16O-rich SO2. Model shielding calculations were undertaken using spectra that were shifted due to changes in rotational and vibrational energy levels. The model calculations suggest that processes in addition to rotational and vibrational shifts in absorption spectra play a role in the experimentally produced isotope effects. Such additional processes may include differences in primary photoexcitation arising from smaller peak-to-valley amplitudes for fine structure of 18O-rich SO2 absorption spectra or an isotopically selective process associated with transitions between excited states. [Copyright &y& Elsevier]

The Archean-Proterozoic transition is characterized by the widespread deposition of organic-rich shale, sedimentary iron formation, glacial diamictite, and marine carbonates recording profound carbon isotope anomalies, but notably lacks bedded evaporites. All deposits reflect environmental changes in oceanic and atmospheric redox states, in part associated with Earth's earliest ice ages. Time-series data for multiple sulfur isotopes from carbonate associated sulfate as well as sulfides in sediments of the Transvaal Supergroup, South Africa, capture the concomitant buildup of sulfate in the ocean and the loss of atmospheric mass-independent sulfur isotope fractionation. In phase with sulfur is the earliest recorded positive carbon isotope anomaly, convincingly linking these environmental perturbations to the Great Oxidation Event (ca. 2.3 Ga). [ABSTRACT FROM AUTHOR]

An unresolved question in the origin and evolution of life is whether a continuous path from geochemical precursors to the majority of molecules in the biosphere can be reconstructed from modern-day biochemistry. Here we identified a feasible path by simulating the evolution of biosphere-scale metabolism, using only known biochemical reactions and models of primitive coenzymes. We find that purine synthesis constitutes a bottleneck for metabolic expansion, which can be alleviated by non-autocatalytic phosphoryl coupling agents. Early phases of the expansion are enriched with enzymes that are metal dependent and structurally symmetric, supporting models of early biochemical evolution. This expansion trajectory suggests distinct hypotheses regarding the tempo, mode and timing of metabolic pathway evolution, including a late appearance of methane metabolisms and oxygenic photosynthesis consistent with the geochemical record. The concordance between biological and geological analyses suggests that this trajectory provides a plausible evolutionary history for the vast majority of core biochemistry., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Although biological systems are more complex and can actively respond to their environment, an effective entry point to the development of a universal theory of biological stress is the physical concepts of stress and strain. If you apply stress to the end of a beam of steel, the strain will accumulate within that steel beam. If the stress is weak then the strain will disappear when the force is removed and the beam will return to its original state of form and functionality. If the stress is more severe, then the strain becomes permanent and the beam will be deformed, potentially losing some degree of functionality. In extremely stressful situations, the beam will break and lose most or all of its original functional capabilities. Although this stress-strain theory applies to the abiotic, stress and strain are also rules of life and directly relate to the form and function of living organisms. The main difference is that life can react and adjust to stress and strain to maintain homeostasis within a range of limits. Here, we summarize the rules of stress and strain in living systems ranging from microbes to multicellular organisms to ecosystems with the goal to identify common features that may underlie a universal biological theory of stress. We then propose to establish a range of experimental, observational, and analytical approaches to study stress across scales, including synthetic microbial communities that mimic many of the essential characteristics of living systems, thereby enabling a universal theory of biological stress to be experimentally validated without the constraints of timescales, ethics, or cost found when studying other species or scales of life. Although the range of terminology, theory, and methodology used to study stress and strain across the scales of life presents a formidable challenge to creating a universal theory of biological stress, working toward such a theory that informs our understanding of the simultaneous and interconnected unicellular, multicellular, organismal, and ecosystem stress responses is critical as it will improve our ability to predict how living systems respond to change, thus informing solutions to current and future environmental and human health challenges., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology.)

Bacterial microcompartments (BMCs) are protein-encapsulated compartments found across at least 23 bacterial phyla. BMCs contain a variety of metabolic processes that share the commonality of toxic or volatile intermediates, oxygen-sensitive enzymes and cofactors, or increased substrate concentration for magnified reaction rates. These compartmentalized reactions have been computationally modeled to explore the encapsulated dynamics, ask evolutionary-based questions, and develop a more systematic understanding required for the engineering of novel BMCs. Many crucial aspects of these systems remain unknown or unmeasured, such as substrate permeabilities across the protein shell, feasibility of pH gradients, and transport rates of associated substrates into the cell. This review explores existing BMC models, dominated in the literature by cyanobacterial carboxysomes, and highlights potentially important areas for exploration., (Copyright © 2021 Elsevier Ltd. All rights reserved.)