The widespread presence of ribonucleic acid (RNA) catalysts and cofactors in the Earth′s biosphere today suggests that RNA was the first biopolymer to support Darwinian evolution. However, most “path‐hypotheses” to generate building blocks for RNA require reduced nitrogen‐containing compounds not made in useful amounts in the CO2−N2−H2O atmospheres of the Hadean. We review models for Earth′s impact history that invoke a single ∼1023 kg impactor (Moneta) to account for measured amounts of platinum, gold, and other siderophilic (“iron‐loving”) elements on the Earth and Moon. If it were the last sterilizing impactor, by reducing the atmosphere but not the mantle Moneta, would have opened a “window of opportunity” for RNA synthesis, a period when RNA precursors rained from the atmosphere onto land holding oxidized minerals that stabilize advanced RNA precursors and RNA. Surprisingly, this combination of physics, geology, and chemistry suggests a time when RNA formation was most probable, ∼120±100 million years after Moneta′s impact, or ∼4.36±0.1 billion years ago. Uncertainties in this time are driven by uncertainties in rates of productive atmosphere loss and amounts of sub‐aerial land.

The availability of nucleotides on the early Earth is of great significance for the origin of a self-replicating system capable of undergoing evolution. We hereby report the successful phosphorylation reactions of the nucleoside uridine under heating in the “drying pool” prebiotic model at temperatures ranging from 60–75 °C, and by using pyrophosphate as a phosphorylation agent. Uridine monophosphates (UMP) such as uridine-5′-monophosphate (5′-UMP), 2′-UMP, and 3′-UMP, as well as cyclic 2′-3′-UMP, were identified by 31P-NMR. In addition to the above-mentioned products, a dimer of uridine-phosphate-uridine (U-P-U) was also observed. The reactions were promoted by white quartz sand, Mg2+, and by using urea as a condensation agent. The reactions also proceeded without this mixture; however, the yields increased remarkably with the presence of the above-mentioned materials. The results suggest that a hot/evaporating-drying pool of water containing organics, salts, and reactive phosphorus could be sufficient to form significant phosphate esters.

Sugars are essential for the formation of genetic elements such as RNA and as an energy/food source. Thus, the formose reaction, which autocatalytically generates a multitude of sugars from formaldehyde, has been viewed as a potentially important prebiotic source of biomolecules at the origins of life. When analyzing our formose solutions we find that many of the chemical species are simple carboxylic acids, including α-hydroxy acids, associated with metabolism. In this work we posit that the study of the formose reaction, under alkaline conditions and moderate hydrothermal temperatures, should not be solely focused on sugars for genetic materials, but should focus on the origins of metabolism (via metabolic molecules) as well.

The possibility of life in the venusian clouds was proposed in the 1960s, and recently this hypothesis has been revived with the potential detection of phosphine (PH 3 ) in Venus' atmosphere. These observations may have detected *5-20 ppb phosphine on Venus (Greaves et al., 2020), which raises questions about venusian atmospheric/geochemical processes and suggests that this phosphine could possibly be generated by biological processes. In such a claim, it is essential to understand the abiotic phosphorus chemistry that may occur under Venus-relevant conditions, particularly those processes that may result in phosphine generation. Here, we discuss two related abiotic routes for phosphine generation within the atmosphere of Venus. Based on our assessment, corrosion of large impactors as they ablate near Venus' cloud layer, and the presence of reduced phosphorus compounds in the subcloud layer could result in production of phosphine and may explain the phosphine detected in Venus' atmosphere or on other rocky planets. We end on a cautionary note: although there may be life in the clouds of Venus, the detection of a simple, single gas, phosphine, is likely not a decisive indicator.

Sucralose was developed as a low cost artificial sweetener that is nonmetabolizable in humans. Sucralose can withstand changes in pH and temperature and is not degraded by the wastewater treatment process. Since the molecule can withstand heat, acidification, and microbial degradation, it is accumulating in the environment and has been found in wastewater, estuaries, rivers, and the Gulf Stream. Environmental isolates were cultured in the presence of sucralose looking for potential sucralose metabolism or growth acceleration responses. Sucralose was found to be nonnutritive and demonstrated bacteriostatic effects on all six isolates. This growth inhibition was directly proportional to the concentration of sucralose exposure, and the amount of the growth inhibition appeared to be species-specific. The bacteriostatic effect may be due to a decrease in sucrose uptake by bacteria exposed to sucralose. We have determined that sucralose inhibits invertase and sucrose permease. These enzymes cannot catalyze hydrolysis or be effective in transmembrane transport of the sugar substitute. Current environmental concentrations should not have much of an effect on environmental bacteria since the bacteriostatic effect seems to be consecration based; however, as sucralose accumulates in the environment, we must consider it a contaminant, especially for microenvironments.

The Front Cover summarizes the discussions of a path‐hypothesis to make prebiotic RNA, via mineral‐guided maturation of carbonyl species and base precursor formation in a post‐impact reduced atmosphere, presented in the review.More information can be found in the Review by S. A. Benner et al.

The front cover artwork was provided by Steven Benner (Foundation for Applied Molecular Evolution) and Lucy Kwok (Earth Life Science Institute at Tokyo Institute of Technology). The image shows a path‐hypothesis to make prebiotic RNA, via mineral‐guided maturation of carbonyl species and base precursor formation in a post‐impact reduced atmosphere, with dates when these most likely gave RNA. Read the full text of the Review at 10.1002/syst.201900035.

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