Sulfidic Anion Concentrations on Early Earth for Surficial Origins-of-Life Chemistry

Abstract

A key challenge in origin-of-life studies is understanding the environmental conditions on early Earth under which abiogenesis occurred. While some constraints do exist (e.g., zircon evidence for surface liquid water), relatively few constraints exist on the abundances of trace chemical species, which are relevant to assessing the plausibility and guiding the development of postulated prebiotic chemical pathways which depend on these species. In this work, we combine literature photochemistry models with simple equilibrium chemistry calculations to place constraints on the plausible range of concentrations of sulfidic anions (HS−, HSO3−, SO32−) available in surficial aquatic reservoirs on early Earth due to outgassing of SO2 and H2S and their dissolution into small shallow surface water reservoirs like lakes. We find that this mechanism could have supplied prebiotically relevant levels of SO2-derived anions, but not H2S-derived anions. Radiative transfer modeling suggests UV light would have remained abundant on the planet surface for all but the largest volcanic explosions. We apply our results to the case study of the proposed prebiotic reaction network of Patel et al. (2015) and discuss the implications for improving its prebiotic plausibility. In general, epochs of moderately high volcanism could have been especially conducive to cyanosulfidic prebiotic chemistry. Our work can be similarly applied to assess and improve the prebiotic plausibility of other postulated surficial prebiotic chemistries that are sensitive to sulfidic anions, and our methods adapted to study other atmospherically derived trace species.

Sulfur Chemistry in Protoplanetary Disks: CS and H2CS

“…In addition to better constraints on disk sulfur chemistry, addressing this question requires models that couple chemistry and dynamics from disk formation to planet assembly. This long-term goal is needed to address the sulfur budgets on planets and thus the planet hospitality to the origins of life (Ranjan et al 2018).…”

Origin of Life’s Building Blocks in Carbon- and Nitrogen-Rich Surface Hydrothermal Vents

“…which can be reduced further to form sulfite (SO 3 2 -) and sulfate (SO 4 2 -), or oxidized to form sulfuric acid (H 2 SO 4 ) [57]. Because there is a relatively small amount of available oxygen, the bulk of the sulfur will be in the form of bisulfite (HSO 3 -) and hydrogen sulfide (HS -); the relatively small amount of sulfate will react rapidly with the hydrogen cyanide to form thiocyanate (CNS -).…”

Phylogenomic analysis of novel Diaforarchaea is consistent with sulfite but not sulfate reduction in volcanic environments on early Earth

“…However, at temperatures <150°C, SO 3 2− is stable in aqueous solutions in the absence of strong oxidants (e.g., ferric iron ions or O 2 ; [16]). As such, modeling studies have suggested that concentrations of SO 3 2− may have equaled or exceeded those of SO 4 2− in waters during the early Archean [17,18] and this may have been especially true for anoxic, moderate temperature hydrothermal systems.…”