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Geochemical and Photochemical Constraints on S[IV] Concentrations in Natural Waters on Prebiotic Earth
  • +6
  • Sukrit Ranjan,
  • Khaled Abdelazim,
  • Gabriella G Lozano,
  • Sangita Mandal,
  • Cindy Y Zhou,
  • Corinna L Kufner,
  • Zoe R Todd,
  • Nita Sahai,
  • Dimitar D Sasselov
Sukrit Ranjan
University of Arizona

Corresponding Author:sukrit@alum.mit.edu

Author Profile
Khaled Abdelazim
Harvard University
Gabriella G Lozano
Harvard University
Sangita Mandal
National Institute of Science Education and Research
Cindy Y Zhou
Boston University
Corinna L Kufner
Harvard University
Zoe R Todd
University of Washington
Nita Sahai
University of Akron
Dimitar D Sasselov
Harvard University


Sulfur is important to planetary habitability, but the early sulfur cycle is poorly understood. In particular, S[IV] species (HSO3-, SO32-), derived from volcanogenic SO2, are critically invoked in recent proposals for origins-of-life chemistry and also influence atmospheric sulfur haze formation, but their abundance in early natural waters is unclear. Here, we combine new laboratory constraints on the kinetics of S[IV] disproportionation with a novel aqueous photochemistry model to estimate the concentrations of S[IV] in natural waters on prebiotic Earth. We show that S[IV] disproportionation is slow in pH≥7 waters, with timescale T≥1 year at room temperature, meaning that S[IV] was present in prebiotic natural waters. However, we also show that photolysis of S[IV] limits [S[IV]]< 100 μM in global-mean steady state. Marine S[IV] was sub-saturation with respect to atmospheric SO2, meaning that climate-altering, UV-attenuating sulfur hazes did not persist on prebiotic Earth. [S[IV]] was much lower in natural waters compared to the concentrations generally invoked in laboratory simulations of origins-of-life chemistry (≥10 mM), meaning further work is needed to confirm whether S[IV]-dependent prebiotic chemistries discovered in the lab could have realistically functioned in nature. [S[IV]]≥1 μM in terrestrial waters for: (1) SO2 outgassing ≥20× modern, (2) pond depths <10 cm, or (3) UV-attenuating agents present in early waters or the prebiotic atmosphere. Our work illustrates the synergy between planetary science, geochemistry and synthetic organic chemistry experiments in understanding the emergence and maintenance of life on early Earth.
23 May 2023Submitted to ESS Open Archive
25 May 2023Published in ESS Open Archive