Nitrogen Oxide Concentrations in Natural Waters on Early Earth

Abstract

A key challenge in origins‐of‐life studies is estimating the abundances of species relevant to the chemical pathways proposed to have contributed to the emergence of life on early Earth. Dissolved nitrogen oxide anions ( NOX−), in particular nitrate ( NO3−) and nitrite ( NO2−), have been invoked in diverse origins‐of‐life chemistry, from the oligomerization of RNA to the emergence of protometabolism. Recent work has calculated the supply of NOX− from the prebiotic atmosphere to the ocean and reported steady state [ NOX−] to be high across all plausible parameter space. These findings rest on the assumption that NOX− is stable in natural waters unless processed at a hydrothermal vent. Here, we show that NOX− is unstable in the reducing environment of early Earth. Sinks due to ultraviolet photolysis and reactions with reduced iron (Fe2+) suppress [ NOX−] by several orders of magnitude relative to past predictions. For pH = 6.5–8 and T = 0–50 °C, we find that it is most probable that [ NOX−] <1μM in the prebiotic ocean. On the other hand, prebiotic ponds with favorable drainage characteristics may have sustained [ NOX−] ≥1μM. As on modern Earth, most NOX− on prebiotic Earth should have been present as NO3−, due to its much greater stability. These findings inform the kind of prebiotic chemistries that would have been possible on early Earth. We discuss the implications for proposed prebiotic chemistries and highlight the need for further studies of NOX− kinetics to reduce the considerable uncertainties in predicting [ NOX−] on early Earth.

Magnetite Synthesis in the Presence of Cyanide or Thiocyanate under Prebiotic Chemistry Conditions

“…Nitrate played an important role in magnetite synthesis. The concentration of nitrate used in the experiments is much higher than probably in the prebiotic seas (< 1 µmol L −1 ) [53]. Ranjan et al also suggested that nitrate concentration could be higher than 1 µmol L −1 in prebiotic pounds [53] Previous studies showed that depending on the concentration of sulfide, the concentration of iron in the early oceans could reach a value around 100 µmol L −1 [54][55][56].…”

The Hot Spring Hypothesis for an Origin of Life

“…Most readers are probably familiar with this quote, but we reiterate it here because Darwin's intuition of a warm little pond makes perfect sense. In contrast to the dilution that inevitably would occur in a global salty ocean, potential organic reactants can accumulate and be concentrated sufficiently for reactions to occur in small bodies of fresh water on volcanic land masses emerging from the ocean (Pearce et al, 2017;Ranjan et al, 2019). Darwin also proposed that a ''protein compound'' must first form, ''ready to undergo still more complex changes.''…”

The origin of life as a planetary phenomenon

“…Effective attenuation of x-rays, cosmic rays, and UV light below 200 nm coexists naturally with direct sunlight in these atmospheres. The planet surfaces will provide access to metals (and nonmetals), namely, Fe and P, as well as trace amounts of HCN, SO 2 , H 2 S, and NO • in sufficient concentrations for prebiotic chemistry (12,60,74).…”