Nova hipótese da origem da vida: concentrações de óxido de nitrogênio em águas naturais na Terra Primeva

sábado, abril 13, 2019

Geochemistry, Geophysics, Geosystems

Nitrogen Oxide Concentrations in Natural Waters on Early Earth

Sukrit Ranjan  Zoe R. Todd  Paul B. Rimmer  Dimitar D. Sasselov  Andrew R. Babbin

First published: 12 April 2019

This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1029/2018gc008082

Resultado de imagem para early earth images


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 (NOurn:x-wiley:ggge:media:ggge21866:ggge21866-math-0001), in particular nitrate (NOurn:x-wiley:ggge:media:ggge21866:ggge21866-math-0002) and nitrite (NOurn:x-wiley:ggge:media:ggge21866:ggge21866-math-0003), 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 NOurn:x-wiley:ggge:media:ggge21866:ggge21866-math-0018 from the prebiotic atmosphere to the ocean, and reported steady‐state [NOurn:x-wiley:ggge:media:ggge21866:ggge21866-math-0005] to be high across all plausible parameter space. These findings rest on the assumption that NOurn:x-wiley:ggge:media:ggge21866:ggge21866-math-0004 is stable in natural waters unless processed at a hydrothermal vent. Here, we show that NOurn:x-wiley:ggge:media:ggge21866:ggge21866-math-0006 is unstable in the reducing environment of early Earth. Sinks due to UV photolysis and reactions with reduced iron (urn:x-wiley:ggge:media:ggge21866:ggge21866-math-0019) suppress [NOurn:x-wiley:ggge:media:ggge21866:ggge21866-math-0007] 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 [NOurn:x-wiley:ggge:media:ggge21866:ggge21866-math-0008]<1 alt="urn:x-wiley:ggge:media:ggge21866:ggge21866-math-0020" class="section_image" img="" nbsp="" src="" style="border-style: none; box-sizing: border-box; max-width: 100%; vertical-align: middle;">M in the prebiotic ocean. On the other hand, prebiotic ponds with favorable drainage characteristics may have sustained [NOurn:x-wiley:ggge:media:ggge21866:ggge21866-math-0009]≥1μM. As on modern Earth, most NOurn:x-wiley:ggge:media:ggge21866:ggge21866-math-0010 on prebiotic Earth should have been present as NO urn:x-wiley:ggge:media:ggge21866:ggge21866-math-0011, 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 NOurn:x-wiley:ggge:media:ggge21866:ggge21866-math-0012 kinetics to reduce the considerable uncertainties in predicting [NOurn:x-wiley:ggge:media:ggge21866:ggge21866-math-0013] on early Earth.