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 https://doi.org/10.1029/2018GC008082
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
Source/Fonte: .NASA Goddard Space Flight Center Conceptual Image Lab.
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 (NO
), in particular nitrate (NO
) and nitrite (NO
), 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 NO
from the prebiotic atmosphere to the ocean, and reported steady‐state [NO
] to be high across all plausible parameter space. These findings rest on the assumption that NO
is stable in natural waters unless processed at a hydrothermal vent. Here, we show that NO
is unstable in the reducing environment of early Earth. Sinks due to UV photolysis and reactions with reduced iron (
) suppress [NO
] 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 [NO
]<1 alt="urn:x-wiley:ggge:media:ggge21866:ggge21866-math-0020" class="section_image" img="" nbsp="" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/2a0116a6-29d1-44f7-b669-6d2697d1616e/ggge21866-math-0020.png" 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 [NO
]≥1μM. As on modern Earth, most NO
on prebiotic Earth should have been present as NO 
, 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 NO
kinetics to reduce the considerable uncertainties in predicting [NO
] on early Earth.
), in particular nitrate (NO) and nitrite (NO), 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 NO from the prebiotic atmosphere to the ocean, and reported steady‐state [NO] to be high across all plausible parameter space. These findings rest on the assumption that NO is stable in natural waters unless processed at a hydrothermal vent. Here, we show that NO is unstable in the reducing environment of early Earth. Sinks due to UV photolysis and reactions with reduced iron () suppress [NO] 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 [NO]<1 alt="urn:x-wiley:ggge:media:ggge21866:ggge21866-math-0020" class="section_image" img="" nbsp="" src="https://wol-prod-cdn.literatumonline.com/cms/attachment/2a0116a6-29d1-44f7-b669-6d2697d1616e/ggge21866-math-0020.png" 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 [NO]≥1μM. As on modern Earth, most NO on prebiotic Earth should have been present as NO , 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 NO kinetics to reduce the considerable uncertainties in predicting [NO] on early Earth.
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