标题： 早期地球天然水中的一氧化二氮浓度 显示英文标题

标题： Nitrogen Oxide Concentrations in Natural Waters on Early Earth

摘要： 生命起源研究中的一个关键挑战是估计与早期地球上生命起源可能相关的化学途径中物种的丰度。 特别是溶解的氮氧化物阴离子（NO$_{X}^{-}$），包括硝酸盐（NO$_{3}^{-}$）和亚硝酸盐（NO$_{2}^{-}$），已在从RNA聚合到原始代谢出现的各种生命起源化学反应中被提出。 近期的研究计算了从前生物大气向海洋供应NO$_{X}^{-}$的速率，并报告了稳态[NO$_{X}^{-}$] 在所有可能的参数空间内均较高。 这些发现基于如下假设：除非在热液喷口处被处理，否则NO$_{X}^{-}$在天然水中是稳定的。 在这里，我们表明NO$_{X}^{-}$在早期地球的还原环境中是不稳定的。 由于紫外线光解和与还原态铁（Fe$^{2+}$）的反应，[NO$_{X}^{-}$] 被抑制到过去预测值的几个数量级以下。 对于 pH$=6.5-8$和$T=0-50^\circ$摄氏度，我们发现前生物海洋中 [NO$_{X}^{-}$] 最有可能为$<1~\mu$M。 另一方面，具有有利排水特性的前生物池塘可能维持了 [NO$_{X}^{-}$]$\geq 1~\mu$M. 就像现代地球一样，由于其更高的稳定性，在前生物 地球上的大部分 NO$_{X}^{-}$应该以 NO$_{3}^{-}$的形式存在。 这些发现告知了早期地球上可能存在的前生物化学反应类型。 我们讨论了这些发现对提出的前生物化学反应的影响，并强调了进一步研究 NO$_{X}^{-}$动力学的必要性，以减少预测早期地球上 [NO$_{X}^{-}$] 存在的相当大的不确定性。 显示英文摘要

摘要： 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$_{X}^{-}$), in particular nitrate (NO$_{3}^{-}$) and nitrite (NO$_{2}^{-}$), 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$_{X}^{-}$ from the prebiotic atmosphere to the ocean, and reported steady-state [NO$_{X}^{-}$] to be high across all plausible parameter space. These findings rest on the assumption that NO$_{X}^{-}$ is stable in natural waters unless processed at a hydrothermal vent. Here, we show that NO$_{X}^{-}$ is unstable in the reducing environment of early Earth. Sinks due to UV photolysis and reactions with reduced iron (Fe$^{2+}$) suppress [NO$_{X}^{-}$] by several orders of magnitude relative to past predictions. For pH$=6.5-8$ and $T=0-50^\circ$C, we find that it is most probable that NO$_{X}^{-}$]$<1~\mu$M in the prebiotic ocean. On the other hand, prebiotic ponds with favorable drainage characteristics may have sustained [NO$_{X}^{-}$]$\geq 1~\mu$M. As on modern Earth, most NO$_{X}^{-}$ on prebiotic Earth should have been present as NO$_{3}^{-}$, 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$_{X}^{-}$ kinetics to reduce the considerable uncertainties in predicting [NO$_{X}^{-}$] on early Earth.