Freshwater and Evaporite Brine Compositions on Hadean Earth: Priming the Origins of Life
Freshwater and Evaporite Brine Compositions on Hadean Earth: Priming the Origins of Life
复制标题
冥古宙地球上的淡水和蒸发盐卤水成分：启动生命的起源
DOI：
10.1089/ast.2020.2396
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发表时间：
2022
期刊：
影响因子：
4.2
通讯作者：
Schoonen, Martin A.
中科院分区：
文献类型：
--
作者：
Sahai, Nita;Adebayo, Segun;Schoonen, Martin A.
Hadean时代水溶液的化学成分决定了生命的分子构件的益生素合成所需的基本元素的可用性。在这里，我们在一系列环境条件下对大气-水-岩石相互作用进行了定量反应路径模拟，以估计淡水和蒸发岩卤水的成分。然后，我们评估了溶液化学对核糖核苷酸合成和聚合以及原细胞膜稳定性的影响。具体地说，研究了科马提岩和英云母(原始地壳岩石)风化和蒸发-再水化(干燥-润湿)循环形成的溶液，假定大气成分为中性，大气二氧化碳分压(PCO2)和温度(T)的值范围很大。溶液pH随二氧化碳分压的增加而降低，无机磷、镁、钙、铁和碳(PT、MgT、CAT、FeT和CT)的总溶解浓度增加。PCO2和T决定了溶液如何根据沉淀的矿物质和留在溶液中的离子而演变。在温度 = 为75℃， 为0.05atm时，镁钙离子浓度比为 1，主要为金属硅铝酸盐(含粘土)、白云石、三水铝石和黄铁矿(FeS_2)，而在 为0.05atm时，镁/钙离子浓度为>； 1，主要为菱镁矿、白云石、黄铁矿、玉髓(SiO_2)和高岭石(Al2Si2O5)。在T = 为75℃， 为0.05atm时，羟基磷灰石在风化过程中析出，但在蒸发过程中不析出，因此，PT随蒸发-再水化循环而增加，而镁、CAT和FeT则随其他矿物的析出而减少。在T = 75°C和pCO_2∼5大气压下，与科马提石的反应提供了足够高的镁离子浓度的风化结束溶液，以促进核糖核酸模板引导和蒙脱土促进的非酶核糖核酸聚合，但与原细胞膜不相容；然而，蒙脱石促进的核糖核酸聚合可以在很少或不存在镁离子的情况下进行。在T = 75°C和pCO_2∼5大气压下，科马提石风化后的卤水循环蒸发/复水得到以下结果：(1)高的PT值可以促进核苷酸合成，(2)低的二价阳离子浓度与氨基酸促进的蒙脱土催化的核糖核酸聚合和与原细胞膜的二价阳离子聚合，但太低，不适合模板导向的非酶核糖核酸聚合。对于所有的PCO2值，由于控制这些离子浓度的矿物的逆行溶解性，镁离子和PT2+浓度随着温度的升高而降低，而HCO3−浓度随着温度的升高而增加；Fe2+浓度随着温度的升高而增加。黑云母风化和循环湿干反应没有产生有利于促进益生RNA形成的溶液组合物。相反，与原细胞出现相容的离子浓度限制了早期地球大气中的二氧化碳。综上所述：(1)即使在中性大气条件下，通过大气-水-科马提岩相互作用，也可以实现益生RNA合成和膜自组装；(2)对生命起源和早期PCO2元素有效性的限制，是通过大气-水-岩石相互作用的单一全球运行机制解决的，而不需要调用特殊的微环境。目前的结果支持一种简单的生命起源假说，即使在中性大气层下，只要其他有利的地球物理和行星条件也得到满足。
The chemical composition of aqueous solutions during the Hadean era determined the availability of essential elements for prebiotic synthesis of the molecular building blocks of life. Here we conducted quantitative reaction path modeling of atmosphere-water-rock interactions over a range of environmental conditions to estimate freshwater and evaporite brine compositions. We then evaluated the solution chemistries for their potential to influence ribonucleotide synthesis and polymerization as well as protocell membrane stability. Specifically, solutions formed by komatiite and tonalite (primitive crustal rocks) weathering and evaporation-rehydration (drying-wetting) cycles were studied assuming neutral atmospheric composition over a wide range of values of atmospheric partial pressure of CO2(PCO2) and temperatures (T). Solution pH decreased and total dissolved concentrations of inorganic P, Mg, Ca, Fe, and C (PT, MgT, CaT, FeT, and CT) increased with increasing PCO2. The PCO2and T dictated how the solution evolved with regard to minerals precipitated and ions left in solution. At T = 75°C and PCO2< 0.05 atm, the concentration ratio of magnesium to calcium ion concentrations (Mg2+/Ca2+) was < 1 and predominantly metal aluminosilicates (including clays), dolomite, gibbsite, and pyrite (FeS2) precipitated, whereas at PCO2> 0.05 atm, Mg2+/Ca2+was > 1 and mainly magnesite, dolomite, pyrite, chalcedony (SiO2), and kaolinite (Al2Si2O5) precipitated. At T = 75°C and PCO2> 0.05 atm, hydroxyapatite (HAP) precipitated during weathering but not during evaporation, and so, PTincreased with each evaporation-rehydration cycle, while MgT, CaT, and FeTdecreased as other minerals precipitated. At T = 75°C and PCO2∼5 atm, reactions with komatiite providedend-of-weathering solutionswith high enough Mg2+concentrations to promote RNA-template directed and montmorillonite-promoted nonenzymatic RNA polymerization, but incompatible with protocell membranes; however, montmorillonite-promoted RNA polymerization could proceed with little or no Mg2+present.Cyclically evaporating/rehydrating brinesfrom komatiite weathering at T = 75°C and PCO2∼5 atm yielded the following: (1) high PTvalues that could promote ribonucleotide synthesis, and (2) low divalent cation concentrations compatible with amino acid-promoted, montmorillonite-catalyzed RNA polymerization and with protocell membranes, but too low for template-directed nonenzymatic RNA polymerization. For all PCO2values, Mg2+and PTconcentrations decreased, whereas the HCO3−concentration increased within increasing temperature, due to the retrograde solubility of the minerals controlling these ions' concentrations; Fe2+concentration increased because of prograde pyrite solubility. Tonalite weathering and cyclical wetting-drying reactions did not produce solution compositions favorable for promoting prebiotic RNA formation. Conversely, the ion concentrations compatible with protocell emergence, placed constraints on PCO2of early Earth's atmosphere. In summary: (1) prebiotic RNA synthesis and membrane self-assembly could have been achieved even under neutral atmosphere conditions by atmosphere-water-komatiite rock interactions; and (2) constraints on element availability for the origins of life and early PCO2were addressed by a single, globally operating mechanism of atmosphere-water-rock interactions without invoking special microenvironments. The present results support a facile origins-of-life hypothesis even under a neutral atmosphere as long as other favorable geophysical and planetary conditions are also met.