Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California.
Department of Chemistry and Biochemistry, University of California at Santa Barbara, Santa Barbara, California.
Astrobiology. 2020 Mar;20(3):307-326. doi: 10.1089/ast.2018.1949.
The molecules feeding life's emergence are thought to have been provided through the hydrothermal interactions of convecting carbonic ocean waters with minerals comprising the early Hadean oceanic crust. Few laboratory experiments have simulated ancient hydrothermal conditions to test this conjecture. We used the JPL hydrothermal flow reactor to investigate CO reduction in simulated ancient alkaline convective systems over 3 days (T = 120°C, = 100 bar, pH = 11). H-rich hydrothermal simulant and CO-rich ocean simulant solutions were periodically driven in 4-h cycles through synthetic mafic and ultramafic substrates and Fe>Ni sulfides. The resulting reductants included micromoles of HS and formate accompanied possibly by micromoles of acetate and intermittent minor bursts of methane as ascertained by isotopic labeling. The formate concentrations directly correlated with the CO input as well as with millimoles of Mg ions, whereas the acetate did not. Also, tens of micromoles of methane were drawn continuously from the reactor materials during what appeared to be the onset of serpentinization. These results support the hypothesis that formate may have been delivered directly to a branch of an emerging acetyl coenzyme-A pathway, thus obviating the need for the very first hydrogenation of CO to be made in a hydrothermal mound. Another feed to early metabolism could have been methane, likely mostly leached from primary CH present in the original Hadean crust or emanating from the mantle. That a small volume of methane was produced sporadically from the CO-feed, perhaps from transient occlusions, echoes the mixed results and interpretations from other laboratories. As serpentinization and hydrothermal leaching can occur wherever an ocean convects within anhydrous olivine- and sulfide-rich crust, these results may be generalized to other wet rocky planets and moons in our solar system and beyond.
生命起源所需的分子被认为是通过对流的碳酸海洋水与早期哈德逊海洋地壳组成矿物之间的热液相互作用提供的。很少有实验室实验模拟古代热液条件来检验这一假设。我们使用 JPL 热液流动反应器在模拟的古代碱性对流系统中进行了为期 3 天的 CO 还原实验（T=120°C，=100 巴，pH=11）。富 H 热液模拟物和富 CO 海洋模拟物溶液每隔 4 小时通过合成镁铁质和超镁铁质基质和 Fe>Ni 硫化物周期性地驱动。所得还原剂包括毫摩尔 HS 和甲酸盐，可能还有毫摩尔乙酸盐和间歇出现的少量甲烷爆发，这是通过同位素标记确定的。甲酸盐浓度与 CO 输入以及几毫米的镁离子直接相关，而乙酸盐则没有。此外，在似乎开始蛇纹石化的过程中，几十微米的甲烷不断地从反应器材料中提取出来。这些结果支持了这样一种假设，即甲酸盐可能直接被输送到一个新兴的乙酰辅酶 A 途径分支，从而避免了在热液丘中对 CO 进行第一次加氢的必要性。早期代谢的另一种进料可能是甲烷，可能主要是从原始哈德逊地壳中存在的原始 CH 或从地幔中浸出的甲烷。从 CO 进料中偶尔产生少量的甲烷，也许是由于瞬时封闭，这与其他实验室的混合结果和解释相呼应。由于只要海洋在无水橄榄石和富含硫化物的地壳中对流，蛇纹石化和热液浸出就会发生，因此这些结果可能会推广到我们太阳系内和其他太阳系内的其他潮湿岩石行星和卫星。
