Shock E L, McCollom T, Schulte M D
Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, USA.
Orig Life Evol Biosph. 1995 Jun;25(1-3):141-59. doi: 10.1007/BF01581579.
Thermodynamic calculations provide the means to quantify the chemical disequilibrium inherent in the mixing of reduced hydrothermal fluids with seawater. The chemical energy available for metabolic processes in these environments can be evaluated by taking into account the pressure and temperature dependence of the apparent standard Gibbs free energies of reactions in the S-H2-H2O system together with geochemical constraints on pH, activities of aqueous sulfur species and fugacities of H2 and/or O2. Using present-day mixing of hydrothermal fluids and seawater as a starting point, it is shown that each mole of H2S entering seawater from hydrothermal fluids represents about 200,000 calories of chemical energy for metabolic systems able to catalyze H2S oxidation. Extrapolating to the early Earth, which was likely to have had an atmosphere more reduced than at present, shows that this chemical energy may have been a factor of two or so less. Nevertheless, mixing of hydrothermal fluids with seawater would have been an abundant source of chemical energy, and an inevitable consequence of the presence of an ocean on an initially hot Earth. The amount of energy available was more than enough for organic synthesis from CO2 or CO, and/or polymer formation, indicating that the vicinity of hydrothermal systems at the sea floor was an ideal location for the emergence of the first chemolithoautotrophic metabolic systems.
热力学计算提供了一种手段，用于量化还原态热液流体与海水混合时所固有的化学不平衡。通过考虑S - H₂ - H₂O系统中反应的表观标准吉布斯自由能对压力和温度的依赖性，以及对pH值、水溶态硫物种的活度和H₂和/或O₂逸度的地球化学限制，可以评估这些环境中代谢过程可用的化学能。以当今热液流体与海水的混合为起点，研究表明，对于能够催化H₂S氧化的代谢系统而言，每摩尔从热液流体进入海水的H₂S代表约200,000卡路里的化学能。推断到早期地球，其大气可能比现在更具还原性，结果表明这种化学能可能减少了大约一半。然而，热液流体与海水的混合本应是化学能的丰富来源，并且是初始处于高温的地球上存在海洋的必然结果。可用的能量足以进行由CO₂或CO进行的有机合成和/或聚合物形成，这表明海底热液系统附近是首个化能自养代谢系统出现的理想场所。
