Department of Geosciences, University of Oslo, Oslo, Norway.
Astrobiology. 2011 Sep;11(7):711-24. doi: 10.1089/ast.2010.0559.
The release and oxidation of ferrous iron during aqueous alteration of the mineral olivine is known to reduce aqueous solutions to such extent that molecular hydrogen, H2, forms. H2 is an efficient energy carrier and is considered basal to the deep subsurface biosphere. Knowledge of the potential for H2 generation is therefore vital to understanding the deep biosphere on Earth and on extraterrestrial bodies. Here, we provide a review of factors that may reduce the potential for H2 generation with a focus on systems in the core temperature region for thermophilic to hyperthermophilic microbial life. We show that aqueous sulfate may inhibit the formation of H2, whereas redox-sensitive compounds of carbon and nitrogen are unlikely to have significant effect at low temperatures. In addition, we suggest that the rate of H2 generation is proportional to the dissolution rate of olivine and, hence, limited by factors such as reactive surface areas and the access of water to fresh surfaces. We furthermore suggest that the availability of water and pore/fracture space are the most important factors that limit the generation of H2. Our study implies that, because of large heat flows, abundant olivine-bearing rocks, large thermodynamic gradients, and reduced atmospheres, young Earth and Mars probably offered abundant systems where microbial life could possibly have emerged.
水蚀变过程中橄榄石释放和亚铁氧化会使水溶液还原到形成分子氢（H2）的程度。H2 是一种高效的能量载体，被认为是深地下生物圈的基础。因此，了解 H2 产生的潜力对于理解地球和外星体的深地下生物圈至关重要。本文综述了可能降低 H2 产生潜力的因素，重点关注嗜热和超嗜热微生物生命核心温度区域的系统。结果表明，水合硫酸盐可能会抑制 H2 的形成，而低温下碳和氮的氧化还原敏感化合物不太可能产生显著影响。此外，我们认为 H2 的生成速率与橄榄石的溶解速率成正比，因此受到反应表面积和水与新鲜表面接触等因素的限制。我们还提出，水的可用性和孔隙/裂缝空间是限制 H2 生成的最重要因素。我们的研究表明，由于热通量大、富含橄榄石的岩石、大的热力学梯度和还原大气，年轻的地球和火星可能提供了大量微生物可能出现的系统。
