Abstract
Abiotic H(2) and hydrocarbons are found in fluids discharged from ultramafic-hosted hydrothermal vents. Beneath the hydrothermal vents, abiotic H(2) and hydrocarbons can be formed by serpentinization reactions and Fischer-Tropsch-type hydrocarbon-forming reactions, respectively, over ultramafic rocks. However, the source rocks that form abiotic H(2) and hydrocarbons may extend to broader subsurface rocks. Here, we show that various rock constituents (solid acids) play a catalytic role in the formation of H and OH radicals via H(2)O dissociation, as well as in the formation of diverse hydrocarbons via the synthesis reactions of H radicals and inorganic carbons or by H radical-induced dissociation of organic carbons. The mechanisms and characteristics of these formation processes were explored through a series of reactor-based laboratory experiments. Four types of solid acid-containing rocks were mixed with H(2)O and a carbon source and reacted at different temperatures and pressures for different reaction periods. The product gases were analyzed via GC/MS. Twenty-nine hydrocarbons up to C(11), predominantly including CH(4) and aromatic hydrocarbons, were identified when CO(2) (inorganic carbon source) and basalt particles were used; in contrast, 42 hydrocarbons up to C(11), predominantly including CH(4) and aliphatic hydrocarbons, were identified when soybean oil (organic carbon source) and basalt particles were used. The results of this study imply that abiotic H(2) and diverse hydrocarbons are produced in the subsurface of Earth regardless of the presence of living organisms and suggest that solid acid-containing rocks near hot springs or volcanic areas can promote CO(2) conversion into CH(4) with the aid of H radicals supplied from H(2)O dissociation over the rocks.