P042-0010
Impact-induced hydrothermal systems on early Earth: Potential places for efficient CO2 reduction and formation of complex organic molecules

Friday, 11 December 2020
Poster
Kazumu Kaneko1, Yasuhito Sekine2, Takazo Shibuya3, Hisahiro Ueda3, Natsumi Noda2, Hidenori Genda4 and Yoshio Takahashi5, (1)Tokyo Institute of Technology, Tokyo, Japan, (2)Earth-Life Science Institute, Meguro, Japan, (3)JAMSTEC Japan Agency for Marine-Earth Science and Technology - JAMSTEC, Kanagawa, Japan, (4)Tokyo Institute of Technology, Meguro, Japan, (5)University of Tokyo, Bunkyo-ku, Japan
Abstract:
Hydrothermal vents on early Earth are suggested to have been a promising emergence place of life; however, CO2 reduction to form organic matter would have been inhibited there even high abundances of H2 if no metallic catalysts exist (McCollom, 2016). On the other hand, recent planetary formation theory suggests the frequent occurrence of impacts of differentiated bodies and their fragments (Kendall and Melosh, 2016). These impactors should have supplied Fe-Ni alloy to impact-induced hydrothermal systems generated within craters.

Here, we perform both hydrological modelling and hydrothermal experiments to examine whether organic synthesis could have proceeded within such a crater of Fe-Ni-containing impactor on early Earth. Using a hydrological model, we simulated hydrothermal groundwater circulations emerged within a crater with diameter of ~200 km. Our results suggest that hydrothermal circulations would be closed within the crater cavity when the heat source at several km in depth is 200ºC or greater. The experienced temperature of hydrothermal fluids would be at most ~200ºC in the hydrothermal circulations. We conducted hydrothermal experiments using a 13CO2-containing solution and a mixture of synthesized basalt and Fe-Ni alloy at 200ºC and 300 bars. We find the formation of 13CH4, 13C2H6, and HCOOH from 13CO2 in the fluids. In the solid samples collected after the experiments, complex organic matter having aliphatic carbons and carboxylate is also found on the surface of Fe-bearing minerals using scanning transmission X-ray microscopy. At alkaline pH controlled by alteration of basalt, reactive HCO3- would be reduced to HCOOH using H2. HCOOH would be subsequently hydrogenated on Fe-Ni catalyst to form hydrocarbons and complex organic matter. Combining these results, we suggest that impact-generated hydrothermal systems could have promoted organic synthesis on Hadean Earth.

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