初期地球の海底熱水活動は生命進化の場として重要であったか? : オーストラリア・サルファースプリングス鉱床からの報告(<特集>2010年学術講演会におけるシンポジウム「海底熱水系と生命の起原」)

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Anciet submarine hydrothermal environments have been considered as important locations where the first life flourished. On the other hand, many experimental results postulate if submarine hydrothermal environments were suitable for the chemical evolution for origin of life. Geological records of Archean submarine hydrothermal ore deposits are present allover the world. Those ore deposits often accompany with carbonaceous sediments, suggesting high microbial activities around the discharging hydrothermal fluids. Such carbonaceous sediments may provide an opportunity to examine evolution of early life in submarine hydrothermal environments. Here I present the evidence of high microbial activities at ca. 3.2-billion-years-old submarine hydrothermal fields of Sulfur Springs in Australia. It is found that examine samples associated with the ore deposit were rich in organic carbon. Relatively high Mo concentrations were found in those organic matter. Such Mo behavior implies direct microbial mediation of bio-essential elements from submarine hydrothermal fluids. Microscopic occurrence of organic carbon is often closely associated with sulfide minerals forming onion- or stromatolite-like structures. Such structures imply biologically induced sulfide mineralization in submarine hydrothermal environments. Stable isotope analyses indicate high activities of methanogens and methanotrophs with sulfate reducers only around the hydrothermal discharging zone. Those results indicate that ancient submarine hydrothermal fields were important for early ecosystem not only for metabolic energy usage but also uptake of bio-essential elements. However, the total energy flux from interior of the early Earth is known to be small. Such small energy flux constraints the extents of submarine hydrothermal activities on the early ocean floor and further suggests that biomass around the ancient submarine hydrothermal environments was also small. Therefore it is still an open question as to if ancient submarine hydrothermal environments were major geological fields for evolution of early life.
2011-06-01

初期地球の海底熱水活動は生命進化の場として重要であったか? : オーストラリア・サルファースプリングス鉱床からの報告(<特集>2010年学術講演会におけるシンポジウム「海底熱水系と生命の起原」)

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