地球化学と微生物学から迫る非生命圏と生命圏の境界(<特集>有機物・微生物・生態系の地球化学)

概要

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Boundary between abiotic and biotic zones is an important scientific concept to understand limits of life and biosphere in the Earth and in the Universe. It has been addressed by extension of realistic physical and chemical limits of growth and survival in the record holders of microorganisms and theoretical definition of habitability. Energy balance concept for habitability proposed by Hoehler (2007) well documents the energetic condition where life and its function are sustained. Biological energy quantum and maintenance energy, both of which synergetically define infimum of the concept of habitability, have been estimated by the kinetic and the thermodynamic calculations of natural microbial communities and cellular organic components' reproduction, respectively. These challenges will signify the boundary between habitable and uninhabitable environments by certain geochemical indices. Finding a boundary between the habitable and the uninhabitable, or biotic and abiotic zones is quite difficult in any of the accessible environments in the Earth. Future ultra-deep drilling and coring projects down to the Earth crust are excellent opportunities. However, a deep crustal, serpentinization-driven hyper-alkaline environment beneath the South Chamorro Seamount in the Mariana Forearc is the best candidate at the present. Exploration of the boundary biosphere would provide great insights into limits of life and biosphere in this planet.
2010-12-25