低温蛇紋岩化反応においてその水素生成量に与える鉱物学的もしくは地球化学的な要因を明らかにするために様々な産地の超苦鉄質岩を用いて水素生成実験を行なった。その結果、紋岩化の程度が低い試料ほど水素生成量が高い傾向がみられた。また、ハルツバージャイトの方がダナイトよりも水素生成量が高い傾向がみられた。溶液分析の結果から溶存シリカ濃度が高い試料が水素生成量が高く、高シリカ濃度の系においては溶液の化学組成はマグネシウムケイ酸塩水和物 (M-S-H) によって規定されていると考えられ、M-S-HがMg(OH)2に比べて低いpHに緩衝することでカンラン石や輝石の溶解速度が上昇し、高い水素生成量をもたらしたと考えられる。

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海底熱水噴出孔は,天体内部からの放熱場であるとともに水-岩石相互作用の場である.地球における熱水噴出孔は母岩相によって異なる還元的物質を供給することで酸化的な海水との境界で多様な酸化還元勾配をつくり,多彩で豊かな生物群集を形成する.一方,木星の氷衛星であり内部海を持つことが強く示唆されているエウロパにおいては,熱水噴出孔は潮汐加熱等の放熱場として氷殻の底を融かす物理的な作用が一義的に重要であり,その水-岩石相互作用からの物質供給が内部海の形成に寄与すると考えられる.ただし,エウロパでは酸化力源の供給は必ずしも潤沢ではなく,むしろ,想定し得る生命活動や生物量に対して制限的であるに違いない.

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 Phylogenetic analysis is one of the useful tools available for revealing the evolution of life on the Earth; however, it has difficulty in principle distinguishing old and new genomes just by comparing phylogenomic trees. To overcome this difficulty, a new method is introduced which utilizes the Earth's history derived from geologic information to trace genomic evolution. This idea is inspired by Darwin's natural selection, and explains how living organisms change with the environment. In other words, life's genome does not change if the environment remains the same. A key is the birthplace of life on Hadean Earth, which is thought to be an ultra-reducing environment with H₂ produced in abundance through serpentinization. OD1 is a potential microbe that has survived on the Earth since the Hadean. Its habitat, Hakuba-Happo in Japan, is a unique serpentinite-hosted hydrothermal system on land, and it has avoided evolution by remaining in a super-reducing environment from the Hadean to the present. OD1 is regarded as a “living fossil” of the Hadean microbe. Ultra-reducing environments have disappeared over the Earth's history. How has OD1 survived since the Hadean to the present? A possible scenario is proposed based on Plate Tectonics. OD1 habitats have gone through the following transitions: (1) super-reducing environment in a natural nuclear geyser on a primordial continent in the Hadean; (2) serpentinite-hosted hydrothermal system along a mid-oceanic ridge transform fault during the Archean-Proterozoic; (3) subduction-accretion and escape from oxygenated Phanerozoic ocean floor; and, (4) jacked up by growth of accretionary complexes and taking refuge in a hydrothermal system above a volcanic front. OD1 habitats have been reduced with geological age as free oxygen has increased in the surface environment. OD1 may be a “living microfossil” of the Hadean, making its way continuously through ultra-reducing environments on a tightrope.

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隕石中の有機化合物は, 約46億年前の太陽系誕生時に生成されたものである。これらの有機化合物には我々になじみの深いアミノ酸など種々ある。地球だけでなく, 隕石の母天体である小惑星にもこのような有機化合物が存在することは, 生命の起源や地球外生命について化学者にロマンをあたえてくれる。

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Substantial amounts of methane with seasonal variation have been discovered from discrete regions of Mars. What is the origin of methane on Mars-abiotic (geochemical) or biotic? Is the methane produced ancient or recently? Compound-specific stable carbon isotope analysis will be a potential tool for addressing this most intriguing question. NASA's Mars Science Laboratory (MSL), which will launch in autumn 2011, loads a Tunable Laser Spectrometer (TLS) into the Sample Analysis at Mars (SAM) instrument to conduct in-situ stable isotope analyses of volatile compounds and organic molecules on Mars with high precision and accuracy. This technique may provide an important, Astrobiological insight for understanding the past and present planetary processes and habitability of our Earth's brother planet.

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Mid-ocean ridges are places where interactions between seawater and oceanic crust take place. Hydrothermal interactions govern the chemistry of the oceans while hydrothermal vent fields host unique and diverse biological communities even in barren ocean floor settings, and are candidates for the birthplace of the earliest life forms. This paper presents the important roles of the hydrothermal carbonatization of Archean oceanic crust that is one of the characteristic seafloor alterations in the early Earth. Based on the mineralogical, geochemical, and geological features of calcite in the Archean greenstones, the CO₂ flux from ocean to oceanic crust was estimated to be two orders of magnitude larger than the modern value, which points to the significance of seafloor hydrothermal carbonatization in the Archean carbon cycle. Furthermore, thermodynamic calculations of phase equilibria in the high-temperature alteration zone indicate that the hydrothermal fluid was alkaline due to the presence of calcite in the alteration minerals under a high-CO₂ condition, and predict a generation of SiO₂-rich and Fe-poor hydrothermal fluids in the subseafloor hydrothermal system. Such high-temperature alkaline fluids could have had a significant role not only in the early ocean geochemical processes but also in the early evolution of life.

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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.

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「地球外生命は存在するだろうか．」この問いは，「生命とは何か」というもうひとつの問いに対して宇宙で普遍的に通用する答えを得ることに繋がる．このふたつの問いに答える最も直接的な手段が，太陽系における地球外生命探査である．地球外生命の証拠はまだ見出されてはいないが，近年の様々な探査を通して，生命探査の対象となる天体，すなわちエネルギーや物質の観点で生命を育み得る環境を持つ天体の候補がいくつか見つかってきている．本稿では，火星，木星衛星エウロパ，土星衛星エンセラダスおよびタイタンを具体的な対象に，それらの天体がなぜ地球外生命の存在可能性を有するのかについて現状の知見をまとめる．

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 Reported are the origins and chemistry of hot spring water unique to the Ohmi–Hakuba region in the northern Japan Alps, central north Honshu, where a variety of rock types, derived from accretionary complex formed in the Ediacaran (presumably ca. 620 Ma), are regionally exposed. One of the largest bodies of serpentinized peridotite in Japan intersects the Quaternary volcanic front. Featuring an unusual geochemistry, the resulting unique hydrothermal hot springs yield a high pH (ca. 10-11) and a continuous supply of H₂. Research reveals four types of hot spring in the Hakuba region: (1) serpentinite hosted hot spring water, (2) high-salinity and carbonated water, (3) Archean type low pO₂ hot spring water, and (4) acidic and sulfuric hot spring water with a H₂S gas input from magma. The high alkali and H₂-enriched hot spring water (Type 1) differs remarkably from other hot springs in this region. In terms of geochemistry, there is a dissolved oxygen content due to the production of abundant H₂, which is the reason why a Hadean-type microbial community is present. The origins and evolution of life are closely related to atmospheric oxygen level. Generally, anaerobic microbes inhabit subsurface areas where free oxygen is limited, while oxygen adaptive creatures cannot survive in an anaerobic environment. This means anaerobic microbes have not evolved, and remain as “living fossils”. Hakuba OD1 is one of the most important candidates for the oldest form of life directly connected to LUCA, because it has survived in a Hadean-like environment since emerging. The next research target is the ecosystem in a H₂-enriched environment without free oxygen.

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 High-pressure and high-temperature hydrothermal experiments were initially conducted to measure mineral solubility and growth rate. Since then, considerable efforts have been made to characterize the alteration assemblages produced by a wide variety of hydrothermal fluids in different rock types. Based on such information, the conditions of sub-sea floor hydrothermal systems and the formation processes of ore deposits were investigated. These studies significantly depended on many important experimental results obtained by a batch (closed)-type experimental system which gives equilibrium conditions. On the other hand, attention has been also paid to a flow-type experimental system, because natural systems can not only constrained by experiments under equilibrium conditions but, more importantly, by non-equilibrium experiments. Recently, hydrothermal experiments were carried out to better understand interactions among rocks, hydrothermal fluids, and microbes. It has been suggested that microbial ecosystems might be widely distributed within oceanic crusts and be sustained by chemical energy derived from water-rock interactions. However, little is known about the flux of energy and materials involved in microbial activity within the crustal aquifer because of technical difficulties in accessing sub-seafloor environments. A flow-type cultivation system simulating natural hydrothermal environments including crustal aquifers could provide insights into the ecological significance of microorganisms and their contribution to the biogeochemical cycle in global oceans and crusts.

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