地学雑誌
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
総説
冥王代の「生きた微化石」OD1と超還元場の歴史
佐藤 友彦吉屋 一美丸山 茂徳
著者情報
キーワード: 冥王代, OD1, 蛇紋岩, 熱水系, 超還元
ジャーナル フリー

2019 年 128 巻 4 号 p. 571-596

詳細
抄録

 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.

著者関連情報
© 2019 公益社団法人 東京地学協会
前の記事 次の記事
feedback
Top