Ｄｅｅｐ Ｓｕｂｓｕｒｆａｃｅ Ｂｉｏｓｐｈｅｒｅ―地下に拡がる生物圏―

Abstract

The distribution of living organisms extends deep into the Earth's interior, according to the results of studies that have identified microbial communities in samples from deep-sea and land boreholes. Microbial communities found in bore-hole rocks and water mainly consist of both chemoautotrophic and heterotrophic prokaryotes. Most prokaryotes are extremophiles that can survive or adapt to extreme subsurface environmental conditions. Heterotrophic eukaryotes such as fungi, ciliates, and yeast are also sometimes found. We collectively call such microbial communities “the deep subsurface biosphere”. This is an important component of the Earth's biosphere, because the biomass of the deep subsurface biosphere is considered to be generally similar to surface dwelling biotic communities. Almost nothing is known about the new organisms found in the deep subsurface biosphere in terms of phylogenic relations with deep subsurface organisms and surface dwelling organisms whether there are any relict organisms that are completely isolated from modern fauna and the roles the subsurface biosphere plays in the Earth's interior. Here, I review the current status of deep subsurface biosphere research. Research on the deep subsurface biosphere is link to wide variety of interdisciplinary topics such as the roles of global biogeochemical cycles, origin of life, and astrobiology. I heartily encourage any fields of geoscientists to join in this fascinating research field.