The study of possible astrobiological and ancient terrestrial biospheres might be based on an actualistic approach. The survey of relict microbial communities and their habitats demonstrates that actualistic microbial biogeochemistry might bring light to the early biosphere if it is based on the data from Earth sciences, which comprise the larger system. Scaling is the key issue for systemic approach. The general features of relict microbial communities, which are found in extreme habitats such as hydrotherms, hypersaline lagoons, and soda lakes, are described. They conform to demands for autonomous communities with closed biogeochemical cycles. Incomplete cycling leads to the biogeochemical succession. Reconstruction from actualistic studies should be based on the firm base of the paleorecord, obtained by geologists from the field studies of ancient rocks and the empirical data of microbial paleontology.
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