西オーストラリア・ピルバラ地塊における前～中期太古代微化石記録とその生物進化史における意義

抄録

Early to Middle Archean fossil-like carbonaceous and pyritic microstructures from the Pilbara Craton, Western Australia were reviewed, referring to origins and depositional environments of host rocks. While their biogenicity is not always widely accepted but even controversial, it is plausible that Early to Middle Archean microorganisms were significantly diverse (filamentous, lenticular, spheroidal, film-like) and adapted to wide ranges of environments including deep-sea hydrothermal area, shallow sea and even hyper-saline lake. Hence, these records of microfossil and stromatolites reported from contemporaneous strata could not provide direct information about origin of life and its very early evolution. On the other hand, recently accumulated data of large microfossils (>20μm in major dimension), some of which are morphologically similar to cyanbacteria and eukaria, could provide new framework for studies on the early evolution of life.