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Fossils of Ancient Microorganisms

Authored by: Kenichiro Sugitani

Handbook of Astrobiology

Print publication date:  December  2018
Online publication date:  December  2018

Print ISBN: 9781138065123
eBook ISBN: 9781315159966
Adobe ISBN:


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Representative early (Paleo- and Meso-)Archean microfossils and possible microfossils from the Pilbara craton, Western Australia, and the Kaapvaal craton, South Africa, are reviewed, referring to peculiar surface environments of the ancient Earth and rock types potentially preserving microfossils, criteria for identifying Archean microbe-like structures as microfossils. Evidently, until 3.0 Ga microbes of various morphologies and various physiologies had already emerged. They inhabited various environments from deep-sea hydrothermal vent systems to shallow water and even terrestrial hydrothermal field. It is likely that anoxigenic photosynthesis emerged at least to 3.4 Ga, and oxygenic photosynthesis did at least to 3.0 Ga. Microbes had diversified significantly during the first billion years from the emergence of life around 4.0 Ga, including large, organic-walled, lenticular microfossils in the Archean that appear to be out of place in an evolutionary context. Their biological affinities have long been unrevealed, and we may now consider the possibility that they have no phylogenic relationship to any of extant organisms. Through controversies on biogenicity of putative microfossils and revisions of previously reported materials, we have sophisticated methodologies by which we can identify cellularly preserved microfossils. The methodologies could be applied to search for life on other planets.

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