Recent progress in understanding of early earth biosphere

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  • Ohtomo Yoko
    Post-doctral fellow, Japan Society for the Promotion of Science Faculty of Engineering, Hokkaido University

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  • 初期地球生命圏研究の近年の動向について
  • ショキ チキュウ セイメイケン ケンキュウ ノ キンネン ノ ドウコウ ニ ツイテ

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Abstract

<p>When the first biosphere was formed on the early earth has been actively discussed recent years. Oldest biogenic graphite and microfossils have been repeatedly tested from early 2000s, due to unclear geological settings and discovery of abiotic production of organic compounds in native environments. Here, I introduce our discovery of novel graphite-rich metasedimentary rocks in the northwest of ca. 3.8 billion-years-old Isua Supracrustal Belt, western Greenland by detail geological investigation. Isotopic and nano-scale structural signatures of graphite show that graphite is originated in biogenic organic matter, providing further oldest evidence of biological activity in the ca. 3.8 Ga ocean. Evidence of early biosphere could be found outside of carbonaceous materials in old rocks. Banded iron formations, chemical marine sediments including Fe-bearing minerals, have been a subject of active research connecting redox state to biosphere on early earth's surface. Previous studies indicate that atmospheric oxygen increased at ca. 2.45 Ga (Great Oxidation Event: GOE),suggesting that oxygenic photosynthesizing bacteria have been flourished and emitted oxygen. However, more recent geological and geochemical records reveal that shallow part of ocean and atmosphere have been slightly oxidized before GOE, which evokes that oxygenic photosynthesizing bacteria was active earlier than that anticipated.</p>

Journal

  • Chikyukagaku

    Chikyukagaku 50 (3), 177-186, 2016

    The Geochemical Society of Japan

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