Viva Origino
Online ISSN : 1346-6933
Print ISSN : 0910-4003
45 巻, 4 号
  • Eiichi Tajika, Mariko Harada
    2017 年 45 巻 4 号 p. 5-
    発行日: 2017年
    公開日: 2021/11/16
    ジャーナル フリー

      Recent progresses of studies on the rise of atmospheric oxygen during 2.4-2.1 billion years ago (the Great Oxidation Event), the Paleoproterozoic snowball Earth event occurred 2.3-2.2 billion years ago, and a possible relationship between them are reviewed and discussed. Formation of manganese ore deposits at 2.2 billion years ago suggests that the rise of oxygen may have occurred just after the Paleoproterozoic snowball Earth event and, also, an overshoot of the atmospheric oxygen level is suggested to have occurred 2.2-2.1 billion years ago. Numerical results with a coupled model of biogeochemical cycle, photochemical reactions, and hydrogen escape to space shows that an extremely hot climate in the aftermath of the snowball Earth events causes unusually high primary productivity in the ocean through intensive chemical weathering, which results in a transition of the atmospheric oxygen levels from low to high stable steady-states, with an extensive and long-lasting overshoot. Thus, the rise of oxygen should have required perturbation to the system which made the oxygen production rate one order of magnitude higher than the normal rate. Such an extremely large perturbation could have been caused only by the snowball Earth event.