Clear Search sequence regions


  • carbon (2)
  • feedbacks (1)
  • hydrogen (1)
  • oxygen (8)
  • photosynthesis (1)
  • redox (1)
  • sulfur (1)
  • Sizes of these terms reflect their relevance to your search.

    Geological records of atmospheric oxygen suggest that pO2 was less than 0.001% of present atmospheric levels (PAL) during the Archean, increasing abruptly to a Proterozoic value between 0.1% and 10% PAL, and rising quickly to modern levels in the Phanerozoic. Using a simple model of the biogeochemical cycles of carbon, oxygen, sulfur, hydrogen, iron, and phosphorous, we demonstrate that there are three stable states for atmospheric oxygen, roughly corresponding to levels observed in the geological record. These stable states arise from a series of specific positive and negative feedbacks, requiring a large geochemical perturbation to the redox state to transition from one to another. In particular, we show that a very low oxygen level in the Archean (i.e., 10-7 PAL) is consistent with the presence of oxygenic photosynthesis and a robust organic carbon cycle. We show that the Snowball Earth glaciations, which immediately precede both transitions, provide an appropriate transient increase in atmospheric oxygen to drive the atmosphere either from its Archean state to its Proterozoic state, or from its Proterozoic state to its Phanerozoic state. This hypothesis provides a mechanistic explanation for the apparent synchronicity of the Proterozoic Snowball Earth events with both the Great Oxidation Event, and the Neoproterozoic oxidation. © 2017 John Wiley & Sons Ltd.

    Citation

    T A Laakso, D P Schrag. A theory of atmospheric oxygen. Geobiology. 2017 May;15(3):366-384

    Expand section icon Mesh Tags

    Expand section icon Substances


    PMID: 28378894

    View Full Text