Researchers have proposed a hypothesis that may help explain Earth's "boring billion" years, when the oceans remained in an intermediate oxidation state that prevented the development of complex multicellular life. David Johnston et al. propose that anoxygenic photosynthetic bacteria in the surface ocean used sulfide, rather than water, as an electron donor. The resulting chemical reaction reduced the rate at which oxygen was produced, which likely kept oxygen from accumulating in the sea and air.
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