Research Articles

Redox stratification of an ancient lake in Gale crater, Mars

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Science  02 Jun 2017:
Vol. 356, Issue 6341, eaah6849
DOI: 10.1126/science.aah6849

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  • RE: Life and oxygen
    • Tanai Cardona, Research Fellow, Life Sciences, Imperial College London

    Fascinating paper! Thanks. I have a few questions.

    The authors write: “The recognition of a stable redox-stratified water body adds important detail to our understanding of the potential for microbial chemoautotrophy within the ~3.8- to 3.1-billion-year-old Gale crater lake system.”

    I am just wondering on what assumptions photoautotrophy is excluded as a possibility from the above statement. It is well known that, at the very least, anoxygenic photosynthesis was ongoing 3.8 billion years ago (Nisbet & Fowler, 2014). While the exact date for the origin of oxygenic photosynthesis on Earth is debated, there are many reports for the presence of biogenic oxygen hundreds of millions of years before the Great Oxidation Event (Lyons et al., 2014). So it is not unreasonable to think that some forms of biological water oxidation to oxygen already existed before 3.0 billion years ago on Earth. So time it is not the issue...

    The authors write: “The model depends on the depth of penetration of ultraviolet (UV) light and low levels of photochemically generated atmospheric O2 into the water column to establish a depth-dependent boundary between oxidized and anoxic zones”.

    How much oxygen could be produced photochemically on Mars 3.8 to 3.1 billion years ago? I am not a geochemist, but from discussions regarding the oxygenation of Earth, I understand that it was an almost negligible contribution. With the levels of O2 being only a maximum of 10E-8 of the cu...

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    Competing Interests: None declared.

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