What would the sky color be with a Proterozoic earth during the "Boring Billion" (1.8 By-0.8 By) with a Canfield (Euxinic) ocean and a high atmospheric concentration of colorless hydrogen sulfide and very low atmospheric oxygen? Would it really be a light green as proposed by Professor Peter Ward in his book Under a Green Sky, which he states but did not provide a rationale? Thank you.


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  • $\begingroup$ I am not sure but my perception is that the color of sky comes from light scattering by dust particles. $\endgroup$ – hsinghal Jun 13 '16 at 17:23
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    $\begingroup$ No offense to everybody who wants to close, but I think this is a perfectly physical question. While there is a perception component, it is 100% determined by the physics of the light scattering in the atmosphere. Planetary atmospheres do have a color and it can be calculated from first principles, even though it is not trivial (one has to perform proper ray-tracing trough multiple layers) and we may not be able to actually do it correctly within the scope of SE. I do agree that the earth sciences folks may have the models, though, which we lack. $\endgroup$ – CuriousOne Jun 13 '16 at 18:06
  • $\begingroup$ I tracked down a copy of Ward's book, and I think he is suggesting that $H_2S$ preferentially absorbs red light - this is absorption not Rayleigh scattering. The absorption is very weak, but strong enough that on the scale of many kilometres it would make transmitted light slightly green. I have Googled for details of visible light absorption by $H_2S$ but without any luck. $\endgroup$ – John Rennie Jun 14 '16 at 9:28

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