1. timberwoof says

    Dramatic. I’d have expected more superficial evidence of blue-green algae. What liberated the oxygen to make the sky so blue?

  2. Andrew Dalke says

    You don’t need oxygen to get a blue sky. Read up on Rayleigh scattering for the details on why Earth’s atmosphere is blue. Scattering isn’t the only factor which can affect the sky color. The current Martian sky color is mostly due to dust in the air, and not from scattering by the very thin Martian atmosphere. According to one source, “After the main part of the protoatmosphere was lost, impact-related volatiles and mantle outgassing may have resulted in accumulation of a secondary CO2 atmosphere of a few tens to a few hundred mbar around ∼4–4.3 Gyr ago.” The current atmosphere is 0.6 mbar, so Rayleigh scattering would have been stronger 4 billion years ago, and I presume the water would have helped reduce the dust load.

  3. lpetrich says

    This video indicates which parts of Mars would be covered by an ocean: ▶ Mars Once had Oceans [HD] – YouTube

    Mars’s former ocean indicates that Mars’s atmosphere was once much thicker that it is today, and thus much warmer. This was despite the Sun being fainter — it was something like 70% – 75% as bright as it is today back then. However, Mars was helped by its obliquity often being relatively large in the past, as much as 60 degrees in various numerical calculations.. When it happened, it gave the poles very warm summers.

    But what was the Earth like 4 billion years ago? It was spinning faster, and the Moon was closer, but I can’t find good numbers on either. The Earth was warm enough to have liquid water, but the Earth was much less familiar otherwise. The Earth’s atmosphere almost certainly had no free oxygen, and it may have contained lots of methane as well as lots of carbon dioxide. The continents were unrecognizable: lots of small ones a few hundred km across that covered much less of the Earth’s surface than the present-day continents.

    Life on the Earth back then? There’s hardly any good fossil evidence or geochemical evidence from back then, and it’s likely that organisms back then were very primitive: chemolithotrophic ones like methanogens.

  4. CompulsoryAccount7746, Sky Captain says

    Article: Wikipedia – Mars’ Noachian Period
    @lpetrich #4:

    But what was the Earth like 4 billion years ago?

    Article: Wikipedia – Earth’s Hadean Period

    * The tail end of that period. Archean was about to begin, which was when cyanobacteria show up.

  5. birger johansson says

    The rocks may have soaked up much of the Martian atmosphere. As for a Martian ocean, it was probably not such a big collection of water. At its wettest, Mars was probably more like Nevada.

    Terraforming enthusiasts have a lot of ideas about how to make Mars hospitable for plants (and maybe humans). Personally I think that would require a brute-force terraforming, diverting ice-rich objects from the Kuiper Belt. It could work but it would take millennia.

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