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Accummulation of Gases in the Atmosphere

  1. Sep 2, 2005 #1
    I was reading that helium does not accummulate in the earth's atmosphere due to the fact (a claim) that it is too light to be retained by gravity and diffuses out into space.

    Does anyone know the physics that prevent the atmosphere seeking the vacuum at whooshing out into space.

    Is there a molecular weight cut off that has been theoretically calculated whereby a gas will accummulate in the atmosphere or escape the gravitational pull and disperse?
     
  2. jcsd
  3. Sep 2, 2005 #2
    That's interesting question indeed. I know that for the moist greenhouse gas theory for Venus, it was required that H2 would escape it's gravtitional field, to explain the water to dissapear that would have triggered the heating initially.

    Hypothesis can be falsified easily but anyway.
     
  4. Sep 3, 2005 #3
    .

    So how do you falsify it?

    As I understand the reason that we "know" helium does not accummulate is because we "know"
    1) The earth is x billion years old
    2) The rate at which it is cooling
    3) The fact in order to have the x billion we need an additional source of heat
    4) That source of heat is radiation from the decay of Uranium
    5) That decay produces Helium
    6) But despite large amounts of helium in natural gas and oil there is very little in the earth's atmosphere.

    Ergo it must all escape into space. Or roughly.

     
  5. Sep 3, 2005 #4
    What I meant was falsifying the moist greenhouse theory for Venus of Kastings, Toon and Pollack concerning the diffusion of the H2. I agree on the Helium diffusion.

    But that's off topic here.
     
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