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Thread: Is amount of water on earth a constant?

  1. #1 Is amount of water on earth a constant? 
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    is there a constant amount of water on earth, generally speaking? is water being created in any significant amount by natural forces? is water being destroyed in any significant amount by natural forces? by destroyed i mean broken down into O and H.


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    Evaporation and condensation are the greatest manipulators of water on the planet in terms of volume. As for the creation of water, innumerable natural processes produce it as a side reaction. It's pretty negligible as it is cancelled out by processes that "destroy" water.

    A certain amount of water is "destroyed" by plants in the process of photosynthesis, where carbon dioxide and water are reacted to form glucose. I suppose you could include scientists carrying out electrolysis reactions too...


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    I can't say for sure, but I think Quinta is referring to a more encompassing view of water on earth. While water itself will change forms quite often, its constituent particles will (in almost all cases that don't involve fission or fusion reactions) stay relatively constant. The only way we would lose hydrogen and oxygen molecules would be from nuclear reactions, or being brought into space (by astronauts, for example).
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    I can throw out one idea - we do lose some atmosphere even with our magnetic field. And in the coming few centuries when it completes the polarity flip, we'll lose even more per time. I doubt it's very significant, I don't even know if water concentration is that high that far up.
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    Not exactly. At high altitudes a small amount of water is dissociated into hydrogen and oxygen by UV radiation. The hydrogen molecules have a typical range (Gaussian distribution) of velocities. A small number of these molecules are travelling faster than escape velocity and are lost to the Earth.
    The total volume of water lost since the formation of the Earth is small in absolute terms. It has probably been more than exceeded by the water provided by the occassional impacting comet. After all, the majority of the water on the planet probably came from comets during the Late Heavy Bombardment Phase of planetary formation.
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    Ah, my mistake, thanks for the correction
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    My interpretation of Quinta's question is:- is the amount of water (not hydrogen or oxygen) constant? (If I am wrong, it won't be the first time :?

    I can't see that it can be constant. We have all heard of the increase in carbon dioxide levels arising from combustion of fossil fuels, but when hydrocarbons are burnt, the products are not only carbon dioxide but water as well. If there is an increase in carbon dioxide as a result of burning oil and coal, there must surely be a parallel increase in the amount of water.

    Water vapour also absorbs infra-red radiation and is probably classed as greenhouse gas.

    (I'm not a chemist, so please regard my views accordingly)
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    Quote Originally Posted by Old Fool
    If there is an increase in carbon dioxide as a result of burning oil and coal, there must surely be a parallel increase in the amount of water.
    Right, but that water is really being returned to the atmosphere from whence it came millions of years ago. Over a very long time span perhaps the water is roughly constant?
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