Is the total amount of water on the planet constant?

  1. Maybe not the correct sub-forum for the question, but is the total amount of water on the planet constant ?

    I know the basics of meteorology and the whole sky, sea and land cycle but we put so much water into the land, how does that water get recycled ?

    If it is constant then why is it still fresh and pure in streams (streams that don't have industrial dumping!) and rivers ?


  2. jcsd
  3. Where do you think the water in streams and rivers comes from?
  4. Chronos

    Chronos 10,348
    Science Advisor
    Gold Member

    It is estimated the earth's oceans have lost about a quarter their water over the past ~ four billion years - The current supply of water on earth is estimated to be around 1.4 billion cubic kilometers.
    1 person likes this.
  5. Borek

    Staff: Mentor

    Some water decomposes (for whatever reasons - high temperatures in volcanoes, radiolysis in high parts of atmosphere), and some of the hydrogen produced is able to escape to space. But we are talking about small amounts, if memory serves me well something like 100kt per year. Oxygen is too heavy for this path.
  6. Chronos

    Chronos 10,348
    Science Advisor
    Gold Member

    Water can be broken down by natural processes into hydrogen and oxygen, as Borek noted. Hydrogen can escape to space, explaining the mechanism for water loss on earth. While hydrogen and helium are light enough to escape into space, Earth's gravity severely constrains the amount of heavier elements that can escape into space. Earth also vast reserves of water trapped in the mantle and this water is slowly released over time, so the surface supply is continually replenished. Water is also supplied to earth via solar system debris. While current contributions are difficult to quantify, it is still widely believed they were a major source of earth's primordial water supply.
  7. That's a geology question. When water enters the ground, it sinks until it reaches a layer of nonporous rock, at which point it's called groundwater. Groundwater slowly makes its way downhill through porous rocks and eventually it empties into the ocean.
  8. It would depend where you are drawing the line.

    If you mean to include the components of water - Hydrogen and Oxygen - then the only losses would be that which escapes the atmosphere into space and that which Man has brought with him on his various explorations off-planet.

    Otherwise, it's all here in some form or another.
  9. If you're talking about manned spaceflight, then I'd expect the water losses to be slight, because most missions never left Earth orbit. The water would have fallen back into the atmosphere. The moon missions may have left some water on the moon, though.
  10. Not just manned.

    I also mean the random water molecules that may have stuck to or in travelers like Voyager, Galileo, Deep Impact, etc.
  11. The solar wind is mostly hydrogen, it's easy to imagine this material getting caught in, and becoming part of our atmosphere. It seems like the quantity of hydrogen we aquire from the solar wind should be constant (neglecting short term fluctuations). The quantity that we lose from the upper atmosphere should depend on the concentration of hydrogen in the atmosphere. Wouldn't the atmosphere settle to an equilibrium concentration where hydrogen in = hydrogen out? Are we at that level?

    Back to the original question about water...
    Similar logic should apply. We lose a certain amount of water to space, we get a certain amount of water from space, there should be an equilibrium level where water in = water out. Is there any reason to believe we are not at that level?
  12. Borek

    Staff: Mentor

    Interesting point. Simple estimate based on geometry - mass of the Solar wind per year of 4×1016 kg, Earth radius of 6731 km, distance of Earth from Sun of 150×106 km - tells me we could catch around 18 kt per year (which would be mostly hydrogen), compared to 100 kt per year that we loose. The signal is obvious - we are loosing.

    Where is the water in space? Or more precisely - where is the oxygen? Solar wind is mostly hydrogen (protons and electrons) as far as I am aware.
  13. OmCheeto

    OmCheeto 2,240
    Gold Member
    2014 Award

    And what about the production of H2O from burning hydrocarbons?
    I can't find a number for annual water vapor generation, but according to the EPA, we generated about 5.7 billion tons of CO2 in 2010.
    Even if all of that CO2 was generated by burning coal, that would be close to 1 billion tons of water produced per year.
    Though according to Chronos's link, there is over a billion times that amount already here.
  14. OmCheeto

    OmCheeto 2,240
    Gold Member
    2014 Award

  15. The water in the streams and oceans evaporates, and this distillation process purifies the water. The contaminants are not, for the most part, able to evaporate with it. It then forms rain droplets in the atmosphere which return to earth as uncontaminated water. Of course, I'm sure you've heard about acid rain. In this case, acidic species in the atmosphere dissolve in the rain drops and return to earth. That's why it's important to minimize air pollution.

  16. Dotini

    Dotini 756
    Gold Member

    "The process of solar-wind hydrogen ions reacting with oxygen in silicate minerals is ubiquitous throughout our solar system, and we can expect that any other star producing a stellar wind with hydrogen ions will be irradiating silicate minerals in dust and on airless bodies in its vicinity, also,"
    "In no way do we suggest the amount of water from solar wind-irradiated dust was sufficient to form oceans," Ishii said. Still, "because the rainfall of interplanetary dust has been continuous, the cumulative amount of solar-wind–produced water may well have been significant."


    The solar wind (SW), composed of predominantly ∼1-keV H+ ions, produces amorphous rims up to ∼150 nm thick on the surfaces of minerals exposed in space. Silicates with amorphous rims are observed on interplanetary dust particles and on lunar and asteroid soil regolith grains. Implanted H+ may react with oxygen in the minerals to form trace amounts of hydroxyl (−OH) and/or water (H2O). Previous studies have detected hydroxyl in lunar soils, but its chemical state, physical location in the soils, and source(s) are debated. If −OH or H2O is generated in rims on silicate grains, there are important implications for the origins of water in the solar system and other astrophysical environments. By exploiting the high spatial resolution of transmission electron microscopy and valence electron energy-loss spectroscopy, we detect water sealed in vesicles within amorphous rims produced by SW irradiation of silicate mineral grains on the exterior surfaces of interplanetary dust particles. Our findings establish that water is a byproduct of SW space weathering. We conclude, on the basis of the pervasiveness of the SW and silicate materials, that the production of radiolytic SW water on airless bodies is a ubiquitous process throughout the solar system.
  17. Borek

    Staff: Mentor

    Interesting. Still, I wonder if amount of water that we could get on Earth from such a source now (I mean: in today's Solar system) is large enough to be significant in the context of the thread.
Know someone interested in this topic? Share this thead via email, Google+, Twitter, or Facebook

Have something to add?

Draft saved Draft deleted