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Why are the Earth's oceans and seas full of sodium chloride?

  1. Dec 13, 2016 #1
    Why are the Earth's oceans and seas full of sodium chloride?
    I know there are other salts and compound dissolved in it, but comparatively small amounts.
    Where did all the Sodium and Chlorine originate from?, these are not rare on Earth, but other elements like aluminum are magnesium are in greater abundance and easily make water soluble compounds.
     
  2. jcsd
  3. Dec 13, 2016 #2

    Bystander

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    Read Ch. 6, Mason, Principles of Geochemistry, and come back with something more specific than a "why is there air question."
     
  4. Dec 13, 2016 #3

    davenn

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    can find it online without having to pay for it ... if the OP doesn't come back
    I would be interested in you copying and pasting the relevant section
     
  5. Dec 13, 2016 #4

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    "Can," or "can not?"
     
  6. Dec 13, 2016 #5

    davenn

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    oops .. typo too early in morning

    cannot
     
  7. Dec 13, 2016 #6

    Astronuc

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    http://water.usgs.gov/edu/whyoceansalty.html

    Note we find salt deposits inland. Look at locations of salt mines. Also, note the Great Salt Lake in Utah.

    Look at the abundance of sodium and chlorine with respect to the other elements, and also the solubility of NaCl compared to the salts.

    Also - http://oceanservice.noaa.gov/facts/whysalty.html

    https://en.wikipedia.org/wiki/Seawater
     
  8. Dec 13, 2016 #7
    Ah thanks, I think got it.
    Other elements in sea water tend to be get more involved in reactions that cause them to drop out as sediment, or get used up by life and other things.
    Sodium and Chlorine don't have many sinks once they are there in sea water, so it builds up
     
  9. Dec 13, 2016 #8

    Bystander

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    For your next effort/project explain the relatively short "residence time" of NaCl in seawater, ~70 Ma.
     
  10. Dec 14, 2016 #9
    The abundance of sodium and chlorine in the present biosphere is ultimately due to their behavior in the differentiation of the igneous melts, presumably all the way back to the initial formation of the earth. In basaltic magmas, both elements end up as residual ions in late stage minerals, or more importantly, in residual brines or brine inclusions. Presumably, the brines would have been spewed out of early volcanic eruptions, undersea initially. As a crust developed, brines would have accumulated on land. There they eventually formed salt flats and other deposits, eventually mixing with sediments filling in low elevations. I recall reading that the brines found in inclusions are several times more concentrated than sea water. I'd have to look up some of the theories that try to explain the fate of sodium and chlorine later in sedimentary rocks and the salinity of the oceans. At any rate, the availability of sodium and chlorine seems to have been fixed by their place in igneous differentiation.

    Actually, the first brines might wells have spewed on hardened lava flows before the hydrosphere even developed, making the first oceans somewhat saline.
     
  11. Dec 15, 2016 #10
    It's all about residence time. River water is not dilute sea water. It's a lot richer in calcium and sulfate than sea water. When water reaches the sea, biological and chemical processes remove certain elements. Calcium and silicon are taken out to build shells for organisms. The residence time of calcium, average time a calcium atom stays in sea water, is tens of thousands of years. Aluminum goes into sea floor minerals and has a residence time of only a few hundred years. But very few processes take sodium and chlorine out of sea water, so they tend to accumulate. Both elements have residence times of tens or hundreds of millions of years. So they've accumulated in the sea over geologic time.
     
  12. Dec 15, 2016 #11
    Although there are comparatively few processes that remove Na and Cl from sea water, there are some processes. Marine salt deposits do end up on dry land and some even gets recycled by wind, since sea spray furnishes salt crystals as nuclei for raindrops. A good deal of sea water soaks into the rocks of the sea floor and some re-emerges at hot sea-floor springs. Other water ends up in magma at subduction zones. And if you're hinting at some creationist style complaint that dating methods are inconsistent, bear in mind the residence time is a minimum age for the oceans (pretty much all geologic ages are minimum ages), and is about 10,000 times too long for the creationist time scale.
     
  13. Dec 15, 2016 #12
    http://www.gly.uga.edu/railsback/3030/3030Tres.pdf
    Bruce Railsback is one of my favorite geologists and very highly regarded for his insights and syntheses. In the above link, he calculates the residence time of Na at 72 million years and that of Cl as 130 million years. I am a bit uneasy about these types of calculations and try to avoid problems that require that sort of info. At the same time, Railsback has a fine website on geochemistry:
    Some Fundamentals of Mineralogy and Geochemistry
    http://www.gly.uga.edu/railsback/FundamentalsIndex.html
     
  14. Dec 15, 2016 #13

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    Geochemical "cycles"/stations of the cross --- as long as it's understood there is more than enough room to over-interpret ....
     
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