The sea wasn't always salty. It's been getting saltier over millions of years as minerals dissolve.

Is there a natural limit to this process, or the will the sea keep getting saltier forever?

Is there a natural process which removes salt from the sea at a significant rate?

How long would it take for the sea to get too salty to support life as we know it?

  • 1
    $\begingroup$ Don't know about the sea, but humanity at least will. $\endgroup$ – Erik Nov 3 '20 at 15:05
  • $\begingroup$ Life adapts to gradual changes , so it is never going to be too salty for life. $\endgroup$ – blacksmith37 Nov 4 '20 at 3:01
  • $\begingroup$ @blacksmith37 hence "life as we know it" $\endgroup$ – spraff Nov 7 '20 at 10:13

No there are natural processes that remove salt as well.

as sea level changes water gets trapped in basins and evaporates leaving the salt behind, this is where many of the salt formation on earth came from. whenever sea levels fall the salinity of the ocean drops. Tectonically isolated basin can remove salt in the same way. The process can even happen repeatedly in the same basin as sea level changes.

There are biological processes that remove it as well the formation of shells and limestone remove some of the ocean salts.

Can it increase yes, but it can also decrease, over earths history there have been saltier and less salty periods.

  • $\begingroup$ i think there is a typo in your answer,when sea level drops the remaining salt in the oceans gets more concentrated. $\endgroup$ – trond hansen Nov 4 '20 at 5:27
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    $\begingroup$ @trondhansen No when seal level drops sea water gets trapped in evaporating basins which recycles water through rain but leaves the salt on the land. there are salt deposits all over the globe that formed this way. $\endgroup$ – John Nov 4 '20 at 5:33
  • $\begingroup$ It is common for oil and gas deposits to be found in the vicinity of evaporite beds buried in the earth many millions of years ago. Salt domes are a classic structure to have related oil/gas. $\endgroup$ – blacksmith37 Nov 4 '20 at 22:06
  • $\begingroup$ @blacksmith37 fair point, I will change it to "many", although many salt domes still source their salt from sea evaporite beds, marine life is trapped just like the evaporating seawater and the dome catches the petrochemicals the same way it does the salt leading to higher concentrations. $\endgroup$ – John Nov 5 '20 at 3:20

@John has answered to the second question: "Is there a natural process which removes salt from the sea at a significant rate?" This is an answer to the first one: "Is there a natural limit to this process, or the will the sea keep getting saltier forever?"

Yes, there is a limit, sea water cannot keep getting saltier forever.

Sea water is a solution of water and salt, i.e., the salt is dissolved in the water. But solubility, the ability of a material to dissolve in another, has a limit called saturation. Once this limit is reached, the material cannot dissolve anymore and precipitate.

Saturation of salt in water is 357 g L$^{-1}$ (at 20 °C, it depends on temperature), about 10 times the current salinity of seawater. If you keep adding more salt to such water, it will not longer be able to dissolve but will instead precipitate at the bottom of the sea.


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