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What is the maximum concentration of NaCl for life in the oceans to be possible?

Was it fortuitous that the concentration was originally no higher, in which case the evolution of life on Earth would not have occurred?

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There are organisms called halophiles which thrive in conditions of high salt concentration - and, indeed, require high salt concentrations in order to grow. According to Wikipedia:

Halophiles can be found in water bodies with salt concentration more than five times greater than that of the ocean ...

Since the earliest life on Earth originated in the oceans over 3.5 billion years ago, it is likely that it was adapted by evolution to suit the salinity of the oceans as they were then. If the salinity of the oceans had been significantly different then life would have evolved in a different direction.

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First thing: the oceans were (probably) much less saline when life first formed. EDIT Well, so much for my ancient primary school data - with thanks to trond hansen for pointing out that

Initial salinity of the oceans was 1.5–2× the modern value and remained high throughout the Archean in the absence of long-lived continental cratons required to sequester giant halite beds and brine derived from evaporating seawater. Marine life was limited to microbes (including cyanobacteria) that could tolerate the hot, saline early ocean.

Living species slowly adapted as salinity, as well as atmospheric and dissolved gas levels, changed over epochs.

Next - there's a maximum salt concentration that water can support in solution. After that it precipitates out, so there's your effective upper bound.

And, dare I say it, "Life, ummm, finds a way."

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  • $\begingroup$ there is room for improvement of your answer sciencedirect.com/science/article/abs/pii/S0031018204005905 $\endgroup$ Sep 13 at 16:08
  • $\begingroup$ Thanks, @trondhansen . I should stick with something I know, i.e. physics. $\endgroup$ Sep 13 at 16:14
  • $\begingroup$ @CarlWitthoft here's an existing answer with a different source that also addresses the relative salinity of Earth's ancient oceans: biology.stackexchange.com/questions/94817 $\endgroup$
    – acvill
    Sep 13 at 20:08
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  • $\begingroup$ Welcome to Biology.SE. Please take the tour and then consult the help center pages for advice on How to Answer effectively on this site and then delete or edit your answer accordingly. In particular, please: 1) focus on clearly answering the original question; 2) don't leave the original incorrect material in your post when editing; and 3) always reference material (e.g. a quote) from someone else. This last is good practice in scientific communication, will help other users understand by providing context, and stops this being plagiarism! $\endgroup$
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