"I suspect it will be in billions of years when the sun goes red giant. If you are referring to some ridiculous Biblical 'prophecy'....
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Every year the earth's oceans waters gets a little bit saltier. In time all the oceans will become just as salty as the Salton Sea is, the Great Salt Lake is, and (eventually) the Dead Sea is.....and that will have a horrible effect on life on this planet as we know it, and not just in the oceans. 
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If you believe that the oceans have been around for billions of years, you might think that that is another problem we don't have to worry about for millions of years. But if, if, if, the earth is only 6,000 years old and the oceans started out with "fresh" water, then the time-frame to "be concerned" is a whole lot less.
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But even the Bible "accurately prophesied" about your own skepticism.
"Where is the promise of Jesus's coming, since things go on as they have always gone on?" is in the Bible...and it's "one of the signs."