Why is the ocean salty?
Rivers did it, over about four billion years. Rain is very slightly acidic from dissolved carbon dioxide, and as it flows over land it erodes rock and carries dissolved minerals, sodium among them, to the sea. Undersea volcanic vents contribute more, including chloride. Then the trap closes: water evaporates from the ocean and returns as fresh rain, but the salts cannot evaporate, so they stay and concentrate. The ocean is the planet's drain, and salt is the residue of everything ever washed down it.
The result is water that is about 3.5 percent salt by weight. If you extracted all of it, USGS estimates the salt would blanket every continent roughly 500 feet deep.
Rivers taste fresh only because they are conveyor belts, not storage: their minerals pass through en route to the sea. And lakes with no outlet, like the Great Salt Lake and the Dead Sea, run the same experiment on fast-forward, which is exactly why they out-salt the ocean itself.
Rain has spent billions of years dissolving minerals out of rock and rivers have delivered them to the sea, where water evaporates but salt cannot. The ocean is Earth's drain, and salt is what stayed.
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https://frequentlyaskedquestions.us/q/why-is-the-ocean-salty/Everybody Asks. (2026, July 28). Why is the ocean salty? https://frequentlyaskedquestions.us/q/why-is-the-ocean-salty/“Why is the ocean salty?” Everybody Asks, 28 July 2026, https://frequentlyaskedquestions.us/q/why-is-the-ocean-salty/.“Why is the ocean salty?” Everybody Asks. Last modified July 28, 2026. https://frequentlyaskedquestions.us/q/why-is-the-ocean-salty/.This page summarizes the primary sources listed above. For academic or encyclopedic work, cite those primary sources directly wherever possible.