If you’ve ever tasted a tiny drop of ocean water (yuck!), you know it’s incredibly salty. But why? After all, rivers aren’t salty, and rain isn’t salty. So where does all the ocean salt come from?
It All Starts on Land
When it rains, raindrops absorb a tiny bit of carbon dioxide from the air. This makes the rainwater slightly acidic — not enough to hurt, but enough to slowly dissolve minerals from rocks and soil.
Rivers Carry It to the Sea
As rivers flow toward the ocean, they pick up these tiny bits of dissolved minerals — including sodium and chloride, which together make salt (NaCl).
Rivers do contain salt, but it’s such a tiny amount that you can’t taste it.
The Big Difference
Here’s the key: when ocean water evaporates (turns into water vapor and goes back up to make rain clouds), the salt stays behind. The water leaves, but the salt doesn’t.
Over millions of years, more and more salt has built up in the oceans while rivers keep delivering more.
How Salty Is It?
🌊 The average ocean is about 3.5% salt. That means in 100 cups of seawater, there’s about 3.5 cups of salt!
🏊 If you could remove all the salt and spread it on land, it would cover every continent in a layer 150 meters thick.
🍳 The Dead Sea is so salty that you can float in it without swimming.
So the ocean is salty because of billions of years of rain, rivers, and evaporation — Earth’s natural salt collector!
