Rivers taste fresh, but the ocean they flow into is salty. Here is where all that salt comes from.
Where does salt come from?
Rain is a tiny bit acidic, so it slowly wears away rocks. That frees tiny bits of salt, and rivers carry them to the sea. Rivers keep flowing, so the salt never has time to pile up. Hot vents and volcanoes on the sea floor add some minerals, too.
Why does it stay there?
The sun lifts water out of the ocean, but the salt stays behind. That water falls again as fresh rain, and the cycle keeps going. Over millions of years, all that salt built up. Spread over all the land, the ocean's salt would pile up about as high as a 40-story building.
Sources
- NOAA: Why is the ocean salty?
- USGS FAQ: Why is the ocean salty?
- USGS Water Science School: Why is the ocean salty?
- Natural History Museum: Why is the sea salty?
- NSTA: Science 101: Why are oceans salty and lakes and rivers not?
- Live Science: Why Is the Ocean Salty?
- Science Notes: Why Is the Ocean Salty but Lakes and Rivers Are Not?
- NASA Aquarius: Salinity FAQ
