Take a mouthful of seawater and you taste salt. But here’s the twist: that salt didn’t start in the ocean. It started on land.
Rain is a slow sculptor
Rainwater is faintly acidic. As it falls on rocks and soil, it dissolves tiny amounts of minerals — including the components of salt. Rivers then carry these dissolved minerals steadily downhill toward the sea.
The salt checks in, but never leaves
When that river water reaches the ocean and evaporates back into clouds, the water leaves but the salt stays behind. Repeat this for hundreds of millions of years and the dissolved salts pile up, making the sea progressively saltier.
Help from the deep
Land isn’t the only source. Underwater volcanic vents and hydrothermal springs on the sea floor add minerals directly to the water too.
Why don’t lakes get salty?
Most lakes have rivers flowing out of them, carrying minerals onward, so salt never builds up. The ocean is the end of the line — there’s nowhere left for the salt to go.
Photo: public domain.