Why is the ocean salty?

1rain on rock

The ocean wasn't born salty. Rain falling on rock is the real starting point of this story.

2weathering

Rainwater is slightly acidic, so it slowly dissolves tiny bits of salt and minerals right out of the rock.

3rivers carry it

Rivers carry those dissolved minerals — sodium and chloride, the two that make table salt — down to the sea.

4the ocean basin

They pour into the ocean — a huge basin. But here's the key part: the sun evaporates pure water back into the sky, leaving the salt behind.

5salt stays

Salt doesn't evaporate — so every river trip adds a little more, and over hundreds of millions of years it built up to today's 3.5 percent salt.