Why is the ocean salty?

Question

askNib · Accepted Answer

The ocean wasn't born salty. Rain falling on rock is the real starting point of this story. Rainwater is slightly acidic, so it slowly dissolves tiny bits of salt and minerals right out of the rock. Rivers carry those dissolved minerals — sodium and chloride, the two that make table salt — down to the sea. 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. 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. The ocean is a giant collecting bowl — rivers keep depositing salt, and only the water ever leaves, so the salt just keeps piling up.