Why is the sea salty?

“Why is the sea salty in the first place?”

Rain dissolves components of rocks. Rivers carry them to the sea; the seafloor adds some too. Water evaporates, but salts remain.

“So, rocks become salty when they dissolve?”

Not every rock becomes salt. Among the dissolved components, sodium and chloride help make seawater salty.

“Has the sea always been salty?”

Ancient seas also contained salts, but their exact saltiness is uncertain. Salts enter the sea and also leave it through rocks and minerals, so the sea does not simply keep getting saltier.