Why is the ocean salty?

   Salt comes from rocks. It has to be loosened from solid rock and washed down to the ocean. Heat and cold, freezing and thawing, make cracks in the rocks, and rain washes the salt out.
   Every year rivers carry tons and tons of salt, dissolved in water, down to the sea. And yet oceans do not get any saltier. Scientists believe that the water is just about the same now as it was two billion years ago. They aren't quite sure how this can be so. Perhaps all the plants and animals that live in the ocean use up some of the salt.