Why is the sea salty?

If you have ever swallowed a mouthful of sea water by accident — yuck, so salty! But the rain that fills the sea is not salty at all. So where does all that salt come from?

Salt hides inside rocks

You might be surprised to learn that there is salt tucked away inside rocks and soil all over the land. It is there even in the ground under your feet.

When rain falls on the land, it soaks into the rocks and washes out teeny bits of salt. Streams and rivers then carry that salty water downhill, all the way to the sea.

The sea keeps the salt

Rivers pour into the ocean day after day, year after year, always bringing a little more salt. But here is the clever part: water leaves the sea by evaporating — the sun warms the surface and turns water into invisible vapour that floats up to make clouds.

The thing is, only the water floats away — the salt is left behind. The salt cannot evaporate, so it stays in the sea and slowly builds up.

A very long time

This has been happening for millions and millions of years. Drip by drip, river by river, the salt has piled up until the whole ocean tastes salty.

Wonder fact: If you spread all the salt from the sea evenly over the land, it would make a layer taller than a 40-storey building!