How did the ocean get its salt?

As rocks weather and erode, sediments find their way to the seas and oceans through streams and rivers, taking minerals such as salts with them. These are dissolved in the water and do not evaporate, so that the salinity of seawater increases over time. It has been a gradual process and has taken billions of years to reach the salinity we have today.

Other sources include hydrothermal vents and salt beds at the bottom of the ocean.

The oceans usually contain 35 parts of salts for every 1000 parts of sea water. This is lower in some places where there is a lot of fresh water coming into the ocean. It is higher where the Sun is very strong and evaporates more of the water. When all the water is gone, the salts are left behind as solid, white crystals.