How does salinity occur?
There is a lot of salt present in the crust of the earth. When it rains, the rains take the salt into solution, and that rain washes it downhill to the lowest place the water can go – the ocean. The water is taken up into the atmosphere through evaporation in what is called the water cycle. The water then condenses and it rains. Rain on land takes more salt into solution and washes it down to the sea. The water does not take the salt (or any other dissolved minerals) with it when it evaporates. The seas collect salt and become salty. Salinity has occurred.
