From where does sea water get salt?
The salt in the oceans came originally from rocks. Rain can dissolve some of the minerals found in rocks, especially rain that is slightly acidic from dissolved $\ce{CO2}$. The chemicals in the minerals are broken down into ions in solution. Some of the ions will tend to precipitate out of solution, or be taken up by living things (for example calcium is removed from water by the shells of molluscs and diatoms). Other ions will tend to build up in the water. Two of the most soluble and common ions are sodium and chloride. Over time these built up in the ocean. The sodium chloride in sea water is what makes the seas salty.