Question submitted by Scott Dennison. As you know, sea water is a solution of many different salts.
Salts are ionic compounds that often dissolve readily in water.
In the oceans, sodium and chloride ions, which form ordinary table salt, are the most abundant. The large majority of solutes come from the mineral constituents of the planet. While pure table salt dissolves quickly in water, most rocks do not. However, given enough time and energy, even stone will wear down and in doing so release soluble constituents. This is called erosion.