Logically, if slowly, the sea should get more salty. Extrapolating from a rough average of the minerals now carried by rivers, scientists estimate that it took a hundred million years for the oceans to achieve their present three percent salinity. But oceans have been around for a lot longer than 100 million years. If ocean basins were simply passive receptacles for drainage from the land, the seas should have grown increasingly salty. Because they haven't, we know something else is going on.
Sodium is necessary for all creatures.
Calcium, a common river-borne element, is especially in demand for skeletons and shells. Some magnesium is needed for these structural components as well. While biochemical processes take care of some minerals, geochemical ones account for others. Eventually the residue of these activities lies as sediment on the seafloor, slowly building up. Yet over millennia, neither biology nor geochemistry could control the steady buildup of minerals.