Salt(sodium chloride)
1. Through a process called weathering, water will dissolve some of the minerals present on the Earth's crust and will carry these elements to the ocean. Sodium and Chlorine are light elements that are abundant on the crust, that is why they are the main constituent of minerals(mainly salt) in sea water.
2. Due to the cycle of water (evaporation-cloud formation-condensation-precipitation-runoff-ocean) the salts will concentrate on the ocean. When water evaporates the salts are left behind, and since the ocean has no outlet, the salts will concentrate.