Many don't know why ocean are salty but here is the reason.
Rivers Flow from mountain lakes to the oceans. As the river flow over the land, they carry materials from the land. Some of these materials are salts. The salts are dissolved in the water. One kind of salt rivers carry is sodium chloride. When river empties into an ocean, the salt mixes with the ocean water.
Ocean water is heated by the sun. As ocean water is heated it evaporates leaving behind a more concentrated solution of salt and water.
Why don't the oceans dry up?