Oceans get their salt from minerals and sand. Rivers pick up minerals, and dump them, along with water, in the ocean. Water evaporates from the ocean, leaving the minerals behind. Over a long period of time, more and more minerals are left in the ocean, making up the salinity. Salinity of the ocean is measured in parts per thousand.

The ocean is comprised of almost every element in the system, however, the most common elements in seawater are the major gases: nitrogen, oxygen, and carbon dioxide. In addition, chlorine ions, sodium ions, sulfur oxide ions, magnesium ions, calcium ions, and potassium ions are quite common in seawater.

Density difference in water makes the water layer. Heat makes water less dense because the water expands as it heats up. Cold water...