One inadvertent taste of seawater at the beach confirms the saltiness of seawater, a testament to its chloride content. Evaporite salt deposits of the geosphere are formed when seawater evaporates in isolated marine basins, forming massive deposits of salt minerals. Chloride minerals from brines and salt deposits are sources of chlorine for the chemical industry. Salt deposits are called salt domes when, over the course of millions of years, they slowly migrate into dome-like shapes, rising buoyantly due to their lower density in comparison to the sediments around them. During this slow upward migration, salt domes trap oil and natural gas in surrounding sediments and rocks, forming economically important deposits of these energy resources.
Scientists believe that chlorine is also enriched in inaccessible regions deep in the Earth.
Weathering of surface rocks and minerals over millions of years yields great quantities of dissolved chlorine to rivers. Rivers drain the Earth s surface, transporting huge amounts of dissolved and particulate matter to the oceans. By this process Earth s oceans have become great chemical sinks for chlorine. While this chemical fate for chlorine has been well-documented by Earth chemists, known as geochemists, for some time, recent attention focuses on some of the lesser known, supporting roles for chlorine in the natural world. Oxygen is an essential component of respiration for humans and terrestrial animals.