Where does the salt in the oceans originate? Are the oceans getting saltier and saltier with time? If not, then why not?

Question

What will be an ideal response?

Answer 1

The salts contained in seawater are largely the result of the weathering of crustal rocks. The oceans are not getting saltier, because many processes also remove salts from seawater. These processes include the following:

i. Evaporation of seawater from shallow seas. The remaining salts are concentrated and precipitate from solution as evaporite deposits, such as halite (table salt, NaCl) and gypsum (CaSO4?2H2O).
ii. Biological processes. For example, some marine organisms remove the elements calcium or silicon from seawater to form their shells, some of which are eventually deposited in ocean sediments.
iii. Chemical reactions between seawater and newly formed volcanic rocks on the sea floor.
iv. The formation of sea spray. As small droplets of seawater become airborne, salts, especially sodium and chlorine, are removed when the spray is deposited on land. These salts are eventually returned to the oceans via rivers.

Overall, salts are removed from seawater at a rate that essentially equals the rate of input, when averaged over geologic time scales (millions of years).