Why is the ocean salty?

The saltiness of the ocean primarily comes from two sources: rocks on land and openings in the seafloor.

1. Runoff from land: As rain falls, it is slightly acidic because it absorbs carbon dioxide from the atmosphere. When this rainwater lands on rocks, it gradually breaks them down through a process called weathering. This releases minerals—including salts—into the water. These minerals are carried by rivers and streams into the ocean.
2. Seafloor openings: Salt also enters the ocean through hydrothermal vents and volcanic activity on the ocean floor. Water seeps into cracks in the ocean crust, gets heated by magma, and dissolves minerals from the surrounding rock before venting back out into the seawater, carrying those dissolved substances with it.

Once these salts reach the ocean, they stay there. Water evaporates from the surface to form clouds, but the salt remains behind, causing the concentration to build up over millions of years.