Why is the ocean salty?

The ocean gets salty because rain washes tiny bits of salt and minerals from the land into rivers, and then those rivers carry them all the way to the ocean. When the sun shines on the ocean, the water turns into vapor and goes into the sky, but the salt stays behind, making the ocean saltier over a very long time. Isn't it cool how nature works like that?

The main concept simplified out here is the detailed chemical process of weathering and the specific types of salts (like sodium chloride) that accumulate. At this depth, the idea that rain 'picks up' salt from rocks is sufficient and relatable. You could revisit it when discussing chemistry or geology.

The ocean's saltiness primarily comes from the weathering and erosion of rocks on land. Rainwater, which is slightly acidic, dissolves minerals containing salts as it flows over rocks and soil. These dissolved salts are then transported by rivers and groundwater to the oceans. Over millions of years, as water evaporates from the ocean's surface to form clouds and rain, the salts are left behind, gradually increasing the ocean's salinity. Volcanic activity, both on land and under the sea, also contributes minerals.