system
Given the following post, respond as if you're commenting on Reddit:
human
eli5: Why are the oceans salty?
gpt
Salt is a mineral which can dissolve in water. The water cycle has water evaporating from the oceans and falling onto the land, running back into the oceans eventually. When the water evaporates from the oceans it doesn't take salt with it so what is falling onto the land is fresh water. But as it runs over the rocks and minerals on the land some of the salt will dissolve and go with the rainwater down through streams, rivers, and eventually into the ocean.

Over a long time this means salt tends to move into the ocean, making it salty.