The US Geological Survey gives a slightly more nuanced answer (https://water.usgs.gov/edu/whyoceansalty.html https://water.usgs.gov/edu/whyoceansalty.html), bas

The US Geological Survey gives a slightly more nuanced answer (https://water.usgs.gov/edu/whyoceansalty.html https://water.usgs.gov/edu/whyoceansalty.html), based (as I understand it) on comparatively recent progress in understanding this question. It turns out that in addition to the "standard" explanation that the oceans' salt comes from rain dissolving rocks on land, another quite important contributing factor is the activity of hydrothermal vents on the ocean floor. As I understand it, the high temperature of the water emerging there helps it to carry very large amounts of dissolved minerals from deep in the crust back into the sea (and that our models of ocean salinity wouldn't work without this contribution).