Why is the ocean salty?

Why is the ocean salty? Rivers discharge mineral-rich water to the oceans is from outflow from rivers, which drain the landscape, thus causing the oceans to be salty.

(July-September 1973) --- A vertical view of the Montevideo, Uruguay area of South America is seen in this Skylab 3 Earth Resources Experiments Package S190-B (five-inch Earth terrain camera) photograph taken from the Skylab space station in Earth orbit. The large body of water is Rio de la Plata which flows into the South Atlantic Ocean at the bottom of the picture. The red plum in the Rio de la Plata is probably sediment moving seaward. The Santa Lucia River enters the Rio de la Plata west of Montevideo and is the major drainage for the region. Note the small Isla del Tigre at the mouth of the Santa Lucia. The white beach and sand dune areas are plainly visible along the coast. A major airport can be seen immediately east of downtown Montevideo. Major thoroughfares and residential areas, such as the bright one in the suburbs, are clearly visible, also. Farm tracts in green and grey rectangular patterns indicate agricultural regions. 

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