The ocean contains salty water and behind such saltiness there are a few reasons. Firstly, rain when falls on earth contains the dissolved form of carbon-dioxide which causes rainwater to be acidic in nature and also contains carbonic acid. The rain when erodes the rock, the acid present in it, breaks down rocks chemically and carries salts and minerals along with it as ions. It goes to some river and then merges into the sea later. Unused ions get dissolved into the sea and salt is added.
The second reason is hydrothermal vents (exit point on ocean floor). From vents sea water seeped into the rocks of ocean crust and reaction takes place between sea water and the rock of ocean crust. As a result, the dissolved form of minerals and salt comes out and gets added to water. The saltiness of the sea always gets increased. One cubic foot of average sea water contains 2.2 pounds of salt.
