Ocean Salinity

Salts do enter and form in the ocean, but they also leave it. Ocean salinity has been stable for billions of years. The two major processes capable of removing significant amounts of salt from the ocean are the formation of evaporites (rocks that form when restricted, salty water evaporates) and the sequestration of brine as groundwater on the continents. It's actually been proposed that the early ocean was saltier than today (maybe up to twice as salty). Salt was removed from the oceans over geologic time as the Earth cooled and the continents grew, providing more space favorable for salt/evaporite deposition and the formation of saline groundwater. It's been argued that modern-day salinity wasn't reached until relatively recently, perhaps playing a role in the origin and radiation of animal life (known as the Cambrian Explosion).