The Development of Earth's Hydrosphere

All water on Earth is part of the hydrosphere, 97%-is in the oceans the remaining 3% is contained in groundwater and in the atmosphere. But where did it come from? As Earth cooled water vapor, release through outgassing, condensed and surface waters began to accumulate. Another source of water vapor, and eventually liquid water, was meteorites and icy comets. It is not known whether outgassing or meteorites and comets was more important, but we do know that oceans were present by the early Archean. Although the extent of this early ocean is not known we can now imagine an Archean Earth with numerous erupting volcanoes an early ocean and undergoing a period of intense meteorite and comet bombardment.

As water accumulated on the surface it would have interacted with minerals just as it does today and some minerals would dissolve within the water. Once dissolved, minerals would contribute sodium (Na) Magnesium (Mg) calcium (Ca) and iron (Fe) to the water producing salty water. These early oceans were probably just as salty as they are now since mineral solubility does not change over time and chemical equilibrium would have been achieved relatively quickly and remain in near-equilibrium conditions ever since.