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An ocean began to form on Earth as soon as the temperature fell from very hot, to about room temperature, a temperature where liquid water is stable. According to the
Goldilocks theory, Earth is at just the right distance from the sun for the temperature of the surface to be appropriate for the formation of liquid water. The presence of running water influenced the rest of the gases in the atmosphere, which began to dissolve into the forming ocean. By this time Earth was busy generating its secondary atmosphere. These atmospheric gases came out of a volcano. All volcanoes are different but in general those gases would include H2O, CO2, SO2, H2S, HCl, N2, NO2.
The process of dissolving was dictated by a chemical balance called "Henry's Law". Henry's Law states that
- The amount of dissolved molecules of a particular species that will form in water depends upon the pressure (the weight) of that species of gas in the atmosphere (how much of it is in the atmosphere) times the solubility properties of that species (how readily it will dissolve).
Gases such as CO2, SO2, and HCl form acids when dissolved in water. These acids would be HCO3-, HSO3-, and H3O+. Such acids would immediately be neutralized via reaction with the surface minerals of the Earth, but the addition of so much acid to both the land and sea changed the pH of the ocean and surface from a reducing environment (hydrogen-based) to an oxidizing environment (oxygen-based).
Scientists think that the Earth's secondary atmosphere may have come to be dominated by N2 because it alone does not readily dissolve in water.
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