• Primary accretionary atmosphere acquired during the accretionary process. This was mostly He and H₂ which was lost early on as these gasses are not easily held by Earth's gravitational pull. Excess volatiles form atmosphere of CO₂, N₂ ,Ar₂,H₂O and a water ocean.
• Secondary atmosphere formed by outgassing as the early Earth began to differentiate.
• Biologically modulated atmosphere formed during changes brought about by physiological processes, esp. oxygenic photosynthesis.

Timing:H₂O present as steam if surface temperature is over 100°C but metasediments occur at 3.85 Ga in Isua (Greenland)so oceans must have been cooled by then, i.e. shortly after the end of the meteoritic bombardment.

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