Earth's Atmosphere

The Earth's atmosphere is mostly nitrogen, with a lot of oxygen too. By numbers of molecules, the composition is

N₂: 79%.
O₂: 20%.
Ar: 1%.
CO₂: 0.04%.
H₂O: up to 4%
Total water, liquid + vapor: a 3 km thick ocean.
Where did this come from?
Gasses emitted by Hawaiian volcanos:

H₂O: 77%
CO₂: 12%.
SO₂: 7%.
N₂: 3%
That gives us plenty of water.
But where did C0₂ go?

One process is that CO₂ can dissolve in water and combine with other molecules to make rocks. (``chemistry'' in the picture.)
Plankton and shellfish in the ocean do the same thing more efficiently.
Plants, bless their hearts, get rid of the carbon dioxide and give us oxygen.

Note one conclusion: were it not for living things, there would be a lot more carbon dioxide in the atmosphere. We should check on this for other planets.

Davison E. Soper, Institute of Theoretical Science, University of Oregon, Eugene OR 97403 USA soper@bovine.uoregon.edu