How much CO2 in the early earth's atmosphere?

[AFJ]

The predominate hypothesis on earth's early atmosphere is that the earth degassed through volcanoes. It was CO2, N, H2O vapor, and methane and some others I believe--no oxygen gas. Has there been any estimates on the amount of CO2 that would have been in the atmosphere? I would assume it would have been alot, if we go by how much CO2 comes out of current volcanoes. Wouldn't that have caused the Earth to be very hot. By what mechanism, then did the earth cool in order for the oceans to form?

[phamquocdat41191]

(sorry if my english is not good)
only 0.038% carbon dioxide in earth's atmosphere. Don't worry much about that. Besides, CH4 causes greenhouse effect 20 times than CO2.
"By what mechanism, then did the earth cool in order for the oceans to form?" I don't understand this question, could you clarify for me??? Is it about earth's history???

[futurezoologist]

By what mechanism, then did the earth cool in order for the oceans to form?

The air would be so saturated with H2O that there would be huge amounts of condensated water on the earths surface. Think of it like this if you bunged a test tube (hard enough so that it wouldn't pop off when heated) quarter filled with water and heated it steadily it would be impossible for all the water to evaporate so it would reach an equilibrium where the net movement of water into and out of the liquid state would be equal. In the earths case the bung would represent gravity.

After hundreds of millions of years photosynthesizing organisms began to populate the oceans(because there was no oxygen and therefore no ozone layer so anything on land would be destroyed by the huge amounts of UV radiation), these organisms slowly turned CO2 into O2 which was able to turn into ozone(O3) when combined with single oxygen from the photodissociation of water from UV light. This slowly created an ozone layer which blocked the UV light so that plants could dominate the land as well and subsequently lower the CO2 levels even more.

Im not sure of the percentage of CO2 in volcanic gases or in the early earths atmosphere but i hope this helps.

P.S phamquocdat is talking about present levels of CO2