After the Giant Impact.

After the Giant Impact, earth had no atmosphere. On the land, volcanic eruptions created gas. Also, due to a large amount of asteroid and comet collisions, ice has been formed. This ice has combined with the gas that the eruptions created. 4.2 billions years ago, our oceans began forming. As the earth cooled, due to the ice, clouds formed in the sky. These clouds then created rain, which created our oceans. This put water vapor in our atmosphere. Our atmosphere contained Water Vapor, Nitrogen, and Carbon Dioxide, among other gases.