Question

What phenomenon contributed to the formation of earth's atmosphere?

Answer 1

The quick version of the answer is that the first atmosphere came from volcanoes and was mostly water and carbon dioxide. "Out-gassing" is another term used for this.

Explanation:

The longer version of the answer is that the first atmosphere came from volcanoes and was mostly water and carbon dioxide. As it cooled down it rained and made the oceans and a lot of the carbon dioxide dissolved. Later some types of algae started making oxygen, until eventually the atmosphere was like it is today.

http://science-at-home.org/kid-questions-how-did-the-earths-atmosphere-form/

http://zebu.uoregon.edu/internet/l2.html

http://forces.si.edu/atmosphere/02_02_01.html