Formation of Earth�s Atmosphere:
1) Earth formed by collision of planetisimals
2) Internal heat in Earth began to escape from volcanoes
3) Nitrogen, carbon dioxide, water vapor, hydrogen, carbon monoxide, and helium
escaped from volcanoes through outgassing.
4) Water vapor then condensed and for millions of years formed oceans, rivers, and
lakes.
5) Carbon dioxide then began to dissolve due to oceans so there was more water
vapor to be found.
6) Highly energetic sunlight splits (disassociates) water vapor into hydrogen and
oxygen. Much of the hydrogen floats up into space due to its low density.
7) More oxygen was produced as plants developed on Earth
8) Oxygen reached levels near what it is today several hundred million years ago.
Most abundant gases in the atmosphere:
1) nitrogen
2) oxygen
3) trace gases (argon, carbon dioxide, hydrogen and many others)