Earth's early atmosphere contained mainly what gas?
1 Answer
Feb 19, 2016
Earth's atmosphere has changed considerably over geological time, so it depends on what you mean by "early".
Explanation:
Earth's first atmosphere, shortly after the planet formed 4.6 billion years ago, was mostly hydrogen, helium, ammonia and methane.
Between 4 to 1 billion years ago, the atmosphere consisted of nitrogen, water vapour, and CO2. In the last 1 billion years or so, life on the planet transformed the atmosphere into primarily nitrogen and oxygen (see pic).
http://ponce.sdsu.edu/plants_and_animals.html