Chemistry-atmosphere
What is the current composition of the Earth's atmosphere?
79% Nitrogen
20% Oxygen
<1% Other gases
How long has the Earth's composition been like this?
200 million years
Why are we not certain why the atmosphere is as it is today
Not enough evidence
What is the volcanic theory
That the earth's atmosphere was very hot and there were lots of volcanic eruptions releasing CO2, other gases (such as ammonia and methane) and water vapour. The water vapour cooled to form oceans. Nitrogen is also unreactive so it built up.