Other contributors have said "What is the make up of the early atmosphere?" is the same question as "What was the early atmosphere made out of?" If you believe that these are not asking the same thing and should be answered differently, click here
The atmosphere is made up of 4 main and 4 minor layers. The 4 main layers are: The Troposphere The Stratosphere The Mesosphere The Thermosphere The 4 minor layers are: The Ozonosphere ( in the...
Well, nobody knows for sure, but the most likely theory is that photosynthesis by cyanobacteria (blue-green algae) was what started the rise in atmospheric oxygen levels; some could also have been...