The current composition of the atmosphere is as a result of CO2 breathing organisms (plants and bacteria) and is composed primarily of a neutral molecule N2 and a POISON. This POISON is O2, and is a waste product of photosynthesis. The evolution of higher lifeforms was a response to the pollution of the atmosphere by early life.
Oxygen breathing life evolved to utilise this waste product and balance the atmosphere. Nevertheless, the CO2 breathing lifeforms have been winning the war of waste products and slowly poisoning themselves. Humans are the final link in the chain, our evolutionary purpose is to change the balance of power, and reverse the trend of lower CO2. We need to release fossil CO2 to the atmosphere so that the cycle of life can continue.