In case you missed it, Part 2 addressed a big question: Are we oxygen breathers important to life on Earth, with respect to life, happiness, temperature, and gas ratios?
The answer is a resounding NO! But we just couldn't leave all those yummy plants lying around. :)
Obviously, when we are talking tiny percentages, we moderns can screw things up with ddt, plastic, and ozone poison (questionable).
Interlude From a Heckler: Hey, if this is all so gosh darn obvious why hasn't anybody stood up?
Would you, Sir? Would anybody? Feynman is dead, and he is only one in all the NASA bullshit that put the o-ring into the ice water. Nobody is into classic physics any more, they are all super-specialists sucking off the dole. We are talking certain suicide here, since 'they' would say: "Oh, your third cousin works for an oil company."
(It's left up to a crazy guy, who is happy that nobody listens to him)
It's amazing that when we talk of Earth processes, we think of uncertainties of a factor of ten or more, yet our gas ratios are held to with one percent.
So, we ask ourselves: Without humans burning oil, how can plants even exist? or grow. How could we have had something like the Carboniferous which gave us all our oil and coal to burn anyway?
The answer my friend, is the point of all this mess - The Large Carbon Cycle.
We know from the Earth's beginning that co2 could go all the way to 100% and the plants would be happy. They produce their own waste, which is oxygen, and is the equivalent of peeing in the pool. At 20% they poison themselves out. Yet, they would merrily overgraze and reduce the co2 to zero, if they could, just like sheep overgrazing the hill. So, they are on the balance of death, like wild Bighorn sheep on the mountains.
What gives them that little puff of co2 to live? We must go back to the beginning again, to the methane world, and the first plate tectonics.