At some point, all that carbon we're emitting was originally in the air. The fossil fuels are from old plants, the plants took the CO2 out of the air and turne

At some point, all that carbon we're emitting was originally in the air. The fossil fuels are from old plants, the plants took the CO2 out of the air and turned it into carbon-based biomass via photosynthesis. A question I don't have the answer to - at that time when all that CO2 was still in the air, what was the CO2 concentration and what was the temperature? And if the two are causally related, would we be OK if the Earth reverted to that state? A flippant point... would someone like Burt Rutan whose life's mission is to build innovative aircraft running on fossil fuels be OK with the notion that fossil fuels were messing up the planet?