Coal and oil are essentially the same with differnt energy densities. They are stored solar energy.
Trouble of course is the time it took to store that solar energy, is much greater than the rate we extract it at.
Next phase after harnesing carbon, is suppose to harnessing the energy of the planet
At which point we become an interplanetary species and the next level of advancement is the energy of the sun
I mean that in reference to the The Kardashev Scale if you buy into it
oh, maybe not, that starts at harnessing some of the neighboring star's energy (like photovoltaics, only efficiently), hmmm. I cant recall what scale I am thinking of now, but we are a class 0 civ on that scale
Of course its all just philisophical, we dont know what comes next
We have not advanced past harnessing the energy in the complex long chain energy stored in carbon
