Replacing Fossil Fuels: Energy Evolution Has Happened Before If renewable energy replaces fossil fuels as our main source of energy it won't be the first time a fuel source was rapidly replaced. On the surface, energy seems like a pretty stagnant industry these days. Oil has dominated transportation for most of the last century while natural gas and coal provide a vast majority of the electricity we consume. That's not all that different than the way things were at the turn of the 20th century.But if you look at the overall energy mix over more than two centuries there's a...