One hundred years from now, the United States (and most of the rest of the industrialized world) will have completed an epochal historical transition from a society based on depletable, fossil energy to one based predominantly on sustainable, virtually inexhaustible energy. This will be the fourth major energy transition in human history, the previous three being:

▼ the transition from hunting and gathering to the harvesting of biomass through agriculture and silviculture;

▼ the transition from biomass harvesting to the mining of fossil energy in the form of coal; and

▼ the most recent transition from predominant reliance on coal to overwhelming reliance on petroleum and natural gas.