This video traces how people have converted natural resources into energy since prehistoric times. The thread of energy production runs through Pennsylvania history. Wood remained the primary source of energy in Pennsylvania until late in the 1800s. The industrial revolution unlocked the energy potential of fossil fuels -- coal, oil and gas. Nuclear power gained importance as scientists discovered nuclear fission and fusion in the first half of the 20th century, and since the late 20th century, attention has shifted to renewable energy sources.