The document discusses humanity's changing use of energy resources over time from relying solely on renewable sources like the sun and human/animal labor, to increasingly using non-renewable fossil fuels after the Industrial Revolution. It notes that fossil fuels are finite and will not be replenished, so conservation and alternative renewable sources like solar, wind, geothermal and biomass need to be pursued. Individual actions like insulating homes, using appliances efficiently, and choosing public transportation can help conserve energy.