Economic energy cost
The economic energy cost of natural resources is the fossil and nuclear fuels required to locate, extract, refine, and otherwise upgrade natural resources to useful raw materials. This work is done by the extractive sector of the economy. This industry includes the mining sector that extracts energy (oil, coal, natural gas), metals (copper, lead, iron) and non-metal minerals (phosphate, salt, sulfur); the forestry and fishery sectors that harvest wood and fish products, respectively; the agricultural sector that harvests crops and livestock as sources of food (grains and meat) and materials (leather and cotton), and utilities that collect water from surface and underground sources.
Without the work done by energy from the sun and the Earth’s interior, there would be no natural resources as we know them. Energy and materials would be randomly distributed in the ocean, crust, and atmosphere at very low concentrations, making them economically and technologically impossible to use. But the work done by energy flows in the environment is only the first step in producing a good or service. An additional investment of energy is needed to concentrate, organize, or upgrade natural resources. Even the richest deposits of copper and the densest stands of timber require further processing before they are useful. Crude oil must be discovered, pumped to the surface, and refined into gasoline. Timber must be felled and sawed into useful forms of lumber. Copper must be mined, concentrated and refined into pure copper metal pipes and wire.