Behind the advances discussed earlier lay the most fundamental revolution of all: the creation and spread of new sources of power. The power revolution laid the foundation for the new technologies that transformed transportation, communication, and production. It hastened the settling of the continent, multiplied the productivity of a people short on labor, and became the indispensable engine driving material progress. Between 1870 and 1920 American consumption of energy increased about 440 percent, and its sources changed dramatically. In 1870 wood accounted for about 73 percent of all energy used, with coal supplying nearly all the remainder. By 1920 wood provided less than 8 percent of energy used, coal soared to 73 percent, oil contributed 12 percent, and natural gas chipped in 4 percent. By the 1880s a growing proportion of energy went into producing a new source of power that became the most vital technology of the twentieth century: electricity.