Due to its abundance, coal has been mined in various parts of the world throughout history and coal mining continues to be an important economic activity today. Compared to wood fuels, coal yields that have higher amount of energy per mass and can often be obtained in areas where wood is not readily available. Though historically used as a domestic fuel, coal is now mostly used in industry, especially in smelting and alloy production as well as electricity generation. Large-scale coal mining developed during the Industrial Revolution, and coal provided the main source of primary energy for industry and transportation in industrial areas from the 18th century to the 1950s. Coal remains an important energy source, due to its low cost and abundance when compared to other fuels, particularly for electricity generation. Coal is also mined today on a large scale by open pit methods wherever the coal strata strike the surface or are relatively shallow. Britain developed the main techniques of underground coal mining from the late 18th century onward with further progress being driven by 19th century and early 20th century progress. However, oil and its associated fuels began to be used as alternative from the 1860s onward. By the late 20th century coal was for the most part replaced in domestic as well as industrial and transportation usage by oil, natural gas, nuclear power, or renewable energy sources. By 2010, coal produced over a fourth of the world's energy, and by 2050 is expected to produce about one-third.