Energy that you can't use over and over.

Fossil Fuels

A hydrocarbon deposit, such as petroleum, coal, or natural gas, derived from the accumulated remains of ancient plants and animals and used as fuel. Carbon dioxide and other greenhouse gases generated by burning fossil fuels are considered to be one of the principal causes of global warming.


a black or dark-brown combustible mineral substance consisting of carbonized vegetable matter, used as a fuel. Compare anthracite, bituminous coal, lignite.


any of a large class of substances typically unctuous, viscous, combustible, liquid at ordinary temperatures, and soluble in ether or alcohol but not in water.

Natural Gas

A mixture of hydrocarbon gases that occurs naturally beneath the Earth's surface, often with or near petroleum deposits. Natural gas contains mostly of methane but also has varying amounts of ethane, propane, butane, and nitrogen. It is used as a fuel and in making organic compounds.

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