Coal is a resource produced deep within the earth over millions of years, and mined for the energy stored within it. Coal is a fossil fuel, meaning it formed from the remains of organic matter which was subjected to intense heat and pressure from mounting dirt and rocks as it slowly became compressed deeper and deeper within the earth. Different types of fossil fuels form from the remains of different types of organic matter, and coal is derived from ancient plants that died in swamps and wetlands in prehistoric times. The United States possesses the largest known coal reserves in the world. Today, we mine coal from the earth and use a majority for generating electricity and in the production of steel. We also use the byproducts of coal in various industries and export some to other countries.