Coal is an 'Ancient Gift Serving Modern Man'.About 300 million years ago, plants and trees grew in swamps that covered much of the earth. After the vegetation died and the build-up of silt as well as other sediments, together with movements in the earth's crust (known as tectonic movements) would bury these swamps and peat bogs, often to great depths. With burial, the plant material would be subjected to high temperatures and pressures generated by the tectonic forces in the earth. This would cause physical and chemical changes in the vegetation, transforming it over time into peat and ultimately into coal.To sum up, coal is the altered remains of prehistoric vegetation that originally accumulated in swamps and peat bogs. Coal formation first began about 360 million to 300 million years ago ("mya"), during a period which geologists referred to as the Carboniferous Period. Coal is classified as a nonrenewable energy source because it takes millions of years to form. The energy we get from coal today comes from the energy that plants absorbed from the sun by photosynthesis millions of years ago. After the plants die, this energy is released as the plants decay.