Coal is just one stop that carbon atoms might make as they move from one location to another as part of the worlds carbon cycle.

Carbon (C) provides the foundation for the organic molecules of all living things on the planet including the peat that is the raw material for coal. Organic molecules are simple to complex carbon chains which include varying amounts of oxygen (O) hydrogen (H) and nitrogen (N). Coal is composed of anywhere between 85% to 99 % C.

Because living things constantly form, die, and decay, carbon atoms are in a continual state of flux or change from one situation to another with carbon dioxide (CO2) serving as the primary transporting agent as they make their rounds through the carbon cycle.

The carbon cycle has a series of reservoirs that trap carbon atoms for varying lengths of time (the residence time). Coal is one such a reservoir holding carbon until it is burned and the atoms are carried off as carbon dioxide to find their way to another reservoir. The various paths and reservoirs create the carbon cycle.

There are four major sinks (reservoirs) in the carbon cycle.

1. The biosphere (all living and preserved plants and animals)
2. The atmosphere (primarily as carbon dioxide)
3. The hydrosphere (primarily calcium bicarbonate in the oceans)
4. The lithosphere (primarily as limestone, coal, gas, and oil)