transformation process; peat must be buried deeply (4-10 km) by sediment. Such deep burial can happen where the surface of the continent gradually sinks, creating a depression, or sedimentary basin, that can collect sediment. Sea level changes, transgression and regression, numerous peat layers in the sediment accumulate. Heat and pressure applied, chemical reactions occur destroying plant fibers and releasing hydrogen, nitrogen, and sulfur gases, once the proportion of carbon in the residue exceeds 70%, we have coal. With further burial and higher temperatures, chemical reactions remove additional hydrogen, nitrogen, and sulfur, yielding progressively higher concentrations of carbon.