After death, most of the biological carbon in organisms (Corg) is returned to the atmosphere as CO2 through the respiration of decomposers and detritivores or by combustion. However, the balance between these processes is not perfect, and when productivity exceeds decomposition, carbon sequestration results. An unparalleled interval of carbon sequestration in Earth's history occurred during the Late Carboniferous (Pennsylvanian) and Permian Periods (ca. 323–252 Ma), when arborescent vascular plants related to living club mosses (Lycophytes), ferns (Monilophytes), horsetails (Equisetophytes) and seed plants (Spermatophytes) formed extensive forests in coastal wetlands. On their death, these plants became buried in sediments, where they transformed into peat, lignite, and, finally, coal.