|Carboniferous (kär'bə-nĭf'ər-əs) Pronunciation Key
The period of geologic time from about 360 to 286 million years ago. The term is used throughout the world, although this period of time has been separated into the Mississippian (lower Carboniferous) and Pennsylvanian (upper Carboniferous) in the United States. During this time, widespread swamps formed in which plant remains accumulated and later hardened into coal. See Chart at geologic time.