Carboniferous Period

Carboniferous Period, fifth division of the Paleozoic Era of the geologic time scale, spanning a time interval from about 359 million to 299 million years before present. The Carboniferous is preceded by the Devonian Period and followed by the Permian Period. The name originated in Britain, where it was first applied in 1822 to the coal-bearing strata (Latin carbo, “coal” and ferre, “to bear”) of England and Wales.

In North America, this 60-million-year interval of geologic time is considered to comprise two periods rather than one. The earlier of the two, the Mississippian, ranges in age from about 359 million to 318 million years before present, while the later, the Pennsylvanian, ranges from about 318 million to 299 million years before present.

At the beginning of the Pennsylvanian portion of Carboniferous time, when most of the world’s coal was forming, lush forests and tropical peat swamps covered large areas of what would eventually become eastern North America and northern Europe. These areas were situated in the Tropics, immediately north of the equator, and had climates that were uniformly warm and humid. Such conditions promoted growth of the vegetation and marine organisms from which would form not only coal but also oil and gas.

Animal and vegetable remains from the Carboniferous Period are abundant and, in many cases, well preserved. Great uniformity is observed in the character of the plant life: The same genera and often the same species are found in widely separated regions. About 2,000 species are known, most of them flowerless, spore-producing plants. Early club mosses, horsetails, forest trees (Cordaites), and ferns were common. The contemporary land fauna left few traces, but the marine fauna are much better represented. The first true reptiles appeared, developing from earlier amphibians. Corals, crinoids, and minute foraminifers were abundant, and there were a few trilobites and eurypterids. Snails and mollusks, including cephalopods and nautiloids, were widespread. Insects were frequent, particularly a giant form of dragonfly. Polyzoa and brachiopods were common, and sharks and primitive, hard-scaled fish were well represented. See also Paleontology.

Of the ancient landmasses, only the protocontinent of Siberia lay north of the Tropics, extending almost to the North Pole. The supercontinent of Gondwanaland, comprising what would someday be South America, Africa, India, Australia, and Antarctica, lay entirely within the Southern Hemisphere, covering a vast area the center of which was near the South Pole.

Gondwanaland and the various protocontinents had been drifting toward each other since early in the Paleozoic Era. By the end of the Carboniferous Period crustal movements culminated in a four-way collision, so that when the Permian Period began, the plates of Earth’s crust had welded all the world’s landmasses into the single, supercontinent known as Pangaea. See also Plate Tectonics.

A major consequence of this redistribution of land and sea was a global climate change. It had been warm and wet earlier in the Carboniferous, but became cooler and drier as the period ended, resulting in a long interval of glaciation, known as the Permo-Carboniferous. See also Ice Ages.