Carboniferous Period

Carboniferous Period, fifth division of the Palaeozoic Era of the geological timescale, spanning a time interval of some 64 million years, from about 359 to 295 million years ago. It was preceded by the Devonian Period and succeeded by the Permian Period. The name originated in Britain, where it was first applied in 1822 to the coal-bearing strata (Latin, carbo, “coal”; ferre, ”to bear”) of England and Wales. The Carboniferous in North America is often subdivided into the Mississippian (lower part) and the Pennsylvanian.

The surface of the Earth during the Carboniferous was organized into various land masses of different shape and composition to those of today. These ancient continents were destined to drift together and collide, forming the supercontinent of Pangaea during the Permian Period. Major continents of the Carboniferous included Gondwana, Laurentia, Baltica, and Siberia. Gondwana was the largest land mass, comprising what would later fragment to become modern South America, Africa, India, Australia, New Zealand, and Antarctica. This massive continent lay entirely within the southern hemisphere, covering a vast area including the South Pole. Laurentia was made up from North America, Greenland, and parts of western Europe, and Baltica from the major part of northern Europe. Laurentia and Baltica straddled the equator. Only Siberia lay entirely north of the tropics.

During the Carboniferous and Early Permian, continental collisions resulted in the closure of several oceans. Disappearing ocean basins included the Rheic Ocean separating northern Europe from Gondwana, the Phoibic Ocean between Laurentia and Gondwana, and the Pleionic Ocean between Baltica and Siberia/Kazakhstanthe. This collision of continents also initiated several important mountain-building events (orogenies), including the Alleghenian Orogeny of the eastern United States and the Ouachita Orogeny of the southern United States and South America. The squeezing of southern Europe between Africa to the south and Baltica to the north was the cause of the Hercynian and Variscan Orogenies. Elsewhere, Siberia collided with the microcontinents of Kazakhstan to produce the vast Altai Mountains of central Asia, and to the north with Inner Mongolia, producing the Khingan Range.

The Late Palaeozoic was a time of strong climate zonation, ranging from frigid glacial conditions in southern Gondwana, to hot humid and hot dry climates at low latitudes. Widespread glaciation has been recognized in Gondwana, but the presence of carbonate reefs and bauxite deposits is consistent with tropical climates at low latitudes. One of the most powerful and enduring images of the Carboniferous Period is the dense, dark, and damp coal swamp forests. These were widespread during the Late Carboniferous on deltas at equatorial latitudes bordering the incipient Tethys Sea. The vegetation of these forests gave rise to vast quantities of peat, which through geological time was transformed into the economically important coal deposits of western Europe and North America.

The flora of the coal swamp forests was dominated by five major tree groups. Some of the largest trees were lycopsids (clubmosses) and sphenopsids (horsetails), groups whose modern relatives are all herbaceous. Tree ferns were an important part of the understorey by the Late Carboniferous. The other major tree groups are related to gymnosperms (conifers and their relatives), and included the extinct seed ferns and cordaiteans.

Amphibians underwent a major radiation during the Early Carboniferous. These were all insectivorous or carnivorous, and included large frog-like as well as limbless forms. Skeletons of the earliest amniotes (the group including modern reptiles, mammals, and birds) have also been found. Reptiles began to diversify during the Late Carboniferous, as did winged insects. Blattoids (“cockroaches”) were the most widespread and abundant. Predatory insects of note included the Protodonata (dragonflies) and Ephemerata (mayflies). Among chelicerates, scorpions and spiders (arachnids) were the major terrestrial predators. Many arthropods were very large indeed. Gigantic arthropleurid millipedes up to 2 m (6 ft 6 in) long have been documented in the Late Carboniferous. The largest known insect was a Late Carboniferous relative of the dragonfly, with a wingspan of 60 cm (2 ft). Large size may have been made possible by the exceptionally high concentration of atmospheric oxygen thought to have characterized much of the Carboniferous Period.

In the marine environment, the extinctions of the Late Devonian paved the way for a diversification of many invertebrates. Groups that radiated during the Carboniferous include brachiopods (lampshells), ammonoids (see Ammonite), bryozoans, crinoids (sea lilies), foraminifera (including fusulinids), as well as calcareous algae. Sponges and calcareous algae were present as reef builders, although many Carboniferous reefs have no obvious frame-building organisms and instead are often described as mud mounds.