Purring Tiger's
PREHISTORIC TIME LINE
Biological and Geological Changes

CARBONIFEROUS PERIOD

PHANEROZOIC EON
Began: 570 million years ago
Ended: Current
Lasted: Current

PALEOZOIC ERA
Began: 570 million years ago
Ended: 245 million years ago
Lasted: 325 million years

CARBONIFEROUS PERIOD
Began: 360 million years ago
Ended: 286 million years ago
Lasted: 074 million years

The Carboniferous Period occurred from about 360 to 286 million years ago during the late Paleozoic Era. The term "Carboniferous" comes from England, in reference to the rich deposits of coal that occur there. These deposits of coal occur throughout northern Europe, Asia, and midwestern and eastern North America. The term "Carboniferous" is used throughout the world to describe this period, although this period has been separated into the Mississippian (early Carboniferous from 360-320 mya) and the Pennsylvanian (late Carboniferous from 320-286 mya) in the United States. This system was adopted to distinguish the coal-bearing layers of the Pennsylvanian from the mostly limestone Mississippian, and is a result of differing stratigraphy on the different continents.

The stratigraphy of the Lower Carboniferous can be easily distinguished from that of the Upper Carboniferous. The environment of the Lower Carboniferous in North America was heavily marine, when seas covered parts of the continents. As a result, most of the mineral found in Lower Carboniferous is limestone, which are composed of the remains of crinoids, lime-encrusted green algae, or calcium carbonate shaped by waves. The North American Upper Carboniferous environment was alternately terrestrial and marine, with the transgression and regression of the seas caused by glaciation. These environmental conditions, with the vast amount of plant material provided by the extensive coal forests, allowed for the production of coal. Plant material did not decay when the seas covered them and pressure and heat eventually built up over the millions of years to transform the plant material to coal.

The appearance or disappearance of fauna usually marks the boundaries between time periods. The Carboniferous is separated from the earlier Devonian by the appearance of the conodont Siphonodella sulcata or Siphondella duplicata. Conodonts are a series of fossils that resemble the teeth or jaws of primitive eel- or hagfish-like fish. The Carboniferous-Permian boundary is distinguished by the appearance of the fusulinid foram Sphaeroschwagerina fusiformis in Europe and Pseudoschwagerina beedei in North America. Fusulinids are giants among protists and could reach a centimeter in length. They were abundant enough to form sizable deposits of rock, known as "rice rock" because of the resemblance between fusulinids and rice grains.

The Mississippian is differentiated from the Pennsylvanian by the appearance of the conodont Declinognathodus noduliferus, the ammonoid genus Homoceras, and the foraminifers Millerella pressa and Millerella marblensis. The markers of these boundaries apply only to marine deposits. The distinction between the Pennsylvanian and Mississippian subsystems may also be illustrated by a break in the flora due to transistional changes from a terrestrial environment to a marine one and as a result of a change in the climate.

The stratigraphy of the Lower Carboniferous is distinguished by the shallow-water limestones. These limestones are composed of parts of organisms, mostly the remains of crinoids. These thrived in the shallow seas of the Lower Carboniferous. Other limestones include lime mudstones and oolithic limestones. Lime mudstones are composed of the carbonate mud produced by green algae. Oolithic limestones are composed of calcium carbonate in concentric spheres that were produced by high wave energy. Sandstones (sedimentary rock composed of quartz sand and cemented by silica or calcium carbonate) and siltstones (rock composed of hardened silt) are also found in the Lower Carboniferous strata, though not in as great abundance than the limestones.

Coal beds, which can be up to eleven to twelve meters thick, characterize the Upper Carboniferous. Deposits reflect the transgression and regression of the seas over the continents. The layers consist of sandstone, shale, "freshwater" limestone, underclay, and a coal bed. The forests of seedless vascular plants that existed in the tropical swamp forests of Europe and North America provided the organic material that became coal. Dead plants did not completely decay and was turned to peat in these swamp forests. When the sea covered these swamps, marine sediments covered the peat. Eventually, heat and pressure transformed these organic remains into coal. Coal balls found in sites contain these plant remains.

Index fossils are the remains of plants and animals that characterize a well-defined time span and occur over a wide range of geography. Fossils of marine life characterize the Mississippian Period, as shallow epicontinental seas covered the United States at that time. These fossils include solitary corals and Syringopora, tubular colonial corals. Other fossil colonial corals include Stelechophyllum and Siphonodendron. Because conodont fossils are distributed all over the world, they are utilized internationally to date Mississippian rocks.

Index fossils used for the Pennsylvanian Period are fusulinid foraminifers and the pollen and spores from the coal forests prevalent during that time. The Mississippian-Pennsylvanian boundary is marked by the appearance of the fusulinid Pseudostaffella antiqua. Other fossils used to identify the early Pennsylvanian Period are the three ammonoid cephalopod genera: Gastrioceras, Daiboloceras, and Paralegoceras, found in marine deposits.

The Carboniferous was marked by the progressive formation of the supercontinent Pangea. The present day Northern Hemisphere landmasses moved towards the equator to form Laurasia and to join the large Southern Hemisphere landmass Gondwana. The collision between Siberia and Eastern Europe created the Ural Mountains, and China was formed with the collision of several microcontinents and Siberia. The collision between Gondwana and Laurasia led to the formation of the Appalachian belt in North America and the Hercynian Mountains in Europe. Gondwana also shifted towards the equator while the continents moved from east to west.

About 360 million years ago, the Avalon Terrane collides with the easternmost portion of the North American crustal plate. In North Carolina this marked the beginning of a second mountain-building event referred to as the Acadian Orogeny. Here a number of different terranes collided with the North American block resulting in regional metamorphism and igneous intrusions.

During this period North Carolina continued to be a major source area for sediment deposited to the north and west. Only one major igneous intrusion occurred in North Carolina during this time about 324 million years ago in Anson County.

In western Tennessee and Kentucky the land was tilted slightly and raised above sea level. Rapidly flowing waters deposited sediments into the surrounding area.

About 320 million years ago the final surge of Appalachian Mountain building began. First signs of the collision of the North American and Euro-African continents resulting in the uplifting of crust caught between the two gigantic plates.

About 286 million years ago the ancient North American and Euro-African crustal plates were slowly grinding to a halt following the collision. On the surface, the great land masses were finally joined in one enormous land mass named Pangaea.

The relationship of different land masses, such as the location of each of the present day continents relative to each other is determined by comparison of ancient magnetic poles and interpretations of ancient zones of tectonic activity. Rock magnetism is based on the fact that certain types of rocks may contain minerals that are slightly magnetic and so position themselves a specific way when exposed to a magnetic field. When the rock is first laid down, such as during a volcanic explosion, these minerals are free to orientate themselves in any manner they wish, and they are later locked into that position when the rock hardens, thus recording the position of the magnetic field of the Earth at that time. Landmasses placed close to each other will experience the same magnetic field and so the minerals in the rock will be orientated in the same direction.

The amount of land exposed to the air increased during the Carboniferous. This increase is probably due to plate tectonics and to the thickening of the crust. This trend towards increasing elevation of landmasses can be seen by the different types of rock deposits that are found in different locations. The Mississippian period is marked by marine deposits leading to the conclusion that shallow seas covered large areas, but by the Pennsylvanian Period, there was an uneven but progressive trend towards elevation of landmasses and marginal marine and continental environments became dominant. The restriction of oceans to the margins of the continents and the fluctuating sea levels led to the unconformity of the strata associated with the Carboniferous period. These changes to a less marine environment led to the terrestrial radiation that started during the Carboniferous. Terrestrial radiation also occurred because of drying trends that were the result of large glaciers, most of which originated in the South Pole of the time.

In addition to having the ideal conditions for the beginnings of coal, several major biological, geological, and climatic events occurred during this time.

Great coal-forming forests developed as a result of rare freezing temperatures and a warm, humid climate. In the closed swamps, accumulating layers of decaying plant matter produced numerous layers of coal.

One of the greatest evolutionary innovations of the Carboniferous was the amniote egg, which allowed for the further exploitation of the land by certain tetrapods. The amniote egg allowed the ancestors of birds, mammals, and reptiles to reproduce on land by preventing the desiccation of the embryo inside. There was also a trend towards mild temperatures during the Carboniferous, as evidenced by the decrease in lycopods and large insects and an increase in the number of tree ferns.

Scale trees (lepidodendrons) grew to 35 meters (115 feet) forming dense forests. The forerunners of conifers formed and there was a large variety of ferns at ground level.

The beginning of the Carboniferous generally had a more uniform, tropical, and humid climate throughout the year than exists today. Seasons if any were indistinct. These observations are based on comparing the morphology of the plants that exist in the fossil record with plants that are present today. The morphology of the Carboniferous plants resembles the plants that live in tropical and mildly temperate areas today. Many of them lack growth rings, suggesting a uniform climate. This uniformity in climate may have been the result of the large expanse of ocean that covered the entire surface of the globe except for a small, localized section where Pangea, the massive supercontinent that existed during the late Paleozoic and early Triassic, was forming during the Carboniferous.

Shallow, warm, marine waters often flooded the continents. Attached filter feeders such as bryozoans, particularly fenestellids, were abundant in this environment, and the sea floor was dominated by brachiopods. Trilobites were increasingly scarce while foraminifers were abundant. The heavily armored fish from the Devonian became extinct, being replaced with fish fauna that look more modern.

Coelacanths (see' la kanth) swam in streams along with other lung-finned and lobe-finned fish that developed during the period.

Foraminifera (tiny, mostly marine animals that were microscopic to near-microscopic with shell-like chambers) became so abundant that numerous limestone structures were found in Indiana.

Amphibians increased in numbers but remained rather small. Most were less than 20 centimeters (8 inches) long, with the largest growing to about 2 meters (6.5 feet) long.

Near the end of the Mississippian, uplift and erosion of the continents occurred, causing an increase in the number of floodplains and deltas present. The deltaic environment supports fewer corals, crinoids, blastoids, cryozoans, and bryzoans, which were abundant earlier in the Carboniferous. Bryozoa built lacy, moss-like structures and were the most successful shellfish of the period.

Freshwater clams first appear along with an increase in gastropod, bony fish, and shark diversity. At first glance, it may seem that the marine habitat has grown allowing the diversity of marine life to increase, but in actuality, the movement of the continents to form one large continental mass decreased the sea coast area.

The amount of space available for marine life declined, and the sea levels all over the world fluctuated because of the presence of two large ice sheets at the southern pole which suck up large amounts of water and lock it away from the water cycle as ice. Because so much water is taken out of the water cycle, the sea levels drop leading to the mass extinction of shallow marine invertebrates, the gradual decline of swamps, and the increase in terrestrial habitat. These effects are reversed when the glaciers start to recede, releasing the water that they had stored as ice back into the oceans, flooding the swamps again and the floodplains. Carboniferous rock formations often occur in patterns of stripes with shale and coal seams alternating, indicating the cyclic flooding and drying of an area.

The uplift of the continents caused a transition to a more terrestrial environment during the Pennsylvanian period. Swamp forests as well as terrestrial habitats became common and widespread. In the swamp forests, the vegetation was marked by the numerous different groups that were present. Seedless plants such as lycopsids were extremely important in this community and are the primary source of carbon for the coal that is characteristic of the period. The lycopods underwent a major extinction event after a drying trend, most likely caused by the advance of glaciers.

Ferns and sphenopsids became more important later during the Carboniferous, and the earliest relatives of the conifers appeared. The first land snails appeared, and insects with wings that can't fold back such as dragonflies and mayflies flourished and radiated. These insects, as well as millipedes, scorpions, and spiders became important in the ecosystem.

The trend towards aridity and an increase in terrestrial habitat lead to the increasing importance of the amniotic egg for reproduction. The earliest amniote fossil was the lizard-like Hylonomus, which was lightly built with deep, strong jaws and slender limbs. The basal tetrapods became more diverse during the Carboniferous. Fish-like bodies were replaced with large predators with long snouts, short sprawling limbs and flattened heads such as temnospondyls. Anthracosaurs (basal tetrapods and amniotes with deep skulls and a less sprawling body plan which led to increasing agility) appeared during the Carboniferous and were quickly followed by diapsids which divided into two groups: the marine reptiles, lizards, and snakes versus the archosaurs (crocodiles, dinosaurs, and birds). The synapsids also made their first appearance.