Old Earth Ministries Online Earth History Curriculum

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Chapter 7 - The Carboniferous Period

Lesson 36: Carboniferous Overview



     The Carboniferous is a geologic period and system that extends from the end of the Devonian period, about 359.2 ± 2.5 Ma (million years ago), to the beginning of the Permian period, about 299.0 ± 0.8 Ma, with a total duration of about 60.2 million years.
     The Carboniferous was a time of glaciation, low sea level and mountain building; a minor marine extinction event occurred in the middle of the period. The name comes from the Latin word for coal, carbo. Carboniferous means "coal-bearing". Many beds of coal were laid down all over the world during this period.

     In the USA the Carboniferous is usually broken into Mississippian (earlier) and Pennsylvanian (later) Epochs. The Mississippian is about twice as long as the Pennsylvanian, but due to the large thickness of coal bearing deposits with Pennsylvanian ages in Europe and North America, the two subperiods were long thought to have been more or less equal.

Chapter 7 - The Carboniferous Period


Lesson 36: Overview

Lesson 37:  Coal

Lesson 38:  Oil

Lessson 39: Species In-Depth - Bivalves



Carboniferous Fast Facts
Started:  359.2 Ma
Ended:  299.0 Ma
Duration:  60.2 Million Years
Preceded By: Devonian Period
Followed By: Permian Period



Mean atmospheric O2 content over period duration ca. 32.5 Vol %
(163 % of modern level)
Mean atmospheric CO2 content over period duration ca. 800 ppm
(3 times pre-industrial level)
Mean surface temperature over period duration ca. 14 °C
(0 °C above modern level)
Sea level (above present day) Falling from 120m to present day level throughout Mississippian, then rising steadily to about 80m at end of period



     The early part of the Carboniferous was mostly warm; in the later part of the Carboniferous, the climate cooled. Glaciations in Gondwana, triggered by Gondwana's southward movement, continued into the Permian and because of the lack of clear markers and breaks, the deposits of this glacial period are often referred to as Permo-Carboniferous in age.

      A global drop in sea level at the end of the Devonian reversed early in the Carboniferous; this created the widespread epicontinental seas and carbonate deposition of the Mississippian. There was also a drop in south polar temperatures; southern Gondwanaland was glaciated throughout the period, though it is uncertain if the ice sheets were a holdover from the Devonian or not. These conditions apparently had little effect in the deep tropics, where lush coal swamps flourished within 30 degrees of the northernmost glaciers.

     A mid-Carboniferous drop in sea-level precipitated a major marine extinction, one that hit crinoids and ammonites especially hard. This sea-level drop and the associated unconformity in North America separate the Mississippian period from the Pennsylvanian period. This happened about 320 million years ago, at the onset of the Permo-Carboniferous Glaciation.


     The Carboniferous was a time of active mountain-building, as the supercontinent
Late Carboniferous Paleogeography
Global paleogeographic reconstruction of the Earth in the late Carboniferous ("Pennsylvanian") period 300 million years ago. (Picture Source)
 Pangaea came together. The southern continents remained tied together in the supercontinent Gondwana, which collided with North America–Europe (Laurussia) along the present line of eastern North America. This continental collision resulted in the Hercynian orogeny in Europe, and the Alleghenian orogeny in North America; it also extended the newly-uplifted Appalachians southwestward as the Ouachita Mountains. In the same time frame, much of present eastern Eurasian plate welded itself to Europe along the line of the Ural mountains. Most of the Mesozoic supercontinent of Pangea was now assembled, although North China (which would collide in the Latest Carboniferous), and South China continents were still separated from Laurasia. The Late Carboniferous Pangaea was shaped like an "O."

     There were two major oceans in the Carboniferous—Panthalassa and Paleo-Tethys, which was inside the "O" in the Carboniferous Pangaea. Other minor oceans were shrinking and eventually closed - Rheic Ocean (closed by the assembly of South and North America), the small, shallow Ural Ocean (which was closed by the collision of Baltica and Siberia continents, creating the Ural Mountains) and Proto-Tethys Ocean (closed by North China collision with Siberia/Kazakhstania).



Rocks and Coal


     Carboniferous rocks in Europe and eastern North America largely consist of a repeated sequence of limestone, sandstone, shale and coal beds, known as "cyclothems" in the U.S. and "coal measures" in Britain. In North America, the early Carboniferous is largely marine limestone, which accounts for the division of the Carboniferous into two periods in North American schemes. The Carboniferous coal beds provided much of the fuel for power generation during the Industrial Revolution and are still of great economic importance.

    In eastern North America, marine beds are more common in the older part of the period than the later part and are almost entirely absent by the late Carboniferous. More diverse geology existed elsewhere, of course. Marine life is especially rich in crinoids and other echinoderms. Brachiopods were abundant. Trilobites became quite uncommon. On land, large and diverse plant populations existed. Land vertebrates included large amphibians.

Life in the Carboniferous


    Although Earth's poles were covered by ice caps, the equatorial regions of the planet were dominated by vast swamp lands during most of the Carboniferous.  Early Carboniferous land plants were very similar to those of the preceding Late Devonian, but new groups also appeared at this time.  The main Early Carboniferous plants were the Equisetales (Horse-tails), Sphenophyllales (vine-like plants), Lycopodiales (Club mosses), Lepidodendrales (scale trees), Filicales (Ferns), Medullosales (informally included in the "seed ferns", an artificial assemblage of a number of early gymnosperm groups) and the Cordaitales. These continued to dominate throughout the period, but during late Carboniferous, several other groups, Cycadophyta (cycads), the Callistophytales (another group of "seed ferns"), and the Voltziales (related to and sometimes included under the conifers), appeared.
     The Carboniferous lycophytes of the order Lepidodendrales, which are cousins (but not ancestors) of the tiny club-moss of today, were huge trees with trunks 30 meters high and up to 1.5 meters in diameter. These included
Lepidodendron (with its fruit cone called Lepidostrobus), Halonia, Lepidophloios and Sigillaria. The roots of several of these forms are known as Stigmaria.
     The fronds of some Carboniferous ferns are almost identical with those of living species. Probably many species were
epiphytic (an epiphyte is a plant that grows upon another plant (such as a tree) non-parasitically or sometimes upon some other object). Fossil ferns and "seed ferns" include Pecopteris, Cyclopteris, Neuropteris, Alethopteris, and Sphenopteris; Megaphyton and Caulopteris were tree ferns.
     The Equisetales included the common giant form
Calamites, with a trunk diameter of 30 to 60 cm and a height of up to 20 meters. Sphenophyllum was a slender climbing plant with whorls of leaves, which was probably related both to the calamites and the lycopods.
Cordaites, a tall plant (6 to over 30 meters) with strap-like leaves, was related to the cycads and conifers; the catkin-like inflorescence, which bore yew-like berries, is called Cardiocarpus. These plants were thought to live in swamps and mangroves. True coniferous trees (Walchia, of the order Voltziales) appear later in the Carboniferous, and preferred higher drier ground.


Marine invertebrates

     In the oceans the most important marine invertebrate groups were the
foraminifera, corals, bryozoa, brachiopods, ammonoids, hederelloids and echinoderms (especially crinoids).
     For the first time foraminifera take a prominent part in the marine faunas. The large spindle-shaped genus
Fusulina and its relatives were abundant in what is now Russia, China, Japan, North America; other important genera include Valvulina, Endothyra, Archaediscus, and Saccammina (the latter common in Britain and Belgium). Some Carboniferous genera are still extant.

      Sponges are known from spicules and anchor ropes, and include various forms such as the Calcispongea Cotyliscus and Girtycoelia, and the genus of unusual colonial glass sponges Titusvillia.
     Other common fossils of this period include
Gastropods and Ostracods (a class of crustacean zooplankton).  Trilobites are rarer than in previous periods, represented only by the proetid group.
     Amongst the
echinoderms, the crinoids were the most numerous. Dense submarine thickets of long-stemmed crinoids appear to have flourished in shallow seas, and their remains were consolidated into thick beds of rock. The blastoids, which included the Pentreinitidae and Codasteridae and superficially resembled crinoids in the possession of long stalks attached to the seabed, attain their maximum development at this time.


     Many fish inhabited the Carboniferous seas; predominantly
Elasmobranchs (sharks and their relatives). These included some, like Psammodus, with crushing pavement-like teeth adapted for grinding the shells of brachiopods, crustaceans, and other marine organisms. Other sharks had piercing teeth, such as the Symmoriida; some, the petalodonts, had peculiar cycloid cutting teeth. Most of the sharks were marine, but the Xenacanthida invaded fresh waters of the coal swamps.

      Among the bony fish, the Palaeonisciformes found in coastal waters also appear to have migrated to rivers. Sarcopterygian fish were also prominent, and one group, the Rhizodonts, reached very large size.
     Most species of Carboniferous marine fish have been described largely from teeth, fin spines and dermal ossicles, with smaller freshwater fish preserved whole.
     Sharks (especially the Stethacanthids) underwent a major evolutionary radiation during the Carboniferous. It is believed that this evolutionary radiation occurred because the decline of the placoderms at the end of the Devonian period caused many environmental niches to become unoccupied and allowed new organisms to evolve and fill these niches. As a result of the evolutionary radiation carboniferous sharks assumed a wide variety of bizarre shapes including Stethacanthus who possessed a flat brush-like dorsal fin with a patch of denticles on its top. Stethacanthus unusual fin may have been used in mating rituals.

Terrestrial Invertebrates


     Late Carboniferous giant dragonfly-like insect Meganeura grew to wingspans of 75 cm. Gigantic Pulmonoscorpius from the early Carboniferous reached a length of up to one meter.
     Fossil remains of air-breathing
insects, myriapods and arachnids are known from the late Carboniferous, but so far not from the early Carboniferous. Their diversity when they do appear, however, shows that these arthropods were both well developed and numerous. Their large size can be attributed to the moistness of the environment (mostly swampy fern forests) and the fact that the oxygen concentration in the Earth's atmosphere in the Carboniferous was much higher than today. (The oxygen concentration in the Earth's atmosphere during the Carboniferous was 35% whereas the oxygen concentration in earth's current atmosphere is 21%.) This required less effort for respiration and allowed arthropods to grow larger with the up to 2.6 metres long centipede Arthropleura being the largest known land invertebrate of all time.



     Carboniferous amphibians were diverse and common by the middle of the period, more so than they are today; some were as long as 6 meters, and those fully terrestrial as adults had scaly skin. They included a number of basal tetrapod groups classified in early books under the Labyrinthodontia. These had long bodies, a head covered with bony plates and generally weak or undeveloped limbs. The largest were over 2 meters long. They were accompanied by an assemblage of smaller amphibians included under the Lepospondyli, often only about 15 cm long. Some Carboniferous amphibians were aquatic and lived in rivers, while others may have been semi-aquatic or terrestrial.
     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. These included the earliest sauropsid reptiles (Hylonomus), and the earliest known synapsid (Archaeothyris). These small lizard-like animals quickly gave rise to many descendants. The amniote egg allowed these ancestors of all later birds, mammals, and reptiles to reproduce on land by preventing the desiccation, or drying-out, of the embryo inside. By the end of the Carboniferous period, the amniotes had already diversified into a number of groups.


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