The Carboniferous Period is a part of the Paleozoic Era. This geologic period occurred in the later part of the era, beginning from the end of the Devonian Period and followed by the Permian Period. It’s the longest period of the Paleozoic Era, lasting 60 million years from around 358.9 million years ago (at the end of the Devonian) till 298.9 million years ago when the Permian started.
This period was named “Carboniferous,” meaning “coal-bearing,” due to a large amount of coal deposited during this period, particularly throughout Asia, Northern Europe, and Eastern and Midwestern North America. Unsurprisingly, it’s the period when most of the coal on earth was produced. The bark-bearing trees that grew in the lowland swamp forests produced the coal. There were also lots of vegetation, such as giant club mosses, great horsetails, towering trees, and tree ferns. Organic deposits from the plant debris formed the coal deposits, which we still burn to date. However, many also refer to it as the “age of amphibians” because of their dominance for most of the period.
Carboniferous Period – Timeline
The Carboniferous Period is divided into two main subperiods (epochs)—the Mississippian and Pennsylvanian epochs. Each of these is further divided into the upper, middle, and lower stages spanning several million years.
The Mississippian began about 359.2 million years ago and lasted till about 318.1 million years ago. On the other hand, the Pennsylvanian began at the end of the Mississippian, roughly 318.1 million years ago, and lasted until about 299 million years ago.
A couple of events took place during the Carboniferous that shaped the earth’s history and remain relevant to date. This period began with a high concentration of carbon dioxide, leading to a high global average temperature during the early years. However, the rapid growth of the forests led to the carbon dioxide levels dropping by eight times what it was. Glaciers also started to form, and the global average temperature reduced during the middle part of this period. This also led to a surplus amount of oxygen in the atmosphere, peaking at 35%, compared to 21% in recent times. The forests of the Carboniferous Period were swampy and covered most of the land surface.
Collision of Land Masses
During the Carboniferous, earth’s continents started coming together to form the Pangea supercontinent. The Gondwana and Euramerica land masses collided after moving toward one another for several million years due to tectonic plate movements. This collision caused the upliftment of some land masses, leading to the creation of mountains. No plants covered these mountains, so weathered parts were washed off into deltas and floodplains. The African Plate also collided with the eastern North American Plate towards the end of the Pennsylvanian.
This fusion of the continents also affected the climate, disrupting the warm ocean currents and creating widespread glaciation. Consequently, the climate became dryer and cooler, affecting the dominant rainforest and leading to its eventual decline. This is the origin of the large formation of coal deposits on earth.
The Evolution of Amphibians
The Carboniferous Period saw a massive growth in the diversity and size of the amphibians. Some of these animals were predatory, resembling modern-day crocodiles. They had vicious teeth and were up to 20 feet long. Some also developed thick, scaly skins that helped them survive for long periods away from water.
Some amphibians evolved to produce amniotic eggs. This was an important evolutionary adaptation for the amphibians during this period, as it ensured they didn’t have to rely on wetland habitats. The embryo inside the egg was protected by a membrane that retained fluid and allowed airflow. This eventually paved the way for reptiles to evolve.
The Collapse of the Carboniferous Rainforest
Eventually, the Carboniferous rainforest that characterized most of the period started to decline toward the end. This is mainly due to the climate changing from humid and hot to arid and cool. This climate change resulted from intense glaciation and sea level reduction. The resulting climatic conditions were unfavorable for the rainforest and the animals that thrived in it. The rainforests soon became isolated islands with seasonally dry habitats surrounding them. The towering forests with lots of heterogeneous vegetation made way for less diverse flora with tree ferns.
The amphibians thriving and dominant throughout this period also fared poorly during this collapse and started dying off. This extinction event led to a significant loss of biodiversity. However, reptiles adapted to survive and thrive in the new, drier climate because of their key adaptation features, such as scales and hard-shelled eggs, which retained water better than the amphibians.
The average global temperature during the early Carboniferous Period was high—about 68 degrees Fahrenheit. However, the temperature dropped during the middle Carboniferous to around 53.6 degrees Fahrenheit. During this period, the level of carbon dioxide in the atmosphere also dropped (from eight times the current level) to a similar level to what we have today.
During this period, the latitudinal position of the landmasses determined the climate. The equatorial regions were characterized by tropical conditions. The higher latitudes were moist and cool, while midlatitudes were dry.
The Gondwana had a colder climate (below 86 degrees Fahrenheit in the southern latitudes), allowing it to form continental glaciers similar to those that occurred during the Pleistocene Epoch in the Northern Hemisphere. However, during this period, there was no glaciation in the Northern Hemisphere because the landmasses couldn’t sustain huge ice fields.
The climate warmed during the Tournaisian (the earliest part of the Mississippian) before it cooled again and made way for another episode of warming and cooling during the Visean and early Serpukhovian, respectively (the later part of the Mississippian).
By the start of the Pennsylvanian subperiod, glaciers formed at the South Pole and grew enough to cover most of Gondwana. Cyclothems indicate that the glaciers’ sizes were controlled by the Milankovitch cycles, similar to recent ice ages having interglacial and glacial periods. The deep ocean temperature was cold during this time because of the flow of cold bottom waters caused by the seasonal melting of the ice caps.
The climate’s drying and cooling resulted in the Carboniferous rainforest collapse towards the end of this period.
Plant and Animal Life of the Carboniferous Period
This period had a diversity of plant and animal life, many of which were lost during the Carboniferous rainforest collapse and the mass extinction it caused. The life forms present during the Carboniferous include plants, marine and terrestrial invertebrates, fish, and tetrapods.
The Carboniferous was a period of great diversity, especially for marine invertebrates. Life in the Carboniferous seas was remarkably different from the preceding Devonian. This was due to the extinction event that occurred during the Late Devonian, which wiped out most of the marine invertebrates at the time. Thus, the Carboniferous marine faunas had a different composition.
There was a diversity of land animals during the Carboniferous as well. This increased with the growing land area and receding seas. Tetrapods, for instance, thrived during this period. More species of these four-legged vertebrates evolved after their first appearance on land during the Late Devonian.
Some of the animals that dominated this period started their lives in water as early amphibians before moving onto land. Early reptiles developed leathery skin, moving to the dry parts of the land. They also developed a leathery covering for their eggs to prevent them from drying out as they develop.
The high oxygen condition of the mid-Carboniferous period and the humid conditions allowed insects to grow very big on land. This was a period dominated by giant insects, such as the Meganeura. This insect was one of the largest insects of the time, with a wingspan of 23–28 inches. It’s known to be the ancestor of dragonflies. The Arthropleura was another large insect living on the Carboniferous forest floor during this period. It was a giant millipede with about 30 pairs of legs and could grow more than 19.7 inches long.
The Carboniferous Period is also characterized by big trees in massive forests. The climate’s warmness allowed lots of plants to grow and grow big! The large trees were covered with barks, and huge ferns were growing in the swamps, but there was no grass. The high oxygen concentration in the atmosphere came from the numerous plants that grew and thrived in the carbon-dioxide-rich environment. So, both plants and animals could grow to huge sizes. When the ferns and trees died, they ended up inside water without bacteria to decompose them, forming peat beds. The weight of these layers of peat beds eventually turned into coal.
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- Britannica, Available here: https://www.britannica.com/science/Carboniferous-Period/Carboniferous-life
- National Geographic, Available here: https://www.nationalgeographic.com/science/article/carboniferous
- Wikipedia, Available here: https://en.wikipedia.org/wiki/Carboniferous
- Fossils, Facts and Finds, Available here: https://www.fossils-facts-and-finds.com/carboniferous_period.html