Life in the Swamp
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Carboniferous Period

The Age of Coal

Published in The EarthSphere Blog. Feature Image: Life in the Coal Swamps (©ArcheanEnterprises, LLC; ArcheanArt)


The last article in the Forgotten Origins saga addressed the end of the Devonian period when a mass extinction ravaged the planet. But during the Carboniferous, the planet warmed, and new life replaced the old, filling the ecological void created by massive species loss.

Last time: End of the Devonian

Setting the Stage

The Carboniferous Period derives its name from our love of fossil fuels. Between 359 and 299 million years ago, life laid the foundations for Anthropocene climate change as massive coal deposits formed. These ancient coal deposits provided the energy that fueled the Industrial Revolution. The world learned to extract cheap energy from the Earth’s bowels and convert it into work, driving the development of industry, manufacturing, and transportation. It would be another century before human’s understood this ‘cheap energy’ came at a high price, and even longer before we grasped the long-term environmental and climate implications. Oddly enough, the creation of the fossil fuels that now warm our planet resulted in catastrophic cooling at the end of the Carboniferous Period.

The Carboniferous Period divides into two intervals. North American geologists treat these intervals as distinct periods, with the Early Carboniferous designated as the Mississippian Period and the Late Carboniferous is called the Pennsylvanian Period. These divisions relate to the prevailing environmental conditions during each period. The Early Carboniferous was dominated by large, shallow continental seas, whereas the Late Carboniferous was marked by more dry land.

During the Carboniferous, Gondwana migrated northward towards the equator and fully fused with Laurasia completing the supercontinent of Pangea. The tectonic collisions associated with building Pangea resulted in an uplift in many areas, creating highland glaciation and interior lowlands where the surrounding mountains trapped warm moist air.

Carbon and Oxygen

Tectonic uplift made the Late Carboniferous (Pennsylvanian) more terrestrial than the preceding marine conditions of the Early Carboniferous (Mississippian). This, in turn, led to vast swamplands where forests grew and died so rapidly the trees and other plants were buried in anoxic bogs before they had time to fully decay. These buried organic remains eventually formed the thick and widespread Carboniferous coal deposits we now exploit for cheap energy. Like a double-edged sword, the availability of coal cuts two ways, simultaneously setting the stage for technological success and environmental failure. It provided cheap energy driving industrial expansion and modern technology. It also initiated climate warming at a rate not seen in our geological history.

The Carboniferous Period also heralded an unprecedented rise in atmospheric oxygen levels. Near the end of this period, oxygen levels rose to 35 percent, a 75 percent increase over modern-day levels. The planet was warm, and as plant life and forests recovered from an extinction disaster in the Devonian, the continents again became lush and green. Vascular plants dominated a variety of ecosystems.

Giant horsetails, ferns and fern-like trees, primitive conifers called cordaites, and a host of other plants carpeted the landscape doing what they do best, sucking carbon dioxide from the atmosphere and producing oxygen. Their activity changed the balance of gases in the atmosphere and tilted it towards higher oxygen levels.

Higher oxygen levels created a denser atmosphere and intensely blue skies. But this oxygen also affected the plants and animals in Earth’s terrestrial ecosystems.

Insects and Fire

Anthropocene climate warming is increasing the frequency and intensity of wildfires. Warmer and dryer conditions around the globe have created massive forest fires in the boreal forest of Siberia and propagated devastating fires in Australia, ravaging large areas of the country. Each year fires in California and the Pacific Northwest become more intense, sparking fierce firenadoes and burning whole communities to the ground.

It was not always this way on Earth, and for most of the planet’s history, wildfires were unknown because atmospheric oxygen levels were too low. At oxygen levels of 16 percent or lower, wildfires won’t propagate, and at levels of 23 percent or higher, destructively intense fires spread uncontrollably. With atmospheric oxygen levels of 35 percent, Earth often degenerated into a burning hell during the Carboniferous

Evidence of frequent fires in the Carboniferous is found in fossil records which track the occurrence of charcoal from wildfires. Increasing fire frequency is correlated to periods during Earth’s history where high oxygen levels prevailed.

Animal life in the Carboniferous was also affected by high oxygen levels. Some forms of life benefit greatly from extra oxygen, and the Late Carboniferous marked the reign of giant insects. Like all animals, insects need oxygen for cellular respiration. But insects don’t use lungs and a circulatory system to distribute needed oxygen. Instead, they have a network of tiny tubes distributed throughout their bodies, allowing oxygen to reach all necessary tissues. It is a relatively inefficient way to distribute oxygen, and it limits their ultimate size since tubes that are too long run out of oxygen before reaching their final destination.

But air rich in oxygen allows the insects to grow larger. The predatory Carboniferous griffinflies, dragonfly-like creatures, had wingspans of over two feet. Giant carnivorous dragonflies, I don’t like the sound of that.

(Next Amniote Eggs and a CO2 Crisis)



The Age of Oxygen (Source: Smithsonian Environmental Research Center) 

Carboniferous : Tectonics and Paleoclimate (Source: Berkeley) 

The Carboniferous (Source: Berkeley) 

Effects of Uplift on Carboniferous Exhumation and Mountain Glaciations in Pericratonic Areas of SW Gondwana, Central Argentina (Source: Tectonics) 

A flammable planet: Fire finds its place in Earth history (Source: Earth) 

Reign of the giant insects ended with the evolution of birds (Source: UC Santa Cruz News Center) 

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.