Mean atmospheric O2
Geologic Time Scale
Fire rages through a prehistoric forest of towering Sigillaria and Cordaites, Asterophyllites, Calamites, and ferns. In the foreground a potpourri of giant Carboniferous invertebrates flee the conflagration, heading for the only real estate not subject to burning: water. On the left is a giant, 3 foot centipede; in the center is a giant Arthropleura, the largest known arthropod ever to walk the earth; on the right is a two-foot-long scorpion, and in between are dozens of prehistoric "roachoids," some taking briefly to the searing air. On the far left submerged in the relative comfort of the water is an amphibian of the genus Dendrerpeton awaiting the prospect of an easy meal.
300 million years ago the Earth's atmosphere may have held considerably more oxygen than today; the air may have been as much as 35% oxygen (the air we breathe now is 21% oxygen). Such high oxygen levels may help to explain why so many terrestrial invertebrates--insects, arachnids and some crustaceans--grew to such enormous sizes. These invertebrates "breathe" by adsorbing oxygen directly through their skin. Another consequence of such an oxygen-rich environment would be an increased propensity for organic matter to combust. Forest fires sparked by lightning or volcanic activity must have burned with a special ferocity.
|*AKA Carboniferous/ Pennsylvanian|
Copyright © Walter B. Myers. All rights reserved.
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