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 6 foot centipede, in the center is a terrestrial isopod (ancestor to modern Sea Slaters and Sow Bugs), on the right is a two-foot-long scorpion, and in between are dozens of prehistoric cockroaches, some taking briefly to the searing air. Submerged in the relative comfort of the water, a salamander awaits the prospect of an easy meal.

300 million years ago during the Carboniferous period, the Earth's atmosphere may have contained 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.