Giants and Wildfires in the Carboniferous

360 million years ago, the descendants of the first photosynthetic algae had claimed land all over the Earth's supercontinents in the form of high forests and dense thickets as the Earth entered the Carboniferous Period. As these flora expired, they were quickly buried by new layers of flora, forming thick organic deposits which, under immense heat and pressure of overlying sediments, came to form what humans now know as coal, petroleum and natural gas deposits, thus inspiring the period's name. The Carboniferous is famous for its colossal trees, monstrous millipedes and hawk-sized dragonflies-an ostensible crossbreed between the worlds of Tim Burton and Dr. Seuss. At the heart of the science of the Carboniferous lies a single molecule: free oxygen.

Oxygen is an element with as much life-giving force as it has destructive force. While plants and animals perform a respiratory tango, oxygen itself waltzes life from birth to death by being both a necessary element and that which eventually oxidizes cells to their demise. Oxygen further subverts against its life-giving qualities by being extremely combustible. This said, findings that oxygen levels were significantly higher during the Carboniferous are likely of important consequence. In spite of its its seemingly doomsday characteristics, there is evidence that these elevated oxygen levels allowed an extraordinary evolutionary step regarding the number of insect families, their individual sizes, and the efficiency of flight. It also may have eased the respiratory transition of our earliest ancestors from marine to terrestrial environments.

In North American geology, the Carboniferous is bisected into two sub-periods: the Mississippian (359-318 million years ago) and the Pennsylvanian (318-299 million years ago). The Mississippian bore witness to the continents of Laurasia and Gondwana-the former including the modern North America and Eurasia, and the latter made up of South America, Africa, India, Australia and Antarctica. Laurasia was located near the equator and was mainly large swamp lands and tropical rain forests. Evidence for this lies in the fossil record from the coal basins of North America, Western Europe, and the Donets Basin in the Ukraine: examination of growth rings in fossilized plants from these areas show weak seasonal growth, indicative of a year-round warm climate (Wickander and Monroe, 2007). Conversely, the strong tree rings of Carboniferous Siberia indicate a more temperate location with defined seasons. Southern Gondwana was covered in glaciers, as shown by present day tillite deposits and glacial striations (Wickander and Monroe, 2007). As today, the areas of warmer climate facilitated higher populations of and diversity amongst fauna and flora.