The southern supercontinent Gondwana had assembled by 550 MYA. Its wanderings and collisions, notably with the smaller Laurentia to the north, greatly affected life.
During the Carboniferous period (359–299 MYA), Gondwana drifted south, over the pole. The seas stood tall during the Early Carboniferous – some 200 meters above present day sea levels – but dropped precipitously during the Late Carboniferous, as Gondwana sprawled over the South Pole, locking up water in ice caps.
Sea levels fluctuated widely during the Carboniferous, as glaciers advanced and retreated. The causes of these dynamics are not well understood.
Climatic belts were well-developed during the Carboniferous: cold, temperate, and tropical. The tropics were a broad swath, at times reaching above the 30th parallel in both hemispheres. The term Carboniferous derives from the Latin for coal (carbo) carrying (ferre).
The evolution of the first woody plants during the Carboniferous resulted in vast freshwater and marginal marine swamps which were the hot spots of biodiversity at the time. These swamps were in the southern part of Laurentia, and the portion of Gondwana that is now the Appalachian Mountains, which was formed by collisions of the 2 continents.
Sea level fluctuations during the Late Carboniferous alternately exposed and drowned the swamps. Vast quantities of plant matter were buried by new growth during favorable conditions. The prodigious forests of the Paleozoic formed the great coal beds of Europe and eastern North America.
The burial of organic matter during the Carboniferous was not restricted to plants. Marine algae and zooplankton – the oceanic equivalent of forests – were rich stores of carbon. Large volumes of organic sediments accumulated on sea bottoms, creating vast reservoirs of petroleum in geologic time.