Coal forest

Coal forests were the vast swathes of wetlands that covered much of the Earth's tropical land areas during the late Carboniferous (Pennsylvanian) and Permian times. As vegetable matter from these forests decayed, enormous deposits of peat accumulated, which later changed into coal.

Much of the carbon in the peat deposits produced by coal forests came from photosynthetic splitting of existing carbon dioxide, which released the accompanying split-off oxygen into the atmosphere. This process may have greatly increased the oxygen level, possibly as high as about 35%, making the air more easily breathable by animals with inefficient respiratory systems, as indicated by the size of Meganeura compared to modern dragonflies.

Coal forests covered tropical Euramerica (Europe, eastern North America, northwesternmost Africa) and Cathaysia (mainly China). Climate change devastated these tropical rainforests during the Carboniferous period. The Carboniferous Rainforest Collapse was caused by a cooler drier climate that initially fragmented, then collapsed the rainforest ecosystem. During most of the rest of Carboniferous times, the coal forests were mainly restricted to refugia in North America (such as the Appalachian and Illinois coal basins) and central Europe.

At the very end of the Carboniferous period, the coal forests underwent a resurgence, expanding mainly in eastern Asia, notably China; they never recovered fully in Euramerica. The Chinese coal forests continued to flourish well into Permian times. This resurgence of the coal forests in very late Carboniferous times seems to have coincided with a lowering of global temperatures and a return of extensive polar ice in southern Gondwana, perhaps due to lessening of the greenhouse effect as the massive coal deposition process abstracted carbon dioxide from the atmosphere.

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Wikipedia