The supercontinent Pangea formed. Major changes in ocean circulation; biogeographic differentiation; high bio-provincialism; diversification of land plants and increased continental weathering rates and storage of organic carbon as coal; drawdown of atmospheric CO2 and significant cooling, major glaciation, and sharp sea-level fluctuations; cyclic marine sequences; appearance of reptiles (with amniotic egg reproduction) and occupation of new (dry-land) niches; extinction or decreasing role of early Paleozoic biota such as stromatoporids, tabulate corals, trilobites, ostracods, heavily armored marine fish; appearance or very rapid diversification of foraminifera, ammonoids, fresh water pelecpods, gastropods, sharks, ray-finned fishes, and wingless insects. Late Carboniferous–Early Permian Kiaman Superchron is the longest known period of predominantly reversed polarity. HISTORY AND SUBDIVISIONS Because of climatic variability, the Carboniferous was a time of incredible diversification and abundant terrestrial biota. It signifies Earth's first episode of massive coal formation. The commercial production of coal led to the early development of Carboniferous stratigraphic classifications in three major regions: western Europe, eastern Europe, and North America.