In the U.S.A. the Carboniferous is divided into the Mississippian (lower part, 358.9–323.2 mya) and the Pennsylvanian (upper part, 323.2–298.9 mya). In Europe the terms upper, middle and lower are used, or the specific names of the constituent series or stages.
The early tetrapods split first into two major groups: the amphibians, which laid their eggs in water, and the amniotes, distinguished by laying their cleidoic eggs on land. The amniotes gave rise to two groups both of which became dominant at different times. They were the Synapsids, which eventually gave rise to the mammals, and the Sauropsids, which gave rise to the dinosaurs and other reptiles. These momentous events took place in the lower part of the Carboniferous, the Mississippian.
The Carboniferous is named after the Coal Measures, the remains of peat formed by dense tropical wetland forests. This biota occurred in the upper part of the period, the Pennsylvanian, from 315–300 million years years ago.
These forests were on the equator, and the wetlands, which are always low-lying, stretched from America in the west, through what is now Europe to China in the east, because the continents were all together at the time (Pangea). The river plain which was the heart of the wetland stretched 5000 km from eastern Canada to the Ukraine, and was 700 km wide.p6
The kind of climate and geography has no exact parallel today, but the Amazon Basin, the Mississippi River system and the Okeefenokee swamp give some idea. The swamps were dominated by giant clubmosses, including Lepidodendron. They were the earliest trees, later superseded by conifers and flowering plants. Also occasionally swept down by the river were the plants from the levee, such as horsetails, ferns and tree-like pteridosperms.
The wetland forests ended when the land level was raised by the pressure of the Gondwana continent against Laurussia, causing the zone of contact to be raised. The end of the Coal Measures marks the end of the Carboniferous period. China was too far away to be affected, and there the wetland forests continued for another 50 million years, into the early Permian.p30
|Precambrian (4.567 gya – 541 mya)|
|In the left column are Eons, bold are Eras, not bold are Periods. gya = billion years ago, mya = million years ago|
|Hadean (4.567 gya – 4 gya)|
|Archaean (4 gya – 2.5 gya)||Eoarchaean (4 gya – 3.6 gya)|
|Proterozoic (4 gya – 2.5 gya)||Palaeoproterozoic (2.5 gya – 1.6 gya) Siderian (2.5 gya – 2.3 gya) Rhyacian (2.3 gya – 2.05 gya) Orosirian (2.05 gya – 1.8 gya) Statherian (1.8 gya – 1.6 gya)|
|Phanerozoic (541 mya – today)|
|In the left column are Eras, bold are Periods, not bold or italics are Epochs, Italics are stages. kya = thousand years ago, mya = million years ago|
|Palaeozoic (541 mya – 252.17 mya)||Cambrian (541 mya – 485.4 mya)|
|Mesozoic (252.17 mya – 66.0 mya)||Triassic (252.17 mya – 201.3 mya) Lower Triassic (252.17 mya – 247.2 mya) Middle Triassic (247.2 mya – 237 mya) Upper Triassic (237 mya – 201.3 mya)|
|Cainozoic (66.0 mya – today)||Palaeogene (66.0 mya – 23.03 mya) Palaeocene (66.0 mya – 56 mya) Eocene (56 mya - 33.9 mya) Oligocene (33.9 mya – 23.03 mya)|
|Source||International Chronostratigraphic Chart 2013. International Commission on Stratigraphy, retrieved 8 April 2013. Divisions of geologic time – major chronostratigraphic and geochronologic units USGS, retrieved 8 April 2013.|