Paleozoic

The Paleozoic Era is the earliest major division of the Phanerozoic Eon, spanning about 541 to 252 million years ago. It succeeds the Precambrian time and precedes the Mesozoic. The era is conventionally divided into six periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian; in some regional schemes the Carboniferous is split into Mississippian and Pennsylvanian, and the transitional boundaries vary.

Life in the Paleozoic began in the oceans with a rapid diversification of multicellular life, especially in the Cambrian following the Cambrian explosion, when many major animal phyla first appear in the fossil record. Marine communities included arthropods, mollusks, echinoderms, and early chordates. The Ordovician and Silurian saw further diversification and the first evidence of colonization of land by plants and arthropods. The Devonian is known as the Age of Fishes and marks the rise of jawed vertebrates and the first forests and terrestrial tetrapods.

In the Carboniferous, vast swampy forests produced extensive coal deposits, and land ecosystems supported diverse amphibians and the earliest amniotes, which gave rise to reptiles. Plate tectonics led to the formation of the supercontinent Pangaea late in the Paleozoic, accompanied by climate fluctuations and sea-level changes that shaped habitats.

The era ended with the end-Permian mass extinction, the largest extinction event in Earth’s history, eliminating many marine and terrestrial groups and paving the way for the Mesozoic. The Paleozoic, characterized by the evolution of hard parts and extensive fossil records, set the stage for later terrestrial ecosystems and modern vertebrates.