Palaeozoic Era

Major periods

The Palaeozoic is conventionally divided into six well‑known geologic periods, each characterized by particular evolutionary and environmental trends:

• Cambrian – a rapid increase in the diversity of marine animals, often called the "Cambrian explosion".
• Ordovician – continued diversification of marine life and the first evidence for widespread plankton; ended with a significant glaciation and extinction event.
• Silurian – stabilization of sea levels, reef expansion, and early vascular plants appearing on land.
• Devonian – the "age of fishes," with major fish diversification and the earliest tetrapods and forests.
• Carboniferous – extensive swampy forests that produced large coal deposits and the rise of terrestrial arthropods and amniotes.
• Permian – the assembly of the supercontinent Pangaea and the close of the era with the largest known mass extinction.

Life and environments

Marine ecosystems dominate the early record: trilobites, brachiopods, molluscs and early echinoderms were common. Over the course of the era, life moved onto land. Simple plants, fungi and arthropods appear first, followed by vascular plants, forests and terrestrial vertebrates. By the late Palaeozoic, complex ecosystems with trees, seed‑bearing plants and fully terrestrial vertebrates—including early reptiles—had become established. These biological advances set the stage for subsequent Mesozoic ecosystems.

Geology, climate and tectonics

Tectonic activity during the Palaeozoic rearranged continents and ocean basins. Several orogenies (mountain‑building events) and the progressive collision of landmasses contributed to the formation of the supercontinent Pangaea by the end of the Permian. Climate varied from warm greenhouse intervals to episodes of cooling and glaciation, particularly affecting southern continents. Extensive peat swamps in the Carboniferous were later transformed into major coal seams that are economically important today.

Extinctions and legacy

The era contains multiple extinction events of varying magnitude. The terminal Permian extinction, often called the Permian–Triassic extinction, was the most severe in Earth history and marks the end of the Palaeozoic; for more detail see Permian–Triassic extinction. The biological turnover across these crises reshaped ecosystems and influenced which groups dominated in the Mesozoic.

Notable facts

• The Palaeozoic saw the first hard skeletons and abundant fossil record that allow detailed study of early animal evolution.
• Many modern groups (insects, amphibians, reptiles, seed plants) have their roots in this era.
• Coal and other fossil resources formed from Palaeozoic vegetation are economically and historically significant.

Because of its duration and the dramatic biological and geological changes it records, the Palaeozoic is a central focus for studies of evolution, paleoclimate, and plate tectonics.