Complex life first became abundant in the oceans and later moved onto land during the Paleozoic Era. Spanning from about 541 to 252 million years ago, the era includes the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods.

The Cambrian explosion produced a wide array of marine animals with hard parts. Fish diversified, plants and invertebrates colonized the land, and vast coal swamps formed in the Carboniferous. The era closed with the largest mass extinction in the fossil record, eliminating many marine groups.

Paleozoic rocks contain important coal, petroleum, and mineral resources. Their fossils document the assembly of early ecosystems and the changing geography of continents that were assembling into Pangaea. The era sets the stage for the Mesozoic world that followed.

• Geologic era from 541 to 252 million years ago
• Records rise of complex marine and terrestrial life
• Includes six periods from Cambrian to Permian
• Ended by the largest known mass extinction