The Paleozoic ERA is a period of time in Earth's history that lasted from 541 million years ago to 251 million years ago. It is divided into six periods: the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. During this time, life on Earth evolved from simple, single-celled organisms to complex, multi-celled animals. The Paleozoic ERA is known for the emergence of fish, amphibians, reptiles, and the first land plants. It was also a time of great geological change, with the formation of mountain ranges and the breakup of the supercontinent Pangaea.