The Paleozoic era is the geological era that ran from the end of the Precambrian era, about 543 million years ago, to the beginning of the Mesozoic era, about 251 million years ago. It is generally subdivided into six periods:
The Cambrian, Ordovician, and Silurian make up the Lower Paleozoic, and the Devonian, Carboniferous, and Permian comprise the Upper Paleozoic.
At the start of the Paleozoic, multicelled animals underwent a spectacular growth in diversity, called the Cambrian Explosion, and almost all living animal phyla appeared within a few millions of years. At the end of the Paleozoic occurred the largest mass extinction in Earth's history, wiping out roughly 90% of all marine animal species.