541–252 Million Years Ago

Paleozoic Era

The Paleozoic Era, meaning 'ancient life,' spans nearly 300 million years and witnessed some of the most transformative events in the history of life. It began with the Cambrian Explosion — an evolutionary burst that produced most major animal body plans within a few tens of millions of years. Trilobites, brachiopods, and early echinoderms filled Paleozoic seas, while the first vertebrates — jawless fish — appeared in the Ordovician. By the Devonian, fish had diversified enormously, earning that period the title 'Age of Fishes.' The colonization of land by plants and arthropods reshaped terrestrial ecosystems, and by the Carboniferous, vast coal swamps supported giant insects and the first reptiles. The era concluded with the Permian–Triassic extinction, the deadliest mass extinction in Earth's history, which eliminated roughly 90% of marine species.