Paleozoic Era, also spelled Palaeozoic, major interval of geologic time that began 541 million years ago with the Cambrian explosion, an extraordinary diversification of marine animals, and ended about 252 million years ago with the end-Permian extinction, the greatest extinction event in Earth history. The major divisions of the Paleozoic Era, from oldest to youngest, are the Cambrian (541 million to 485.4 million years ago), Ordovician (485.4 million to 443.8 million years ago), Silurian (443.8 million to 419.2 million years ago), Devonian (419.2 million to 358.9 million years ago), Carboniferous (358.9 million to 298.9 million years ago), and Permian (298.9 million to 252.2 million years ago) periods. The Paleozoic takes its name from the Greek word for ancient life.