Original: The Paleozoic spanned from roughly ( ICS , 2004 ) , and is subdivided into six geologic periods ; from oldest to youngest they are : the Cambrian , Ordovician , Silurian , Devonian , Carboniferous , and Permian .
Simplified: The Palaeozoic ( or Paleozoic ) era is the earliest of the three eras of the Phanerozoic .