Subdivisions of eras based on the relative abundance of certain types of fossils. For example, the Paleozoic Era is divided into the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian Periods.
Subdivisions of eras based on the relative abundance of certain types of fossils. For example, the Paleozoic Era is divided into the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian Periods.