What is a Geological Age?

The term "Pleistocene Series" in "Middle Pleistocene Series Jiuquan Formation" denotes chronostratigraphy, and the Pleistocene it corresponds to is what geologists call the geological age. The hierarchical geochronologic units are eon, era, period, epoch, age, and chron, and the corresponding chronostratigraphic units are eonothem, erathem, system, series, stage, and chronozone. "Period" is a basic unit of geological time in the Geologic Time Scale. It is divided into the Precambrian, Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Paleogene (Paleocene, Eocene, Oligocene), Neogene (Miocene, Pliocene), and Quaternary (Pleistocene, Holocene) in descending order.