era

Any of the major divisions of geological time that includes several periods but is part of an eon. The eras of the current Phanerozoic in chronological order are the Palaeozoic, Mesozoic, and Cenozoic. We are living in the Recent epoch of the Quaternary period of the Cenozoic era.

Geological time is broken up into geochronological units of which era is just one level of division. The hierarchy of geochronological divisions is eon, era, period, epoch, age, and chron. Eras are subdivisions of eons and periods are subdivisions of eras. Rocks representing an era of geological time comprise an erathem.