Definition that contains geological time
- period a unit of geological time during which a system of rocks formed
- era a major division of geological time; an era is usually divided into two or more periods
- eon the longest division of geological time
- epoch a unit of geological time that is a subdivision of a period and is itself divided into ages
- aeon the longest division of geological time
- synchronic (of taxa) occurring in the same period of geological time
- geological era a major division of geological time; an era is usually divided into two or more periods
- geological period a unit of geological time during which a system of rocks formed