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BGS Geological Time Division Ranks
The rank of a geochronological division specifies how large it is and what sort of sub-divisions it contains.
Geologists label divisions of geological time with named ranks which indicate which level of the hierarchy of terms they belong to. The preferred labels in this scheme are the chronological rank names; the equivalent stratigraphical rank name is provided as an alternative label.
Age
Stage
A sub-division of a Sub-epoch.
Eon
Eonothem
The largest division of geological time, measured in hundreds or thousands of millions of years.
Aeon
Epoch
Series
A sub-division of a Sub-period.
Era
Erathem
A sub-division of an Eon. Typically measured in tens of millions years.
Marine Isotope Stage
A fine subdivision of the Quaternary Period. There are over 100 recognised marine isotope stages.
Period
System
A sub-division of a Sub-era.
Sub-Age
Sub-Stage
A sub-division of an Age.
Sub-Epoch
Sub-Series
A sub-division of an Epoch.
Sub-Era
Sub-Erathem
A sub-division of an Era.
Sub-Period
Sub-System
A sub-division of a Period.