A geologic age is a subdivision of geologic time that divides an epoch into smaller parts. A succession of rock strata laid down in a single age on the geologic timescale is a stage.
This is a list of official and unofficial names for time spans in the geologic timescale and units of chronostratigraphy. Since many of the smallest subdivisions of the geologic timescale were in the past defined on regional lithostratigraphic units, there are many alternative names that overlap.