epoch

nouns

a period marked by distinctive character or reckoned from a fixed point or event

epoch, era

is derived from

(astronomy) an arbitrarily fixed date that is the point in time relative to which information (as coordinates of a celestial body) is recorded

date of reference, epoch

a unit of geological time that is a subdivision of a period and is itself divided into ages

epoch

is a part of

a unit of geological time during which a system of rocks formed

"ganoid fishes swarmed during the earlier geological periods"

is a type of (narrower)

the time of the physical formation and development of the earth (especially prior to human history)