epoch vs modern era

epoch and modern era both are nouns.

Word	Noun	Adjective	Verb	Adverb
epoch	Yes	No	No	No
modern era	Yes	No	No	No

As nouns, modern era is a hyponym of epoch; that is, modern era is a word with a more specific, narrower meaning than epoch:

epoch: a period marked by distinctive character or reckoned from a fixed point or event
modern era: the present or recent times

Other hyponyms of epoch include day, age, historic period.

epoch (noun)	modern era (noun)
a period marked by distinctive character or reckoned from a fixed point or event	the present or recent times
a unit of geological time that is a subdivision of a period and is itself divided into ages
(astronomy) an arbitrarily fixed date that is the point in time relative to which information (as coordinates of a celestial body) is recorded