Phanerozoic eon vs Phanerozoic aeon

Phanerozoic eon and Phanerozoic aeon both are nouns.

Word	Noun	Adjective	Verb	Adverb
Phanerozoic eon	Yes	No	No	No
Phanerozoic aeon	Yes	No	No	No

As nouns, Phanerozoic eon and Phanerozoic aeon are synonyms defined as:

Phanerozoic eon and Phanerozoic aeon: the period from about 540 million years ago until the present, a period when abundant life existed

Other synonyms of Phanerozoic eon include Phanerozoic.

Phanerozoic eon (noun)	Phanerozoic aeon (noun)
the period from about 540 million years ago until the present, a period when abundant life existed	the period from about 540 million years ago until the present, a period when abundant life existed