archean vs archaean

archean and archaean both are adjectives.

Word	Noun	Adjective	Verb	Adverb
archean	No	Yes	No	No
archaean	No	Yes	No	No

As adjectives, archean and archaean are synonyms defined as:

archean and archaean: of or relating to the earliest known rocks formed during the Precambrian Eon

archean (adjective)	archaean (adjective)
of or relating to the earliest known rocks formed during the Precambrian Eon	of or relating to the earliest known rocks formed during the Precambrian Eon