Upper Carboniferous vs Upper Carboniferous period

Upper Carboniferous and Upper Carboniferous period both are nouns.

Word	Noun	Adjective	Verb	Adverb
Upper Carboniferous	Yes	No	No	No
Upper Carboniferous period	Yes	No	No	No

As nouns, Upper Carboniferous and Upper Carboniferous period are synonyms defined as:

Upper Carboniferous and Upper Carboniferous period: the period from 310 million to 280 million years ago; characterized by warm climate and swampy land

Other synonyms of Upper Carboniferous include Pennsylvanian, Pennsylvanian period.

Upper Carboniferous (noun)	Upper Carboniferous period (noun)
the period from 310 million to 280 million years ago; characterized by warm climate and swampy land	the period from 310 million to 280 million years ago; characterized by warm climate and swampy land