the pits vs hell on earth

the pits and hell on earth both are nouns.

Word	Noun	Adjective	Verb	Adverb
the pits	Yes	No	No	No
hell on earth	Yes	No	No	No

As nouns, the pits and hell on earth are synonyms defined as:

Other synonyms of the pits include hell, hellhole, inferno, snake pit.

the pits (noun)	hell on earth (noun)
any place of pain and turmoil	any place of pain and turmoil