Here the 1830 typesetter added the definite article the before earth, although the preceding heaven also lacks the definite article (“things in heaven”). As explained under Mosiah 12:36, when the preposition is in, the most common conjoining of heaven and earth in the Book of Mormon (as well as in the King James Bible) is without the for both of the two nouns (that is, the most common phraseology is “in heaven … in earth”). Here in Helaman 8:24, the critical text will restore the earliest text, which lacks the the before earth.
Summary: Remove in Helaman 8:24 the intrusive the before earth; the earliest extant text (the printer’s manuscript) reads without the before earth, which is the most common way in the text of expressing conjuncts of heaven and earth in prepositional phrases headed by in.