This is one of the riddles collected by Nikolaus Reusner, which you can read online at the University of Mannheim.
Aenigma: Quid Sum?
Sum terra, ex terra genitus, mox terra futurus;
Me terra genitum terra recondet item.
The vocabulary is keyed to the DCC Latin Vocabulary list. There are two words in this poem that are not on the DCC list:
aenigma (aenigmatis, n.): riddle, enigma
recondō, recondere: hide, conceal again
ego meī mihi mē: I, me
ex ē: out of, from (+ abl.)
homo hominis m.: human being
sum, esse, fuī: be, exist
terra -ae f.: land