Earth in a tasting note means the smoke reminded someone of dry soil, a damp cellar, or mineral dust. It is a common description for Nicaraguan cigars and some Cuban-seed cigars. It does not mean that soil was added to the cigar.
Use it as a general description, not as an exact measurement. Two smokers will not experience it in exactly the same way. When a review on Smoke Rings says earth, it means this ordinary association, not a score on a numbered flavor chart.
Related words in this glossary: leather and cocoa. None of them describes strength or body.