I'm 29 african american and recently noticed faint lines in both thumb nails.i can't tell if there ridges.is this normal?

Black Nail Pigment: Melanonychia, or melanin-derived brown-to-black nail pigmentation, is a diagnostic challenge for clinicians. The most serious disease of the nail unit, melanoma, primarily presents with melanonychia. However, melanonychia most often occurs as a result of benign etiologies such as nail matrix melanocytic activation, nail matrix melanocytic hyperplasia, and nail invasion by pathogens.