He investigates interesting artifacts that others tell him about. Can he or anyone prove that the things he investigates are actually true? How can anyone prove that carving on a rock wall is 100 years or 1000 years old? No one can but that doesn’t keep them from being interesting to consider.
Actually, you can determine relative age of stone carving if it is exposed to the elements. Differential weathering, growth of lickens, etc. Also, check out Gloria Farley’s book: “In Plain Sight”. It examines in great detail many rock drawings and writing in the US which could be several thousand years old and written in European and North African scripts. Especially, Celtic runes, Iberian and Libyan scripts. Also celebrating various old gods and godesses like Epona, Tanit, Anubis. Quite amazing and fascinating.