Rock Art can be “interpreted” in many ways, including by modern artists and spiritual practitioners with purposes which may have either a lot or very little to do with the reasons it was produced long ago.
These modern interpretations can be useful to those who engage in them, even giving great pleasure and serenity.
Stones used for pecking petroglyphs, brushes used for applying paint, mortars used to grind pigments and small fireplaces used to change minerals into pigments, these and other objects can link rock art with more typical archaeological materials found in the ground.
Rock art, whether shields, large human-like figures, or even mere handprints, may have been used mark territory, homes, food storage, or other things.
Or they may record partial histories of entire villages or peoples.
Such records are partly like the buffalo skins known as “Winter Counts” which could continue for 80 years, one important event each year. Quite a large vocabulary of signs can now be interpreted in this style of rock art, not because of any single “Rosetta Stone”, but because of the combination of details preserved in many places.
As soon as patina is removed, bacteria start to create patina again on the new surface.
Roughly, we can say that darker petroglyphs are older, because they have been exposed longer to formation of patina.
Stone is not directly datable in the time frame of human history. It is created by bacteria living on the rock and attaching clay particles to the rock.