conservation for art is "preserving, fixing, or just restoring old art or other things like artifacts etc." (found in an article on www.msaconservation.com) it's most likely controversial because if something's old and valuable, people want to keep it in it's original form. (just a guess) but that's how it is in the art world.
It is believed that the majority of the petroglyphs were carved from about 1300 through the late 1680s.
