>I agree with you on the question of when. I'm sticking with the Neolithic.
Probably waaay off with this, but is it possible that early copper tools from the Levant could have fashioned tall prowed wooden craft which then made their way around the seaboard, whereupon they would have made such an impression on the (still stone using) inhabitants, that the images of the boats were deemed worthy of engraving?
I'm a bit hazy on how long it took for copper to get from down there to up here, but I know from experience that it makes a sharp enough edge to cut wood quite cleanly. A copper adze would probably make for a ship-worthy plank.
