We can presume with near certainty that there are vast quantities of lost artifacts from lost civilizations of early humans that were crafted from organic matter that have just deteriorated to dust. We say "Stone Age" only because stone artifacts are the only to survive. You can assume there were orders of magnitude more and more sophisticated artifacts and art works made from wood or mud or skins that are just gone forever. It's also entirely possible some of those artifacts contained something akin to written language but whatever it was is long gone.