Imagine an old map, a map with a path to a treasure, like the ones you remember from cartoons. The map's partially destroyed, because it's so old, and it has been exposed to air, and heat, and water, and people touching it, you name it.

My question is: what happened to the paper? Which verb describes it best? I mean the proces of paper getting thinner and more delicate, to the point where a touch can make it turn into powder. Does paper decay? Decompose? I guess not in this case, as the two IMHO refer to what happens when bacteria "feed" on organic matter. So what is it?