While Digging Through an Old Wooden Chest Kept in the Attic

While digging through an old wooden chest kept in the attic, Mark finds an old newspaper under a rubber toy. He lifts up the toy and sees that the paper is still white and the print is easily readable under the toy, but the rest of the paper is yellowing and almost brown. In at least three sentences, discuss whether a physical or chemical change has occurred with the yellowing of the paper, and provide information to support your conclusion.