How does an eraser remove pencil marks?

When you write with a pencil, you leave a thin layer of graphite particles sitting on the surface of the paper rather than soaking into it. An eraser grips those particles: its material is a little tacky, and the friction of rubbing helps it pick them up, so the graphite sticks to the eraser better than to the paper. The worn-off crumbs trap the graphite and are brushed away. Before erasers, people used balls of moist bread. In 1770 the English instrument maker Edward Nairne is said to have picked up a piece of natural rubber by mistake and found it worked much better. The same year, Joseph Priestley noted that the substance was excellent for wiping away pencil marks, and the name 'rubber' comes from its ability to rub them out.