Scientists have discovered what is believed to be one of the world's oldest doodles - an ancient scrawl carved onto a rock by a caveman 4,500 years ago. Cambridge University experts believe the crudely etched circles are the Neolithic version of a modern office worker's scribbles on a post-it note. The 6.6in (17cm) chunk of sandstone was discovered by an amateur archaeologist from the bottom of a deep quarry in Over, Cambs., during a university fun day.