Around 3,200 BCE, writing appeared in the Sumerian area of Mesopotamia, and it was made by making imprints in clay or cutting onto other surfaces. The emergence of writing with ink occurred around 2,500 BCE, roughly at the same time in Egypt and China. Writing with ink is much more durable than writing in clay or stone and thus has survived longer. Ink was probably first used by hunters who scratched their marks on animal skins to identify friends and food sources. It may have been later developed for use in religious ceremonies since many ancient drawings show that people were experimenting with how symbols looked when they were written with ink rather than charcoal. The first evidence of ink comes from studies of dirt found under the nails of mummies. The color of this dirt indicates which part of the world early writers lived in. Black dirt shows that the writer came from Africa while red dirt shows that the writer came from Asia or Europe. Blue dirt means that the writer came from America or Australia. In addition to identifying where people came from, dirt under the fingernails also tells us about what they wrote. A deep scratch pattern that covers most of the nail bed indicates that the person used a tool called a "graver" to write. Smaller scratches or dots that are closer together indicate that the person used a brush instead. The difference between gravers and brushes affects how their writings look.