The Aboriginal people did not develop writing but they painted pictures on rocks and bark. They also scratched or carved designs into rocks. They used paint that they made from crushed rocks and water in colours like brown, red, orange, and yellow. Many ancient cave paintings have been all over Australia. As the paints made form crushed rock and clay are not organic, it is not possible to use carbon dating to date these pictures. Some paintings have been found showing megafauna that became extinct over 40,000 years ago. These paintings may be the oldest known paintings in the world. Another site in Arnhem Land has charcoal drawings that have been radiocarbon-dated at 28,000 years old.