The Shang Dynasty was also believed to be a myth for a long time, but its existence has been corroborated by many archaeological discoveries since 1959. The Shang Dynasty supposedly began when the last Xia ruler was overthrown in a rebellion. During this time, the Chinese developed a fairly sophisticated writing system, a very early version of written Chinese character still used to this day. Written inscriptions have been found on turtle shells and animal bones (known as oracle bones) as early as 1500 BCE. Such oracle bones "shell bone") were used by ancient Chinese rulers for divination. These ancient Chinese believed that the natural elements of the world came from some mystical power which could cause natural disasters such as floods and drought. They would try to predict or divine the future by drilling holes in the bones, then heating them until they cracked. A diviner would then read the cracks which were viewed to be messages from nature and inscribe the messages on the shells or bones