When did people start divining with tortoise shells?

People didn't use tortoise shells for divination from the beginning. According to legend, Fu was inspired by the negative image of the dragon and horse, and "began to draw gossip to understand the virtue of the gods." It shows that as early as the matriarchal clan period, the ancestors had invented the method of "good luck" to predict good or bad luck. Later, Shennong "called the king by fire" and invented the method of divination by fire. At that time, people regarded fire as an extremely sacred thing, and all gatherings in the clan lit bonfires and discussed around them. When the tribe faces some major events, the more people gather, the bigger the fire will be. Wanghuo often makes a burst sound. People call this burst spark "heat" and often associate it with major events after heat. From this development, people will consciously barbecue bamboo joints and animal bones to make them burst and predict the success or failure of a thing. If there is a crisp and loud crack, it is "chastity" and things can be done; If you make a low, weak voice, it is "disloyalty" and things are difficult to achieve; If there is no movement after burning, it is an ominous sign. Perhaps, people have found a lot of barbecue things, and finally they all focus on tortoise shells.