Small seal script was adopted in the Qin Dynasty for the purpose of standardizing the script which was issued by the first emperor of Qin dynasty，and it was stem from large seal script(大篆). At that time, every country had their own written words. When Yingzheng unified those countries, communication became a problem. As a result, he omitted and changed the Seal script which his own country used before to let it become a Common script. So we also call it Qin seal.
It has gone through quite a long process of historical development for pictographic writing to transform into a symbol of the recorded languages - Chinese characters. We can now see the earliest stereotypes text is the Oracle of the Yin and Zhou dynasty.
They were carved on tortoise shells and animal bones for continually divination in Shang dynasty. During divination, people would burn the tortoise shells first .When those tortoise shells cracked, people would judge good and bad according to them and carve the results of the divination on tortoise shells. So we call the characters which carved on tortoise shells or animal bones oracle-bone inscription.