East of F1 is a space named F2, believed to be a place of sacrifice, from which archaeologists have unearthed stunning cultural relics, like exquisite white and black pottery that has never been found on the Loess Plateau, and a large amount of carbonized rice.

"Some parts of the white pottery are as thin as eggshells. We don't know how ancient people made them," says Li Xiaolong, a member of the Nanzuo archaeological team, who is also an assistant professor at the Institute of Culture and Heritage of the Northwestern Polytechnical University in Xi'an, Shaanxi province.

Zhang Xiaoning, a member of the Nanzuo archaeological team, who is from the Gansu Provincial Institute of Cultural Relics and Archaeology, further explains: "Skills to make white pottery, and even kaolin, the raw material, have rarely been found on the Loess Plateau before.

"The black pottery may be related to the Qujialing Culture, dating back 4,500 to 5,100 years in the middle and lower reaches of the Yangtze River. Maybe there was some transportation or a trade route at that time."

Another perplexing discovery is the carbonized rice. "Such a large amount of rice found in the Yellow River basin, it's unprecedented and unbelievable," says Han.

According to him, the main crops in Gansu should be millet, and its scarcity is what made rice precious. People used the precious crops for sacrifice. Maybe rice was collected in administrative ways, but the possibility that it could be planted locally at that time cannot be excluded.