According to Hai, in foreign countries, this step is mainly accomplished by machines, and the difference in methods is related to the different situations of layer deposit between East Asian and Western countries.

Although technology has been applied for this work in China as well, it cannot replace manpower as of now. "In China, conducting archaeological exploration with Luoyang shovel is still the most time-consuming and labor-consuming method," says Hai.

"At first, the work was really tiring for me," says Zhang, 35.

He learned the coring technique from senior workers in Shouxian county, Anhui province, for a year, going to the field every day to listen to their teaching and trying by himself. Although he wore gloves at work, he soon had blisters in his hands, which later turned to calluses.

"I didn't want to show my hands to others at that time," recalls Zhang, who couldn't identify the layers at first, but mastered the skills after about four to five years.

His work brings rewards.

"My satisfaction came when our exploration work finished. People excavated the site and discovered that the result of our exploration was close to their final conclusion. It means our work could really provide a reference for them," says Zhang.

For veteran technician Niu Xiuping, 60, who has been devoted to field archaeological projects at the Shanxi Provincial Institute of Cultural Relics and Archaeology for nearly 40 years and is about to retire in June, field archaeology is "quite interesting, but boring as well".

Repetition can lead to boredom. But when they discover something, everyone is amazed.