Photo taken on Aug. 10, 2015 shows a copper blade excavated from Jiren Taigoukou Ruins in Qialege'e Village in Nilka County in Ili Valley, northwest China's Xinjiang Uygur Autonomous Region. Archaeologists here found the earliest site where coal was used as fuel by human beings. The discovery, which indicates human beings had been using coal as fuel 3,500 years ago, is 1,000 years earlier than previous finds. (Photo: Xinhua/Shen Qiao)
