This file photo provided by Tibet Institute for Protection and Research of Cultural Relics on Aug. 16, 2018 shows members of an archaeology team working at the Melong Tagphug cave site in Ngari Prefecture, southwest China's Tibet Autonomous Region. The Melong Tagphug cave site containing delicate stone tools and pottery shards believed to be at least 4,000 years old was unearthed in Ngari Prefecture of China's Tibet. It is the first prehistoric cave site confirmed on the Qinghai-Tibet Plateau. (Xinhua)