The Chinese have consumed tea for thousands of years. The earliest physical evidence known to date, found in 2016, comes from the mausoleum of Emperor Jing of Han in Xi'an, indicating that tea was drunk by Han dynasty emperors as early as the 2nd century BC. The samples were identified as tea from the genus "Camellia" particularly via mass spectrometry, and written records suggest that it may have been drunk earlier. People of the Han dynasty used tea as medicine (though the first use of tea as a stimulant is unknown). China is considered to have the earliest records of tea consumption, with possible records dating back to the 10th century BC. Note however that the current word for tea in Chinese only came into use in the 8th century AD, there are therefore uncertainties as to whether the older words used are the same as tea. The word "tu" appears in "Shijing" and other ancient texts to signify a kind of "bitter vegetable" (苦菜), and it is possible that it referred to several different plants, such as sow thistle, chicory, or smartweed, including tea. In the "Chronicles of Huayang", it was recorded that the Ba people in Sichuan presented "tu" to the Zhou king. The state of Ba and its neighbour Shu were later conquered by the Qin, and according to the 17th century scholar Gu Yanwu who wrote in "Ri Zhi Lu" (日知錄): "It was after the Qin had taken Shu that they learned how to drink tea."