A fossil from a pine tree proves the Turpan-Hami Basin in the Xinjiang Uygur autonomous region, one of the hottest areas in China during summer, was cool 255 million years ago, with an average temperature of 13 C, Modern Express reported on Wednesday.

The fossil was found in 2012 and has a diameter of 15 cm. "After two years' study, we found it was a part of a pine tree that grew in Turpan more than 255 million years ago," said Wang Jun, a researcher at the Nanjing Institute of Geology and Palaeontology, under the Chinese Academy of Science. "Plants are a temperature gauge."

Wang said the xylem cells in the tree fossil are still whole. Through microscopic analysis, scientists found the tree was in poor shape and suffered damage from mites, the feces of which surrounded the tree.

Although Turpan was once cool enough for pines to grow, the current temperatures reach higher than 40 C.

The present drought-prone climate might have resulted from the formation of the Bogda Mountains, which influenced the circulation of air and blocked the movement of rain clouds, said Wan Mingli, a doctorate student at the institute.

The ultimate goal of the study is to explore why pines in the area became extinct suddenly after a thriving biological diversity from 300 million to 250 million years ago.