On 8 July 2002, a team of Chinese and US scientists announced their discovery of rocks indicating that plate tectonics were active on Earth some 2.5 billion years ago. This is around 500 million years earlier than previously thought. The evidence comes from a belt of highly-folded rock, not far from the Great Wall of China. The 2.5 billion-year-old rock contains the mineral chromite (iron chromium oxide), which is only normally found in rocks from the deep ocean floor. The chromite and other minerals have been highy deformed at high temperature, suggesting that they had been moving away from a mid-ocean ridge. The work was carried out by Jianghai Li, Xiongnan Huang (Peking University) and Timothy Kusky (St Louis University) and was published by the Geological Society of America on 8 July 2002.