Coals were originally formed from plants that require plenty of water or precipitation. Thus, regions with coal were wet and warm. In contrast, evaporites were formed in arid and hot regions where evaporation is strong. Therefore, coals and evaporites are commonly used as qualitative indicators of wet and dry climate conditions, respectively, in deep-time climate studies. However, quantitative relationships of coals and evaporites with temperature and precipitation have never been established.