The study looked at ancient soil in Xi'an, China, to figure out what the climate and water levels were like in the past. By studying certain minerals in the soil, they found that the area used to have a warm, wet climate with lots of rain and lush forests. The soil was very moist, with groundwater reaching deep underground. This suggests that the region had a positive water balance, meaning it received more water than it lost. Overall, the findings indicate that the Xi'an area had a subtropical climate with plenty of moisture for plants to grow well.