地层

例句：

1. 1. The geologist studied the rocks in this area to understand its geological history.
   这位地质学家研究了该地区的岩石以了解其地质历史。
2. 2. The layers of rock are visible through a microscope.
   通过显微镜可以观察到岩石的层次。
3. 3. The formation of these layers is crucial for understanding the Earth's past climate.
   这些地层的形成对于理解地球过去气候至关重要。