Answer the following question given this paragraph: 

The study of rock strata is called stratigraphy . The laws of stratigraphy can help scientists understand Earth’s past. The laws of stratigraphy are usually credited to a geologist from Denmark named Nicolas Steno. He lived in the 1600s. The laws are illustrated in the Figure below ; refer to the figure as you read about Steno's laws below.


Q: What is the study of rock strata called?


A:
stratigraphy