Select the option that can be used as a one-word substitute for the given group of words.
A person who studies the Earth and the materials of which it is made

Let's look at the definitions:
Geologist: An expert in or student of geology, the science that deals with the Earth's physical structure and substance, its history, and the processes that act on it. (Correct)

Anthropologist: A person who studies human societies and cultures and their development.

Biologist: A scientist who studies living organisms.

Zoologist: A scientist who studies the behavior, physiology, classification, and distribution of animals.