The scientist who studies the Earth's crust, mantle, continents, and ocean floor is called a geologist.

Here's why:

* Geology is the study of the Earth, including its composition, structure, history, and the processes that shape it.

* Geologists study a wide range of topics, including rocks, minerals, fossils, earthquakes, volcanoes, and the formation of mountains and oceans.

While there are sub-specialties within geology, like geophysicists who focus on the Earth's physical properties, all geologists contribute to our understanding of the Earth's structure and how it changes over time.