Final answer:
The correct answer is a) oceanic crust, made of denser basaltic rock, and continental crust, composed of less dense granitic rock. Oceanic crust is thinner and denser while continental crust is thicker and less dense, both being types of igneous rock.
Step-by-step explanation:
Earth has two different types of crust: oceanic crust, which is made of denser basaltic rock, and continental crust, which is made of less-dense granitic rock. The correct answer to the student's question is a) oceanic, continental.
Oceanic crust is typically about 6 kilometers thick and is composed of volcanic rocks known as basalt, which are denser and made primarily of elements like silicon, oxygen, iron, aluminum, and magnesium. On the other hand, the continental crust is considerably thicker, ranging from 20 to 70 kilometers, and predominantly consists of granite, a volcanic class of silicates with a lower density that allows the continental crust to rise higher on the mantle.
Both the oceanic and continental crusts are forms of igneous rock, cooling from a molten state. The key difference lies in their density and composition, which in turn affects their structure and position in relation to the mantle.