What are oceanic and continental crust?

• A. Oceanic crust is thin and dense under oceans; Continental crust is thicker and less dense
• B. Oceanic crust is thicker and less dense; Continental crust is thinner and more dense
• C. Oceanic crust is thinner and less dense; Continental crust is thicker and more dense
• D. Oceanic crust is thin and dense under oceans; Continental crust is thicker and less dense

Answer: (A)

The question is testing how oceanic and continental crust differ in thickness and density. Oceanic crust is relatively thin—about 7 kilometers on average—but very dense, because it’s made mostly of basaltic rocks. Continental crust, on the other hand, is much thicker—often tens of kilometers—yet less dense, since it’s composed largely of lighter granitic rocks. This combination means oceanic crust sinks lower and forms the ocean basins, while continental crust sits higher and forms the continents.

The described option captures the real relationship: oceanic crust is thin and dense under the oceans, while continental crust is thicker and less dense. The other statements mix up which crust is thicker or denser, so they don’t fit observed facts about crust properties.