Science Olympiad Dynamic Planet Practice Test

What distinguishes the oceanic lithosphere from the continental lithosphere?

1. It is less dense than continental lithosphere

2. It consists mainly of mafic crust and ultramafic mantle

3. It is significantly thicker than continental lithosphere

4. It does not exist in ocean basins

The correct answer is: It consists mainly of mafic crust and ultramafic mantle

The oceanic lithosphere is primarily distinguished by its composition, which consists mainly of mafic crust and ultramafic mantle materials. Mafic rocks, rich in magnesium and iron, form the oceanic crust mainly as basalt, which is denser than the granitic composition of continental crust, which is more silicic. Below this oceanic crust lies the ultramafic mantle, characterized by olivine and pyroxenes, further contributing to the overall density of the oceanic lithosphere. The compositional difference is crucial for understanding various geological processes, including tectonics and the dynamics of plate movements. This composition is a key factor in explaining how oceanic plates behave differently than continental plates during subduction and other tectonic activities. Understanding this distinction helps to clarify why the oceanic lithosphere is typically thinner and denser compared to its continental counterpart, but the primary identifying feature is indeed its composition of mafic crust over an ultramafic mantle.