Which layer of the Earth's interior is described as semi-liquid?

• A. Outer Core
• B. Mantle
• C. Crust
• D. Inner Core

Answer: (B)

The concept being tested is how the layers of Earth differ in how they behave physically. A semi-liquid layer means something that is not fully liquid but can flow slowly over long times. The mantle fits this description because, while it is mostly solid rock, its upper part is hot enough that rocks become partially molten and can deform and move like a viscous fluid. This partial melting in the upper mantle lets it behave as a semi-fluid layer, enabling convection currents that drive the movement of tectonic plates above. In contrast, the crust is solid and rigid, the inner core remains solid under extreme pressure, and the outer core is a fully liquid layer of iron-nickel, not semi-liquid.