Which Earth layer is described as having viscous rock?

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

Answer: (B)

Viscosity describes how easily a material flows. In Earth’s interior, the temperature and pressure allow rocks to deform and flow slowly rather than break like a rigid solid. The mantle contains rocks that behave in a plastic, slow-flowing way, so they are described as viscous. This slow flow, especially in the layer just beneath the rigid crust (the asthenosphere), enables mantle convection that drives the movement of tectonic plates. The crust above is mostly rigid and brittle, not viscous, while the outer core is a liquid metal that flows differently and isn’t described as viscous rock; the inner core is solid. Therefore, the mantle is the layer with viscous rock.