Which layer of the earth is a solid but behaves like a liquid?

The asthenosphere is the correct answer because it is a layer of the Earth's upper mantle that is characterized by its ability to flow and deform over geological time despite being composed of solid rock. This layer exists beneath the lithosphere and extends from about 100 kilometers to 700 kilometers below the surface.

The unique properties of the asthenosphere allow it to accommodate the movements of tectonic plates on the Earth's surface. Although it is solid, the temperature and pressure conditions are sufficient to enable the solid material to exhibit plasticity, meaning it can flow slowly like a viscous liquid over long periods. This flow is crucial for processes such as mantle convection, which plays a significant role in plate tectonics.

In contrast, the core is primarily composed of iron and nickel and is mostly liquid in the outer core and solid in the inner core. The lithosphere is a rigid layer that includes the crust and the uppermost mantle, while the crust is the Earth's outermost layer that is also solid but does not exhibit the same liquid-like characteristics of the asthenosphere.