The planet's internal structure is characterized by several distinct, layered zones that vary in composition and physical state. The outermost layer is the crust, a relatively thin and rigid silicate rock that forms the solid surface. Beneath the crust lies the mantle, which extends to depths where it transitions into a more plastic state, allowing for large-scale convection currents. The deeper mantle includes a transition zone and an underlying lower mantle. At the planet's deepest levels is the core, composed primarily of iron and nickel. This core is further differentiated into a solid inner core and a liquid outer core, the latter of which generates a protective global magnetic field through the movement of conductive material.