Which statement is TRUE regarding Earth's core and its magnetic field?

• A. Earth's core is entirely liquid.
• B. The inner core is solid.
• C. Earth's core contains no iron.
• D. All layers of the core are solid.

Answer: (B)

The inner core being solid is corroborated by extensive seismic data which indicates that the inner core is primarily composed of iron and nickel that exists in a solid state due to the immense pressure found at that depth. The pressures are so high in the inner core that even though temperatures are comparable to the surface of the sun, the metals cannot melt and remain solid.

Further supporting this, the outer core is indeed liquid, and this movement of liquid iron underpins the generation of Earth’s magnetic field through the dynamo effect. Therefore, the characterization of the inner core as solid is key to understanding both the structure of the Earth's core and the nature of the magnetic field it generates.

The other statements misrepresent the structure and composition of the Earth's core; for instance, the outer core is liquid, indicating that not all layers of the core are solid, and iron is the primary component of both the outer and inner cores, making any claim that the core contains no iron inaccurate.