The Earth's innermost layer is a solid ball primarily composed of iron. Which term describes this layer?

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

Answer: (B)

The main idea is identifying the solid, iron-rich center of the Earth. Even though temperatures are extremely high at the center, the immense pressures keep this region solid, not liquid. That solid sphere, primarily iron with some nickel, is the inner core. Surrounding it is a liquid iron-nickel layer—the outer core—that moves and creates Earth’s magnetic field. Above that lies the mantle, made of silicate rock, and then the crust, which is the outermost solid shell. So the term for this solid innermost layer is the inner core.