The center of the Earth consists of which core structure?

• A. A single metallic sphere at the center with no distinct layers.
• B. A hollow core made of nickel.
• C. An inner core of solid iron and nickel and an outer core of liquid iron and nickel.
• D. A liquid iron core with no solid phase.

Answer: (C)

Two distinct core layers exist at Earth's center: a solid inner core and a surrounding liquid outer core. The inner core is a solid sphere made mainly of iron with some nickel, kept solid by the immense pressures present deep inside the planet. Surrounding it is the outer core, a layer of liquid iron–nickel.

Seismic evidence underpins this structure. S-waves cannot travel through liquids, so their absence in the outer core region shows that layer is liquid. P-waves do travel through but slow and bend at the boundaries, consistent with a transition from a solid inner core to a liquid outer core. The liquid motion in the outer core also accounts for Earth’s magnetic field through the geodynamo.

The idea of no distinct layers, a hollow core, or a single liquid core without a solid center doesn’t fit the seismic and geophysical observations.