What is the innermost layer of Earth, primarily iron with nickel?

• A. Core
• B. Crust
• C. Echo Sounder
• D. Curie Point

Answer: (A)

The innermost layer is the core, a region formed mostly of iron with nickel. It consists of a solid inner core surrounded by a liquid outer core. The extreme pressures at Earth’s center keep the inner core solid, while slightly lower pressures in the surrounding zone keep the outer core molten. Seismic waves reveal this structure: S-waves don’t travel through liquids, signaling the liquid outer core, while P-waves speed up and refract through a very dense, metallic region that includes the inner core. The iron–nickel composition is also inferred from meteorites and seismic data. The crust and mantle are rocky, while the other terms—echo sounder and Curie point—refer to a depth-measuring instrument and a magnetic-temperature concept, not a layer of Earth.