Which term refers to Earth's central solid sphere?

• A. Core
• B. Crust
• C. Density Stratified
• D. Echo Sounder

Answer: (A)

Earth's interior is organized into layers: a crust on the outside, a mantle beneath, and a central region called the core. The core has two parts: a solid inner core at the very center and a surrounding liquid outer core. The term that refers to that central solid sphere is the core, specifically the inner core. The inner core is mainly iron and nickel and remains solid under immense pressures, while the outer core is liquid and drives the geodynamo that creates Earth's magnetic field. The crust is the outermost solid shell, and an echo sounder is a device used to measure ocean depth, not a layer of Earth. Density stratified isn’t a standard term for a central layer.