What is the dense sphere of solid iron and nickel at the center of Earth called?

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

Answer: (A)

The dense solid sphere at Earth's center is the inner core. This part is a solid ball primarily made of iron with nickel, kept solid by the enormous pressures present at the planet’s center even though temperatures are extremely high. Surrounding it is the liquid iron-nickel outer core, whose currents generate Earth’s magnetic field. Above that lie the mantle and the crust. Understanding why one region is solid and the other liquid comes down to how temperature and pressure interact: the center has such intense pressure that iron stays solid, while the slightly lower pressure and higher temperature in the outer core allow the metal to melt.