Which statement describes the states of Earth's inner and outer cores?

Which statement describes the states of Earth's inner and outer cores?

• A. The inner core is solid and the outer core is liquid.
• B. The inner core is liquid and the outer core is solid.
• C. Both cores are gas.
• D. The inner core is solid and the outer core is solid.

Answer: (A)

The state of Earth's cores is governed by the balance of temperature and pressure inside the planet. Deep in the center, the pressure is immense enough to keep iron-nickel alloy solid, even though temperatures are extremely high. Surrounding this solid core, the temperatures are hot enough to melt the metal, so the outer core behaves as a liquid. This liquid layer is what allows convection to occur, driving the geodynamo that generates Earth’s magnetic field. So the correct description is that the inner core is solid and the outer core is liquid. The other possibilities don’t fit because a solid outer core would not support the convective motion needed for the magnetic field, a liquid inner core is inconsistent with the pressures at the center, and a gas core would not be present in Earth’s interior.

The state of Earth's cores is governed by the balance of temperature and pressure inside the planet. Deep in the center, the pressure is immense enough to keep iron-nickel alloy solid, even though temperatures are extremely high. Surrounding this solid core, the temperatures are hot enough to melt the metal, so the outer core behaves as a liquid. This liquid layer is what allows convection to occur, driving the geodynamo that generates Earth’s magnetic field.

So the correct description is that the inner core is solid and the outer core is liquid. The other possibilities don’t fit because a solid outer core would not support the convective motion needed for the magnetic field, a liquid inner core is inconsistent with the pressures at the center, and a gas core would not be present in Earth’s interior.