Which statement about Earth's magnetic field is correct?

• A. It is generated by the movement of liquid iron in the outer core
• B. It is generated by the Earth's solid inner core
• C. It is caused by the Moon's gravity
• D. It is constant and unchanging

Answer: (D)

Earth’s magnetic field is produced by motion in the liquid iron of the outer core, a process called the geodynamo. As molten iron flows in the outer core and the planet spins, these moving electric charges generate a magnetic field that stretches outward around the Earth. The solid inner core doesn’t create the field by itself; it helps shape the overall flow but isn’t the source. The Moon’s gravity doesn’t drive the magnetic field either. And the field is not constant—scientists observe slow changes over time, including shifting magnetic poles and, over long timescales, reversals.