Final answer:
The Earth's magnetic field indicates it has a liquid metal outer core spinning with its rotation, generating electric currents and creating the magnetic field.
Step-by-step explanation:
The presence of a magnetic field is an indication that the Earth has a liquid metal outer core, rotating and spinning rapidly with the rotation of the Earth. This movement of the liquid metal generates electric currents, which in turn produce the magnetic field observed. The correct answer to the question is A: the Earth has a liquid metal outer core, spinning rapidly as it rotates.
We can compare this with other celestial bodies such as the Moon, which has a weak magnetization in some patches, suggesting it once had a molten metallic core that allowed for a magnetic field when it solidified. Mars also showed similar characteristics. Additionally, because mantle rock is not magnetic, Earth's core must be metallic to generate a magnetic field, with evidence pointing to a composition primarily of iron and nickel.