Final answer:
The evidence that Earth's core is metal includes its overall density, the composition of metallic meteorites, the generation of the magnetic field, and the differentiation of Earth's layers by density. Iron and nickel make up the majority of the core's composition.
Step-by-step explanation:
To complete the sentence using the words provided, the correct term based on the scientific evidence is 'metal'. The existence of metallic meteorites and calculations regarding Earth's density provide evidence that the Earth's core is metal. This is because the overall density of the planet, as calculated from Earth's rotation, suggests that if the surface layers are less dense, the interior, including the core, must be denser.
The core is composed predominantly of iron and nickel, with the former making up about 85% and the latter most of the remaining 15%. The existence of a metallic core is further supported by the generation of Earth's magnetic field, which requires the presence of a metallic composition.
The mantle rock above the core deforms and flows slowly with increasing density, indicating the presence of a dense metallic core beginning at a depth of 2900 kilometers. This core, influenced by its composition and the pressure at such depths, is largely responsible for the differentiation process, where heavier metals like iron and nickel sank to form the core during a period when Earth's interior was hot enough to melt.