Final answer:
Accretion refers to the building up of a planetary body, while differentiation describes the process by which internal layers of different compositions and densities form due to gravity. Differentiation explains how Earth's dense core formed, which is supported by evidence from Earth's overall density measurements.
Step-by-step explanation:
The statement about accretion is not entirely accurate in the context provided. The process of accretion refers to the gradual accumulation of mass, such as when a planet forms from colliding particles in the solar nebula. Differentiation, on the other hand, is the correct term for the gravitational separation of materials of different density into layers within the interior of a planet. This process led to the formation of Earth's core, mantle, and crust as heavier materials like metals sank towards the center, while lighter ones rose to the surface.
Evidence of differentiation is observed through density measurements. Earth's bulk density is measured at approximately 5.5 g/cm³, which is significantly denser than the average density of the surface materials which is about 3 g/cm³. This suggests the presence of much denser materials in the Earth's core. Additionally, examples of differentiation in action include phenomena such as lava rising in a volcano and mountain ranges 'floating' on the higher-density crust and mantle beneath them, demonstrating that the seemingly solid Earth has fluid characteristics on geological timescales.