The separation of the earth into layers was the result of the:

a. presence of water at earth's surface.
b. initial collection of materials and their position in earth.
c. decrease in temperature downward toward the core.
d. differing densities of the rock and mineral materials.
e. gravitational force created by the rotating earth.

D. Differing densities of the rock and mineral materials.

Explanation:

Differentiation is thought to occur in all planets, whereby denser elements sink to the core of the planet and lighter elements move upward. Once this process is completed, the planet takes on a layered look. This process also formed the earth into its layer by differing densities of rock and mineral of the earth.

2,407.2 miles. or 32 hours.