What caused the interior of earth to separate into layers?

Separation into Layers. After several million years, the Earth separated into several layers. Iron, nickel and other heavy metals mostly settled to the core; lighter elements remained in the mantle around the core. The lightest elements, such as oxygen and silicon, floated to the top and cooled, forming a solid crust. read more

In its first few million years, the Earth was a hot, semiliquid mass that separated into layers according to the density of each layer, a process similar to what happens when oil floats on water. Most, though not all, of the heavy elements sank to the center while the lighter ones rose to the top. read more

a. a decrease in the rate of rotation of earth b. the gravitational pull on materials of varying densities read more