What key physical property determines the layers of the earth through the process differentiation?

Density

Explanation:

Density is defined as the mass per unit volume of a substance.

The differentiation of the early earth into separate layers was density driven. Denser elements such as Nickel and iron partitioned to the innermost layer of the earth to form the core.

Lighter compounds formed from oxides of silicon and aluminum rose to the surface to form the crust. The surface was rich in oxygen and thus furnished the vast silicates minerals we have on our crust.

Compounds whose density falls in between the silicates and Ni-Fe partitioned into the mantle. The mantle is rich in ultramafic rocks.