One of the 2 ways that the layers of the earth are separated from one another (2words)

Radioactive Decay

Explanation:

The stratification of Earth into its geologic layers was brought about by the formation of the Earth's iron core. The iron core was generated by a combination of radioactive decay and gravitation, which raised the temperature enough for molten iron to form. The migration of molten iron to the center of the Earth displaced the less dense materials toward the surface forming layers.