Who explains why the earth is layered?

The layered structure of the Earth is primarily explained by the theory of planetary differentiation, which was proposed by geologists and planetary scientists. During the early formation of the Earth, heat generated from radioactive decay and impacts caused materials to melt and separate based on density. Heavier elements, like iron and nickel, sank to form the core, while lighter materials formed the mantle and crust. This process resulted in the distinct layers we observe today.