Planetary Differentiation

Planetary differentiation is the separation of a planet's materials into layers of different density. When a young planet is hot enough to be partly or fully molten, heavy iron and nickel sink toward the centre and lighter silicate rock rises.

The result is the layered structure of rocky planets: a metal core, a rocky mantle and a thin crust. In Earth's case, the core formed within the first few tens of millions of years.

Differentiation matters because a liquid metal core can generate a magnetic field, which helps protect a planet's atmosphere.

Read more in Step 3: Building the core and crust.