Planetary Differentiation
The process where a young, molten planet separates into layers: heavy iron sinks to the core while lighter rock rises to form the crust, creating Earth's layered structure.
Planetary differentiation is the process by which a planetary body separates into distinct layers of different composition and density, occurring when internal heat melts the planet and allows heavier materials like iron to sink toward the core while lighter silicates rise to form the crust. This process, driven by thermal evolution and gravity, shaped Earth and other terrestrial planets into their current layered structures.
What this means in real life
When you stir oil and water together, they briefly mix, but gravity and density cause them to separate again—oil floating on top, water sinking below. A forming planet works similarly: molten iron and nickel sink to the center under gravity, while lighter rock stays near the surface.
What it isn’t
It is not the same as plate tectonics or continental drift. Those processes involve movement of solid crustal plates after a planet has already cooled and solidified; differentiation is the initial chemical separation that happens while the planet is still largely molten.
Commonly misused online
People sometimes use the term to describe any layering in a planet (like sedimentary rock layers), when it specifically refers to the gravity-driven separation of materials by density during planetary formation.
Based on 1 reference source, including primary sources. Last verified July 12, 2026.