Evolution of Lithosphere

The story of the lithosphere begins with a young Earth that was nothing like the planet we stand on today. In its primordial stage, the Earth was mostly in a volatile state — hot, unstable, and largely molten. The solid, rocky surface we know came later, and it emerged through a slow, physical sorting of materials driven by density.

The key trigger was a gradual increase in density inside the Earth, which raised the internal temperature. As the interior heated up, the material inside began to separate based on density. Heavier materials, like iron, sank towards the centre of the Earth, while lighter materials moved towards the surface. This process of separation is called differentiation — it is the very mechanism through which the Earth-forming material got divided into distinct layers.

With the passage of time, the Earth cooled further. The cooling allowed the material to solidify and condense into a smaller size. This contraction and solidification eventually led to the development of an outer surface in the form of a crust. The crust, therefore, is not an original feature but a product of cooling and differentiation.

One dramatic event accelerated this heating. During the formation of the Moon, a giant impact struck the Earth and heated it up further. This extra heat contributed to the ongoing differentiation, ensuring that the separation of materials into layers was thorough.

The final result of differentiation is a layered Earth. Starting from the surface and moving towards the central parts, the layers are:

• Crust — the outermost, lightest layer
• Mantle — beneath the crust
• Outer core — deeper still
• Inner core — the central part …