Earth’s Internal Structure

Earth is a telluric (or terrestrial) planet whose surface is made up of solid rocks. This solid surface constitutes the outer shell under which are located other layers of material. From Earth’s surface to its centre, three main structures can be identified.

The core, at the centre of the Earth, forms |\small 17\ \%| of its volume. The radius of the core alone is equal to half the Earth’s radius. The core is mainly composed of iron, mixed with a little nickel. It is the hottest and also the densest structure on Earth. The core is divided into two layers: the outer core and the inner core.

The inner core is solid (due to the great pressure exerted on it) and is made of metals. The temperature can reach above |\small 6\ 000\ ^{\circ}\text {C}|. The thickness of the inner core has been estimated to be |\small \text {1 200 km}|.

The outer part of the nucleus reaches temperatures up to |\small 3\ 800\ ^{\circ}\text {C}|. At this very high temperature, the metals that make up this layer are in liquid form and are animated by convection cells generating electric currents, which themselves give rise to a magnetic field called the Earth's magnetic field. The thickness of the outer core is approximately |\small \text {2 300 km}|.

Directly beneath the Earth's crust lies the mantle. The mantle’s temperature is much higher |\small (1\ 000\ ^{\circ}\text {C})| than that of the Earth's crust, and the matter is much denser there. The set of two mantles (upper and lower) constitutes almost |\small 81\ \%| of the Earth’s volume. The mantle is composed of two parts.

The lower mantle is the more viscous part of the mantle as it is formed of molten rock (magma). It surrounds the core, and it is about |\small \text {2 100 km}| thick.

The predominantly solid upper mantle is located directly below Earth's crust. The thickness of the upper mantle varies between |\small \text {550}| and |\small \text {700 km}|.

Although it represents only |\small 2\ \%| of the Earth's volume, the crust is the best-known part of the Earth because humans walk along it every day. It is divided into a continental crust (which corresponds to the continents) and an oceanic crust (which corresponds to the ocean floor). The continental crust is between |\small \text {30}| and |\small \text {100 km}| thick, while the oceanic crust is about |\small \text {10 km}| thick. This difference in thickness is explained by the fact that Earth's relief is sometimes formed by plains, but sometimes also by high mountain ranges.