Earth's Major Internal Divisions – GCSE Astronomy Edexcel Revision

Earth’s Major Internal Divisions

The Earth is divided into three major layers based on chemical compositions: the crust, the mantle, and the core.

The Earth’s outer layer or skin is known as the crust.
It is the thinnest of the three layers, ranging from 5 km (in the oceanic crust) to 70 km (in the continental crust) thick.
It is made up of lighter rocks such as granite and basalt.
The crust is broken into pieces called tectonic plates. These plates float on the semi-fluid asthenosphere underneath.

Beneath the crust lies the mantle, a layer of silicate rock approximately 2,900 km thick.
The mantle is divided further into the upper mantle (also known as the asthenosphere) and the lower mantle.
The upper mantle is semi-fluid and allows for the movement of tectonic plates above it. The lower mantle is solid and more rigid.
Convection currents within the mantle cause the movement of tectonic plates at the surface.

The Earth’s core is the furthest layer in the Earth’s interior and is divided into two parts: the inner core and the outer core.
The outer core is a layer of molten iron and nickel. It is about 2,200 km thick and is responsible for Earth’s magnetic field.
The inner core, a solid ball of iron-nickel alloy, is about 1,216 km in radius. The extreme pressures and temperatures solidify the metals.
The core is the hottest part of the planet, with temperatures almost as hot as the surface of the Sun.