A cut peach offers a vivid model of the structure of the Earth’s body (Fig. 1.1.1): It has a solid core, a soft shell of fruit mass and a very thin outer shell, which can be compared to the outer, solid shell of the Earth known as the lithosphere. Relative to the diameter of the peach, the peach skin is even thicker than the lithosphere: an 8 cm peach is compared to the globe with a diameter of 12,740 km. A 1 mm thick peach skin would correspond to a 160 km thick lithosphere. However, the lithosphere is on average only about 100 km thick.

A section through the Earth’s body shows the different spheres (Fig. 1.1.2): the solid inner core, the liquid outer core, the solid lower and upper mantle with the soft, fluid asthenosphere directly beneath the solid outer shell of the Earth.

Fig. 1.1.3: Non-exaggerated and exaggerated representations of the lithosphere (Meschede, unpubl., 2021; partly modified from Frisch & Meschede, 2021).

In representations of the entire Earth’s body, details about the structure of the solid outer shell, known as the lithosphere, cannot be shown because it appears far too thin in relation to the Earth’s mantle. The Earth’s mantle is around 2,800 km thick, the lithosphere is only 100 km thick on average.
In order to be able to represent the conditions in the lithosphere, an exaggeration is therefore necessary. The figure above shows a 1:1 representation in which the lithosphere only appears as a thin line. For the exaggerated view, only the upper mantle is shown and the curvature of the Earth is reduced slightly. In the bottom two figures, the exaggerated representation of the lithosphere is shown in a ratio of approximately 1:10. The 3D block diagram shows the central Atlantic between South America and Africa. Here the lower part of the upper mantle has been omitted for illustration purposes.

The representation of the basic plate tectonic principles also uses exaggeration, as the structures would otherwise not be recognizable on a global scale. This summary depicts the basic principles of plate tectonics with continental rifts, spreading zones, subduction zones, transform faults and hot spots. However, the illustration is not to scale. In particular, the lithosphere and the location at the contact with the Earth’s outer core are greatly exaggerated.