Internal structure of the earth

The Earth is divided into three main concentric layers, crust, mantle and core, on the basis of seismic wave behaviour. Its radius is about 6371 km.

        _______________
      /   Crust (5-70)  \
     /  ______________   \
    /  /   Mantle      \   \
   |  |   (to 2900 km)  |   |
   |  |  __________     |   |
   |  | / Outer core \  |   |
   |  | | (liquid)   |  |   |
   |  | |  Inner     |  |   |
   |  | |  core      |  |   |
   |  | \__(solid)__/   |   |
    \  \______________/   /
     \___________________/

1. Crust

• Outermost layer, thickness about 5-10 km under oceans and 30-70 km under continents.
• Continental crust: granitic (sial), density about 2.7 g/cm³.
• Oceanic crust: basaltic (sima), density about 3.0 g/cm³.
• Separated from the mantle by the Mohorovicic (Moho) discontinuity.

2. Mantle

• Extends from the Moho to 2900 km depth; about 84% of Earth's volume.
• Made of ultramafic rock (peridotite), density 3.3-5.5 g/cm³.
• Upper mantle includes the partly molten asthenosphere; lithosphere = crust + top of upper mantle.
• Separated from the core by the Gutenberg discontinuity.

3. Core

• From 2900 km to 6371 km; mostly iron and nickel (nife).
• Outer core (2900-5150 km): liquid, since S-waves do not pass through it.
• Inner core (5150-6371 km): solid due to high pressure; density about 13 g/cm³.
• Temperature reaches about 5000-6000 °C at the centre.

The structure is known from the speed and path of earthquake (seismic) waves.