Earth's Internal Structure: Geochemical and Geodynamic Models

Geochemical Model of Earth's Internal Structure

Seismologists have defined two models of the internal structure of the Earth: the geochemical model and the geodynamic model. Both are based on the behavior of P-waves and S-waves.

The geochemical model is based on the chemical composition of the internal layers of the Earth. It divides the Earth into three layers: crust, mantle, and core. These layers are separated by three seismic discontinuities, each named after its discoverer.

The Mantle

This layer is made up of igneous rocks rich in iron and magnesium silicates. One primary rock type is peridotite, which consists mainly of the mineral olivine. It is divided into the upper and lower mantle, separated by the transition zone, where materials become denser due to increased pressure and temperature.

The Core

This layer consists of almost pure iron mixed with a small percentage of iron sulfides and nickel. It is divided into two parts based on their physical state:

• Inner Core: Solid.
• Outer Core: Liquid.

The Geodynamic Model

The geodynamic model of the internal structure of the Earth is based on the physical state of the layers: plasticity, rigidity, and density. According to this model, the Earth acts as a heat engine. This thermal agitation modifies the structure and composition of materials, generating movement and pressure. This energy is released either slowly or quickly, transforming thermal energy into mechanical energy.

Lithosphere

The lithosphere consists of the crust and the uppermost part of the mantle. It is dragged by the movement of the mantle underneath, causing it to fracture into large blocks called lithospheric plates. These plates move via:

• Horizontal movements: Due to plate tectonics.
• Vertical movements: Due to isostatic adjustment.

Asthenosphere

Also known as the sublithospheric upper mantle, this layer lies between the lithosphere and the mesosphere. Scientists believe it coincides with the lower part of the upper mantle.

Mesosphere

The mesosphere corresponds to the lower mantle. It extends from a depth of 670 km to the D" layer. Although it is solid, it remains dynamic.

The D" Layer

The D" layer is one of the most dynamic regions of the Earth. Heat from the outer core accumulates here, and hot magma escapes as mantle plumes. These plumes break through the lithosphere, creating hotspots—areas of intense volcanic activity.

The Core

In both models, the core consists of two parts: inner and outer. The heat in the solid inner core spreads to the liquid outer core, generating convection currents that push heat outward.