Earth’s Interior: Structure, Composition, and Dynamics

Posted on Mar 11, 2025 in Geology

Study of the Interior of the Earth

Direct Methods: The study of the geosphere is based on the analysis of material extracted from boreholes or mining polls. Max depth achieved: Kola borehole (Russia) 13km. Earth’s radius: 6371 km.

Indirect Methods: It is believed that meteorites, originating from other destroyed planets, provide information about the chemical composition of the core, mantle, and crust. They are classified as:

  • Siderite or iron meteorites: Composed of 80% to 90% iron and nickel.
  • Siderolites (stony-iron meteorites): A mixture of silicate and metallic iron and nickel.
  • Stony meteorites: Composed of silicates of sodium, potassium, and calcium.
  • Inner crust: Heat increases 3 degrees per 100 m.
  • Density: Ground mass 5.97 x 1027 g, volume 1.08 x 1027 cm3.
  • Oceanic crust is less intense gravitationally than continental crust.
  • Mountains are less dense than plains.

Seismic Waves

Seismic waves originate at the hypocenter:

  • Primary Waves (P-waves): The fastest waves, capable of traveling through solids and liquids.
  • Secondary Waves (S-waves): Slower than P-waves and cannot travel through liquids. They propagate faster through solid and dense materials.

Earth’s Internal Structure

Chemical Models: Based on the chemical composition of the layers: Crust, Mantle, Core.

Mechanical or Physical Model: Based on the solid/liquid behavior of the layers:

  • Lithosphere: Approximately 100km thick.
  • Asthenosphere: Extends to a depth of 660km.
  • Mesosphere: Located between the asthenosphere and the core, extending to a depth of 2900 km.
  • Endosphere: Lies between the mesosphere and the center of the Earth, divided into:
    • Outer Core: Extends to a depth of 5150km.
    • Inner Core: Occupies the central part of the planet.

Lithosphere

The lithosphere is the surface layer, solid and rigid, composed of the outer crust and upper mantle (residual mantle). It is divided into fragments called tectonic plates that float and move.

Asthenosphere

The asthenosphere is a layer with plastic behavior beneath the lithosphere. It features a zone of high plasticity (200-250km), which allows for the movement of magma currents, and a more rigid bottom layer.

Relief

Relief refers to the elevations and depressions present on the Earth’s surface.

Orogeny

Orogeny is the relief-building process that causes elevations on the Earth’s surface. It involves internal geological agents (heat) and lateral pressure from the plates. (Isostasy explains the vertical movements of the plates.)

Gliptogenesis

Gliptogenesis is the destructive process of erosion of the Earth’s surface relief. It is carried out by atmospheric and external geological agents (atmosphere, ice, rivers, streams, living organisms).

Geologic Stress

Geologic stress refers to the forces that crustal rocks undergo.

  • Lithostatic Stress: Caused by the weight of overlying materials.
  • Tectonic Stress: Caused by the movement of tectonic plates:
    • Compression, tension, shear stress, deformation, and rupture.

Diaclases

Diaclases are fractures in rocks where there has been no significant displacement of one block relative to the other.

Faults

Faults are fractures in rocks where there is a relative displacement between the two blocks formed.

Folds

Folds are bends that form in some rock strata when subjected to compressive tectonic forces.

  • Anticline: The oldest layers are at the core.
  • Syncline: The most recent strata are found in the nucleus.

Nappes and Overthrusts

Nappes and overthrusts occur when a fold is broken, resulting in the older rocks being thrust over younger ones.

Volcanoes

Volcanoes are structures formed around openings where magma emerges due to the existence of weaknesses in the Earth’s crust.

  • Occasional eruptions: