Internal Structure of the Earth

The Earth, though appearing as a solid sphere, is a highly dynamic planet with a layered internal structure. Knowledge about the Earth’s interior comes from indirect evidence such as seismic waves, gravitation, magnetic field, density calculations, and meteorite studies. Broadly, the Earth can be divided into three main layers: Crust, Mantle, and Core, each with unique composition, density, and physical properties.

The Crust

• Outer shell of the Earth, forming less than 1% of Earth’s volume.
• Thickness:
  • Continental crust: ~30–70 km
  • Oceanic crust: ~5–10 km
• Composition:
  • Continental crust → granitic (SiAl: silica + aluminium).
  • Oceanic crust → basaltic (SiMa: silica + magnesium).
• Density:
  • Continental: ~2.7 g/cm³
  • Oceanic: ~3.0 g/cm³
• Mohorovičić Discontinuity (Moho) separates the crust from the mantle.

The Mantle

• Extends from the Moho to 2,900 km depth.
• Accounts for about 84% of Earth’s volume.
• Upper Mantle (up to 660 km):
  • Contains the asthenosphere (~100–400 km depth).
  • Weak, partially molten zone → allows plate tectonic movements.
• Lower Mantle (660–2,900 km):
  • Solid, denser, and high-pressure minerals.
• Composition: Mostly silicate minerals rich in iron and magnesium (peridotite).
• Key Boundary: Gutenberg Discontinuity (Mantle–Core boundary).

The Core

• Extends from 2,900 km to Earth’s center (6,371 km).
• Accounts for about 15% of Earth’s volume but ~33% of its mass.
• Outer Core:
  • Depth: 2,900–5,150 km
  • State: Liquid (mainly molten iron and nickel).
  • Responsible for Earth’s magnetic field (geodynamo).
• Inner Core:
  • Depth: 5,150–6,371 km
  • State: Solid (iron–nickel alloy) due to immense pressure.
• Density: ~10–13 g/cm³.

REFERENCE :

1. Gervilla, Fernando & González-Jiménez, Jose & Hidas, Károly & Marchesi, Claudio & Piña, Rubén. (2019). Geology and Metallogeny of the Upper mantle Rocks from the Serranía de Ronda.