Interior of the Earth: A Layered Structure

• The Earth consists of three main concentric layers

1. Crust (Lithosphere)

• Depth: 5 to 56 km
• 5–11 km → Under oceans (oceanic crust)
• 35–56 km → Under continents (continental crust)
• Density: 2.6 to 3.0 g/cc
• Composition: Primarily silicon (Si), oxygen (O), aluminum (Al), and magnesium (Mg).

Subdivisions:

• Sial (Silicon + Aluminum) → Found in continental crust; less dense, granite-rich.
• Sima (Silicon + Magnesium) → Found in oceanic crust; denser, basalt-rich.

B.Mantle (Mesosphere)

• Depth: 56 to 2900 km
• Thickness: ~2900 km
• Density: 3.0 to 4.5 g/cc
• Composition: Silicate rocks rich in magnesium (Mg) and iron (Fe).

Layers:

• Upper Mantle (Asthenosphere) → Semi-solid; allows tectonic plates to move.
• Lower Mantle → More rigid due to immense pressure.

Core (Barysphere)

• Depth: 2900 km to 6371 km
• Thickness: ~3500 km
• Density: 9.0 to 12.0 g/cc
• Composition: Primarily iron (Fe) and nickel (Ni) (a.k.a. NiFe).

Layers:

• Outer Core → Molten, generates Earth’s magnetic field. 🧲
• Inner Core → Solid due to extreme pressure.