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Difficulty: MediumInternal and External Structure of the Earth

The interior of the Earth is divided into distinct structural layers based on physical properties and chemical composition. Which semi-fluid layer, located within the upper mantle directly beneath the rigid outer shell, provides the plastic medium that enables tectonic plate movements?

  1. AsthenosphereAnswer
  2. B
    Lithosphere
  3. C
    Barysphere
  4. D
    Hydrosphere

Answer

Asthenosphere
The asthenosphere lies directly beneath the lithosphere in the upper mantle (between approximately 100 km and 200 km below the surface). Its high temperatures and pressure render it plastic and ductile, enabling convection currents that move tectonic plates above it.

Step-by-Step Solution

1
Identify the target structural layer described in the stem.
The stem describes a semi-fluid layer situated in the upper mantle below the solid crust.
Understanding the physical state of each layer is essential to distinguishing internal Earth structures.
2
Distinguish between the rigid lithosphere and the plastic asthenosphere.
The lithosphere floats on top of the ductile, semi-molten asthenosphere.
Convection currents within the asthenosphere drive lithospheric plate movement.

Key Concept

Internal Structure of the Earth - Asthenosphere vs Lithosphere
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Topics

Internal and External Structure of the Earth

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