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Difficulty: HardInternal and External Structure of the Earth

Geophysical investigations reveal distinct internal structural layers and seismic boundary zones within the Earth. What is the correct sequence of these internal layers and discontinuities when arranged in order of increasing depth from the Earth's surface to its center?

  1. 1Conrad Discontinuity
  2. 2Mohorovičić Discontinuity
  3. 3Asthenosphere
  4. 4Gutenberg Discontinuity
  5. 5Lehmann Discontinuity

Answer

The correct order from Earth's surface to the center is: Conrad Discontinuity, Mohorovičić Discontinuity, Asthenosphere, Gutenberg Discontinuity, and Lehmann Discontinuity.
Arranged from the surface downward, the Earth's structural boundaries and zones progress from the Conrad Discontinuity (~10–20 km within continental crust), to the Mohorovičić Discontinuity (~35 km at the crust-mantle interface), followed by the Asthenosphere (~100–250 km in the upper mantle), the Gutenberg Discontinuity (~2,900 km at the mantle-core boundary), and finally the Lehmann Discontinuity (~5,150 km at the outer core-inner core boundary).

Step-by-Step Solution

1
Identify the shallowest seismic boundary within the continental crust.
The Conrad Discontinuity lies within the upper crust at ~10–20 km depth, separating sial from sima.
It is the shallowest boundary listed.
2
Locate the boundary separating the crust from the underlying mantle.
The Mohorovičić (Moho) Discontinuity lies at the base of the crust at ~35 km average depth.
It marks the structural boundary between the crustal rocks and the denser mantle rocks.
3
Identify the ductile layer in the upper mantle.
The Asthenosphere lies beneath the lithosphere in the upper mantle (~100–250 km depth).
It is a semi-fluid zone of partial melting beneath the solid crust-upper mantle lithospheric cap.
4
Locate the deep mantle-core boundary.
The Gutenberg Discontinuity is situated at ~2,900 km depth.
It separates the silicate mantle from the metallic outer core.
5
Identify the boundary separating the outer and inner core zones.
The Lehmann Discontinuity is located at ~5,150 km depth near the Earth's center.
It defines the seismic transition between the liquid metallic outer core and the solid inner core.

Key Concept

Internal Structure of the Earth and Seismic Discontinuities
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Topics

Internal and External Structure of the Earth

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