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Difficulty: Very hardInternal and External Structure of the Earth

Geophysical measurements reveal critical physical transitions within Earth's internal structure as well as distinct operational mechanisms across its external spheres. Which of the following options correctly pairs a boundary transition within Earth's interior with an accurate description of a surface process reshaping the external lithosphere?

  1. The Gutenberg discontinuity marks the boundary between the solid lower mantle and liquid outer core where S-waves cease to propagate, while weathering acts as an in-situ breakdown of surface rocks without direct gravitational transportation.Answer
  2. B
    The Gutenberg discontinuity marks the boundary between the solid lower mantle and liquid outer core where S-waves cease to propagate, while weathering acts as the active downslope movement of rock debris under the direct force of gravity.
  3. C
    The Mohorovičić discontinuity separates the liquid continental crust from the solid ocean floor, while weathering represents the metamorphic alteration of sedimentary rocks under extreme mantle pressures.
  4. D
    The Mohorovičić discontinuity separates the lithosphere from the atmosphere, while mass wasting breaks down surface rocks in-situ before chemical decay occurs.

Answer

The Gutenberg discontinuity marks the boundary between the solid lower mantle and liquid outer core where S-waves cease to propagate, while weathering acts as an in-situ breakdown of surface rocks without direct gravitational transportation.
The Gutenberg discontinuity lies at the boundary between the lower mantle and the outer core (at a depth of around 2900 km2900\text{ km}). Because the outer core is liquid, transverse SS-waves cannot pass through it. Externally, weathering is the static, in-situ breakdown of rock materials on Earth's surface, distinct from downslope mass movement.

Step-by-Step Solution

1
Analyze internal boundary physical properties
The Gutenberg discontinuity occurs at a depth of approximately 2900 km2900\text{ km}, marking the transition from the solid silicate mantle to the liquid iron-nickel outer core. Because secondary (SS) seismic waves cannot travel through liquids, they terminate at this boundary.
Establishing the correct geophysical behavior of seismic waves at Earth's internal boundaries is necessary to evaluate the internal structure component.
2
Evaluate external lithospheric surface processes
Weathering is defined strictly as the static, in-situ physical disintegration and chemical decomposition of rocks exposed at Earth's surface.
Distinguishing weathering from mass movement processes is essential to correctly characterize external sphere dynamics.
3
Synthesize and select the correct pairing
The statement combining the Gutenberg discontinuity SS-wave shear cutoff with in-situ weathering accurately represents both internal and external structural processes.
Matching both validated components identifies the unique correct choice.

Key Concept

Internal Discontinuities and External Lithospheric Processes
Estimated Time:2m 0s
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Topics

Internal and External Structure of the Earth

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