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Difficulty: Very hardInternal and External Structure of the Earth

Geological analyses of the Earth's crust and outer physical spheres demonstrate distinct compositional differences between continental and oceanic crustal layers, as well as specific exogenic mechanisms operating on surface rocks. Which of the following statements accurately differentiates between the sial and sima layers of the lithosphere while correctly identifying the exogenic process responsible for the in-situ physical breakdown of exposed sialic bedrock?

  1. Sial is predominantly granitic, less dense, and composed of silica and alumina forming continental crust, whereas sima is basaltic, denser, and composed of silica and magnesium forming oceanic crust; exposed sialic bedrock disintegrates in situ through weathering.Answer
  2. B
    Sial is predominantly granitic, less dense, and composed of silica and alumina forming continental crust, whereas sima is basaltic, denser, and composed of silica and magnesium forming oceanic crust; exposed sialic bedrock disintegrates in situ through mass wasting.
  3. C
    Sial is a denser layer of sedimentary marine deposits underlying oceanic basins, whereas sima is a lighter granitic layer formed through regional metamorphism; exposed sialic bedrock disintegrates in situ through weathering.
  4. D
    Sial is denser than sima and forms the lower basaltic layer of the lithosphere, whereas sima forms the lighter continental crust; exposed sialic bedrock disintegrates downslope through mass wasting.

Answer

Sial is predominantly granitic, less dense, and composed of silica and alumina forming continental crust, whereas sima is basaltic, denser, and composed of silica and magnesium forming oceanic crust; exposed sialic bedrock disintegrates in situ through weathering.
The correct statement accurately defines sial as the lighter, silica- and alumina-rich granitic layer forming continental landmasses and sima as the denser, silica- and magnesium-rich basaltic layer forming ocean floors. Furthermore, it correctly identifies weathering as the process responsible for breaking down rock in situ at the surface.

Step-by-Step Solution

1
Analyze the internal composition and density of sial and sima.
Sial (Silica + Alumina) forms continental crust with lower density (≈2.7 g/cm3\approx 2.7\text{ g/cm}^3). Sima (Silica + Magnesia) forms oceanic crust and underlying layer with higher density (≈3.0 g/cm3\approx 3.0\text{ g/cm}^3).
Internal structural layers of the Earth's crust are differentiated by chemical composition and specific gravity.
2
Differentiate exogenic processes acting on exposed rock at the Earth's surface.
In-situ breakdown of rock without transportation is defined as weathering. Downslope movement under gravity is mass wasting.
External surface dynamics require distinguishing between in-situ disintegration (weathering) and gravity-driven transport (mass wasting).
3
Synthesize structural layer properties with the correct exogenic process.
The correct option must state that sial is granitic/lighter, sima is basaltic/denser, and in-situ disintegration occurs via weathering.
Combines internal crustal differentiation with external physical breakdown.

Key Concept

Crustal differentiation (Sial vs Sima) and surface weathering mechanisms
Estimated Time:2m 0s
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Topics

Internal and External Structure of the Earth

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