Question

Lithosphere is characterized by \(\underline{\hspace{1cm}}\).
A. A thickness of about 100 km
B. Average density of 3.6 g/cc
C. Silicon and aluminum as dominant constituents
D. Basalt as the dominant rock

• A. A and C only
  (B) B and D only
  (C) A, B, and D only
  (D) A and D only
• B. B and D only
• C. A, B, and D only
• D. A and D only

Hint:

Remember the key distinctions: - Lithosphere: Crust + Rigid Upper Mantle. - Continental Crust: Thicker, less dense, granitic (SiAl). - Oceanic Crust: Thinner, denser, basaltic (SiMa).

Answer 1

The Correct Option is D

Step 1: Analyze statement A.
The lithosphere is the rigid outer layer of the Earth, consisting of the crust and the upper part of the mantle. Its thickness varies but is typically in the range of 50-200 km, so 100 km is a representative average value. Statement A is correct.

Step 2: Analyze statement B.
The average density of continental crust is ~2.7 g/cc, oceanic crust is ~3.0 g/cc, and the underlying rigid mantle is ~3.3 g/cc. A weighted average for the entire lithosphere would be around 3.1-3.2 g/cc. A value of 3.6 g/cc is too high and more representative of the asthenosphere below. Statement B is incorrect.

Step 3: Analyze statement C.
Silicon and aluminum ("SiAl") are the dominant constituents of the continental crust, but the oceanic crust is dominated by silicon and magnesium ("SiMa"). Since the lithosphere includes both, this statement is not universally true.

Step 4: Analyze statement D.
Basalt is the dominant rock type of the oceanic crust, which covers about 70% of the Earth's surface. While continental crust is predominantly granitic, basalt is a major component of the entire lithosphere's crust. Statement D is considered correct in the context of the most widespread rock type. Conclusion: A and D are the most accurate statements. Combining them gives the answer "A and D only".