Which one of the following factors leads to an abrupt increase in density at the mantle–outer core boundary?
Show Hint
- Composition change
- Temperature change
- Phase change
- Viscosity change
The Correct Option is A
Solution and Explanation
Step 1: Understanding the mantle–outer core boundary.
At the core–mantle boundary (CMB), seismic observations show a sharp increase in density. This is primarily due to a composition change—from silicate rocks (mantle) to metallic iron-nickel alloy (core).
Step 2: Evaluate other options:
(B) Temperature does increase, but not enough to cause an abrupt density jump.
While temperature rises near the CMB, it is the compositional change that primarily causes the sharp density increase.
(C) Phase change occurs gradually near other boundaries (like upper to lower mantle).
Phase changes in the mantle occur gradually, but the CMB has a more distinct, abrupt transition due to the compositional difference.
(D) Viscosity changes do not directly affect density.
Viscosity changes may influence flow, but they do not directly cause the density increase at the CMB.
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