Asthenosphere is

Options

A. Solid part of mantle
B. Semi-molten part of mantle
C. Semi-molten part of core
D. Solid part of core.

Answer

**Step-by-Step Solution:**

1. **Understanding Earth's Layers**: The Earth is divided into three main layers: the crust, the mantle, and the core.
- **Crust**: The outermost layer.
- **Mantle**: The layer beneath the crust.
- **Core**: The innermost layer.

2. **Dividing the Mantle**: The mantle itself is further divided into two parts:
- **Asthenosphere**: The upper part of the mantle.
- **Mesosphere**: The lower part of the mantle.

3. **Characteristics of the Asthenosphere**:
- The asthenosphere is described as being in a semi-solid state, which means it is not completely solid but also not entirely molten. It behaves somewhat like a viscous fluid or jelly.
- This semi-solid state allows for the movement of tectonic plates and is also the source of magma (lava).

4. **Analyzing the Options**:
- **Option A**: Solid part of the mantle - Incorrect, as the asthenosphere is not solid.
- **Option B**: Semi-molten part of the mantle - Correct, as it accurately describes the asthenosphere.
- **Option C**: Semi-molten part of the core - Incorrect, as this refers to the core, which is not the asthenosphere.
- **Option D**: Solid part of the core - Incorrect, as the core is primarily solid.

5. **Conclusion**: The correct answer is **Option B**: the asthenosphere is a semi-molten part of the mantle.

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