Asthenosphere is

Options

A. Part of mantle
B. Part of crust
C. Part of core
D. Discontinuity between crust and mantle.

Answer

**Step-by-Step Solution:**

1. **Understanding Earth's Layers**: The Earth is divided into three main layers: the crust (outermost layer), the mantle (middle layer), and the core (innermost layer).

2. **Identifying the Asthenosphere**: The asthenosphere is a specific region within the mantle. It is characterized as a weak, highly viscous, and ductile part of the upper mantle.

3. **Characteristics of the Asthenosphere**: The asthenosphere is not solid like the crust; instead, it allows for the movement of tectonic plates. This movement is facilitated by the asthenosphere's viscous nature.

4. **Depth of the Asthenosphere**: It can extend down to about 700 kilometers deep within the mantle, indicating that it is a significant part of the mantle rather than a separate layer.

5. **Evaluating the Options**:
- **Part of Mantle**: This is correct as the asthenosphere is indeed a part of the mantle.
- **Part of Crust**: This is incorrect because the asthenosphere is not part of the crust.
- **Part of Core**: This is also incorrect as the asthenosphere is not related to the core.
- **Discontinuity between Crust and Mantle**: This refers to the Mohorovičić discontinuity (Moho), which is not the asthenosphere.

6. **Conclusion**: Based on the characteristics and location of the asthenosphere, the correct answer is that the asthenosphere is a **part of the mantle**.

**Final Answer**: The asthenosphere is a part of the mantle.

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