2. Over which layer do tectonic plates move? \[ \begin{array}{l}\text { a. Mesosphere } \\ \text { b. Stratosphere } \\ \text { c. Asthenosphere } \\ \text { d. Troposphere }\end{array} \]

The correct answer is: **c. Asthenosphere** **Explanation:** Tectonic plates are large sections of the Earth's lithosphere (the rigid outer layer) that move and interact at their boundaries. These plates float atop the **asthenosphere**, which is a semi-fluid layer of the upper mantle located just below the lithosphere. The asthenosphere's partially molten and ductile nature allows it to flow slowly, enabling the rigid tectonic plates to slide over it. This movement is responsible for various geological phenomena, including earthquakes, volcanic activity, and the creation of mountain ranges. In contrast: - **a. Mesosphere**: Refers to a layer of the Earth's atmosphere located above the stratosphere, not related to tectonic plate movement. - **b. Stratosphere**: Another atmospheric layer above the troposphere, also unrelated to tectonic activities. - **d. Troposphere**: The lowest layer of the atmosphere where weather phenomena occur; it does not involve tectonic plate dynamics. Therefore, the **asthenosphere** is the correct layer over which tectonic plates move.