The region of the Earth's interior where heat increases to the point that rocks can begin to melt is called the asthenosphere.

Here's a breakdown:

* Asthenosphere: This is a layer within the upper mantle, located below the lithosphere (the rigid outer layer of the Earth). It's characterized by its partial melting, where the rocks are not fully molten but rather behave like a very viscous fluid over long periods.

* Why rocks melt: The asthenosphere is hot due to the heat generated from the Earth's core and the radioactive decay of elements within the mantle. This heat, combined with the pressure at those depths, brings the rocks close to their melting point.

* Importance of the asthenosphere: The partially molten nature of the asthenosphere is crucial for plate tectonics. It allows the rigid lithospheric plates to move over it, driving processes like earthquakes, volcanic activity, and mountain building.

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