Final answer:
The mantle is the part of the Earth described as "semi-molten" and lies between the crust and the core.
Step-by-step explanation:
The part of the Earth that is described as "semi-molten" is the mantle. The mantle is the layer of the Earth that lies between the crust and the core. It is made up of semi-molten rock called magma, which is responsible for volcanic activity and plate tectonics.
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