Answer:
Heat generated from the radioactive decay of elements deep in the interior of the Earth
Step-by-step explanation:
Heat is generated from the radioactive decay of elements deep in the interior of the Earth creates magma (molten rock) in the asthenosphere.
The asthenosphere is the highly viscous, mechanically weak and ductile region of the upper mantle of the Earth.
The asthenosphere (70 ~ 250 km) is part of the mantle, the middle sphere of the Earth that extends to 2900 km.