Answer:
D) Earth's internal heat is thermal energy generated from radioactive decay and continual heat loss from Earth's formation.
Step-by-step explanation:
The geothermal energy of the Earth's crust originates from the original formation of the planet and from the radioactive decay of materials. The geothermal gradient, which is the difference in temperature between the core of the planet and its surface, drives a continuous conduction of thermal energy in the form of heat from the core to the surface.