Present day heat flow from within Earth is twice as high as could be expected from radioactivity's contribution. This suggests that
A) more radioactivity is occurring than what scientists have accounted.
B) volcanic action contributes more than scientists presently understand.
C) Earth used to be much hotter.
D) movement within the core causes heating by friction.

Question

Quizplus · Accepted Answer

Earth's current heat flow being twice as high as what can be accounted for by radioactivity suggests that the planet used to be much hotter, and it is still cooling down.

Present Day Heat Flow from Within Earth Is Twice as High