Introduction to Earth Sciences I
Topic 3
The Earth as a Heat Engine
The Earth is a body of stored heat, radiating into space. This heat is associated with two things; one is that the temperatures of the inner parts of the Earth are very high, and the other is the result of heat generated due to radioactive decay of material in the deep Earth. Were it not for the second of these factors the Earth would long ago have frozen solid -- it has had plenty of time to cool from its initial hot state. This internal heat, combined with the fact that we know from several lines of evidence discussed under Topic 2 that the Earth is not internally rigid, causes the interior to be in continuous motion in a complex pattern of slow upwelling and downwelling that is becoming clearer as seismic methods (Topic 4) reveal the internal structure of the Earth in increasing detail. First, we need to review some basics about heat and how it moves around.