Energy resources: An introduction to energy resources
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# 3.3 The Earth's internal heat

The occurrence of both volcanoes and hot springs shows that the Earth's interior is hot, producing molten rock at temperatures up to 1250 °C, and also superheated steam. However, these phenomena are mainly confined to several narrow zones along the world's active plate boundaries. Many measurements have now been made of the amount of heat flowing from the Earth's interior. Outside the distinctive zones mentioned above, heat flow varies from 40-120 milliwatts per square metre (mW m−2), largely generated by the decay of long-lived radioactive isotopes within the Earth. The total power output from the Earth's interior, estimated at some 10 TW, is many orders of magnitude less than the total incident solar power (Figure 1.7).

## Question 7

Could the global energy requirement come entirely from geothermal sources eventually?

## Answer

No. At 10 TW, this source is roughly only the same as current power demand for human activities. All of it would need to be used (including that from the ocean floor) at an impossible 100% efficiency.

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