When planet Earth came into being more than four billion years ago, its form was considerably different from what it is now. At that time Earth was in a partially melted state. It was not until about three billion years ago that the temperature of the Earth's surface dropped to below 100 °C and the Earth's crust gradually began to harden.
It may not seem like it in the depths of a northern winter, but today our planet is anything but a cold ball. About 99% of the Earth is hotter than 1000 °C and 90% of the rest has temperatures of over 100 °C. Fortunately for us, these high temperatures are almost exclusively found in the Earth's interior. Every so often volcanoes produce impressive eruptions spewing molten matter from depths of up to 100 km. Different geothermal energy technologies enable us to tap the heat of the Earth's interior in a controlled way so that we can satisfy some of our heat and electricity demands (Figure 10.1).
10.1 Tapping into the Earth's Heat
The Earth itself is made up of concentric bands (Figure 10.2) comprising the core, the mantle, and the crust. The Earth's core has a diameter of around 6900 km (4290 mi). A differentiation ...