Ninety-nine percent of the Earth is hotter than 1000 degrees Celsius. Inside Earth's core, temperatures rise to 7000 degrees. In total, the power within our planet amounts to thousands of billions of watts. This reservoir has its origins in the residual heat dating from the time the Earth was created, roughly 4.6 billion years ago, and in the ongoing radioactive decay of long-lived isotopes of uranium, thorium and potassium. The question we need to ask ourselves is why, given these gigantic amounts of energy, does geothermal power still only account for far less than one percent of our energy usage?