Energy

The Earth’s energy

Our planet constantly emits energy, as heat that comes to the surface from the deepest areas: it’s the so called heat flux, or geothermal flux. The heat from the Sun gives warmth to the Earth’s surface with a flux that is almost 6000 times bigger than the one produced inside the Earth, however the constant and continuous geothermal flux represents an important form of heating for our planet: with an average of 0,06 watt/m2, the entire surface of the Earth radiates a quantity of heat equal to about 30.000 billion watt. The increase in temperature as you go deeper into the Earth is a well-known phenomenon to miners: in some mines and deep tunnels temperatures reach levels that are hardly bearable by human beings (this is not so in grottoes, where the natural air and water circulation lowers the temperature substantially, such that the increase in temperature with depth is hardly perceptible). The heat of the Earth is for the great part due to the liberation of energy in the decay processes of some elements’ radioisotopes such as, for example, potassium, thorium and uranium. Because of the different levels of thickness of the terrestrial crust and of the different geological situations, which can cause the seeping of hotter materials from deep zones, the geothermal gradient (that is the increase in temperature with depth) is not the same on the whole Earth’s surface: on average the temperature increases by 2-3° C every 100 m of depth, but the increase can vary from 1 to 5° C/100 m. To measure the geothermal gradient you have to dig wells of at least 300 m of depth (so as not to be influenced by daily and yearly variations in temperature due to climate changes), where specific thermometers are lowered in order to register temperatures at different depths. The heat flux is greater in the areas where the lithosphere’s thickness is reduced, for example, along the oceanic ridges or in the areas of continental rifting, or in volcanic areas, where various geological processes cause the fusion of rocks, or in areas where the subsurface holds magma undergoing a slow cooling process.