H Heat is a form of energy, and geothermal energy is the heat contained in the earth, which causes

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Writing: Mary H. Dickson and Mario Fanelli Istituto di Geoscienze e Georisorse, CNR, Pisa, Italy Translation: Michael Plant and Maria Papachristou Aristotle University of Thessaloniki / Department of Geology
H Heat is a form of energy, and geothermal energy is the heat contained in the earth, which causes the creation of various geological phenomena on a planetary scale. Usually, however, the term "geothermal" is used today to indicate that part of the earth's heat can be recovered and used by humans, and in this sense we use the term from now on.
The presence of volcanoes, electric food hot springs and other thermal phenomena that led our ancestors to the conclusion that the earth is hot. However, only during the period between the 16 th and 17 th century, ie when the first mines were excavated to a depth of several hundred meters below the surface, people with the help of some simple physical considerations, concluded that the Earth's temperature increases with depth.
The first measurements by thermometer were probably in 1740, in a mine near Belfort, France (Bullard, 1965). Already in 1870, to study the thermal regime of the land used for some advanced modern scientific methods, while the thermal condition that governs the earth, the heat balance and evolution comprehend the 20th century, with the discovery of role of 'radiogenic heat. " Indeed, in all the modern models (models) of the thermal regime of the land must be included heat continually generated by the decay of long-lived radioactive isotopes of uranium (U 238, U 235), thorium (Th 232) and potassium (K 40), which are in the earth (Lubimova, 1968). In addition to the radioactive electric food heat, acting together, in uncertain proportions, and other potential sources of heat, such as "primal energy" since the creation and growth of the planet. Until the 1980s, electric food these models are not based on some realistic theories. But then it turned out that there was no equilibrium between the radiogenic heat generated in the earth and the heat escaping from the Earth into space, and second, that our planet is slowly cooling and inside.
As a general idea of the nature and scale of the phenomenon concerned, we can mention the so-called "thermal equilibrium", as given by Stacey and Loper (1988). According to this, the total heat flow from the earth (conduction, convection and radiation) is estimated at 42 x 10 12 W. Of these, 8 x 10 12 W from the cortex, electric food which represents only 2% of the total volume of the Earth is rich in radioactive isotopes, 32,3 x 10 12 W from the mantle, which represents 82% of total volume of the earth, and 1,7 x 10 12 W from the nucleus, which represents 16% of the total volume and contains electric food no radioactive isotopes (see Figure 1, a schematic of the internal structure of the Earth). Since the radiogenic heat of the mantle is estimated electric food at 22 x 10 12 W, the reduction of heat in this part of the land is 10,3 x 10 12 W. According to most recent estimates, based on a larger number of data, the total heat flow of the earth is about 6% higher than the values used by Stacey and Loper in 1988 anyway, however, the cooling process is still slow. The temperature of the mantle has fallen more than 300-350º C over the last 3 billion years, remaining at about 4000º C at its base. It has been estimated that the total heat content of the earth (for temperatures above the middle surface of 15º C) is of the order of 12,6 x 10 24 MJ and cortical 5,4 x 10 21 MJ (Armstead, 1983).
So, as shown above, the thermal electric food energy of the earth is immense, but only part of it may be used by mankind. To date, the exploitation of geothermal energy has been limited to areas where geological conditions permit a carrier (water in the liquid or gaseous phase) to 'transfer' the heat