Warmth of the Earth. Probable sources of internal heat
Geothermy- a science that studies the Earth's thermal field. The average temperature of the Earth's surface has a general tendency to decrease. Three billion years ago, the average temperature on the Earth's surface was 71 o, now it is 17 o. Sources of heat (thermal ) The Earth's fields are internal and external processes. The Earth's heat is caused by solar radiation and originates in the bowels of the planet. The magnitudes of heat influx from both sources are quantitatively extremely unequal and their roles in the life of the planet are different. Solar heating of the Earth accounts for 99.5% of the total amount of heat received by its surface, and internal heating accounts for 0.5%. In addition, the influx of internal heat is very unevenly distributed on Earth and is concentrated mainly in places where volcanism occurs.
External source- this is solar radiation . Half solar energy absorbed by the surface, vegetation and subsurface layer of the earth's crust. The other half is reflected into the world space. Solar radiation maintains the temperature of the Earth's surface on average about 0 0 C. The sun warms up the near-surface layer of the Earth to a depth of an average of 8 - 30 m, with an average depth of 25 m, the influence of solar heat ceases and the temperature becomes constant (neutral layer). This depth is minimal in areas with a marine climate and maximum in the Subpolar region. Below this boundary there is a zone of constant temperature corresponding to the average annual temperature of the area. For example, in Moscow, on agricultural territory. Academy named after Timiryazev, at a depth of 20 m, the temperature since 1882 has invariably remained equal to 4.2 o C. In Paris, at a depth of 28 m, the thermometer has consistently shown 11.83 o C for more than 100 years. The layer with a constant temperature is the deepest where perennial ( permafrost. Below the zone of constant temperature is the geothermal zone, which is characterized by heat generated by the Earth itself.
Internal sources are the bowels of the Earth. The Earth radiates more heat into space than it receives from the Sun. Internal sources include residual heat from the time when the planet was molten, the heat of thermonuclear reactions occurring in the bowels of the Earth, the heat of the gravitational compression of the Earth under the influence of gravity, the heat of chemical reactions and crystallization processes, etc. (for example, tidal friction). Heat from the interior comes mainly from moving zones. The increase in temperature with depth is associated with the existence internal sources heat - decay of radioactive isotopes - U, Th, K, gravitational differentiation of matter, tidal friction, exothermic redox chemical reactions, metamorphism and phase transitions. The rate of temperature increase with depth is determined by a number of factors - thermal conductivity, permeability of rocks, proximity of volcanic sources, etc.
Below the belt constant temperatures There is an increase in temperature, on average 1 o per 33 m ( geothermal stage) or 3 o every 100 m ( geothermal gradient). These values are indicators of the Earth's thermal field. It is clear that these values are average and vary in magnitude in various areas or zones of the Earth. The geothermal stage is different at different points on the Earth. For example, in Moscow - 38.4 m, in Leningrad 19.6, in Arkhangelsk - 10. So, when drilling a deep well on the Kola Peninsula at a depth of 12 km, the temperature was assumed to be 150 o, in reality it turned out to be about 220 degrees. When drilling wells in the northern Caspian region at a depth of 3000 m, the temperature was assumed to be 150 o degrees, but it turned out to be 108 o.
It should be noted that the climatic features of the area and the average annual temperature do not affect the change in the value of the geothermal stage; the reasons lie in the following:
1) in different thermal conductivities rocks that make up a particular region. The measure of thermal conductivity is the amount of heat in calories transferred in 1 second. Through a cross section of 1 cm 2 with a temperature gradient of 1 o C;
2) in the radioactivity of rocks, the greater the thermal conductivity and radioactivity, the lower the geothermal stage;
3) in different conditions occurrence of rocks and age of disturbance of their occurrence; observations have shown that the temperature increases faster in layers collected in folds, they are more likely to have irregularities (cracks), through which the access of heat from the depths is facilitated;
4) character groundwater: flows of hot underground waters warm up rocks, cold ones cool them;
5) distance from the ocean: near the ocean due to the cooling of rocks by the mass of water, the geothermal step is greater, and at the contact it is less.
Knowledge of the specific value of the geothermal step is of great practical importance.
1. This is important when designing mines. In some cases, it will be necessary to take measures to artificially lower the temperature in deep workings (temperature - 50 o C is the limit for humans in dry air and 40 o C in humid air); in others, it will be possible to carry out work at great depths.
2. Great value has an assessment of temperature conditions during tunneling in mountainous areas.
3. The study of the geothermal conditions of the Earth's interior makes it possible to use steam and hot springs emerging on the Earth's surface. Underground heat is used, for example, in Italy, Iceland; In Russia, an experimental industrial power plant was built using natural heat in Kamchatka.
Using data on the magnitude of the geothermal step, we can make some assumptions about temperature conditions deep zones of the Earth. If we accept average value geothermal stage for 33 m and assume that the temperature increases uniformly with depth, then at a depth of 100 km there will be a temperature of 3000 o C. This temperature exceeds the melting points of all substances known on Earth, therefore at this depth there must be molten masses. But due to the enormous pressure of 31,000 atm. Superheated masses do not have the characteristics of liquids, but are endowed with the characteristics of a solid.
With depth, the geothermal stage apparently should increase significantly. If we assume that the level does not change with depth, then the temperature in the center of the Earth should be about 200,000 o degrees, and according to calculations it cannot exceed 5,000 - 10,000 o.
The term “ geothermal energy” comes from Greek word earth (geo) and thermal (thermal). Essentially geothermal energy comes from the earth itself. Heat from the earth's core, which averages 3,600 degrees Celsius, radiates toward the planet's surface.
Heating of springs and geysers underground at a depth of several kilometers can be carried out using special wells through which hot water (or steam from it) flows to the surface, where it can be used directly as heat or indirectly to generate electricity by turning on rotating turbines.
Since the water beneath the earth's surface is constantly replenished, and the Earth's core will continue to produce heat relative to human life indefinitely, geothermal energy will eventually clean and renewable.
Methods for collecting the Earth's energy resources
Today there are three main methods for collecting geothermal energy: dry steam, hot water and the binary cycle. The dry steam process directly drives the turbine drives of electricity generators. Hot water flows from the bottom up, then is sprayed into the tank to create steam to drive the turbines. These two methods are the most common, generating hundreds of megawatts of electricity in the US, Iceland, Europe, Russia and other countries. But location is limited, as these plants operate only in tectonic regions where access to heated water is easier.
With binary cycle technology, warm (not necessarily hot) water is extracted to the surface and combined with butane or pentane, which has low temperature boiling. This liquid is pumped through a heat exchanger where it is evaporated and sent through a turbine before being recirculated back into the system. Binary cycle technologies provide tens of megawatts of electricity in the United States: California, Nevada and Hawaii.
The principle of energy production
Disadvantages of Geothermal Energy
At the utility level, geothermal power plants are expensive to build and operate. Finding a suitable location requires expensive well surveys with no guarantee of hitting a productive underground hot spot. However, analysts expect this capacity to nearly double over the next six years.
In addition, areas with high underground source temperatures are located in areas with active geological and chemical volcanoes. These "hot spots" form at the boundaries of tectonic plates in places where the crust is quite thin. The Pacific region, often referred to as the ring of fire for many volcanoes, has many hot spots, including in Alaska, California and Oregon. Nevada has hundreds of hot spots covering much of the northern United States.
There are other seismic active areas. Earthquakes and the movement of magma allow the water to circulate. In some places, water rises to the surface and natural hot springs and geysers occur, such as in Kamchatka. The water in the geysers of Kamchatka reaches 95° C. 
One of the problems with an open geyser system is the release of certain air pollutants. Hydrogen sulfide is a toxic gas with a very recognizable "rotten egg" smell - small amounts of arsenic and minerals released with the steam. Salt can also pose an environmental problem.
In offshore geothermal power plants, significant amounts of interfering salt accumulate in the pipes. In closed systems there are no emissions and all liquid brought to the surface is returned.
Economic potential of the energy resource
Seismically active spots are not the only places where geothermal energy can be found. There is a constant supply of useful heat for direct heating purposes at depths anywhere from 4 meters to several kilometers below the surface almost anywhere on earth. Even the soil in your own backyard or local school has economic potential in the form of heat to be released into the house or other buildings.
In addition, there is a huge amount of thermal energy in dry rock formations very deep below the surface (4 – 10 km).
Usage new technology could expand geothermal systems, where people could use that heat to produce electricity on a much larger scale than conventional technologies. The first demonstration projects of this principle of generating electricity were shown in the United States and Australia back in 2013.
If the full economic potential of geothermal resources can be realized, it will represent a huge source of electricity for production capacity. Scientists suggest that ordinary geothermal springs have a potential of 38,000 MW, which can produce 380 million MW of electricity per year.
Hot dry rocks occur at depths of 5 to 8 km everywhere underground and at shallower depths in certain places. Access to these resources requires the introduction cold water, circulating through hot rocks and discharging heated water. There are currently no commercial applications for this technology. Existing technologies do not yet allow restoration thermal energy directly from the magma, very deep, but this is the most powerful resource geothermal energy.
With the combination of energy resources and its consistency, geothermal energy can play an indispensable role as a cleaner, more sustainable energy system.
Geothermal power plant structures
Geothermal energy is clean, sustainable heat from the Earth. Large resources are found in a range of several kilometers below the earth's surface, and even deeper, up to high temperature molten rock called magma. But as described above, people have not yet reached the magma.
Three designs of geothermal power plants
The technology of application is determined by the resource. If the water comes from the well as steam, it can be used directly. If hot water is at a high enough temperature it must pass through a heat exchanger.
The first well for energy production was drilled before 1924. More deep wells were drilled in the 1950s, but real development occurred in the 1970s and 1980s.
Direct use of geothermal heat
Geothermal sources can also be used directly for heating purposes. Hot water is used to heat buildings, grow plants in greenhouses, dry fish and crops, improve oil production, help in industrial processes like milk pasteurizers and water heating in fish farms. In the United States, Klamath Falls, Oregon and Boise, Idaho, have used geothermal water to heat homes and buildings for over a century. On the East Coast, Warm Springs, Virginia gets its heat directly from spring water using heat sources at one of the local resorts.
In Iceland, almost every building in the country is heated by hot spring water. In fact, Iceland gets more than 50 percent of its primary energy from geothermal sources. In Reykjavik, for example (population 118 thousand), hot water is conveyed by conveyor over 25 kilometers, and residents use it for heating and natural needs.
New Zealand, receives an additional 10% of its electricity. is underdeveloped, despite the presence of thermal waters.
People have long known about the spontaneous manifestations of gigantic energy hidden in the depths of globe. The memory of mankind preserves legends about catastrophic volcanic eruptions that killed millions human lives, which have changed the appearance of many places on Earth beyond recognition. The power of the eruption of even a relatively small volcano is colossal; it is many times greater than the power of the largest power plants created by human hands. True, there is no need to talk about the direct use of the energy of volcanic eruptions: people do not yet have the ability to curb this rebellious element, and, fortunately, these eruptions are quite rare events. But these are manifestations of energy hidden in the bowels of the earth, when only a tiny fraction of this inexhaustible energy finds release through the fire-breathing vents of volcanoes.
The small European country of Iceland (“the land of ice” in literal translation) is completely self-sufficient in tomatoes, apples and even bananas! Numerous Icelandic greenhouses receive energy from the heat of the earth; there are practically no other local energy sources in Iceland. But this country is very rich hot springs and famous geysers - fountains hot water, with the precision of a chronometer bursting out of the ground. And although Icelanders do not have priority in using the heat of underground sources (even the ancient Romans brought water from underground to the famous baths - the Baths of Caracalla), the inhabitants of this small northern country the underground boiler room is operated very intensively. The capital city of Reykjavik, where half the country's population lives, is heated only by underground sources. Reykjavik is the ideal starting point for exploring Iceland: from here you can go on the most interesting and varied excursions to any corner of this unique country: geysers, volcanoes, waterfalls, rhyolite mountains, fjords... Everywhere in Reykjavik you will feel PURE ENERGY - the thermal energy of geysers gushing from underground, the energy of purity and space of a perfectly green city, the energy of cheerful and incendiary nightlife Reykjavik all year round.
But people draw energy from the depths of the earth not only for heating. Power plants using hot underground springs have been operating for a long time. The first such power plant, still very low-power, was built in 1904 in the small Italian town of Larderello, named after the French engineer Larderelli, who back in 1827 drew up a project for using the numerous hot springs in the area. Gradually, the power of the power plant grew, more and more new units were put into operation, new sources of hot water were used, and today the power of the station has already reached an impressive value - 360 thousand kilowatts. In New Zealand, there is such a power plant in the Wairakei area, its capacity is 160 thousand kilowatts. 120 km from San Francisco in the USA, a geothermal station with a capacity of 500 thousand kilowatts produces electricity.
Geothermal energy
People have long known about the spontaneous manifestations of gigantic energy hidden in the depths of the globe. The memory of mankind contains legends about catastrophic volcanic eruptions that claimed millions of human lives and changed the appearance of many places on Earth beyond recognition. The power of the eruption of even a relatively small volcano is colossal; it is many times greater than the power of the largest power plants created by human hands. True, there is no need to talk about the direct use of the energy of volcanic eruptions - people do not yet have the ability to curb this rebellious element, and, fortunately, these eruptions are quite rare events. But these are manifestations of energy hidden in the bowels of the earth, when only a tiny fraction of this inexhaustible energy finds release through the fire-breathing vents of volcanoes.
A geyser is a hot spring that spews its water at a regular or irregular height, like a fountain. The name comes from the Icelandic word for "to pour". The appearance of geysers requires a certain favorable environment, which is created only in a few places on earth, which makes them quite rare. Almost 50% of geysers are located in national park Yellowstone (USA). The activity of a geyser may cease due to changes in the subsoil, earthquakes and other factors. The action of a geyser is caused by the contact of water with magma, after which the water quickly heats up and, under the influence of geothermal energy, is thrown upward with force. After the eruption, the water in the geyser gradually cools, seeps back into the magma, and gushes out again. The frequency of eruptions of different geysers varies from several minutes to several hours. The need for high energy for the geyser to operate – main reason their rarity. Volcanic areas may have hot springs, mud volcanoes, fumaroles, but there are very few places where geysers are found. The fact is that even if a geyser was formed in a place of volcanic activity, subsequent eruptions will destroy the surface of the earth and change its condition, which will lead to the disappearance of the geyser.
Earth energy (geothermal energy) is based on the use natural warmth Earth. The bowels of the Earth contain a colossal, almost inexhaustible source of energy. The annual radiation of internal heat on our planet is 2.8 * 1014 billion kW * hour. It is constantly compensated by the radioactive decay of certain isotopes in the earth's crust.
Geothermal energy sources can be of two types. The first type is underground pools of natural coolants - hot water (hydrothermal springs), or steam (steam thermal springs), or a steam-water mixture. Essentially, these are ready-to-use "underground boilers" from which water or steam can be extracted using conventional boreholes. The second type is the heat of hot rocks. By pumping water into such horizons, it is also possible to obtain steam or superheated water for further use for energy purposes.
But in both uses, the main drawback is perhaps the very weak concentration of geothermal energy. However, in places where peculiar geothermal anomalies form, where hot springs or rocks come relatively close to the surface and where, when immersed deeper for every 100 m, the temperature increases by 30-40 ° C, concentrations of geothermal energy can create conditions for its economic use. Depending on the temperature of water, steam or steam-water mixture, geothermal sources are divided into low and medium temperature (with temperatures up to 130 - 150° C) and high temperature (over 150°). The nature of their use largely depends on the temperature.
It can be argued that geothermal energy has four beneficial distinguishing features.
Firstly, its reserves are practically inexhaustible. According to estimates from the late 70s, to a depth of 10 km they amount to a value that is 3.5 thousand times higher than reserves traditional types mineral fuel.
Secondly, geothermal energy is quite widespread. Its concentration is mainly associated with belts of active seismic and volcanic activity, which occupy 1/10 of the Earth's area. Within these belts, we can identify some of the most promising “geothermal areas”, examples of which are California in the USA, New Zealand, Japan, Iceland, Kamchatka, North Caucasus in Russia. Only in former USSR By the beginning of the 90s, about 50 underground hot water and steam pools had been opened.
Thirdly, the use of geothermal energy does not require large costs, because in this case we're talking about about “ready-to-use” energy sources created by nature itself.
Finally, fourthly, geothermal energy is completely harmless from an environmental point of view and does not pollute the environment.
Man has long been using the energy of the internal heat of the Earth (remember, for example, the famous Roman baths), but its commercial use began only in the 20s of our century with the construction of the first geoelectric power stations in Italy, and then in other countries. By the beginning of the 80s, there were about 20 such stations in the world with a total capacity of 1.5 million kW. The largest of them is the Geysers station in the USA (500 thousand kW).
Geothermal energy is used to generate electricity, heat homes, greenhouses, etc. Dry steam, superheated water or any coolant with a low boiling point (ammonia, freon, etc.) are used as a coolant.
For Russia, the Earth's heat energy can become a constant, reliable source of cheap and accessible electricity and heat using new high, environmentally friendly technologies for its extraction and supply to the consumer. This is especially true nowadays
Limited resources of fossil energy raw materials
The demand for organic energy raw materials is great in industrialized and developing countries (USA, Japan, countries of united Europe, China, India, etc.). At the same time, these countries’ own hydrocarbon resources are either insufficient or reserved, and a country, for example the United States, buys energy raw materials abroad or develops deposits in other countries.
In Russia, one of the richest countries in terms of energy resources, economic needs for energy are so far satisfied by the possibilities of using natural resources. However, the extraction of fossil hydrocarbons from the subsoil occurs at a very fast pace. If in the 1940–1960s. The main oil-producing areas were “Second Baku” in the Volga region and the Urals, then, from the 1970s to the present time, such an area has been Western Siberia. But here, too, there is a significant decrease in the production of fossil hydrocarbons. The era of “dry” Cenomanian gas is becoming a thing of the past. The previous stage of extensive development of natural gas production has come to an end. Its recovery from such giant deposits as Medvezhye, Urengoyskoye and Yamburgskoye amounted to 84, 65 and 50%, respectively. The share of oil reserves favorable for development is also decreasing over time.
Due to the active consumption of hydrocarbon fuels, onshore oil and natural gas reserves have decreased significantly. Now their main reserves are concentrated on the continental shelf. And although the raw material base of the oil and gas industry is still sufficient for oil and gas production in Russia in required volumes, in the near future it will be ensured to an increasing extent through the development of deposits with complex mining and geological conditions. The cost of hydrocarbon production will increase.
Most of the non-renewable resources extracted from the subsoil are used as fuel for power plants. First of all, this is , whose share in the fuel structure is 64%.
In Russia, 70% of electricity is generated at thermal power plants. The country's energy enterprises burn about 500 million tons of coal annually. t. in order to generate electricity and heat, while the production of heat consumes 3–4 times more hydrocarbon fuel than the generation of electricity.
The amount of heat obtained from the combustion of these volumes of hydrocarbon raw materials is equivalent to the use of hundreds of tons of nuclear fuel - the difference is huge. However, nuclear energy requires ensuring environmental safety (to prevent a repeat of Chernobyl) and protecting it from possible terrorist acts, as well as the safe and costly decommissioning of obsolete and expired nuclear power plant units. Proven recoverable uranium reserves in the world are about 3 million 400 thousand tons. Over the entire previous period (until 2007), about 2 million tons were mined.
RES as the future of global energy
The growing interest in alternative renewable energy sources (RES) in the world in recent decades is caused not only by the depletion of hydrocarbon fuel reserves, but also by the need to solve environmental problems. Objective factors (fossil fuel and uranium reserves, as well as changes environment associated with the use of traditional fire and nuclear energy) and energy development trends suggest that the transition to new methods and forms of energy production is inevitable. Already in the first half of the 21st century. There will be a complete or almost complete transition to non-traditional energy sources.
The sooner a breakthrough is made in this direction, the less painful it will be for the entire society and the more beneficial for the country where decisive steps will be taken in this direction.
The world economy has now already set a course for the transition to a rational combination of traditional and new energy sources. Energy consumption in the world by 2000 amounted to more than 18 billion tce. t., and energy consumption by 2025 may increase to 30–38 billion tce. t., according to forecasts, by 2050 consumption at the level of 60 billion tce is possible. t. Characteristic trends in the development of the world economy in the period under review are a systematic decrease in the consumption of fossil fuels and a corresponding increase in the use of non-traditional energy resources. The thermal energy of the Earth occupies one of the first places among them.
Currently, the Ministry of Energy of the Russian Federation has adopted a program for the development of non-traditional energy, including 30 large projects for the use of heat pump units (HPU), the operating principle of which is based on the consumption of low-potential thermal energy of the Earth.
Low-grade heat energy of the Earth and heat pumps
The sources of low-potential heat energy of the Earth are solar radiation and thermal radiation from the heated interior of our planet. Currently, the use of such energy is one of the most dynamically developing areas of energy based on renewable energy sources.
The Earth's heat can be used in various types buildings and structures for heating, hot water supply, air conditioning (cooling), as well as for heating paths in the winter, preventing icing, heating fields in open stadiums, etc. In the English-language technical literature, systems that utilize the Earth’s heat in heat supply systems and air conditioning are designated as GHP - “geothermal heat pumps” (geothermal heat pumps). The climatic characteristics of the countries of Central and Northern Europe, which, together with the USA and Canada, are the main areas for the use of low-grade heat from the Earth, determine this mainly for heating purposes; Air cooling is required relatively rarely even in summer. Therefore, unlike the USA, heat pumps in European countries operate mainly in heating mode. In the USA, they are more often used in air heating systems combined with ventilation, which allows both heating and cooling of outside air. In European countries, heat pumps are usually used in water heating systems. Since their efficiency increases as the temperature difference between the evaporator and condenser decreases, systems are often used to heat buildings. underfloor heating, in which a coolant circulates at a relatively low temperature (35–40 o C).
Types of systems for using low-potential heat energy from the Earth
In general, two types of systems for using low-potential heat energy from the Earth can be distinguished:
– open systems: groundwater supplied directly to heat pumps is used as a source of low-grade thermal energy;
– closed systems: heat exchangers are located in the soil mass; when a coolant with a lower temperature relative to the ground circulates through them, thermal energy is “selected” from the soil and transferred to the evaporator of the heat pump (or when using a coolant with a higher temperature relative to the ground, it is cooled).
Cons open systems are that wells require maintenance. In addition, the use of such systems is not possible in all areas. The main requirements for soil and groundwater are as follows:
– sufficient permeability of the soil, allowing water reserves to be replenished;
- good chemical composition groundwater(e.g. low iron content), avoiding problems associated with the formation of deposits on pipe walls and corrosion.
Closed systems for using low-potential heat energy from the Earth
Closed systems can be horizontal or vertical (Figure 1).
Rice. 1. Scheme of a geothermal heat pump installation with: a – horizontal
and b – vertical ground heat exchangers.
Horizontal ground heat exchanger
In Western and Central Europe horizontal ground heat exchangers are usually individual pipes laid relatively tightly and connected to each other in series or parallel (Fig. 2).
Rice. 2. Horizontal ground heat exchangers with: a – serial and
b – parallel connection.
To save the area where heat is removed, improved types of heat exchangers have been developed, for example, heat exchangers in the shape of a spiral (Fig. 3), located horizontally or vertically. This form of heat exchangers is common in the USA.
The main sources of thermal energy of the Earth are [, ]:
To date, only the first four sources have been quantified. In our country, the main credit for this goes to O.G. Sorokhtin And S.A. Ushakov. The data below is mainly based on the calculations of these scientists.
Heat of Earth's gravitational differentiation
One of the most important patterns in the development of the Earth is differentiation its substance, which continues to this day. Due to this differentiation, the formation occurred core and crust, change in the composition of the primary mantle, while the division of an initially homogeneous substance into fractions of different densities is accompanied by the release thermal energy, and the maximum heat release occurs when the earth's matter is divided into dense and heavy core and residual lighter silicate shell - earth's mantle. Currently, the bulk of this heat is released at the boundary mantle - core.
Energy of gravitational differentiation of the Earth over the entire period of its existence, it stood out - 1.46*10 38 erg (1.46*10 31 J). This energy for the most part first goes into kinetic energy convective currents of mantle matter, and then in warm; the other part of it is spent on additional compression of the earth's interior, arising due to the concentration of dense phases in the central part of the Earth. From 1.46*10 38 erg the energy of the Earth's gravitational differentiation went into its additional compression 0.23*10 38 erg (0.23*10 31 J), and was released in the form of heat 1.23*10 38 erg (1.23*10 31 J). The magnitude of this thermal component significantly exceeds the total release of all other types of energy in the Earth. Time distribution total value and the rate of release of the thermal component of gravitational energy is shown in Fig. 3.6 .
Rice. 3.6.
The current level of heat generation during gravitational differentiation of the Earth is 3*10 20 erg/s (3*10 13 W), which is from the size of the modern heat flow, passing through the surface of the planet at ( 4.2-4.3)*10 20 erg/s ((4.2-4.3)*10 13 W), is ~ 70%
.
Radiogenic heat
Caused by the radioactive decay of unstable isotopes. The most energy-intensive and long-lived ( with half-life, commensurate with the age of the Earth) are isotopes 238U, 235 U, 232 Th And 40 K. Their main volume is concentrated in continental crust . Current level of generation radiogenic heat:
- by American geophysicist V. Vaquier - 1.14*10 20 erg/s (1.14*10 13 W) ,
- by Russian geophysicists O.G. Sorokhtin And S.A. Ushakov - 1.26*10 20 erg/s(1.26*10 13 W) .
This is ~ 27-30% of the current heat flow.
From the total heat of radioactive decay in 1.26*10 20 erg/s (1.26*10 13 W) in the earth's crust stands out - 0.91*10 20 erg/s, and in the mantle - 0.35*10 20 erg/s. It follows that the share of mantle radiogenic heat does not exceed 10% of the total modern heat losses of the Earth, and it cannot be the main source of energy for active tectono-magmatic processes, the depth of which can reach 2900 km; and the radiogenic heat released in the crust is relatively quickly lost through the earth's surface and practically does not participate in heating the deep interior of the planet.
In past geological epochs, the amount of radiogenic heat released in the mantle must have been higher. Its estimates at the time of the formation of the Earth ( 4.6 billion years ago) give - 6.95*10 20 erg/s. Since this time, there has been a steady decrease in the rate of release of radiogenic energy (Fig. 3.7 ).
For all the time in the Earth, it has been released ~4.27*10 37 erg(4.27*10 30 J) thermal energy of radioactive decay, which is almost three times lower than the total heat of gravitational differentiation.
Tidal Friction Heat
It stands out during the gravitational interaction of the Earth primarily with the Moon, as the nearest large cosmic body. Due to mutual gravitational attraction, tidal deformations occur in their bodies - swelling or humps. The tidal humps of the planets, with their additional attraction, influence their movement. Thus, the attraction of both tidal humps of the Earth creates a pair of forces acting both on the Earth itself and on the Moon. However, the influence of the near swelling, facing the Moon, is somewhat stronger than that of the distant one. Due to the fact that the angular speed of rotation modern Earth (7.27*10 -5 s -1) exceeds the orbital speed of the Moon ( 2.66*10 -6 s -1), and the substance of the planets is not ideally elastic, then the tidal humps of the Earth seem to be carried away by its forward rotation and noticeably advance the movement of the Moon. This leads to the fact that the maximum tides of the Earth always occur on its surface somewhat later than the moment climax Moon, and an additional moment of force acts on the Earth and Moon (Fig. 3.8 ) .
The absolute values of the tidal interaction forces in the Earth-Moon system are now relatively small and the tidal deformations of the lithosphere caused by them can reach only a few tens of centimeters, but they lead to a gradual slowdown of the Earth’s rotation and, conversely, to an acceleration of the orbital movement of the Moon and to its distance from the Earth. The kinetic energy of the movement of the earth's tidal humps turns into thermal energy due to internal friction of the substance in the tidal humps.
Currently, the rate of tidal energy release is G. Macdonald amounts to ~0.25*10 20 erg/s (0.25*10 13 W), while its main part (about 2/3) is presumably dissipates(dissipates) in the hydrosphere. Consequently, the fraction of tidal energy caused by the interaction of the Earth with the Moon and dissipated in the solid Earth (primarily in the asthenosphere) does not exceed 2 %
total thermal energy generated in its depths; and the share of solar tides does not exceed 20 %
from the effects of lunar tides. Therefore, solid tides now play virtually no role in feeding tectonic processes with energy, but in some cases they can act as “triggers”, for example earthquakes.
The amount of tidal energy is directly related to the distance between space objects. And if the distance between the Earth and the Sun does not assume any significant changes on a geological time scale, then in the Earth-Moon system this parameter is variable. Regardless of ideas about almost all researchers admit that early stages development of the Earth, the distance to the Moon was significantly less than modern, but in the process of planetary development, according to most scientists, it gradually increases, and according to Yu.N. Avsyuku this distance experiences long-term changes in the form of cycles "coming and going" of the Moon. It follows from this that in past geological epochs the role of tidal heat in the overall heat balance of the Earth was more significant. In general, over the entire period of the Earth’s development, it has evolved ~3.3*10 37 erg (3.3*10 30 J) tidal heat energy (this is subject to the gradual removal of the Moon from the Earth). The change in the rate of release of this heat over time is shown in Fig. 3.10 .
More than half of the total tidal energy was released in catarchaea (shit)) - 4.6-4.0 billion years ago, and at that time only due to this energy the Earth could additionally warm up by ~500 0 C. Starting from the late Archean, lunar tides made only a negligible impact on the development energy-intensive endogenous processes .
Accretion heat
This is the heat retained by the Earth since its formation. In progress accretion, which lasted for several tens of millions of years, thanks to the collision planetesimals The Earth experienced significant heating. However, there is no consensus on the magnitude of this heating. Currently, researchers are inclined to believe that during the process of accretion the Earth experienced, if not complete, then significant partial melting, which led to the initial differentiation of the Proto-Earth into a heavy iron core and a light silicate mantle, and to the formation "magma ocean" on its surface or at shallow depths. Although even before the 1990s, the model of a relatively cold primary Earth, which gradually warmed up due to the above processes, accompanied by the release of a significant amount of thermal energy, was considered almost universally accepted.
An accurate assessment of the primary accretion heat and its fraction preserved to the present day is associated with significant difficulties. By O.G. Sorokhtin And S.A. Ushakov, who are supporters of the relatively cold primary Earth, the amount of accretion energy converted into heat is - 20.13*10 38 erg (20.13*10 31 J). This energy, in the absence of heat loss, would be enough for complete evaporation earthly matter, because the temperature could rise to 30 000 0 С. But the accretion process was relatively long, and the energy of planetesimal impacts was released only in the near-surface layers of the growing Earth and was quickly lost with thermal radiation, so the initial heating of the planet was not great. The magnitude of this thermal radiation, going in parallel with the formation (accretion) of the Earth, these authors estimate at 19.4*10 38 erg (19.4*10 31 J)
.
In the modern energy balance of the Earth, accretion heat most likely plays a minor role.
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