The internal structure of the earth. The internal structure and history of the geological development of the earth

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Introduction - general geological information about the Earth

1. The origin of the Earth

2. The shape, size and movement of the Earth

3. The internal structure of the Earth

4. Theory of natural reactor

5. Evolution of the Earth

Conclusion - the direction of the geological development of the Earth

List of used literature

Introduction- general geological information about the Earth

In the history of the earth, 3 stages are distinguished - accretion, pre-geological and geological. It is possible to consider the geological history of our planet only from the time from which the most ancient witnesses of this history, rocks and minerals, have survived. However, the first ancient stage in the formation of the earth should be considered the time interval during which it was formed as one of the planets of the solar system, i.e. since the time of accretion of the matter of the gas-dust nebula, which, according to the researchers, was not long and apparently did not exceed 100 million years.

The second oldest stage is often called the pregeological one, since the rocks of this time were practically not preserved, and the processes that took place at this stage led to the differentiation of matter inside the planet, the formation of some kind of primary earth's crust of the basic composition, the release of the outer liquid core of the Earth and, accordingly, the appearance magnetic field. Most likely, at that time, the meteorite bombardment of the Earth was vigorously manifested, and its surface resembled the modern Moon or rather Venus, given that there was an oxygen-free atmosphere, the clouds of which covered the Earth with a dense veil. In 1978, the Precambrian stratigraphic scale was adopted in the USSR, which includes two main divisions: Archaean and Proterozoic, called eons - the duration of which far exceeds the time interval of the Phanerozoic eras.

The age of the earth is estimated at 4.5 billion years. Starting from the turn of about 4.0 - 3.5 billion years ago, the third stage begins, which in general can be called Precambrian or geological, and its upper limit was confined to the border of the Middle - Late Riphean, i.e. about 1 billion years ago. The fact is that in the Late Riphean, the disintegration of the giant continent Pangea-1 began and all the main mobile belts were laid, which later developed in the Phanerozoic. The duration of the geological or Precambrian stage is very long - about 3 billion years, and in its most general form, a number of large stages are distinguished in it:

1) ancient Archean or Catharhean (4.0 - 3.5 billion years);

2) Archean (3.5 - 2.6 billion years);

3) early Proterozoic (2.6 - 1.65 billion years);

4) Late Paleozoic (1.65 - 1.0 billion years).

Up to the Late Riphean;

The appearance of life on earth dates back to 1 billion years ago in harsh climatic conditions Koronovsky N.V., Khain V.E., Yasamanov N.A. "Historical Geology" Publisher: "Academy", 2008.

The development of life is subject to the laws of evolution - cyclicality, progression and irreversibility. Cyclicity - everything that happens on Earth appears and disappears, and all this happens sequentially at a certain interval, so the once-existing supercontinent Pangea-1 split, but later, according to scientific facts and the scientists themselves, after 40,000 million years, the Earth will again exist (formed ) giant supercontinent.

The geological history of the Earth is divided into periods in accordance with the geochronological scale adopted at the International Geological Congress in 1965. In geology, as in no other science, the sequence of establishing events, their chronology, based on the natural periodization of geological history, is important.

1. OriginEarth

According to modern cosmological concepts, the Earth was formed along with other planets about 4.5 billion years ago from pieces and debris that revolved around the young Sun. It grew, engulfing the matter around it, until it reached its current size. At first, the growth process was very violent, and the continuous rain of falling bodies should have led to its significant heating, since the kinetic energy of the particles was converted into heat. During impacts, craters arose, and the substance ejected from them could no longer overcome the force of gravity and fell back, and the larger the falling bodies were, the more they heated the Earth. The energy of falling bodies was no longer released on the surface, but in the depths of the planet, not having time to radiate into space. Although the original mixture of substances may have been homogeneous on a large scale, the heating of the earth mass due to gravitational compression and bombardment of its debris led to the melting of the mixture and the resulting liquids under the influence of gravity separated from the remaining solid parts. The gradual redistribution of the substance along the depth in accordance with the density should have led to its stratification into separate shells. The lighter substances, rich in silicon, separated from the denser ones, containing iron and nickel, and formed the first earth's crust. After about a billion years, when the earth cooled significantly, the earth's crust hardened, turning into a solid outer shell of the planet. Cooling down, the earth ejected many different gases from its core (usually this happened during volcanic eruptions) - light ones, such as hydrogen and helium, mostly escaped into outer space, but since the force of gravity of the earth was already quite large, it kept heavier. They just formed the basis of the earth's atmosphere. Part of the water vapor from the atmosphere condensed, and oceans appeared on the earth. Molodensky M.S. "Selected Works. gravitational field. The figure and internal structure of the Earth”, Nauka Publishing House, M., 2001

2. The shape, size and movement of the Earth

The shape of the Earth is close to an ellipsoid, flattened at the poles and stretched in the equatorial zone. The average radius of the Earth is 6371.032 km, polar 6356.777 km, equatorial 6378.160 km. The mass of the Earth is 5.976 1024 kg, the average density is 5518 kg / m 3.

The Earth moves around the Sun at an average speed of 29.765 km / s in an elliptical, close to circular orbit (eccentricity 0.0167); the average distance from the Sun is 149.6 million km, the period of one orbit is 365.24 solar days. The rotation of the Earth around its own axis occurs at an average angular velocity of 7.292115·10 -5 rad/s, which approximately corresponds to a period of 23 h 56 min 4.1 s. The linear speed of the Earth's surface at the equator is about 465 m/s. The axis of rotation is inclined to the plane of the ecliptic at an angle of 66 ° 33 "22". This tilt and the annual revolution of the Earth around the Sun cause the change of seasons, which is extremely important for the Earth's climate, and its own rotation, the change of day and night. Rotation of the Earth due to tidal influences steadily (albeit very slowly at 0.0015 s per century) slows down.There are also small irregular variations in the length of the day.

The surface area of ​​the Earth is 510.2 million km 2, of which approximately 70.8% is in the World Ocean. Its average depth is about 3.8 km, the maximum (the Mariana Trench in the Pacific Ocean) is 11.022 km; the volume of water is 1370 million km 3, the average salinity is 35 g / l. Land makes up 29.2%, respectively, and forms six continents and islands. It rises above sea level by an average of 875 m; the highest height (the peak of Chomolungma in the Himalayas) is 8848 m. Mountains occupy more than 1/3 of the land surface. Deserts cover about 20% of the land surface, savannas and light forests about 20%, forests about 30%, glaciers over 10%. Over 10% of the land is occupied by agricultural land. The Earth has only one satellite, the Moon. Its orbit is close to a circle with a radius of about 384,400 km.

3. The internal structure of the Earth

EARTH, the third largest planet from the Sun in the solar system. Due to its unique, perhaps the only natural conditions in the Universe, it became the place where organic life originated and developed.

Fig.1 Structure of the Earth Zharkov V.N. "The internal structure of the Earth and planets." Publishing house "Science", 2nd ed. M., 1983.

The number 1 in the figure indicates Earth's crust(outer shell), the thickness of which varies from several kilometers (in the oceanic regions) to several tens of kilometers (in the mountainous regions of the continents). The sphere of the earth's crust is very small, accounting for only about 0.5% total weight planets. The main composition of the crust is the oxides of silicon, aluminum, iron and alkali metals. The continental crust, which contains the upper (granite) and lower (basalt) layers under the sedimentary layer, contains the most ancient rocks of the Earth, whose age is estimated at more than 3 billion years. The oceanic crust under the sedimentary layer contains mainly one layer, similar in composition to basalt. The age of the sedimentary cover does not exceed 100-150 million years.

The earth's crust is separated from the underlying mantle by a largely mysterious Moho layer(named after the Serbian seismologist Mohorovic, who discovered it in 1909), in which the speed of propagation of seismic waves increases abruptly.

To share mantles accounts for about 67% of the total mass of the planet. The solid layer of the upper mantle, extending to various depths under the oceans and continents, together with the earth's crust is called the lithosphere - the most rigid shell of the Earth. A layer is marked under it, where there is a slight decrease in the propagation velocity of seismic waves, which indicates a peculiar state of matter. This layer, less viscous and more plastic in relation to the layers above and below, is called the asthenosphere. It is believed that the matter of the mantle is in continuous motion, and it is suggested that in relatively deep layers of the mantle, with an increase in temperature and pressure, there is a transition of matter into denser modifications. Such a transition is also confirmed by experimental studies.

AT lower mantle at a depth of 2900 km there is a sharp jump not only in speed longitudinal waves, but also in density, and transverse waves disappear completely here, which indicates a change material composition breeds. This is the outer boundary of the Earth's core According to B. Bolt, the following boundaries are given separate zones: the base of layer C - 670 km, layer D - 2885 km, layer F in the interval 4590-5155 km. Close data in the work of V. A. Zharkov.

Earth's core opened in 1936. It was extremely difficult to image it because of the small number of seismic waves reaching it and returning to the surface. In addition, the extreme temperatures and pressures of the core have long been difficult to reproduce in the laboratory. The Earth's core is divided into 2 separate regions: liquid ( outer core) and solid ( internal), the transition between them lies at a depth of 5156 km. Iron is an element that corresponds to the seismic properties of the core and is abundantly distributed in the Universe to represent approximately 35% of its mass in the planet's core. According to modern data, the outer core is a rotating stream of molten iron and nickel, a good conductor of electricity. It is with him that the origin of the earth's magnetic field is associated, believing that, electric currents, flowing in the liquid core, create a global magnetic field. The layer of the mantle that is in contact with the outer core is affected by it, since the temperatures in the core are higher than in the mantle. In some places, this layer generates huge heat and mass flows directed to the Earth's surface - plumes.

Inner hard core unrelated to the mantle. It is believed that its solid state, despite the high temperature, is provided by the gigantic pressure in the center of the Earth. It is suggested that, in addition to iron-nickel alloys, lighter elements, such as silicon and sulfur, and possibly silicon and oxygen, should also be present in the core. The question of the state of the Earth's core is still debatable. As the distance from the surface increases, the compression to which the substance is subjected increases. Calculations show that the pressure in the earth's core can reach 3 million atm. At the same time, many substances seem to be metallized - they pass into a metallic state. There was even a hypothesis that the core of the Earth consists of metallic hydrogen.

4. Natural Reactor Theory

Recently, the American geophysicist M. Herndon hypothesized that in the center of the Earth there is a natural " nuclear reactor» from uranium and plutonium (or thorium) with a diameter of only 8 km http://galspace.spb.ru - Project "Exploration of the Solar System" (2005-2008) . This hypothesis is able to explain the reversal of the earth's magnetic field, which occurs every 200,000 years. If this assumption is confirmed, then life on Earth may end 2 billion years earlier than expected, since both uranium and plutonium burn out very quickly. Their depletion will lead to the disappearance of the magnetic field that protects the earth from short-wave solar radiation and, as a result, to the disappearance of all forms of biological life. This theory was commented on by Corresponding Member of the Russian Academy of Sciences V.P. Trubitsyn Trubitsyn V.P., Zharkov V.N. "Physics of planetary interiors", - M. Science 1980: " Both uranium and thorium are very heavy elements that, in the process of differentiation of the primary matter of the planet, can sink to the center of the Earth. But at the atomic level, they're addicted with lightuhelements that are carried into the earth's crust, therefore all uranium deposits are located in the uppermost layer of the crust. That is, if these elements were also concentrated in the form of clusters, they could descend into the core, but, according to prevailing ideas, there should be a small number of them. Thus, in order to make statements about the uranium core of the Earth, it is necessary to give a more reasonable estimate of the amount of uranium that has gone into the iron core. It should also be noted that the movement of uranium into the core leads to a decrease in the radioactive hazard, since the rocky mantle is a very good screen.».

In the fall of 2002, Harvard University professor A. Dzewonski and his student M. Ishii, based on the analysis of data from more than 300,000 seismic events collected over 30 years, proposed a new model, according to which the so-called "innermost" core lies within the inner core , which is about 600 km across: Its presence may be evidence of the existence of two stages in the development of the inner core. To confirm such a hypothesis, it is necessary to place more more seismographs in order to make a more detailed selection of anisotropy (the dependence of the physical properties of matter on the direction inside it), which characterizes the very center of the Earth.

The individual face of the planet, like the appearance of a living being, is largely determined by internal factors that arise in its deep depths. It is very difficult to study these interiors, since the materials that make up the Earth are opaque and dense, so the volume of direct data on the substance of the deep zones is very limited. These include: the so-called mineral aggregate (large rock components) from a natural super-deep well - a kimberlite pipe in Lesoto (South Africa), which is considered as a representative of rocks occurring at a depth of about 250 km, as well as a core (cylindrical column of rock ), lifted from the deepest well in the world (12,262 m) on the Kola Peninsula. The study of the planet's superdeep is not limited to this. In the 70s of the 20th century, scientific continental drilling was carried out on the territory of Azerbaijan - the Saably well (8,324 m). And in Bavaria, in the early 90s of the last century, an ultra-deep well KTB-Oberpfalz was laid with a size of more than 9,000 m.

There are many other methods for studying our planet, but the main information about its internal structure was obtained as a result of studies of seismic waves that occur during earthquakes and powerful explosions. Every hour, about 10 oscillations of the earth's surface are recorded at various points on the Earth. In this case, seismic waves of two types arise: longitudinal and transverse. Both types of waves can propagate in a solid, but only longitudinal waves can propagate in liquids. Displacements of the earth's surface are recorded by seismographs installed around the globe. Observations of the speed with which waves travel through the earth allow geophysicists to determine the density and hardness of rocks at depths that are inaccessible to direct research. A comparison of the densities known from seismic data and those obtained in the course of laboratory experiments with rocks allows us to draw a conclusion about the material composition of the earth's interior. The latest data of geophysics and experiments related to the study of structural transformations of minerals made it possible to model many features of the structure, composition and processes occurring in the depths of the Earth.

Back in the 17th century, an amazing coincidence of the outlines of the coastlines west coast Africa and the east coast of South America led some scientists to the idea that the continents "walk" around the planet. But it wasn't until three centuries later, in 1912, that the German meteorologist Alfred Lothar Wegener detailed his continental drift hypothesis, according to which the relative positions of the continents have changed throughout the history of the earth. At the same time, he put forward many arguments in favor of the fact that in the distant past the continents were brought together. In addition to the similarity of coastlines, he discovered the correspondence of geological structures, the continuity of relic mountain ranges and the identity of fossil remains on different continents. Professor Wegener actively defended the idea of ​​the existence of a single supercontinent Pangea in the past, its split and the subsequent drift of the formed continents into different sides. But this unusual theory was not taken seriously, because from the point of view of that time it seemed completely incomprehensible that giant continents could independently move around the planet.

The revival of the ideas of this scientist occurred as a result of research on the bottom of the oceans. The fact is that the outer relief of the continental crust is well known, but the ocean floor, for many centuries reliably covered by many kilometers of water, remained inaccessible to study and served as an inexhaustible source of all kinds of legends and myths. an important step forward in the study of its relief was the invention of a precision echo sounder, with the help of which it became possible to continuously measure and record the depth of the bottom along the line of movement of the vessel. One of the striking results of intensive research of the ocean floor has been new data on its topography. Today, the topography of the ocean floor is easier to map, thanks to satellites that measure the “height” of the sea surface very precisely: it accurately reflects the differences in sea level from place to place. Instead of a flat bottom, devoid of any special signs, covered with silt, deep ditches and steep cliffs, giant mountain ranges and largest volcanoes were discovered. The Mid-Atlantic mountain range, which cuts the Atlantic Ocean in the middle, stands out most clearly on maps.

It turned out that the ocean floor ages as it moves away from the mid-ocean ridge, “spreading” from its central zone at a speed of several centimeters per year. The action of this process can explain the similarity of the outlines of the continental margins, if we assume that a new oceanic ridge is formed between the parts of the split continent, and the ocean floor, growing symmetrically on both sides, forms a new ocean. The Atlantic Ocean, in the midst of which lies the Mid-Atlantic Ridge, probably arose in this way. But if the area of ​​the sea floor increases and the Earth does not expand, then something in the global crust must be destroyed to compensate for this process. This is exactly what happens on the outskirts of most Pacific Ocean. Here the lithospheric plates converge, and one of the colliding plates sinks under the other and goes deep into the Earth. Such collision sites are marked by active volcanoes that stretch along the shores of the Pacific Ocean, forming the so-called "ring of fire".

Direct drilling of the seabed and determination of the age of uplifted rocks confirmed the results of paleomagnetic studies. These facts formed the basis of the theory of new global tectonics, or lithospheric plate tectonics, which made a real revolution in the sciences of the earth and brought a new understanding of the outer shells of the planet. The main idea of ​​this theory is the horizontal movement of plates.

5. Earth evolution

The question of the early evolution of the Earth is closely connected with the theory of its origin. Today it is known that our planet was formed about 4.5 billion years ago. In the process of the formation of the Earth from the particles of the protoplanetary cloud, its mass gradually increased. Gravitational forces grew, and consequently, the speed of particles falling on the planet. The kinetic energy of the particles turned into heat, and the Earth warmed up more and more. During impacts, craters arose on it, and the substance ejected from them could no longer overcome the earth's gravity and fell back.

The larger the falling objects, the more they heated the Earth. The impact energy was released not on the surface, but at a depth equal to approximately two diameters of the penetrating body. And since the main mass at this stage was supplied to the planet by bodies several hundred kilometers in size, the energy was released in a layer about 1000 km thick. She did not have time to radiate into space, remaining in the bowels of the Earth. As a result, the temperature at depths of 100-1000 km could approach the melting point. The additional rise in temperature was probably caused by the decay of short-lived radioactive isotopes.

Apparently, the first melts that appeared were a mixture of liquid iron, nickel, and sulfur. The melt accumulated, and then, due to the higher density, seeped down, gradually forming the earth's core. Thus, the differentiation (stratification) of the Earth's matter could begin at the stage of its formation. The impact reworking of the surface and the onset of convection undoubtedly prevented this process. But a certain part of the heavier substance still had time to sink under the stirred layer. In turn, density differentiation stopped convection and was accompanied by additional heat release, accelerating the process of formation of various zones in the Earth.

Presumably, the core was formed over several hundred million years. With the gradual cooling of the planet, the nickel-rich iron-nickel alloy, which has a high melting point, began to crystallize - this is how (possibly) a solid inner core was born. To date, it is 1.7% of the mass of the Earth. About 30% of the earth's mass is concentrated in the molten outer core.

The development of other shells lasted much longer and, in some respects, has not yet ended.

The lithosphere immediately after its formation had a small thickness and was very unstable. It was again absorbed by the mantle, destroyed during the era of the so-called great bombardment (from 4.2 to 3.9 billion years ago), when the Earth, like the Moon, was hit by very large and quite numerous meteorites. On the Moon, and today you can see evidence of meteorite bombardment - numerous craters and seas (areas filled with erupted magma). On our planet, active tectonic processes and the impact of the atmosphere and hydrosphere have practically erased the traces of this period.

About 3.8 billion years ago, the first light and, therefore, "unsinkable" granite crust was formed. At that time, the planet already had an air shell and oceans; the gases necessary for their formation were intensively supplied from the bowels of the Earth in the previous period. The atmosphere then consisted mainly of carbon dioxide, nitrogen and water vapor. There was little oxygen in it, but it was produced as a result, firstly, of the photochemical dissociation of water and, secondly, of the photosynthetic activity of simple organisms such as blue-green algae.

600 million years ago, there were several mobile continental plates on Earth, very similar to modern ones. The new supercontinent Pangea appeared much later. It existed 300-200 million years ago, and then broke up into parts, which formed the current continents.

What awaits the Earth in the future? This question can only be answered with a high degree of uncertainty, abstracting both from the possible external, cosmic influence, and from the activities of mankind, which transforms the environment, and not always for the better.

In the end, the bowels of the Earth will cool down to such an extent that convection in the mantle and, consequently, the movement of the continents (and hence mountain building, volcanic eruptions, earthquakes) will gradually weaken and stop. Weathering will eventually erase the unevenness of the earth's crust, and the surface of the planet will disappear under water. Its further fate will be determined by the average annual temperature. If it drops significantly, the ocean will freeze and the Earth will be covered with an ice crust. If the temperature rises (and most likely this is what the increasing luminosity of the Sun will lead to), then the water will evaporate, exposing flat surface planets. Obviously, in either case, the life of mankind on Earth will no longer be possible, at least in our modern understanding of it.

Conclusion -the direction of the geological development of the Earth

The geological history of the Earth includes the following sequence of events in the development of the Earth as a planet: the formation of rocks, the emergence and destruction of landforms, the sinking of land under water (the advance of the sea), the retreat of the sea, glaciation, the appearance and disappearance of various species of animals and plants, etc. d. The duration of the geological history of the Earth is measured in many millions of years.

The sequence of major events in the history of the earth's crust outlined above, the formation of oceans and continents, does not fit into the framework of the widespread idea that the continents progressively grow at the expense of the oceans. Modern oceans are by no means relics (remains) of the primary ocean, but geological structures of continents, often cut off by younger oceanic depressions; all this contradicts the view that the oceans are primary. Indeed, how can one explain why, over the course of 4.5 billion years, in some areas, the processes of separation of the mantle matter led to the creation of a thick continental crust, while in other areas this process stopped at the stage of formation of a primitive oceanic crust? Suppose such constancy could be explained by the primary inhomogeneity of the mantle. But this does not fit in with a number of facts of the general structural plan of the structure of the lithosphere; This is also contradicted by the history of modern geosynclines and platforms.

Another view is not entirely satisfactory, according to which the development of the earth's crust for a long time followed the path of increment of the continental crust and only in the Mesozoic did the disintegration of the continents begin, while new oceans were formed either due to the expansion of the continental oceans, or due to the collapse, subsidence and reworking of the continental crust. crust ("oceanization").

Obviously, both of these hypotheses oversimplify the much more complicated path of development of the lithosphere in reality. In the early stages, under conditions of strong heat flow and high content volatile and fusible substances in the upper mantle, the primary oceanic crust first formed (by 4.0 billion years BC), and then the primary continental crust (by 3.5-2.0 billion years BC .). This process, gradually weakening, ended mainly by 2.0 billion years BC. e. the creation, probably, of a fairly uniform and relatively small thickness (on average, no more than 30–35 km) of a layer of continental crust. At the same time, the heat flow from the depths also weakened over time, and the ubiquitous mobility of the crust was replaced by its uneven mobility along the network of deep faults in the cooled solid shell of the Earth. Then came the time of fragmentation of the continental crust; wide mobile geosynclinal belts were laid down, the inner parts of which at the initial stages of their development approached the oceans in size and character of the crust. Later, zones of sharp thickening of the crust arose in the mobile belts - in places it is almost twice as thick as the "normal" primary continental crust. In other words, there was a redistribution of the crust: its thickness in some areas increased sharply, while in others it decreased no less sharply, while the thickness (thickness) of the lithosphere under the continents increased due to the subsidence of its sole. At the same time, the thickness of the lithosphere under the oceans began to decrease, which is associated with the formation of deep faults - rifts, in which protrusions of the deep subcrustal layer of reduced density and viscosity reach the bottom of the crust.

Thus, in the course of the evolution of the earth's crust in the upper mantle (i.e., the sphere of the earth covered by tectonic processes), the inhomogeneity of the crust increased, which determined the differences between the oceanic and continental hemispheres of the earth; common law development of our planet - there was a complication of the material composition and structure of the earth's crust, the differentiation and diversity of the flow of deep processes in the course of geological history increased.

Of course, science is advancing, and our understanding of the past is also improving, which is so necessary both for understanding modern geological processes and for predicting the future.

List of used literature

1. Koronovskii N.V., Khain V.E., Yasamanov N.A. "Historical Geology" Publisher: "Academy", 2008

2. Jeffreys G. "Earth, its origin, history and structure": Publishing house of foreign literature, Per. from English. M., 1960.

3. Molodensky M.S. "Selected Works. gravitational field. The figure and internal structure of the Earth”, Nauka Publishing House, M., 2001

4. Zharkov V.N. "The internal structure of the Earth and planets" Publishing house "Nauka", 2nd ed. M., 1983.

5. http://galspace.spb.ru - Solar System Research Project (2005-2008)

6. Trubitsyn V.P., Zharkov V.N. "Physics of planetary interiors", - M. Science 1980

7. Gekhtman G.N. "Outstanding geographers and travelers" T., 1962.

8. Fedynsky V.V. Exploration Geophysics, Moscow, 1964.

9. Magidovich I.P. "Essays on the history of geographical discoveries" M., 2004.

10. Vernadsky V.I. "Favorite tr. on the history of science "M., 1981.

11. Khain V.E., Mikhailov A.E. "General Geotectonics". M., 1985.

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The result of the geological development of the Earth was the formation of the uppermost shells - the atmosphere, hydrosphere and lithosphere. This happened as a result of the cooling of the Earth's surface and led to the formation of primary basaltic or similar in composition to the Earth's crust. Almost simultaneously, due to the condensation of water vapor, the planet's water shell, the hydrosphere, was formed.

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The modern topography of the planet has evolved over many hundreds of millions of years and continues to change under the influence of the combined action of tectonic, hydrospheric, atmospheric and biological processes on its surface. This began about 3.5 billion years ago, when volcanic arcs began to form. The formation of volcanic arcs took place on the primary residual or secondary crust, formed during the stretching of the oceanic crust above the zones of subsidence (collisions of lithospheric plates and their crawling under each other with the formation of a volcanic arc). As a result, approximately 2.7-2.5 billion years ago, significant areas of the continental crust arose, which, apparently, merged into a single supercontinent - the first Pangea in the history of the Earth. The thickness of this crust has already reached the modern thickness of 35-40 km. Its lower part, under the influence of high pressures and temperatures, experienced significant transformations, and at the middle levels, large masses of granite were melted.

The next important moment in the development of the Earth took place approximately 2.5 billion years ago. The supercontinent that arose at the previous stage - the first Pangea - underwent significant changes and 2.2 billion years ago broke up into separate, relatively small

continents separated by basins with newly formed oceanic crust. Separate traces of these stages of plate tectonics can be found even now. The first stage (before the emergence of Pangaea) is commonly called embryonic plate tectonics, and second - small plate tectonics. By the end of the second period, about 1.7 billion years ago, the continents again merged into a single supercontinent. Pangea-N was formed. Its disintegration began about 1 billion years ago, although partial separations and reunions could have taken place even before that.

In the interval of 1-0.6 billion years ago, the structural plan of the Earth underwent radical changes and significantly approached the modern one. From that moment began full scale plate tectonics. It is due to the fact that the Earth's lithosphere is divided into a limited number of large (5 thousand km) and medium (1 thousand km) rigid and monolithic plates in diameter, which are located on a more plastic and viscous shell - the asthenosphere. Lithospheric plates began to move along the asthenosphere in a horizontal direction, forming extensions and crawlings, which, on average, compensate each other on a planetary scale. Thus, in the history of the Earth as a planet, the process of formation and disintegration of Pangea has repeatedly occurred. The duration of such cycles is 500-600 million years. This large-scale periodicity is superimposed by smaller-scale periodicity associated with stretching and compression of the earth's crust.

As a result of tectonic activity, the relief of the earth's surface today is characterized by a global asymmetry of two hemispheres (Northern and Southern): one of them is a giant space filled with water. These are oceans, occupying more than 70% of the entire surface. In the other hemisphere, crustal uplifts are concentrated, forming continents. The global asymmetry in the structure of the surface of our planet was noticed long ago, which made it possible to divide the planetary relief into two main areas - oceanic and continental. The bottom of the oceans and continents differ from each other in the structure of the earth's crust, chemical and petrographic composition, as well as the history of geological development. The crust has an increased thickness in the area of ​​the continents and a reduced one in the areas of the ocean floor.

The average thickness of the continental crust is 35 km. Its upper layer is rich in granitic rocks, the lower layer is rich in basalt magmas. There is no granite layer at the bottom of the oceans, and the earth's crust consists only of a basalt layer. Its thickness is 5-10 km. In addition, continental crust contains more heat-generating radioactive elements than thin oceanic crust.

The earth's crust, which forms the upper part of the lithosphere, mainly consists of eight chemical elements: oxygen, silicon, aluminum

minium, iron, calcium, magnesium, sodium and potassium. Half of the entire mass of the crust is oxygen, which is contained in it in a bound state, mainly in the form of metal oxides.

The earth's crust is composed of rocks of various types and various origins. More than 70% are igneous rocks, 20% are metamorphic, 9% are sedimentary rocks.

We should not forget that the surface of the Earth is composed of lithospheric plates, the number and position of which changed from epoch to epoch. The plate is the entire mass of the earth's crust and the underlying mantle, which move as a whole along the surface of the earth. Today, 8-9 large plates and more than 10 small ones are distinguished. Plates slowly move horizontally (global plate tectonics). In areas of rift valleys, where the mantle material is carried outward, the plates diverge, and in places where the horizontal displacements of neighboring plates turn out to be opposite, they push each other. Along the boundaries of the lithospheric plates there are zones of increased tectonic activity. When the plates move, their edges are crushed, forming mountain ranges or entire mountainous regions. Oceanic plates, originating in rift faults, increase in thickness as they approach the continents. They go under the island arcs or the continental plate, dragging the accumulated sedimentary rocks with them. The substance of the subducting plate reaches depths of up to 500-700 km in the mantle, where it begins to melt.

Formation of the atmosphere and hydrosphere. The constituent parts of the Earth's atmosphere and hydrosphere are volatile substances that appeared as a result of its chemical differentiation. According to available data, water vapor and atmospheric gases arose in the bowels of the Earth and entered its surface as a result of internal heating together with the most fusible substances of the primary mantle during volcanic activity.

Water and carbon dioxide, as components of the gas and dust cloud, remained in the form of molecules for a long time, when most of the solid condensates had already formed. Therefore, the remaining gases were absorbed to some extent by dust particles through adsorption and various chemical reactions. So volatiles invaded terrestrial planets. From the bowels of the Earth, they come to the surface as a result of volcanic activity. In addition, according to Alven and Arrhenius, already during the bombardment of the Earth by planetesimals, when the earth's rocks were heating and melting, gases and water vapor contained in the rocks were released. At the same time, the Earth lost hydrogen and helium, but retained heavier gases. Thus, it was the degassing of the earth's interior that became the source of the atmosphere.

spheres and hydrospheres. According to some calculations, from 65 to 80% of the total amount of volatile components of the Earth was released as a result of impact degassing.

The world's oceans arose from the vapors of mantle material, and the first portions of condensed water were acidic. Then mineralized waters appeared, and the actual fresh waters were formed much later as a result of evaporation from the surface of the primary oceans in the process of natural distillation.

The problem of the origin of the ocean is connected with the problem of the origin of not only water, but also substances dissolved in it. The Earth's hydrosphere, like the atmosphere, also appeared as a result of degassing of the planet's interior. The material of the ocean and the material of the atmosphere arose from a common source.

Ocean water is a unique natural solution containing an average of 3.5% dissolved substances, which provides the salinity of the water. In water earth's oceans contains many chemical elements. Among them, the most important role is played by sodium, magnesium, calcium, chlorine, nitrogen, phosphorus, silicon. These elements are absorbed by living organisms, and their concentration in sea water is controlled by the growth and reproduction of marine plants and animals. An important role in the composition of sea water is played by natural gases dissolved in it - nitrogen, oxygen, carbon dioxide, which are closely related to the atmosphere and living matter of land and sea.

As it is considered today, the primary atmosphere of the Earth in its composition was close to the composition of volcanic and meteorite gases. Most likely, it resembled the modern atmosphere of Venus. Water, carbon dioxide, carbon monoxide, methane, ammonia, hydrogen sulfide, etc. came to the surface of the Earth. They made up the primary atmosphere of the Earth. In general, the primary atmosphere had a reducing character and was practically devoid of free oxygen, although its insignificant fractions were formed in the upper part of the atmosphere as a result of water photolysis.

Thus, the composition of the Earth's primary atmosphere, which arose as a result of impact degassing and volcanic activity, was very different from the composition modern atmosphere. These differences are associated with the presence of life on Earth, which has the most significant impact on all processes occurring on our planet. Thus, the chemical evolution of the atmosphere and hydrosphere took place with the constant participation of living organisms, and the leading role was played by photosynthetic green plants.

The modern nitrogen-oxygen atmosphere is the result of the activity of Life on Earth. The same can be said about modern composition waters of the oceans of the planet. Therefore, today on our

planet life and transformed by it environment form an independent shell of the Earth - the biosphere.

Geospheres of the Earth

The formation of the Earth was accompanied by the differentiation of matter, which resulted in the division of the Earth into concentrically located layers - geospheres. Geospheres differ in chemical composition, state of aggregation and physical properties. In the center, the core of the Earth was formed, surrounded by a mantle. From the lightest components of the matter released from the mantle, the earth's crust, located above the mantle, arose. This is the so-called "solid" Earth, containing almost the entire mass of the planet. Further, the water and air shells of our planet arose. In addition, the Earth has gravitational, magnetic and electric fields.

Thus, we can distinguish a number of geospheres that make up the Earth: core, mantle, lithosphere, hydrosphere, atmosphere, magnetosphere.

In addition to the named shells of the Earth, below we will consider the biosphere and noosphere. In addition, in the literature one can find an analysis of other shells - the anthroposphere, the technosphere, the sociosphere, but their consideration is beyond the scope of natural science.

Geospheres differ mainly in the density of their constituent substances. The densest substances are concentrated in the central parts of the planet. The core is 1/3 of the mass of the Earth, the crust and mantle - 2/3.

All earthly shells are interconnected and penetrate each other. The hydrosphere is always present in the lithosphere and atmosphere, the atmosphere - in the lithosphere and hydrosphere, etc. The inner shells of the Earth are closely connected with the atmosphere, hydrosphere and lithosphere. In addition, in all shells, except for the mantle and the core, there is a biosphere.

Earth's core

The core occupies the central region of our planet. This is the deepest geosphere. The average core radius is about 3500 km, it is located deeper than 2900 km. The core consists of two parts - a large outer and a small inner core.

inner core The nature of the inner core of the Earth, starting from a depth of 5000 km, remains a mystery. This is a ball with a diameter of 2200 km, which scientists believe is composed of iron (80%) and nickel

(twenty%). Suitable alloy at existing pressure inside the earth's interior has a melting point of the order of 4500 ° C.

outer core. Judging by geophysical data, the outer core is a liquid - molten iron with an admixture of nickel and sulfur. This is due to the fact that the pressure in this layer is less. The outer core is a spherical layer 2900-5000 km thick. In order for the inner core to remain solid and the outer core to remain liquid, the temperature in the center of the Earth should not exceed 4500 ° C, but also not be lower than 3200 ° C.

FROM liquid state the outer core is connected by ideas about the nature of terrestrial magnetism. The Earth's magnetic field is changeable, the position of the magnetic poles changes from year to year. Paleomagnetic studies have shown that, for example, over the past 80 million years, there has been not only a change in the field strength, but also multiple systematic remagnetization, as a result of which the North and South magnetic poles of the Earth have changed places. During periods of polarity reversal, there were moments of complete disappearance of the magnetic field. Therefore, terrestrial magnetism cannot be created by a permanent magnet due to the stationary magnetization of the core or any part of it. It is assumed that the magnetic field is created by a process called the self-excited dynamo effect. The role of a rotor (moving element), or a dynamo, can be played by the mass of the liquid core, which moves with the rotation of the Earth around its axis, and the excitation system is formed by currents that create closed loops inside the sphere of the core.

Mantle

The mantle is the most powerful shell of the Earth, occupying 2/3 of its mass and most of its volume. It also exists in the form of two spherical layers - the lower and upper mantle. The thickness of the lower part of the mantle is 2000 km, the upper one is 900 km. All the mantle layers are located between the radii of 3450 and 6350 km.

Data on the chemical composition of the mantle were obtained on the basis of analyzes of the deepest igneous rocks that entered the upper horizons as a result of powerful tectonic uplifts with the removal of mantle material. The material of the upper mantle was collected from the bottom of different parts of the ocean. The density and chemical composition of the mantle differ sharply from the corresponding characteristics of the core. The mantle is formed by various silicates (silicon-based compounds), primarily the mineral olivine.

Due to the high pressure, the material of the mantle is most likely in a crystalline state. The temperature of the mantle

sets about 2500°C. It was high pressures that determined such a state of aggregation of the substance, otherwise the indicated temperatures would lead to its melting.

The asthenosphere, the lower part of the upper mantle, is in a molten state. This is the underlying layer of the upper mantle and lithosphere. The lithosphere, as it were, "floats" in it. In general, the upper mantle has interesting feature- in relation to short-term loads, it behaves like a rigid material, and in relation to long-term loads - like a plastic material.

A more mobile and lighter lithosphere relies on a not too viscous and plastic asthenosphere. On the whole, the lithosphere, asthenosphere, and other layers of the mantle can be considered as a three-layer system, each part of which is mobile relative to other components.

Lithosphere

The lithosphere is called the earth's crust with part of the underlying mantle, which forms a layer about 100 km thick. The earth's crust has a high degree of rigidity, but at the same time, great fragility. In the upper part it is composed of granites, in the lower part - basalts.

The sharp asymmetry of the structure of the surface of our planet was noticed long ago. Therefore, the planetary relief is divided into two main areas - oceanic and continental. The average thickness of the continental crust is 35 km. Its upper layer is rich in granitic rocks, and the lower layer is rich in basalt magmas. There is no granite layer at the bottom of the oceans, and the earth's crust consists only of a basalt layer. The thickness of the oceanic crust is 5-10 km.

The first portions of volcanic material had a composition of basalts or close to it. Basaltic magma, rising to the surface, lost gases that escaped into the atmosphere, and turned into basaltic lava, which spread over the primary surface of the planet. During cooling, it formed solid covers - the primary crust of the oceanic type. However, the melting process of these masses was asymmetric, and more of them were concentrated on one hemisphere of the planet than on the other. In areas of future continents, the young earth's crust was dynamically unstable and moved up and down under the influence of internal causes, the nature of which was not yet well understood.

With general oscillatory movements, individual parts of the primary crust at times turned out to be above the level of the ocean and were destroyed under the influence of chemically active gases of the primary atmosphere, water, and other physical agents. Pro-

The destruction ducts were transported to low areas of land and water bodies, forming sedimentary rocks with mechanical sorting of particles by size and mineralogical composition. These processes went even more actively with the advent of the biosphere. Areas of land uplift - the places of future continents - began to grow into belts formed by strata of sedimentary rocks that arose due to the destruction of more elevated land areas. These belts were subsequently subjected to folding and uplift, and volcanic activity was manifested in them. Ancient mountain ranges arose around the cores of the continents, subsequently also destroyed by geological agents. This is how the continental part of the earth's crust was formed.

The oceanic part, probably, rarely or not at all protruded above the level of the World Ocean, and processes of differentiation of matter did not occur in it, and sedimentary rocks were not deposited.

The geological features of the earth's crust are determined by the combined effects on it of the atmosphere, hydrosphere and biosphere - the three outer shells of the planet. The composition of the bark and outer shells is continuously updated. Due to weathering and drift, the substance of the continental surface is completely renewed in 80-100 million years. The loss of matter of the continents is replenished by uplifts of their crust. If these uplifts did not exist, then over several geological periods all the land would be carried into the ocean, and our planet would be covered with a continuous water shell.

Soil appears on the surface of the lithosphere as a result of the combined activity of a number of factors. The founder of soil science, the Russian scientist V.V. Dokuchaev, called soil outer horizons of rocks naturally altered by the combined influence of water, air and various kinds of organisms, including their remains. Thus, the soil is the most complex system, striving for an equilibrium interaction with the environment.

Hydrosphere

The water shell of the Earth is represented on our planet by the World Ocean, fresh waters of rivers and lakes, glacial and underground waters. The total water reserves on Earth are 1.5 billion km 3 . Of this amount, 97% is salty sea water, 2% is frozen glacier water, and 1% is fresh water.

The hydrosphere is a continuous shell of the Earth, since the seas and oceans pass into groundwater on land, and between land and sea there is a constant circulation of water, the annual volume of which is estimated at 100 thousand km 3. Most of the water evaporated from the surface of the seas and oceans falls in the form of precipitation over them,

about 10% - is carried to land, falls on it, and then is either carried away by rivers to the ocean, or goes underground, or is preserved in glaciers. The water cycle in nature is not an absolutely closed cycle. Today it is proved that our planet is constantly losing part of the water and air that go into the world space. Therefore, over time, the problem of water conservation on our planet will arise.

Water is a substance with many unique physical and chemical properties. In particular, water has a high heat capacity, heat of fusion and evaporation, and due to these qualities, it is the most important climate-forming factor on Earth. Water is a good solvent, so it contains many chemical elements and compounds necessary to sustain life. It is no coincidence that the World Ocean became the cradle of Life on our planet.

World Ocean. Most of the Earth's surface is occupied by the oceans (71% of the planet's surface). It surrounds the continents (Eurasia, Africa, North and South America, Australia and Antarctica) and islands. The ocean is divided by continents into four parts: the Pacific (50% of the area of ​​the World Ocean), the Atlantic (25), the Indian (21) and the Arctic (4%) oceans. The oceans are often referred to as the "stove of the planet". AT warm time year, water warms up more slowly than land, so it cools the air, in winter, on the contrary, warm water warms cold air.

In the oceans, there are constantly progressive movements of masses of water - sea currents. They are formed under the influence of the prevailing winds, the tidal forces of the Moon and the Sun, and also due to the existence of water layers of different densities. Under the influence of the Earth's rotation, all currents in the Northern Hemisphere deviate to the right, and in the Southern Hemisphere - to the left. A huge role in the seas and oceans is played by ebbs and flows, causing periodic fluctuations in the water level and a change in tidal currents. In the open ocean, the height of the tide reaches one meter, off the coast - up to 18 meters. The highest tides are observed off the coast of France (14.7 m) and in England, at the mouth of the Severn River (16.3 m), in Russia - in the Menza Bay of the White Sea (10 m) and in the Penzhina Bay of the Sea of ​​Okhotsk (11 m).

Huge food, energy and mineral reserves of the oceans.

Rivers. An important part of the Earth's hydrosphere are rivers- water flows flowing in natural channels and fed by surface and underground runoff from their basins. Rivers with tributaries form a river system. The flow and flow of water in them depend on the slope of the channel. Usually, mountain rivers with fast flow are distinguished.

and narrow river valleys and lowland rivers with a slow current and wide river valleys.

Rivers are an important part of the water cycle in nature. Their total annual flow into the World Ocean is 38.8 thousand km3. Rivers are sources of drinking and industrial water, a source of hydropower. The rivers are home to a large number of plants, fish and other freshwater organisms. Most big rivers on the planet - Amazon, Mississippi, Yenisei, Lena, Ob, Nile, Amur, Yangtze, Volga.

Lakes and swamps- also part of the Earth's hydrosphere. Lakes are bodies of water filled with water, the entire surface of which is open to the atmosphere and which do not have slopes that create currents, and are not connected to the sea except through rivers and channels. The concept of "lake" includes a wide range of bodies of water, including ponds (small shallow lakes), reservoirs, as well as swamps and bogs with stagnant water. By origin, lakes can be glacial, flowing, thermokarst, saline. From a geological point of view, lakes have a short lifespan. As a rule, they gradually disappear due to an imbalance between the inflow and outflow of water from the lake. The largest lakes include: the Caspian and Aral Seas, Baikal, Lake Superior, Huron and Michigan in the USA and Canada, Victoria, Nyanza and Tanganyika in Africa.

The groundwater- Another part of the hydrosphere. Groundwater is all water below the earth's surface. There are underground rivers that freely flow through underground channels - cracks and caves. There are also filterable waters seeping through loose rocks (sand, gravel, pebbles). The groundwater horizon closest to the earth's surface is called ground water.

Water that has fallen into the soil reaches the water-resistant layer, accumulates on it and impregnates the overlying rocks. This is how aquifers are formed that can serve as sources of water. Sometimes the impervious layer can create permafrost.

glaciers, forming the Earth's ice shell (cryosphere), are also part of the hydrosphere of our planet. They occupy an area equal to 16 million km 2, which is approximately 1/10 of the planet's surface. It is they that contain the main reserves of fresh water (3/4). If the ice in the glaciers suddenly melted, the level of the World Ocean would rise by 50 meters.

Ice massifs are formed where it is possible not only to accumulate snow that has fallen during the winter, but also to keep it during the summer. Over time, such snow compacts to the state of ice and can cover the entire area as an ice sheet or ice cap. Places where accumulation of perennial

of ice are determined by geographic latitude and height above sea level. In the polar regions, the boundary of multi-year ice lies at sea level, in Norway - at an altitude of 1.2-1.5 km above sea level, in the Alps - at an altitude of 2.7 km, and in Africa - at an altitude of 4.9 km.

Glaciologists distinguish between continental covers, or shields, and mountain glaciers. The most powerful continental ice sheets are located in Antarctica and Greenland. In some places, the thickness of the ice reaches 3.2 km. The strata of ice gradually sliding towards the ocean give rise to ice mountains - icebergs. Mountain glaciers are ice rivers descending the slopes of mountains, although their movement is very slow - at a speed of 3 to 300 m per year. During their movement, glaciers change the picture of the landscape, dragging boulders with them, peeling off the slopes of mountains and breaking off significant pieces of rock. The products of destruction are carried away by the glacier along the slope and settle as it melts.

Permafrost. Part of the Earth's cryosphere, in addition to glaciers, are permafrost soils (permafrost). The thickness of such soils on average reaches 50-100 m, and in Antarctica it reaches 4 km. Permafrost occupies vast territories in Asia, Europe, North America and Antarctica, its total area is 35 million km 2. Permafrost occurs in places where average annual temperatures are negative. It contains up to 2% the total amount of ice on Earth.

Atmosphere

The atmosphere is the air shell of the Earth that surrounds it and rotates with it. According to the chemical composition, the atmosphere is a mixture of gases, consisting of 78% nitrogen, 21% oxygen, as well as inert gases, hydrogen, carbon dioxide, water vapor, which account for about 1% of the volume. In addition, the air contains a large amount of dust and various impurities generated by geochemical and biological processes on the Earth's surface.

The mass of the atmosphere is quite large and amounts to 5.15 10 18 kg. This means that each cubic meter of air around us weighs about 1 kg. The weight of the air pressing on us is called atmospheric pressure. The average atmospheric pressure on the Earth's surface is 1 atm, or 760 mm mercury column. This means that for every square centimeter of our body, a load of atmosphere weighing 1 kg is pressing. With height, the density and pressure of the atmosphere decrease rapidly.

There are areas in the atmosphere with stable minima and maxima of temperatures and pressures. So, in the region of Iceland and the Aleutian

The islands have such an area, which is the traditional birthplace of cyclones that determine the weather in Europe. And in Eastern Siberia, the area of ​​low pressure in summer is replaced by the area high pressure in winter. The heterogeneity of the atmosphere causes the movement of air masses - this is how winds appear.

The Earth's atmosphere has a layered structure, and the layers differ in physical and chemical properties. The most important of them are temperature and pressure, the change of which underlies the separation of atmospheric layers. Thus, the Earth's atmosphere is divided into: troposphere, stratosphere, ionosphere, mesosphere, thermosphere and exosphere.

Troposphere- This is the lower layer of the atmosphere that determines the weather on our planet. Its thickness is 10-18 km. Pressure and temperature decrease with altitude, dropping to -55°C. The troposphere contains the main amount of water vapor, clouds form and all types of precipitation form.

The next layer of the atmosphere is stratosphere, stretching up to 50 km in height. The lower part of the stratosphere has a constant temperature, in the upper part there is an increase in temperature due to the absorption of solar radiation by ozone.

Ionosphere- this part of the atmosphere, which begins at a height of 50 km. The ionosphere consists of ions - electrically charged air particles. The ionization of air occurs under the action of the Sun. The ionosphere has a high electrical conductivity and therefore reflects short radio waves, allowing long-distance communications.

From a height of 80 km begins mesosphere, the role of which is the absorption of solar ultraviolet radiation by ozone, water vapor and carbon dioxide.

At an altitude of 90 - 200-400 km is thermosphere. AT It is where the main processes of absorption and conversion of solar ultraviolet and X-ray radiation take place. At an altitude of more than 250 km, hurricane-force winds are constantly blowing, the cause of which is considered to be cosmic radiation.

The upper region of the atmosphere, extending from 450-800 km to 2000-3000 km, is called exosphere. It contains atomic oxygen, helium and hydrogen. Some of these particles are constantly escaping into outer space.

The result of self-regulating processes in the Earth's atmosphere is the climate of our planet. It is not the same as the weather, which can change every day. The weather is very changeable and depends on fluctuations of those interconnected processes as a result of which it is formed. These are temperature, winds, pressure, precipitation. Weather is mainly the result of the interaction of the atmosphere with land and oceans.

Climate is the state of the weather in a region over a long period of time. It is formed depending on the geographical latitude, height above sea level, air currents. Relief and soil type are less affected. There are a number of climatic zones of the world that have a set of similar characteristics related to seasonal temperatures, precipitation and wind strength:

humid tropical zone- average annual temperatures are more than 18°C, there is no cold weather, more precipitation falls than water evaporates;

dry zone- an area of ​​low rainfall. The dry climate can be hot, as in the tropics, or crisp, as in mainland Asia;

warm climate zone- average temperatures in the coldest time here do not fall below -3°C, and at least one month has an average temperature of more than 10°C. The transition from winter to summer is well pronounced;

cold northern taiga climate zone- in cold time, the average temperature drops below -3°C, but in warm time it is above 10°C;

polar climate zone- even in the warmest months, the average temperatures here are below 10°C, so these areas have cool summers and very cold winters;

mountain climate zone- areas that differ in climatic characteristics from the climatic zone in which they are located. The appearance of such zones is due to the fact that average temperatures fall with height and the amount of precipitation varies greatly.

The Earth's climate has a pronounced cyclicity. The most famous example of climate cyclicity is the glaciation that periodically occurred on Earth. Over the past two million years, our planet has experienced from 15 to 22 ice ages. This is evidenced by studies of sedimentary rocks accumulated at the bottom of oceans and lakes, as well as studies of ice samples from the depths of the Antarctic and Greenland ice sheets. So, in the last ice age, Canada and Scandinavia were covered by a giant glacier, and the North Scottish Highlands, the mountains of North Wales and the Alps had huge ice caps.

We are now living in a period global warming. Since 1860, the average temperature of the Earth has risen by 0.5°C. Today, the increase in average temperatures is even faster. This threatens with the most serious climate changes on the entire planet and other consequences, which will be discussed in more detail in the chapter on environmental problems.

Magnetosphere

The magnetosphere - the outermost and extended shell of the Earth - is a region of near-Earth space, the physical properties of which are determined by the Earth's magnetic field and its interaction with streams of charged particles of cosmic origin. On the day side, it extends for 8-24 Earth radii, on the night side it reaches several hundred radii and forms the Earth's magnetic tail. There are radiation belts in the magnetosphere.

The Earth's magnetic field is formed in the outer shell of the core due to the circulation of electric currents. Therefore, the Earth is a huge magnet with clearly defined magnetic poles. The North magnetic pole is located in North America on the Botia Peninsula, the South magnetic pole is in Antarctica at Vostok station.

It is now established that the Earth's magnetic field is not constant. Its polarity has changed several times in the history of the Earth's existence. So, 30,000 years ago, the North Magnetic Pole was at the South Pole. In addition, there are periodic disturbances of the Earth's magnetic field - magnetic storms, main reason the occurrence of which is the fluctuation of solar activity. Therefore, magnetic storms are especially frequent during the years of the active Sun, when many spots appear on it, and auroras appear on the Earth.

The figure and dimensions of the Earth

Words and phrases

The first ideas about the shape and size of the Earth appeared in ancient times. So, Aristotle (III century BC) gave the first evidence of the sphericity of the Earth, when he noticed its rounded shadow on the disk of the Moon during lunar eclipses. The exact answer about the shape and size of the Earth is given by measurements of the length of the meridian arc of one degree in different places on the surface of the Earth. These measurements showed that the length of a meridian arc of 1 0 in the polar regions, the largest is 111.7 km, and at the equator it is the smallest - 110.6 km. Therefore, our Earth is not a sphere in its shape. The equatorial radius of the Earth is greater than the polar one by 21.4 km. Thus, we came to the conclusion that the shape of our planet corresponds to an ellipsoid of revolution.PThe following measurements showed that the Earth is compressed not only at the poles, but also along the equator, because the largest and smallest radii of the equator differ in length by 213 m. on its surface there are deep depressions and hills. The closest to the modern figure of the Earth is the figure called geoid .

geoid - the shape that is determined by the surface of freely distributed water. In such a figure, gravity is everywhere perpendicular to its surface (Fig. 1).

Modern geoid measurement results give the following values: equatorial radius r uh = 6378.16 km, polar radius r P = 6357.78 km, the average value of the radius is 6371.11 km. Equator length: L = 40075.696 km; surface area - 510.2 million km 2 , its volume is 1.083 × 10 12 km 3, mass - 5.976 × 10 27 g.

Based on the difference in length of the equatorial ( a) and polar ( in) radii, the value of the polar compression of the Earth is determined:

r = .

andIt is known that the Earth revolves around the Sun in an elliptical orbit at an average distance of 149.5 million km. Pthe circulation period is 365.242 sr. solar day The circulation speed averages 29.8 km/s. The period of rotation of the Earth around its own axis is 23 hours 56 minutes and 4.1 seconds. The speed of the Earth's rotation gradually decreases, so the duration of the day per century increases by 0.001 sec. The position of the axis of rotation is complicated by its slow rotation along a circular cone (a complete revolution in 26 thousand years) and oscillation of the axis with a period of 18.6 years (phenomena of precession and nutation).

1.2.

Geophysical fields and physical properties of the Earth

Words and phrases

Under the geophysical fields of the Earth understand the natural physical fields created by this planet. These include gravitational, magnetic, thermal and electrical.

Gravity field. The force of attraction directed towards the center and the centrifugal force are constantly acting on the Earth. The resultant of these two forces determines the force of gravity. Gravity measurement unit named after Galileo halo(1 cm/s 2 = 1 Gal).

Features of the distribution of gravity on the surface of the Earth were determined in the XVIII century by the French mathematician A. Clairaut. He was the first to derive a formula for calculating the force of gravity at any geographic latitude of a spheroid with known values ​​of the force of gravity (gravitational acceleration) near the pole and at the equator:

g = g uh+(g n –g uh )sin 2 u,

where g, g uh, g n - free fall acceleration, respectively, for a given geographical latitude (u), at the equator and at the pole.

Normal values ​​of free fall acceleration on Earth decrease from 978 cm/s 2 at the poles up to 983 cm/s 2 at the equator. However, these values ​​differ significantly from those actually measured on the Earth's surface. This difference is due to a change in the density of the rocks that make up the Earth. This feature of the gravitational field underlies the applied use of the gravimetric method. The acceleration of free fall (g) is measured with special devices - gravimeters. Deviation of actual data (g) from theoretical values ​​for a given area are called gravity anomalies. Based on the results of gravimetric measurements, gravimetric profiles and maps are built. Gravimetric anomalies are closely related to the distribution of densities. Over dense rocks, gravity increases, over less dense (light) it decreases. Consequently, the structure of the earth's crust can be determined from gravimetric maps. So, for example, above the ledges of the basement, rocks of basic and ultrabasic composition (gabbro, peridotites), ores of heavy metals, high values gravity (positive anomalies), and over the lighter ones - a relative decrease in the values ​​of gravity (Fig. 2).

M magnetic field of the earth. The magnetic properties of our planet were known in ancient China. OurhThe earth is a giant magnet with a magnetic field around it that extends beyond the planet for several Earth radii. Like any magnet, the Earth has magnetic poles, which, however, do not coincide with the geographic poles, since the center of the magnetic field is shifted relative to the center of our planet by 430 km (Fig. 3). In 1970, the position of the magnetic poles was determined accordingly: South - near North Greenland (74 ° N and 100° w.l.), and the Northern one is to the west of the Ross Sea ina Antarctica (68°S and 145°E).

In the position of the magnetic poles, secular, annual and daily fluctuations are noted. Moreover, secular fluctuations reach 30 0 .

H Most clearly, the Earth's magnetic field is manifested by its action on the magnetic needle, which is set strictly along the magnetic meridian at any point on the earth's surface. Due to the discrepancy between the magnetic and geographic poles, magnetic declination and inclination are distinguished in the readings of the magnetic needle.

Magnetic declination - the angle of deviation of the magnetic needle (magnetic meridian) from the geographic meridian of the area. The declination can be east and west (Fig. 4). Isogony - These are lines connecting points on the map with the same declination. The zero isogon determines the position of the magnetic meridian.

M figurative mood - the angle of inclination of the magnetic needle to the horizon. In the northern hemisphere, the northern end of the magnetic needle is lowered down, in the southern hemisphere - the southern end of the arrow. Lines connecting points of equal inclination are called isoclines. The zero isocline corresponds to the magnetic equator.

In addition to declination and inclination, the magnetic field is characterized by a strength that is small and does not exceed 0.01A/m.l lines that connect points of equal intensity are called isodynamics. The magnetic field strength increases from the magnetic equator to the poles. The deviation of the magnetic field strength from the average value for a given area is called magnetic anomalies. They are associated with various magnetic properties of rocks, in different th degree of magnetization in the Earth's magnetic field.

Due to the heterogeneity of the magnetic properties of various rocks, the search for minerals is carried out by the method of magnetic prospecting. The features of the geological structure of the earth's crust are also being clarified (Fig. 5). Magnetic properties are studied using magnetometers not only ground, but also those that are installed on aircraft and spacecraft.

P about the residual magnetization of rocks, it became possible to restore the elements of the ancient magnetic field (the position of the poles and tension), which gave rise to a new branch of geology - paleomagnetism. Paleomagnetic studies have shown that the magnetic poles have continuously moved westward at a rate of 1 cm/year over the past five hundred million years - migration of magnetic poles(Fig. 6). Another feature of the Earth's magnetic field is the periodic change in the polarity of the magnetic poles, i.e. pole reversal. Every 200-300 thousand years, the North Pole of the Earth's magnet becomes South and vice versa. The scale of magnetic inversions is used to dismember and compare rock strata and determine age. According to modern concepts, the geomagnetic field of the Earth has an electromagnetic nature. It occurs under the influence complex system electric currents that accompany the turbulent convection of matter in the liquid outer core. Consequently, the Earth works like a dynamo (Frenkel-Elsasser dynamo theory).

Thermal field of the Earth. The thermal regime of the Earth is determined by the heat that is released from its interior. In addition, the heat received from the Sun is also important for the surface of the Earth. 1 cm per minute 2 Earth's surface comes from the Sun about 8.173 J of heat. This value is called solar constant. One third of the solar energy is reflected by the atmosphere and the Earth's surface and dissipated.andsolar radiation far exceeds the amount of heat coming from the depths (about 4 × 10 –4 J per minute). Therefore, the temperature on the surface of our planet and the upper layer of the lithosphere is determined by the radiation of the Sun. It fluctuates (changes) at different times of the day and in different times of the year.

At some depth from the surface there is a belt of constant temperature, equal to the average annual temperature of the area. So, in Moscow, at a depth of 20 meters from the surface, a constant temperature is observed equal to + 4.2 0 C, and in Paris +11.8 0 C at a depth of 28 m. nBelow the belt of constant temperature, under the influence of the internal heat of the Earth, the temperature increases by an average of 3 0 C for every 100 m. andThe change in temperature in degrees per unit of depth is called geothermal gradient, and the depth interval in meters at which the temperature rises by 1 ˚ , is called geothermal stage(its average value is 33 m).

The study of the internal heat flow showed that its value depends on the intensity of endogenous processes and on the degree of mobility of the cortex. The average value of the heat flux for the Earth is about 1.4–1.5 μcal/cm 2 ×s. Pelevated values ​​of heat flow are observed in mountain structures (up to 2 - 4 μcal/cm 2 ×s), within the rift valleys of mid-ocean ridges (up to 2 μcal/cm 2 ×s or more, reaching 6.0–8.0 μcal/cm in places 2 × s). inHigh values ​​of heat flow were also noted in the internal rifts of the Red Sea, Lakebaikal . The main sources of internal thermal energy of the Earth are:

Radiogenic heat associated with the decay of radioactive elements ( 238 U , 235 U , 232 th, 40 K and others).

Ggravitational differentiation of matter at the boundary between the mantle and the core, which is accompanied by heat release.

As already noted, with increasing depth, an increase in temperature is observed. So, for example, in the Kola superdeep well, located within the ancient crystalline shield of the EasteEuropean platform, the calculated geothermal gradient was taken as 1 ˚ C per 100 m, and the expected temperature at a depth of 15,000 meters should be 150–160 FROM. andThis is how the temperature was distributed to a depth of 2,500–3,000 m. Dthen the picture changed. The heat flux doubled, and the temperature gradient was 1.7 - 2.2˚ C at 100 m. nand at the mark of 12,000 meters the temperature was above 200 ˚ C instead of the expected 120 ˚ FROM.

P according to the calculations of various authors at a depth of 100 km, the temperature does not exceed 1300 - 1500 ˚ C, because it is from these depths that lava flows to the surface with a temperature of 1100 - 1250 0 C. tthe temperature of the deeper zones of the mantle and core is estimated to be very approximately 4000 - 5000 ˚ C (Fig. 7).

The distribution and change of temperature in the upper layers of the earth's crust is mainly associated with local heat sources, as well as different thermal conductivity of rocks.

To local sources should include: magma chambers, fault zones with active circulation of thermal waters, areas with an increased concentration of radioactive elements, etc.WithThe thermal conductivity of rocks has a significant effect on the distribution of heat. So, for example, crystalline rocks have a higher thermal conductivity than loose sedimentary rocks, and the thermal conductivity along the layers is much higher than in the direction perpendicular to the bedding. Therefore, when the occurrence is close to vertical, the thickness of sedimentary rocks will be characterized by a higher temperature than when it is horizontal. This explains the increase in temperature above oil fields, which are located in the convex bends of the reservoirs (Fig. 8).tSubsurface temperature is one of the main factors controlling the formation of accumulations of many minerals. Thus, the accumulation of hydrocarbons of different phase composition is determined by reservoir temperature and pressure, depending on which deposits are formed mainly single-phase (oil or gas), two-phase (gas-oil) or are in a critical state (gas-condensate).tThus, information about reservoir pressure and temperature makes it possible to purposefully search for oil and gas fields.

Introduction

For many centuries, the question of the origin of the Earth remained the monopoly of philosophers, since the actual material in this area was almost completely absent. The first scientific hypotheses regarding the origin of the Earth and the solar system, based on astronomical observations, were put forward only in 18th century. Since then, more and more new theories have not ceased to appear, in accordance with the growth of our cosmogonic ideas.

The first in this series was the famous theory formulated in 1755 by the German philosopher Emanuel Kant. Kant believed that the solar system arose from some primary matter, previously freely dispersed in space. Particles of this matter moved in different directions and, colliding with each other, lost speed. The heaviest and densest of them, under the influence of gravity, connected with each other, forming a central bunch - the Sun, which, in turn, attracted more distant, smaller and lighter particles.

Thus, a certain number of rotating bodies arose, the trajectories of which mutually intersected. Some of these bodies, initially moving in opposite directions, were eventually drawn into a single stream and formed rings of gaseous matter located approximately in the same plane and rotating around the Sun in the same direction without interfering with each other. In separate rings, denser nuclei were formed, to which lighter particles were gradually attracted, forming spherical accumulations of matter; this is how the planets were formed, which continued to circle around the Sun in the same plane as the original rings of gaseous matter.

1. History of the earth

Earth is the third planet from the Sun in the solar system. It revolves around the star in an elliptical orbit (very close to circular) with an average speed of 29.765 km/s at an average distance of 149.6 million km over a period of 365.24 days. The Earth has a satellite - the Moon, which revolves around the Sun at an average distance of 384,400 km. The inclination of the earth's axis to the plane of the ecliptic is 66033`22``. The period of rotation of the planet around its axis is 23 h 56 min 4.1 sec. Rotation around its axis causes the change of day and night, and the tilt of the axis and circulation around the Sun - the change of seasons. The shape of the Earth is a geoid, approximately a triaxial ellipsoid, a spheroid. The average radius of the Earth is 6371.032 km, equatorial - 6378.16 km, polar - 6356.777 km. The surface area of ​​the globe is 510 million km2, the volume is 1.083 * 1012 km2, the average density is 5518 kg/m3. The mass of the Earth is 5976 * 1021 kg. The earth has a magnetic and closely related electric fields. The gravitational field of the Earth determines its spherical shape and the existence of the atmosphere.

According to modern cosmogonic concepts, the Earth was formed about 4.7 billion years ago from the gaseous matter scattered in the protosolar system. As a result of the differentiation of matter, the Earth, under the influence of its gravitational field, under the conditions of heating of the earth's interior, arose and developed different in chemical composition, state of aggregation and physical properties of the shell - the geosphere: core (in the center), mantle, earth's crust, hydrosphere, atmosphere, magnetosphere. The composition of the Earth is dominated by iron (34.6%), oxygen (29.5%), silicon (15.2%), magnesium (12.7%). The earth's crust, mantle and inner part of the core are solid (the outer part of the core is considered liquid). From the surface of the Earth to the center, pressure, density and temperature increase. The pressure in the center of the planet is 3.6 * 1011 Pa, the density is about 12.5 * 103 kg / m3, the temperature ranges from 50000 to

60000 C. The main types of the earth's crust are continental and oceanic; in the transition zone from the mainland to the ocean, an intermediate crust is developed.

Most of the Earth is occupied by the World Ocean (361.1 million km2; 70.8%), the land is 149.1 million km2 (29.2%), and forms six continents and islands. It rises above the world ocean level by an average of 875 m (the highest height is 8848 m - Mount Chomolungma), mountains occupy more than 1/3 of the land surface. Deserts cover about 20% of the land surface, forests - about 30%, glaciers - over 10%. The average depth of the world ocean is about 3800 m (the greatest depth is 11020 m - the Mariana Trench (trough) in the Pacific Ocean). The volume of water on the planet is 1370 million km3, the average salinity is 35 g/l.

The atmosphere of the Earth, the total mass of which is 5.15 * 1015 tons, consists of air - a mixture of mainly nitrogen (78.08%) and oxygen (20.95%), the rest is water vapor carbon dioxide, as well as inert and other gases. The maximum land surface temperature is 570-580 C (in the tropical deserts of Africa and North America), the minimum is about -900 C (in the central regions of Antarctica).

The formation of the Earth and the initial stage of its development belong to pregeological history. The absolute age of the most ancient rocks is over 3.5 billion years. The geological history of the Earth is divided into two unequal stages: the Precambrian, which occupies approximately 5/6 of the entire geological chronology (about 3 billion years), and the Phanerozoic, covering the last 570 million years. About 3-3.5 billion years ago, as a result of the natural evolution of matter, life arose on Earth, and the development of the biosphere began. The totality of all living organisms inhabiting it, the so-called living matter Earth, had a significant impact on the development of the atmosphere, hydrosphere and sedimentary shell. New

a factor that has a powerful influence on the biosphere is the production activity of man, who appeared on Earth less than 3 million years ago. The high growth rate of the world's population (275 million people in 1000, 1.6 billion people in 1900 and about 6.3 billion people in 1995) and the growing influence human society brought problems to the natural environment rational use all natural resources and nature protection.

The widely known model of the internal structure of the Earth (its division into the core, mantle and earth's crust) was developed by seismologists G. Jeffreys and B. Gutenberg back in the first half of the 20th century. The decisive factor in this was the discovery of a sharp decrease in the velocity of passage of seismic waves inside the globe at a depth of 2900 km with a radius of the planet of 6371 km. The velocity of propagation of longitudinal seismic waves directly above the specified border is 13.6 km/s, and below it - 8.1 km/s. That's what it is mantle-core boundary.

Accordingly, the core radius is 3471 km. The upper boundary of the mantle is the seismic Mohorovicic section allocated by the Yugoslav seismologist A. Mohorovichich (1857-1936) back in 1909. It separates the earth's crust from the mantle. At this boundary, the velocities of longitudinal waves that have passed through the earth's crust increase abruptly from 6.7-7.6 to 7.9-8.2 km/s, but this happens at different depth levels. Under the continents, the depth of the section M (that is, the soles of the earth's crust) is a few tens of kilometers, and under some mountain structures (Pamir, Andes) it can reach 60 km, while under the ocean basins, including the water column, the depth is only 10-12 km . In general, the earth's crust in this scheme appears as a thin shell, while the mantle extends in depth to 45% of the earth's radius.

But in the middle of the 20th century, ideas about a more fractional deep structure of the Earth entered science. Based on new seismological data, it turned out to be possible to divide the core into inner and outer, and the mantle into lower and upper (Fig. 1). This popular model is still in use today. It was started by the Australian seismologist K.E. Bullen, who proposed in the early 40s a scheme for dividing the Earth into zones, which he designated with letters: A - the earth's crust, B - zone in the depth interval of 33-413 km, C - zone 413-984 km, D - zone 984-2898 km, D - 2898-4982 km, F - 4982-5121 km , G - 5121-6371 km (center of the Earth). These zones differ in seismic characteristics. Later, he divided zone D into zones D "(984-2700 km) and D" (2700-2900 km). At present, this scheme has been significantly modified, and only layer D" is widely used in the literature. main characteristic- decrease in seismic velocity gradients compared to the overlying mantle region.

inner core, having a radius of 1225 km, is solid and has a high density - 12.5 g/cm3. outer core liquid, its density is 10 g/cm3. At the boundary between the core and the mantle, there is a sharp jump not only in the velocity of longitudinal waves, but also in density. In the mantle, it decreases to 5.5 g/cm3. Layer D", which is in direct contact with the outer core, is affected by it, since the temperatures in the core significantly exceed the temperatures of the mantle. In some places, this layer generates huge heat and mass flows directed to the Earth's surface through the mantle, called plumes. They can appear on the planet in the form of large volcanic areas, such as, for example, in the Hawaiian Islands, Iceland and other regions.

The upper boundary of the D" layer is uncertain; its level from the surface of the core can vary from 200 to 500 km or more. Thus, one can

It can be concluded that this layer reflects the uneven and different intensities inflow of core energy into the mantle region.

The border of the lower and upper mantle the seismic section at a depth of 670 km serves in the scheme under consideration. It has a global distribution and is justified by a jump in seismic velocities towards their increase, as well as an increase in the density of the lower mantle matter. This section is also the boundary of changes mineral composition rocks in the mantle.

In this way, lower mantle, concluded between the depths of 670 and 2900 km, extends along the radius of the Earth for 2230 km. The upper mantle has a well-fixed internal seismic section passing at a depth of 410 km. When crossing this boundary from top to bottom, seismic velocities increase sharply. Here, as well as on the lower boundary of the upper mantle, significant mineral transformations take place.

The upper part of the upper mantle and the earth's crust are fused together as the lithosphere, which is the upper solid shell of the Earth, in contrast to the hydro and atmosphere. Thanks to the theory of lithospheric plate tectonics, the term "lithosphere" has become widespread. The theory assumes the movement of plates along asthenosphere- softened, partially, possibly, liquid deep layer of reduced viscosity. However, seismology does not show an asthenosphere sustained in space. For many areas, several asthenospheric layers located along the vertical, as well as their discontinuity along the horizontal, have been identified. Their alternation is especially definite within the continents, where the depth of occurrence of asthenospheric layers (lenses) varies from 100 km to many hundreds.

Under the oceanic abyssal depressions, the asthenospheric layer lies at depths of 70–80 km or less. Accordingly, the lower boundary of the lithosphere is in fact indefinite, and this creates great difficulties for the theory of the kinematics of lithospheric plates, which is noted by many researchers. These are the basic concepts of the structure of the earth that have been established to date. Next, we turn to the latest data on deep seismic boundaries, which provide the most important information about the internal structure of the planet.

3. Geological structure of the Earth

The history of the geological structure of the Earth is usually depicted in the form of successively appearing stages or phases. Geological time is counted from the beginning of the formation of the Earth.

Phase 1(4.7 - 4 billion years). Earth is formed from gas, dust and planetesimals. As a result of the energy released during the decay of radioactive elements and the collision of planetesimals, the Earth gradually warms up. The fall of a giant meteorite to the Earth leads to the release of material from which the Moon is formed.

According to another concept, the Proto-Moon, located on one of the heliocentric orbits, was captured by the Proto-Earth, as a result of which the Earth-Moon binary system was formed.

The degassing of the Earth leads to the beginning of the formation of an atmosphere consisting mainly of carbon dioxide, methane and ammonia. At the end of the phase under consideration, due to the condensation of water vapor, the formation of the hydrosphere begins.

Phase 2(4 - 3.5 billion years). The first islands appear, protocontinents, composed of rocks containing mainly silicon and aluminum. Protcontinents slightly rise above still very shallow oceans.

Phase 3(3.5 - 2.7 billion years). Iron collects in the center of the Earth and forms its liquid core, which causes the formation of the magnetosphere. Prerequisites are being created for the appearance of the first organisms, bacteria. The formation of the continental crust continues.

Phase 4(2.7 - 2.3 billion years). A single supercontinent is formed. Pangea, which is opposed by the superocean Panthalassa.

Phase 5(2.3 - 1.5 billion years). Cooling of the crust and lithosphere leads to the disintegration of the supercontinent into blocks-microplates, the spaces between which are filled with sediments and volcanoes. As a result, folded-surface systems arise and a new supercontinent, Pangea I, is formed. The organic world is represented by blue-green algae, the photosynthetic activity of which contributes to the enrichment of the atmosphere with oxygen, which leads to the further development of the organic world.

Phase 6(1700 - 650 million years). The destruction of Pangea I occurs, the formation of basins with oceanic-type crust. Two supercontinents are being formed: Gondavana, which includes South America, Africa, Madagascar, India, Australia, Antarctica, and Laurasia, which includes North America, Greenland, Europe, and Asia (except India). Gondwana and Laurasia are separated by the Tits Sea. The first ice ages are coming. The organic world is rapidly saturated with multicellular non-skeletal organisms. The first skeletal organisms appear (trilobites, mollusks, etc.). oil production takes place.

Phase 7(650 - 280 million years). The Appalachian mountain belt in America connects Gondwana with Laurasia - Pangea II is formed. Contours are indicated

Paleozoic oceans - Paleo-Atlantic, Paleo-Tethys, Paleo-Asiatic. Gondwana is covered twice by a sheet of glaciation. Fish appear, later - amphibians. Plants and animals come to land. Intensive coal formation begins.

Phase 8(280 - 130 million years). Pangea II is permeated by an increasingly dense network of continental reefs, slit-like ridge-like extensions of the earth's crust. The splitting of the supercontinent begins. Africa separates from South America and Hindustan, and the latter from Australia and Antarctica. Finally Australia separates from Antarctica. angiosperms master large areas of land. In the animal world, reptiles and amphibians dominate, birds and primitive mammals appear. At the end of the period, many groups of animals die, including huge dinosaurs. The causes of these phenomena are usually seen either in the collision of the Earth with a large asteroid, or in a sharp increase in volcanic activity. Both could lead to global changes (an increase in the content of carbon dioxide in the atmosphere, the emergence of large fires, gilding), incompatible with the existence of many animal species.

Phase 9(130 million years - 600 thousand years). The general configuration of the continents and oceans undergoes major changes, in particular, Eurasia is separated from North America, Antarctica from South America. The distribution of continents and oceans has become very close to modern. At the beginning of the period under review, the climate throughout the Earth is warm and humid. The end of the period is characterized by sharp climatic contrasts. Following the glaciation of Antarctica comes the glaciation of the Arctic. Fauna and flora are developing close to modern ones. The first ancestors of modern man appear.

Phase 10(modernity). Between the lithosphere and the earth's core, flows of magma rise and fall, through cracks in the crust they break upward. Fragments of the oceanic crust sink down to the very core, and then float up and possibly form new islands. Lithospheric plates collide with each other and are constantly affected by magma flows. Where the plates diverge, new segments of the lithosphere are formed. The process of differentiation of terrestrial matter is constantly taking place, which transforms the state of all geological shells of the Earth, including the core.

Conclusion

The Earth is singled out by nature itself: in the solar system only on this planet there are developed forms of life, only on it the local ordering of matter has reached an unusually high level, continuing the general line of development of matter. It is on Earth that the most difficult stage of self-organization has been passed, which marks a deep qualitative leap to the highest forms of order.

Earth is the largest planet in its group. But, as estimates show, even such dimensions and mass turn out to be minimal at which the planet is able to retain its gaseous atmosphere. The Earth is intensively losing hydrogen and some other light gases, which is confirmed by observations of the so-called Earth plume.

The atmosphere of the Earth is fundamentally different from the atmospheres of other planets: it has a low content of carbon dioxide, a high content of molecular oxygen and a relatively high content of water vapor. There are two reasons why the Earth's atmosphere is distinguished: the water of the oceans and seas absorbs carbon dioxide well, and the biosphere saturates the atmosphere with molecular oxygen formed in the process of plant photosynthesis. Calculations show that if we release all the carbon dioxide absorbed and bound in the oceans, simultaneously removing all the oxygen accumulated as a result of plant life from the atmosphere, then the composition of the earth's atmosphere in its main features would become similar to the composition of the atmospheres of Venus and Mars.

In the Earth's atmosphere, saturated water vapor creates a cloud layer covering a significant part of the planet. Earth's clouds are an essential element in the water cycle that occurs on our planet in the hydrosphere - atmosphere - land system.

Tectonic processes are actively taking place on the Earth in our days, its geological history far from complete. From time to time, the echoes of planetary activity manifest themselves with such force that they cause local catastrophic upheavals that affect nature and human civilization. Paleontologists argue that in the era of the early youth of the Earth, its tectonic activity was even higher. The modern relief of the planet has developed and continues to change under the influence of the combined action of tectonic, hydrospheric, atmospheric and biological processes on its surface.

Bibliography

1. V.F. Tulinov "Concepts of modern natural science": A textbook for universities. - M .: UNITI-DANA, 2004

2. A.V. Byalko "Our planet - Earth" - M. Nauka, 1989

3. G.V. Voitkevich "Fundamentals of the theory of the origin of the Earth" - M Nedra, 1988

4. Physical encyclopedia. Tt. 1-5. - M. Great Russian Encyclopedia, 1988-1998.

Introduction………………………………………………………………………..3

1. History of the Earth…………………………………………..…………………4

2. Seismic model of the structure of the Earth………………………………...6

3. Geological structure of the Earth………………………………………...9

Conclusion…………………………………………………………………….13

References……………………………………………………………15

INSTITUTE OF ECONOMY AND ENTREPRENEURSHIP

Extramural

ESSAY

On the subject "Concepts of modern natural science"

on the topic "The structure of the Earth"

Student of group 06-H11z Surkova V.V.

Scientific adviser E.M. Permyakov

The internal structure of the Earth

Recently, the American geophysicist M. Herndon hypothesized that in the center of the Earth there is a natural "nuclear reactor" of uranium and plutonium (or thorium) with a diameter of only 8 km. This hypothesis is able to explain the reversal of the earth's magnetic field, which occurs every 200,000 years. If this assumption is confirmed, then life on Earth may end 2 billion years earlier than expected, since both uranium and plutonium burn out very quickly. Their depletion will lead to the disappearance of the magnetic field that protects the earth from short-wave solar radiation and, as a result, to the disappearance of all forms of biological life. This theory was commented on by Corresponding Member of the Russian Academy of Sciences V.P. Trubitsyn: “Both uranium and thorium are very heavy elements that, in the process of differentiation of the primary substance of the planet, can sink to the center of the Earth. But at the atomic level, they are carried away with light elements that are carried into the earth's crust, which is why all uranium deposits are located in the uppermost layer of the crust. That is, if these elements were also concentrated in the form of clusters, they could descend into the core, but, according to prevailing ideas, there should be a small number of them. Thus, in order to make statements about the uranium core of the Earth, it is necessary to give a more reasonable estimate of the amount of uranium that has gone into the iron core. It also follows the Structure of the Earth

In the fall of 2002, Harvard University professor A. Dzewonski and his student M. Ishii, based on the analysis of data from more than 300,000 seismic events collected over 30 years, proposed a new model, according to which the so-called "innermost" core lies within the inner core , which is about 600 km across: Its presence may be evidence of the existence of two stages in the development of the inner core. To confirm such a hypothesis, it is necessary to place even more seismographs around the globe in order to make a more detailed selection of anisotropy (the dependence of the physical properties of matter on the direction inside it), which characterizes the very center of the Earth.

The individual face of the planet, like the appearance of a living being, is largely determined by internal factors that arise in its deep depths. It is very difficult to study these interiors, since the materials that make up the Earth are opaque and dense, so the volume of direct data on the substance of the deep zones is very limited. These include: the so-called mineral aggregate (large rock components) from a natural super-deep well - a kimberlite pipe in Lesoto (South Africa), which is considered as a representative of rocks occurring at a depth of about 250 km, as well as a core (cylindrical column of rock ), lifted from the deepest well in the world (12,262 m) on the Kola Peninsula. The study of the planet's superdeep is not limited to this. In the 70s of the twentieth century, scientific continental drilling was carried out on the territory of Azerbaijan - the Saably well (8,324 m). And in Bavaria, in the early 90s of the last century, an ultra-deep well KTB-Oberpfalz was laid with a size of more than 9,000 m.

There are many witty and interesting methods studies of our planet, but the main information about its internal structure was obtained as a result of studies of seismic waves that occur during earthquakes and powerful explosions. Every hour, about 10 oscillations of the earth's surface are recorded at various points on the Earth. In this case, seismic waves of two types arise: longitudinal and transverse. Both types of waves can propagate in a solid, but only longitudinal waves can propagate in liquids. Displacements of the earth's surface are recorded by seismographs installed around the globe. Observations of the speed with which waves travel through the earth allow geophysicists to determine the density and hardness of rocks at depths that are inaccessible to direct research. Comparison of the densities known from seismic data and those obtained in the course of laboratory experiments with rocks (where temperature and pressure corresponding to a certain depth of the earth are modeled) makes it possible to draw a conclusion about the material composition of the earth's interior. The latest data of geophysics and experiments related to the study of structural transformations of minerals made it possible to model many features of the structure, composition and processes occurring in the depths of the Earth.

Back in the 17th century, the surprising coincidence of the outlines of the coastlines of the western coast of Africa and the eastern coast of South America suggested to some scientists that the continents were “walking” around the planet. But it wasn't until three centuries later, in 1912, that the German meteorologist Alfred Lothar Wegener detailed his continental drift hypothesis, according to which the relative positions of the continents have changed throughout the history of the earth. At the same time, he put forward many arguments in favor of the fact that in the distant past the continents were brought together. In addition to the similarity of coastlines, he discovered the correspondence of geological structures, the continuity of relic mountain ranges and the identity of fossil remains on different continents. Professor Wegener actively defended the idea of ​​the existence of a single supercontinent Pangea in the past, its split and the subsequent drift of the formed continents in different directions. But this unusual theory was not taken seriously, because from the point of view of that time it seemed completely incomprehensible that giant continents could independently move around the planet. In addition, Wegener himself could not provide a suitable "mechanism" capable of moving the continents.

The revival of the ideas of this scientist occurred as a result of research on the bottom of the oceans. The fact is that the outer relief of the continental crust is well known, but the ocean floor, for many centuries reliably covered by many kilometers of water, remained inaccessible to study and served as an inexhaustible source of all kinds of legends and myths. An important step forward in the study of its relief was the invention of a precision echo sounder, with the help of which it became possible to continuously measure and record the depth of the bottom along the line of movement of the ship. One of the striking results of intensive research of the ocean floor has been new data on its topography. Today, the topography of the ocean floor is easier to map, thanks to satellites that measure the “height” of the sea surface very precisely: it accurately reflects the differences in sea level from place to place. Instead of a flat bottom, devoid of any special signs, covered with silt, deep ditches and steep cliffs, giant mountain ranges and largest volcanoes were discovered. The Mid-Atlantic mountain range, which cuts the Atlantic Ocean exactly in the middle, stands out especially clearly on the maps.

It turned out that the ocean floor ages as it moves away from the mid-ocean ridge, “spreading” from its central zone at a speed of several centimeters per year. The action of this process can explain the similarity of the outlines of the continental margins, if we assume that a new oceanic ridge is formed between the parts of the split continent, and the ocean floor, growing symmetrically on both sides, forms a new ocean. The Atlantic Ocean, in the midst of which lies the Mid-Atlantic Ridge, probably arose in this way. But if the area of ​​the sea floor increases and the Earth does not expand, then something in the global crust must be destroyed to compensate for this process. This is exactly what is happening on the fringes of much of the Pacific Ocean. Here the lithospheric plates converge, and one of the colliding plates sinks under the other and goes deep into the Earth. Such collision sites are marked by active volcanoes that stretch along the shores of the Pacific Ocean, forming the so-called "ring of fire".

Direct drilling of the seabed and determination of the age of uplifted rocks confirmed the results of paleomagnetic studies. These facts formed the basis of the theory of new global tectonics, or lithospheric plate tectonics, which made a real revolution in the sciences of the earth and brought a new understanding of the outer shells of the planet. The main idea of ​​this theory is the horizontal movement of plates.

How the earth was born

According to modern cosmological concepts, the Earth was formed along with other planets about 4.5 billion years ago from pieces and debris that revolved around the young Sun. It grew, engulfing the matter around it, until it reached its current size. At first, the growth process was very violent, and the continuous rain of falling bodies should have led to its significant heating, since the kinetic energy of the particles was converted into heat. During impacts, craters arose, and the substance ejected from them could no longer overcome the force of gravity and fell back, and the larger the falling bodies were, the more they heated the Earth. The energy of falling bodies was no longer released on the surface, but in the depths of the planet, not having time to radiate into space. Although the original mixture of substances may have been homogeneous on a large scale, the heating of the earth mass due to gravitational compression and bombardment of its debris led to the melting of the mixture and the resulting liquids under the influence of gravity separated from the remaining solid parts. The gradual redistribution of the substance along the depth in accordance with the density should have led to its stratification into separate shells. The lighter substances, rich in silicon, separated from the denser ones, containing iron and nickel, and formed the first earth's crust. After about a billion years, when the earth cooled significantly, the earth's crust hardened, turning into a solid outer shell of the planet. Cooling down, the earth ejected many different gases from its core (usually this happened during volcanic eruptions) - light ones, such as hydrogen and helium, mostly escaped into outer space, but since the force of gravity of the earth was already quite large, it kept heavier. They just formed the basis of the earth's atmosphere. Part of the water vapor from the atmosphere condensed, and oceans appeared on the earth.

What now?

Earth is not the largest, but not the smallest planet among its neighbors. Its equatorial radius, equal to 6378 km, due to the centrifugal force created by the daily rotation, is greater than the polar one by 21 km. The pressure in the center of the Earth is 3 million atm, and the density of matter is about 12 g/cm3. The mass of our planet, found by experimental measurements of the physical constant of gravity and the acceleration of gravity at the equator, is 6*1024 kg, which corresponds to an average density of matter of 5.5 g/cm3. The density of minerals on the surface is approximately half the average density, which means that the density of matter in the central regions of the planet should be higher than the average value. The moment of inertia of the Earth, which depends on the distribution of the density of matter along the radius, also indicates a significant increase in the density of matter from the surface to the center. A heat flux is constantly released from the bowels of the Earth, and since heat can only be transferred from hot to cold, the temperature in the depths of the planet must be higher than on its surface. Deep drilling has shown that the temperature increases with depth by about 20°C per kilometer and varies from place to place. If the temperature increase continued continuously, then in the very center of the Earth it would reach tens of thousands of degrees, but geophysical studies show that in reality the temperature here should be several thousand degrees.

The thickness of the Earth's crust (outer shell) varies from a few kilometers (in the oceanic regions) to several tens of kilometers (in the mountainous regions of the continents). The sphere of the earth's crust is very small, accounting for only about 0.5% of the total mass of the planet. The main composition of the crust is the oxides of silicon, aluminum, iron and alkali metals. The continental crust, which contains the upper (granite) and lower (basalt) layers under the sedimentary layer, contains the most ancient rocks of the Earth, whose age is estimated at more than 3 billion years. The oceanic crust under the sedimentary layer contains mainly one layer, similar in composition to basalt. The age of the sedimentary cover does not exceed 100-150 million years.

The still mysterious Moho Layer (named after the Serbian seismologist Mohorovichic, who discovered it in 1909) separates the earth's crust from the underlying mantle, in which the speed of propagation of seismic waves increases abruptly.

The Mantle accounts for about 67% of the total mass of the planet. The solid layer of the upper mantle, extending to various depths under the oceans and continents, together with the earth's crust is called the lithosphere - the most rigid shell of the Earth. A layer is marked under it, where there is a slight decrease in the propagation velocity of seismic waves, which indicates a peculiar state of matter. This layer, less viscous and more plastic in relation to the layers above and below, is called the asthenosphere. It is believed that the matter of the mantle is in continuous motion, and it is suggested that in relatively deep layers of the mantle, with an increase in temperature and pressure, there is a transition of matter into denser modifications. Such a transition is also confirmed by experimental studies.

In the lower mantle at a depth of 2900 km, there is a sharp jump not only in the velocity of longitudinal waves, but also in density, and transverse waves disappear completely here, which indicates a change in the material composition of the rocks. This is the outer boundary of the Earth's core.

The Earth's core was discovered in 1936. It was extremely difficult to image it because of the small number of seismic waves reaching it and returning to the surface. In addition, the extreme temperatures and pressures of the core have long been difficult to reproduce in the laboratory. The Earth's core is divided into 2 separate regions: liquid (OUTER CORE) and solid (BHUTPEHHE), the transition between them lies at a depth of 5156 km. Iron is an element that corresponds to the seismic properties of the core and is abundantly distributed in the Universe to represent approximately 35% of its mass in the planet's core. According to modern data, the outer core is a rotating stream of molten iron and nickel, a good conductor of electricity. It is with him that the origin of the earth's magnetic field is associated, considering that electric currents flowing in the liquid core create a global magnetic field. The layer of the mantle that is in contact with the outer core is affected by it, since the temperatures in the core are higher than in the mantle. In some places, this layer generates huge heat and mass flows directed to the Earth's surface - plumes.

THE INTERNAL SOLID CORE is not connected to the mantle. It is believed that its solid state, despite the high temperature, is provided by the gigantic pressure in the center of the Earth. It is suggested that, in addition to iron-nickel alloys, lighter elements, such as silicon and sulfur, and possibly silicon and oxygen, should also be present in the core. The question of the state of the Earth's core is still debatable. As the distance from the surface increases, the compression to which the substance is subjected increases. Calculations show that the pressure in the earth's core can reach 3 million atm. At the same time, many substances are, as it were, metallized - they pass into a metallic state. There was even a hypothesis that the core of the Earth consists of metallic hydrogen.

To understand how geologists created a model of the structure of the Earth, one must know the basic properties and their parameters that characterize all parts of the Earth. These properties (or characteristics) include:

1. Physical - density, elastic magnetic properties, pressure and temperature.

2. Chemical - chemical composition and chemical compounds, distribution of chemical elements in the Earth.

Based on this, the choice of methods for studying the composition and structure of the Earth is determined. Let's look at them briefly.

First of all, we note that all methods are divided into:

direct - based on the direct study of minerals and rocks and their placement in the Earth's strata;

· indirect - based on the study of the physical and chemical parameters of minerals, rocks and strata with the help of instruments.

By direct methods, we can only study the upper part of the Earth, because. the deepest well (Kolskaya) reached ~12 km. The deeper parts can be judged by volcanic eruptions.

The deep internal structure of the Earth is studied by indirect methods, mainly by a complex of geophysical methods. Let's consider the main ones.

1.seismic method(Greek seismos - shaking) - relies on the phenomenon of the emergence and propagation of elastic vibrations (or seismic waves) in various media. Elastic oscillations arise in the Earth during earthquakes, meteorite falls or explosions and begin to propagate at different speeds from the source of their occurrence (earthquake source) to the Earth's surface. There are two types of seismic waves:

1-longitudinal P-waves (the fastest), pass through all media - solid and liquid;

2-transverse S-waves are slower and only pass through solid media.

Seismic waves during earthquakes occur at depths from 10 km to 700 km. The speed of seismic waves depends on the elastic properties and density of the rocks they cross. Reaching the surface of the Earth, they seem to shine through it and give an idea of ​​the environment that they crossed. The change in velocities gives an idea of ​​the heterogeneity and stratification of the Earth. In addition to changing velocities, seismic waves experience refraction when passing through heterogeneous layers or reflection from a surface separating layers.

2.gravimetric method is based on the study of the acceleration of gravity Dg, which depends not only on the geographical latitude, but also on the density of the Earth's matter. Based on the study of this parameter, the heterogeneity in the density distribution in different parts of the Earth was established.

3.magnetometric method- based on the study of the magnetic properties of the Earth's matter. Numerous measurements have shown that different rocks differ from each other in magnetic properties. This leads to the formation of areas with inhomogeneous magnetic properties, which make it possible to judge the structure of the Earth.

Comparing all the characteristics, scientists have created a model of the structure of the Earth, in which three main areas (or geospheres) are distinguished:

1-Earth's crust, 2-Earth's mantle, 3-Earth's core.

Each of them, in turn, is divided into zones or layers. Consider them and summarize the main parameters in the table.

1.Earth's crust(layer A) is the upper shell of the Earth, its thickness varies from 6-7 km to 75 km.

2.Mantle of the Earth subdivided into upper (with layers: B and C) and lower (layer D).

3. Core - subdivided into outer (layer E) and inner (layer G), between which there is a transition zone - layer F.

border between earth's crust and mantle is the Mohorović section, between mantle and core also a sharp border - Gutenberg section.

The table shows that the speed of the longitudinal and shear waves increases from the surface to the deeper spheres of the Earth.

A feature of the upper mantle is the presence of a zone in which the velocity of transverse waves drops sharply to 0.2–0.3 km/s. This is explained by the fact that, along with the solid state, the mantle is partially represented by a melt. This layer of reduced speeds is called asthenosphere. Its thickness is 200-300 km, depth is 100-200 km.

At the boundary between the mantle and the core, there is a sharp decrease in the velocity of longitudinal waves and attenuation of the velocity of transverse waves. Based on this, an assumption was made that the outer core is in a state of melt.

Average values ​​of density by geospheres show its increase towards the core.

About the chemical composition of the Earth and its geospheres give an idea:

1- chemical composition of the earth's crust,

2 - chemical composition of meteorites.

The chemical composition of the earth's crust has been studied in sufficient detail - its bulk chemical composition and the role of chemical elements in mineral and rock formation are known. The situation is more difficult with regard to the study of the chemical composition of the mantle and the core. We cannot do this by direct methods. Therefore, a comparative approach is used. The starting point is the assumption of a protoplanetary similarity between the composition of meteorites that fell to the earth and the internal geospheres of the Earth.

All meteorites that hit the Earth are divided into types according to their composition:

1-iron, consist of Ni and 90% Fe;

2-ironstones (siderolites) consist of Fe and silicates,

3-stone, consisting of Fe-Mg silicates and nickel iron inclusions.

Based on the analysis of meteorites, experimental studies and theoretical calculations, scientists suggest (according to the table) that the chemical composition of the core is nickel iron. True, in recent years, the point of view has been expressed that, in addition to Fe-Ni, the core may contain impurities of S, Si, or O. For the mantle, the chemical spectrum is determined by Fe-Mg silicates, i.e. peculiar olivine-pyroxene pyrolite composes the lower mantle, and the upper one - rocks of ultramafic composition.

The chemical composition of the earth's crust includes the maximum spectrum of chemical elements, which is revealed in the variety of mineral species known to date. The quantitative ratio between the chemical elements is quite large. A comparison of the most common elements in the earth's crust and mantle shows that Si, Al and O 2 play the leading role.

Thus, having considered the main physical and chemical characteristics of the Earth, we see that their values ​​are not the same, they are distributed zonally. Thus, giving an idea of ​​the heterogeneous structure of the Earth.

The structure of the earth's crust

The types of rocks considered earlier - igneous, sedimentary and metamorphic - are involved in the structure of the earth's crust. According to their physical and chemical parameters, all rocks of the earth's crust are grouped into three large layers. From bottom to top it is: 1-basalt, 2-granite-gneiss, 3-sedimentary. These layers in the earth's crust are distributed unevenly. First of all, this is expressed in power fluctuations of each layer. In addition, not all parts show a complete set of layers. Therefore, a more detailed study made it possible to distinguish four types of the earth's crust in terms of composition, structure and thickness: 1-continental, 2-oceanic, 3-subcontinental, 4-suboceanic.

1. Continental type- has a thickness of 35-40 km to 55-75 km in mountain structures, contains all three layers in its composition. The basalt layer consists of rocks of the gabbro type and metamorphic rocks of amphibolite and granulite facies. It is called so because in physical parameters it is close to basalts. The composition of the granite layer is gneisses and granite-gneisses.

2.Ocean type- sharply differs from the continental thickness (5-20 km, average 6-7 km) and the absence of a granite-gneiss layer. Two layers participate in its structure: the first layer is sedimentary, thin (up to 1 km), the second layer is basalt. Some scientists distinguish the third layer, which is a continuation of the second, i.e. has a basaltic composition, but is composed of ultramafic rocks of the mantle that have undergone serpentinization.

3. Subcontinental type- includes all three layers and is close to the continental one. But it is distinguished by a smaller thickness and composition of the granite layer (less gneisses and more volcanic rocks of acid composition). This type is found on the border of continents and oceans with an intense manifestation of volcanism.

4. Subocean type- located in deep troughs of the earth's crust (inland seas such as the Black and Mediterranean). It differs from the oceanic type in the greater thickness of the sedimentary layer up to 20-25 km.

The problem of the formation of the earth's crust.

According to Vinogradov, the process of formation of the earth's crust took place according to the principle zone melting. The essence of the process: the substance of the Proto-Earth, close to meteorite, melted as a result of radioactive heating and the lighter silicate part rose to the surface, and Fe-Ni concentrated in the core. Thus, the formation of geospheres took place.

It should be noted that the earth's crust and the solid part of the upper mantle are combined into lithosphere, below which is asthenosphere.

tectonosphere- this is the lithosphere and part of the upper mantle to a depth of 700 km (ie, to the depth of the deepest earthquake sources). It is named so because the main tectonic processes that determine the restructuring of this geosphere take place here.