According to US geochemists, the collision of the Earth with the celestial body Theia, which supposedly occurred about 4.5 billion years ago, if it took place, did not make major changes to the structure of the subsoil. At least our planet definitely did not turn into a hot ball.
The modern hypothesis of the origin of the Earth is still the subject of heated debate, but most scientists agree that it all began from a protoplanetary cloud of cosmic dust and gas. Some scientists were sure that it was cold, others that, on the contrary, it was hot, since it was pulled out of the young Sun by the gravity of a massive star passing nearby at that time. The latest version is rapidly losing its fans today, since astrophysicists have proven that such an interpretation of events is extremely unlikely. Therefore, today the hypothesis of a cold protoplanetary cloud dominates.
Approximately 4.54 billion years ago, the Earth began to form from this protoplanetary cloud. The process itself probably took place as follows: since in this cloud the “light” and “heavy” elements were not yet strongly mixed, then, as a result of the action of gravity, the latter (iron and other related metals) began to descend towards the future center of the planet, squeezing out the surface is “lighter” elements. Scientists called this process gravitational differentiation.
Thus, iron accumulated in the center of the cloud, forming the future core. But during the descent, the potential energy of the layer of “heavy” elements began to decrease, and accordingly the kinetic energy began to increase, that is, heating occurred. It is believed that this heat warmed our planet to 1200 degrees Celsius (in some places up to 1600 degrees).
However, the impact of the most perfect refrigerator in nature - space, led to the fact that the surface of the cloud of “light” elements began to quickly cool, turning from a melt into a solid substance. This is how the earth's crust was formed. And the area where gravitational differentiation continued (according to the calculations of some geophysicists, this process will continue for about one and a half billion years), and the high temperature remained, became the modern mantle.
About 4.5 billion years ago, the solid part of the Earth was completely formed (although the atmosphere and hydrosphere appeared somewhat later). And it was at that time, according to recent research, that a catastrophe occurred, the result of which was the appearance of a satellite and a return to an unstructured state. According to many scientists, most likely there was a collision with a certain massive celestial body (dubbed the planet Theia).
At the same time, some geophysicists are confident that the collision was so impressive that the upper part of the Earth melted again. That is, for some time the planet was a ball of molten homogeneous matter, after which, over several tens of millions of years, it again acquired a solid surface.
Still, some scientists have expressed doubt that the consequences of this collision were so significant. They are sure that even a collision with a celestial body could not radically change the existing structure of our planet. More recently, this version has received evidence of its plausibility. And this evidence was provided by stones discovered near Kostomuksha.
Introduction
Earth is the third planet in order from the Sun in the solar system. It ranks fifth in size and mass among the major planets, but of the inner planets of the so-called “terrestrial” group, which includes Mercury, Venus, Earth and Mars, it is the largest.
The composition and structure of the Earth in recent decades continues to be one of the most intriguing problems of modern geology. Knowledge about the internal structure of the Earth is still very superficial, as it was obtained on the basis of indirect evidence. Direct evidence relates only to the surface film of the planet, most often not exceeding one and a half tens of kilometers. In addition, it is important to study the position of planet Earth in outer space. Firstly, in order to understand the patterns and mechanism of development of the Earth and the earth's crust, you need to know the initial state of the Earth during its formation. Secondly, the study of other planets provides valuable material for understanding the early stages of the development of our planet. And thirdly, a comparison of the structure and evolution of the Earth with other planets of the solar system allows us to understand why the Earth became the birthplace of humanity.
The study of the internal structure of the Earth is relevant and vital. The formation and placement of many types of minerals, the relief of the earth's surface, the occurrence of volcanoes and earthquakes are associated with it. Knowledge about the structure of the Earth is also necessary for making geological and geographical forecasts.
Chapter 1. Hypotheses of the origin of the Earth
For many centuries, the question of the origin of the Earth remained the monopoly of philosophers, since factual 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 the 18th century. Since then, more and more new theories have not ceased to appear, corresponding to the growth of our cosmogonic ideas.
One of the first hypotheses was expressed in 1745 by the French naturalist J. Buffon. According to the hypothesis, our planet was formed as a result of the cooling of one of the clumps of solar matter ejected by the Sun during a catastrophic collision with a large comet.
Buffon's idea about the formation of the Earth from solar plasma was used in a whole series of later and more advanced hypotheses of the “hot” origin of the Earth. The leading place is occupied by nebular a hypothesis developed by the German philosopher I. Kant in 1755 and the French mathematician P. Laplace in 1796 independently of each other (Fig. 1). According to the hypothesis, the solar system was formed from a single hot gas nebula. Rotation around the axis caused the nebula to have a disc-shaped shape. After the centrifugal force in the equatorial part of the nebula exceeded the force of gravity, gas rings began to separate along the entire periphery of the disk. Their cooling led to the formation of planets and their satellites, and the Sun emerged from the core of the nebula.
Rice. 1. Nebular hypothesis of Laplace. This figure clearly shows the condensation of a rotating gas nebula into the Sun, planets and asteroids
Laplace's hypothesis was scientific because it was based on the laws of nature known from experience. However, after Laplace, new phenomena were discovered in the solar system, which his theory could not explain. For example, it turned out that the planets Uranus and Venus rotate around their axis in a different direction than the other planets rotate. The properties of gases and the peculiarities of the movement of planets and their satellites were better studied. These phenomena also did not agree with Laplace's hypothesis and it had to be abandoned.
A certain stage in the development of views on the formation of the Solar system was the hypothesis of the English astrophysicist James Jeans (Fig. 2). He believed that the planets were formed as a result of a catastrophe: some relatively large star passed very close to the already existing Sun, which resulted in the emission of gas jets from the surface layers of the Sun, from which the planets subsequently formed. But the Jeans hypothesis, like the Kant-Laplace hypothesis, cannot explain the discrepancy in the distribution of angular momentum between the planets and the Sun.
Rice. 2. Formation of the solar system according to Jeans
A fundamentally new idea lies in the hypotheses of the “cold” origin of the Earth. Most deeply developed meteorite a hypothesis proposed by the Soviet scientist O. Yu. Schmidt in 1944 (Fig. 3). According to the hypothesis, several billion years ago “our” Sun encountered a large gas and dust nebula during its movement in the Universe. A significant part of the nebula followed the Sun and began to revolve around it. Individual small particles stuck together into large clumps. As the clots moved, they also collided with each other and became overgrown with new material, forming dense lumps - the embryos of future planets.
Rice. 3. Formation of the solar system according to the meteorite hypothesis
O. Yu. Shmidt
According to O. Yu. Schmidt, during the formation of the Earth, its surface remained cold, the clumps were compressed, due to this the process of self-gravity of the substance began, the internal part gradually warmed up from the heat released during the decay of radioactive elements. Over the years, Schmidt's hypothesis has developed many weaknesses, one of which is the assumption that the Sun will capture part of the encountered gas and dust cloud. Based on the law of mechanics, in order for the Sun to capture matter, it was necessary to completely stop this matter, and the Sun had to have an enormous gravitational force capable of stopping this cloud and attracting it to itself. The disadvantages of the meteorite hypothesis include the low probability of the Sun capturing a gas-dust (meteorite) cloud and the lack of explanation for the concentric internal structure of the Earth.
Over time, many more theories have emerged regarding the origin of the Earth and the solar system as a whole. Based on the views of O.Yu. Schmidt (1944), V. Ambartsumyan (1947), B.C. Safronov (1969) and other scientists formed modern theory planetary formation of the Earth and other planets of the Solar system (Fig. 4). The cause of the appearance of the planets in our system was the explosion of a supernova. The shock wave from the explosion about 5 billion years ago greatly compressed the gas and dust nebula. The concentration of material matter (dust, mixtures of gases, hydrogen, helium, carbon, heavy metals, sulfides) turned out to be so significant that it led to the onset of thermonuclear fusion, an increase in temperature, pressure, the appearance of self-gravity in the primary Sun and the birth of protoplanets.
Rice. 4. Formation of the solar system (modern theory)
1 – a supernova explosion generates shock waves affecting the gas and dust cloud; 2 – the gas and dust cloud begins to fragment and flatten, while twisting; 3 – primary solar nebula (nebula); 4 – formation of the Sun and giant gas-rich planets – Jupiter and Saturn; 5 – ionized gas – the solar wind blows gas from the inner zone of the system and from small planetesimals; 6 – formation of the inner planets from planetesimals over 100 million years and the formation of Oort clouds consisting of comets
The primordial Earth turned out to be connected to the Moon by tidal interactions. The Moon determined the inclination of its axis of rotation with its orbit and mass and determined the climatic zonation of the Earth, the emergence of electric and magnetic fields.
After the formation of the earth's core (at the border of the Archean and Proterozoic), containing about 63% of the modern mass, the further growth of the Earth occurred more calmly and evenly along tectonomagmatic cycles. Tectonists have counted about 14 such cycles. Significant tectonic activity on Earth was observed about 2.6 billion years ago; the movement of lithospheric plates at that time occurred at a speed of 2-3 m per year. The Earth's surface was shrouded in a dense carbon-nitrogen atmosphere with a pressure of up to 4-5 atm. and temperatures up to +30…+100 °C. The first shallow World Ocean arose, the bottom of which was covered with basalts and serpentinite.
In the Early Proterozoic, the third (serpentinite) layer of the oceanic crust was saturated with primary water. This immediately affected the decrease in carbon dioxide pressure in the primary atmosphere. In turn, the decrease in carbon dioxide in the atmosphere led to a sharp decrease in temperature on the Earth's surface. The appearance of oxygen and the ozone layer in the atmosphere contributed to the formation of the biosphere and geographical envelope.
The process of stratification and differentiation of the interior on Earth is still ongoing, ensuring the existence of a liquid outer core and convection in the mantle. The atmosphere and hydrosphere arose as a result of the condensation of gases released at an early stage of the planet's development.
Related information.
The Earth occupies a special place in the solar system - the only planet on which various forms of life have developed over billions of years.
At all times, people wanted to know where and how the world in which we live came from. When mythological ideas dominated the culture, the origin of the world was explained, as, say, in the Vedas, by the disintegration of the first man Purusha. The fact that this was a general mythological scheme is confirmed by Russian apocrypha, for example, the “Pigeon Book”. The victory of Christianity confirmed religious ideas about God’s creation of the world out of nothing.
With the advent of science in its modern understanding, mythological and religious ones are replaced by scientific ideas about the origin of the world. Science differs from mythology in that it strives not to explain the world as a whole, but to formulate laws of natural development that can be empirically verified. Reason and reliance on sensory reality are more important in science than faith. Science is, to a certain extent, a synthesis of philosophy and religion, which is a theoretical exploration of reality.
2. Origin of the Earth.
We live in the Universe, and our planet Earth is its smallest link. Therefore, the history of the origin of the Earth is closely connected with the history of the origin of the Universe. By the way, how did it come about? What forces influenced the process of formation of the Universe and, accordingly, our planet? Nowadays, there are many different theories and hypotheses regarding this problem. The greatest minds of mankind give their views on this matter.
The meaning of the term Universe in natural science is narrower and has acquired a specifically scientific meaning. The Universe is a place of human habitation, accessible to empirical observation and verifiable by modern scientific methods. The universe as a whole is studied by a science called cosmology, that is, the science of space. This word is not accidental. Although now everything outside the Earth's atmosphere is called space, this was not the case in Ancient Greece, where space was accepted as “order”, “harmony”, as opposed to “chaos” - “disorder”. Thus, cosmology, at its core, as befits science, reveals the orderliness of our world and is aimed at finding the laws of its functioning. The discovery of these laws is the goal of studying the Universe as a single ordered whole.
Currently, the origin of the Universe is based on two models:
a) Model of the expanding Universe. The most generally accepted model in cosmology is the model of a homogeneous isotropic non-stationary hot expanding Universe, built on the basis of the general theory of relativity and the relativistic theory of gravity, created by Albert Einstein in 1916. This model is based on two assumptions:
1) the properties of the Universe are the same at all its points (homogeneity) and directions (isotropy);
2) the best known description of the gravitational field is Einstein's equations. From this follows the so-called curvature of space and the connection between curvature and mass (energy) density. Cosmology based on these postulates is relativistic.
An important point of this model is its nonstationarity. This is determined by two postulates of the theory of relativity:
1) the principle of relativity, which states that in all inertial systems all laws are preserved regardless of the speed at which these systems move uniformly and rectilinearly relative to each other;
2) experimentally confirmed constancy of the speed of light.
Red shift is a decrease in the frequencies of electromagnetic radiation: in the visible part of the spectrum, lines shift towards its red end. The previously discovered Doppler effect stated that when any source of oscillation moves away from us, the oscillation frequency we perceive decreases, and the wavelength increases accordingly. When emitted, “reddening” occurs, that is, the lines of the spectrum shift towards longer red wavelengths.
So, for all distant light sources, the red shift was recorded, and the further away the source was, the greater the degree. The red shift turned out to be proportional to the distance to the source, which confirmed the hypothesis about their removal, that is, about the expansion of the Megagalaxy - the visible part of the Universe.
The red shift reliably confirms the theoretical conclusion that the region of our Universe with linear dimensions of the order of several billion parsecs is nonstationary over at least several billion years. At the same time, the curvature of space cannot be measured, remaining a theoretical hypothesis.
b) Big Bang model. The Universe we observe, according to modern science, arose as a result of the Big Bang about 15-20 billion years ago. The idea of the Big Bang is an integral part of the expanding Universe model.
All the matter of the Universe in the initial state was at a singular point: infinite mass density, infinite curvature of space and explosive expansion that slows down over time at a high temperature, at which only a mixture of elementary particles could exist. Then came an explosion. “At first there was an explosion. Not the kind of explosion that we are familiar with on Earth, which starts from a certain center and then spreads, capturing more and more space, but an explosion that happened everywhere simultaneously, filling all space from the very beginning, with every particle of matter rushing away from every other particles,” wrote S. Weinberg in his work.
What happened after the Big Bang? A clot of plasma was formed - a state in which elementary particles are located - something between a solid and a liquid state, which began to expand more and more under the influence of the blast wave. 0.01 seconds after the start of the Big Bang, a mixture of light nuclei appeared in the Universe. This is how not only matter and many chemical elements appeared, but also space and time.
These models help put forward hypotheses about the origin of the Earth:
1. French scientist Georges Buffon (1707-1788) suggested that the globe arose as a result of a catastrophe. At a very distant time, some celestial body (Buffon believed that it was a comet) collided with the Sun. The collision produced a lot of “splash.” The largest of them, gradually cooling, gave rise to planets.
2. The German scientist Immanuel Kant (1724-1804) explained the possibility of the formation of celestial bodies differently. He suggested that the solar system originated from a giant, cold dust cloud. The particles of this cloud were in constant random motion, mutually attracted each other, collided, stuck together, forming condensations that began to grow and eventually gave rise to the Sun and planets.
3. Pierre Laplace (1749-1827), French astronomer and mathematician, proposed his hypothesis explaining the formation and development of the Solar system. In his opinion, the Sun and planets arose from a rotating hot gas cloud. Gradually, as it cooled, it contracted, forming numerous rings, which, as they became denser, created planets, and the central clot turned into the Sun.
At the beginning of this century, the English scientist James Genet (1877-1946) put forward a hypothesis that explained the formation of the planetary system: once upon a time another star flew near the Sun, which, with its gravity, tore out part of the matter from it. Having condensed, it gave rise to planets.
4. Our compatriot, the famous scientist Otto Yulievich Schmidt (1891-1956) in 1944 proposed his hypothesis of the formation of planets. He believed that billions of years ago the Sun was surrounded by a giant cloud that consisted of particles of cold dust and frozen gas. They all revolved around the Sun. Being in constant motion, colliding, mutually attracting each other, they seemed to stick together, forming clumps. Gradually, the gas and dust cloud flattened, and the clumps began to move in circular orbits. Over time, the planets of our solar system were formed from these clumps.
It is easy to see that the hypotheses of Kant, Laplace, and Schmidt are close in many ways. Many of the thoughts of these scientists formed the basis of the modern understanding of the origin of the Earth and the entire solar system.
Today scientists suggest that
3. Development of the Earth.
The ancient Earth bore very little resemblance to the planet on which we now live. Its atmosphere consisted of water vapor, carbon dioxide and, in some cases, nitrogen, in others - methane and ammonia. There was no oxygen in the air of the lifeless planet, thunderstorms thundered in the atmosphere of the ancient Earth, it was penetrated by the hard ultraviolet radiation of the Sun, and volcanoes erupted on the planet. Research shows that the poles on Earth have changed and Antarctica was once evergreen. Permafrost formed 100 thousand years ago after the great glaciation.
In the 19th century, two concepts of the development of the Earth were formed in geology:
1) through leaps (“catastrophe theory” by Georges Cuvier);
2) through small but constant changes in the same direction over millions of years, which, cumulatively, led to enormous results (“the principle of uniformitarianism” by Charles Lyell).
The advances in physics of the 20th century contributed to significant advances in the knowledge of the history of the Earth. In 1908, the Irish scientist D. Joly made a sensational report on the geological significance of radioactivity: the amount of heat emitted by radioactive elements is quite sufficient to explain the existence of molten magma and volcanic eruptions, as well as the displacement of continents and mountain building. From his point of view, the element of matter - the atom - has a strictly defined duration of existence and inevitably decays. The following year, 1909, the Russian scientist V.I. Vernadsky founded geochemistry - the science of the history of the Earth's atoms and its chemical and physical evolution.
There are two most common points of view on this matter. The earliest of them believed that the original Earth, formed immediately after accretion from planetesimals consisting of nickel iron and silicates, was homogeneous and only then underwent differentiation into an iron-nickel core and a silicate mantle. This hypothesis is called homogeneous accretion. A later hypothesis of heterogeneous accretion is that the most refractory planetesimals, consisting of iron and nickel, accumulated first, and only then the silicate substance, which now composes the Earth’s mantle from a level of 2900 km, entered into accretion. This point of view is now perhaps the most popular, although here too the question arises of isolating the outer core, which has the properties of a liquid. Did it arise after the formation of a solid inner core, or did the outer and inner cores separate during the process of differentiation? But this question does not have a clear answer, but the assumption is given to the second option.
The process of accretion, the collision of planetesimals up to 1000 km in size, was accompanied by a large release of energy, with strong heating of the forming planet, its degassing, i.e. by the release of volatile components contained in falling planetesimals. Most of the volatile substances were irretrievably lost in interplanetary space, as evidenced by a comparison of the compositions of volatiles in meteorites and Earth rocks. According to modern data, the process of formation of our planet lasted about 500 million years and took place in 3 phases of accretion. During the first and main phase, the Earth was formed radially by 93-95% and this phase ended by the turn of 4.4 - 4.5 billion years, i.e. lasted about 100 million years.
The second phase, marked by the end of growth, also lasted about 200 million years. Finally, the third phase, lasting up to 400 million years (3.8-3.9 billion years ended) was accompanied by a powerful meteorite bombardment, the same as on the Moon. The question of the temperature of the primordial Earth is of fundamental importance for geologists. Even at the beginning of the twentieth century, scientists spoke about the primary “fiery liquid” Earth. However, this view was completely contrary to the modern geological life of the planet. If the Earth was molten to begin with, it would have long ago turned into a dead planet.
Therefore, preference should be given to the not very cold, but not molten early Earth. There were many factors for heating the planet. This is gravitational energy; and collision of planetesimals; and the fall of very large meteorites, upon impact of which the increased temperature spread to depths of 1-2 thousand km. If, nevertheless, the temperature exceeded the melting point of the substance, then differentiation occurred - heavier elements, for example, iron, nickel, sank, and lighter ones, on the contrary, floated up.
But the main contribution to the increase in heat was to be made by the decay of radioactive elements - plutonium, thorium, potassium, aluminum, iodine. Another source of heat is solid tides associated with the close location of the Earth's satellite, the Moon. All these factors, acting together, could increase the temperature to the melting point of rocks, for example, in the mantle it could reach +1500 °C. But pressure at great depths prevented melting, especially in the inner core. The process of internal differentiation of our planet has occurred throughout its geological history, and it continues today. However, already 3.5-3.7 billion years ago, when the Earth was 4.6 billion years old, the Earth had a solid inner core, a liquid outer core and a solid mantle, i.e. it has already been differentiated in its modern form. This is evidenced by the magnetization of such ancient rocks, and, as is known, the magnetic field is caused by the interaction of the liquid outer core and the solid outer core. The process of stratification and differentiation of the interior occurred on all planets, but on Earth it is still happening now, ensuring the existence of a liquid outer core and convection in the mantle.
In 1915, the German geophysicist A. Wegener suggested, based on the outlines of the continents, that in the Carboniferous (geological period) there was a single land mass, which he called Pangea (Greek “the whole earth”). Pangea split into Laurasia and Gondwana. 135 million years ago Africa separated from South America, and 85 million years ago North America separated from Europe; 40 million years ago, the Indian continent collided with Asia and Tibet and the Himalayas appeared.
The decisive argument in favor of the adoption of this concept by A. Wegener was the empirical discovery in the late 50s of the expansion of the ocean floor, which served as the starting point for the creation of lithospheric plate tectonics. It is currently believed that the continents are moving apart under the influence of deep convective currents directed upward and to the sides and pulling the plates on which the continents float. This theory is also confirmed by biological data on the distribution of animals on our planet. The theory of continental drift, based on plate tectonics, is now generally accepted in geology.
4. Global tectonics.
Many years ago, a geologist father took his young son to a map of the world and asked what would happen if the coastline of America was moved closer to the coasts of Europe and Africa? The boy was not too lazy and, having cut out the corresponding parts from the physical-geographical atlas, was surprised to discover that the western coast of the Atlantic coincided with the eastern one within, so to speak, experimental error.
This story did not pass without a trace for the boy; he became a geologist and admirer of Alfred Wegener, a retired German army officer, as well as a meteorologist, polar explorer, and geologist, who in 1915 created the concept of continental drift.
High technology also contributed to the revival of the drift concept: it was computer modeling in the mid-1960s that showed a good coincidence of the boundaries of continental masses not only for the Circum-Atlantic, but also for a number of other continents - East Africa and Hindustan, Australia and Antarctica. As a result, the concept of plate tectonics, or new global tectonics, emerged in the late 1960s.
Proposed at first purely speculatively to solve a particular problem - the distribution of earthquakes of various depths on the Earth's surface - it merged with ideas about continental drift and instantly received universal recognition. By 1980 - the centenary of the birth of Alfred Wegener - it became common to talk about the formation of a new paradigm in geology. And even about the scientific revolution, comparable to the revolution in physics at the beginning of the 20th century...
According to this concept, the earth's crust is divided into several huge lithospheric plates, which are constantly moving and producing earthquakes. Initially, several lithospheric plates were identified: Eurasian, African, North and South American, Australian, Antarctic, and Pacific. All of them, except the Pacific, which is purely oceanic, include parts with both continental and oceanic crust. And continental drift, within the framework of this concept, is nothing more than their passive movement along with lithospheric plates.
Global tectonics is based on the idea of lithospheric plates, fragments of the earth's surface, considered as absolutely rigid bodies, moving as if on a cushion of air through a layer of decompressed mantle - the asthenosphere, at a speed of 1-2 to 10-12 cm per year. For the most part, they include both continental masses with a crust conventionally called “granite” and areas with an oceanic crust conventionally called “basaltic” and formed by rocks with a low silica content.
It is not at all clear to scientists where the continents are moving and some of them do not agree that the earth’s crust is moving, and if they are moving, then due to the action of what forces and energy sources. The widespread assumption that thermal convection is the cause of the movement of the earth's crust is, in fact, unconvincing, because it turned out that such assumptions contradict the basic provisions of many physical laws, experimental data and numerous observations, including space research data on tectonics and structure other planets. Real schemes of thermal convection that do not contradict the laws of physics, and a single logically substantiated mechanism for the movement of matter, equally acceptable for the conditions of the interior of stars, planets and their satellites, have not yet been found.
At mid-ocean ridges, new heated oceanic crust is formed, which, when cooled, again sinks into the depths of the mantle and dissipates the thermal energy used to move the crustal plates.
Giant geological processes, such as the uplifting of mountain ranges, powerful earthquakes, the formation of deep-sea trenches, volcanic eruptions - all of them are ultimately generated by the movement of the earth's crust plates, during which the mantle of our planet gradually cools.
The Earth's landmass is formed by solid rocks, often covered with a layer of soil and vegetation. But where do these rocks come from? New rocks are formed from material born deep within the Earth. In the lower layers of the earth's crust, the temperature is much higher than on the surface, and the rocks that make them up are under enormous pressure. Under the influence of heat and pressure, rocks bend and soften, or even completely melt. Once a weak spot forms in the Earth's crust, molten rock - called magma - erupts to the Earth's surface. Magma flows out of volcanic vents in the form of lava and spreads over a large area. When lava hardens, it turns into solid rock.
In some cases, the birth of rocks is accompanied by grandiose cataclysms, in others it occurs quietly and unnoticed. There are many varieties of magma, and they form different types of rocks. For example, basaltic magma is very fluid, easily comes to the surface, spreads in wide streams and quickly hardens. Sometimes it bursts out of the crater of a volcano as a bright “fiery fountain” - this happens when the earth’s crust cannot withstand its pressure.
Other types of magma are much thicker: their density, or consistency, is more like black molasses. The gases contained in such magma have great difficulty making their way to the surface through its dense mass. Remember how easily air bubbles escape from boiling water and how much slower this happens when you heat something thicker, such as jelly. As denser magma rises closer to the surface, the pressure on it decreases. Gases dissolved in it tend to expand, but cannot. When the magma finally breaks out, the gases expand so rapidly that a huge explosion occurs. Lava, rock debris and ash fly out in all directions like shells fired from a cannon. A similar eruption occurred in 1902 on the island of Martinique in the Caribbean Sea. The catastrophic eruption of the Moptap-Pelé volcano completely destroyed the port of Sept-Pierre. About 30,000 people died
Geology has given humanity the opportunity to use geological resources for the development of all branches of engineering and technology. At the same time, intensive technogenic activity has led to a sharp deterioration of the global environmental situation, so strong and rapid that the existence of humanity is often called into question. We consume much more than nature is able to regenerate. Therefore, the problem of sustainable development today is a truly global, world problem that concerns all states.
Despite the increase in the scientific and technological potential of mankind, the level of our ignorance about planet Earth is still very high. And as our knowledge about it progresses, the number of questions remaining unresolved does not decrease. We began to understand that the processes occurring on Earth are influenced by the Moon, the Sun, and other planets, everything is connected together, and even life, the emergence of which is one of the cardinal scientific problems, may have been brought to us from outer space. Geologists are still powerless to predict earthquakes, although volcanic eruptions can now be predicted with a high degree of probability. Many geological processes are still difficult to explain, much less predict. Therefore, the intellectual evolution of mankind is largely connected with the successes of geological science, which someday will allow man to solve the questions that concern him about the origin of the Universe, the origin of life and mind.
6. List of used literature
1. Gorelov A. A. Concepts of modern natural science. - M.: Center, 1997.
2. Lavrinenko V.N., Ratnikov V.P. - M.: Culture and Sport, 1997.
3. Naydysh V. M. Concepts of modern natural science: Textbook. allowance. – M.: Gardariki, 1999.
4. Levitan E. P. Astronomy: Textbook for 11th grade. secondary school. – M.: Education, 1994.
5. Surdin V. G. Dynamics of stellar systems. – M.: Publishing house of the Moscow Center for Continuing Education, 2001.
6. Novikov I. D. Evolution of the Universe. – M., 1990.
7. Karapenkov S. Kh. Concepts of modern natural science. – M.: Academic Avenue, 2003.
How was the Earth born?
There are several theories of the origin of our planet, each of which has its supporters and its right to life. Of course, it is impossible to determine absolutely exactly which theory actually describes the appearance of the Earth and whether such a theory exists at all, but in this article we will consider each of them in detail. The question of the origin of the Earth has not yet been fully studied and does not have an absolutely accurate answer.
Modern idea of the origin of planet Earth
Today, the most recognized theory of the origin of planet Earth is the theory according to which the Earth was formed from gas and dust matter scattered in the solar system.
According to this theory, the Sun appeared before the planets, and the Earth, like other planets in the solar system, was born from debris, gas and dust left after the formation of the Sun. Thus, it is believed that the Earth was formed approximately 4.5 billion years ago, and the process of its formation took approximately 10 - 20 million years.
History of the development of the theory 
The first to put forward this theory in 1755 was the German philosopher I. Kant. He believed that the Sun and the planets of the solar system arose from dust and gas that was scattered in space. Particles of dust and gas, under the influence of the shock wave from the Big Bang, moved randomly, collided with each other, transferring energy. Thus, the heaviest and largest particles were formed, which were attracted to each other and eventually formed the Sun. After the Sun acquired a large size, smaller particles began to revolve around it, the paths of which intersected. Thus, gaseous rings were formed in which light particles were attracted to heavier nuclei, creating spherical clusters that became future planets.
There are other theories about the origin of the Earth, which were put forward by different scientists at different times and even had their followers in the future.
Tidal theory of the origin of the Earth
According to this theory, the Sun appeared much earlier than the planets, and the Earth and other planets of the solar system were formed from substances released by the Sun or another large star.
History of the development of the theory
The history of this theory began in 1776, when the mathematician J. Buffon put forward 
theory about the collision of the Sun with a comet. As a result of this collision, material was released from which both planet Earth and other planets were born.
This theory found its follower in the 20th century. It was then that the scientist astrophysicist I.I. Wulfson, using computer calculations, showed that for material to be torn off, a star does not have to collide with the Sun. According to his theory, any large and cold star from a new cluster of stars could approach the Sun at a short distance and thereby cause giant tides both on its surface and on the Sun. The amplitude of these tides increases until material is torn away from the Sun or an approaching star and takes up space between these stellar bodies in the form of a cigar-shaped stream. Then the cold star leaves, and the emerging jet disintegrates into the planets of the solar system.
How the Earth was born according to the “nebular theory”
The creator of the first nebular theory was the French astronomer and mathematician P.-S. Laplace. He believed that there was some kind of gas disk rotating from compression; the speed of its rotation increased until the centrifugal force at its edge began to exceed the gravitational force of attraction. After this, the disk ruptured, and after some time this process was repeated. Thus, the rings turned into planets, and the central mass into the Sun. 
This theory explains well the fact that the Earth and the Sun rotate in the same plane and in the same direction, but it also has significant gaps.
According to this theory, the Sun should rotate very quickly (with a rotation period of several hours). However, in fact, the Sun rotates much slower - 1 revolution every 27 days. Another drawback of the theory is the mechanism for collecting particles into planets. The theory does not answer the question of why the substances, after the rupture of the disk, divided into rings, and did not take the form of the same disk, but of smaller sizes.
This concludes the story about the birth of planet Earth and recommends that you read about it.
Shape, size and structure of the globe
The earth has a complex configuration. Its shape does not correspond to any of the regular geometric shapes. Speaking about the shape of the globe, it is believed that the figure of the Earth is limited by an imaginary surface that coincides with the surface of the water in the World Ocean, conditionally extended under the continents in such a way that a plumb line at any point on the globe is perpendicular to this surface. This shape is called a geoid, i.e. a form unique to the Earth.
The study of the shape of the Earth has a rather long history. The first assumptions about the spherical shape of the Earth belong to the ancient Greek scientist Pythagoras (571-497 BC). However, scientific evidence of the sphericity of the planet was given by Aristotle (384-322 BC), who was the first to explain the nature of lunar eclipses as the shadow of the Earth.
In the 18th century, I. Newton (1643-1727) calculated that the rotation of the Earth causes its shape to deviate from an exact sphere and gives it some flattening at the poles. The reason for this is centrifugal force.
Determining the size of the Earth has also occupied the minds of mankind for a long time. For the first time, the size of the planet was calculated by the Alexandrian scientist Eratosthenes of Cyrene (about 276-194 BC): according to his data, the radius of the Earth is about 6290 km. In 1024-1039 AD Abu Reyhan Biruni calculated the radius of the Earth, which turned out to be equal to 6340 km.
For the first time, an accurate calculation of the shape and size of the geoid was made in 1940 by A.A. Izotov. The figure he calculated was named after the famous Russian surveyor F.N. Krasovsky, the Krasovsky ellipsoid. These calculations showed that the figure of the Earth is a triaxial ellipsoid and differs from an ellipsoid of revolution.
According to measurements, the Earth is a ball flattened at the poles. The equatorial radius (semi-major axis of the ellipslide - a) is equal to 6378 km 245 m, the polar radius (semi-minor axis - b) is 6356 km 863 m. The difference between the equatorial and polar radii is 21 km 382 m. Compression of the Earth (ratio of the difference between a and b to a) is (a-b)/a=1/298.3. In cases where greater accuracy is not required, the average radius of the Earth is taken to be 6371 km.
Modern measurements show that the surface of the geoid slightly exceeds 510 million km, and the volume of the Earth is approximately 1.083 billion km. The determination of other characteristics of the Earth - mass and density - is carried out on the basis of the fundamental laws of physics. Thus, the mass of the Earth is 5.98 * 10 tons. The average density value turned out to be 5.517 g/cm.
General structure of the Earth
To date, according to seismological data, about ten interfaces have been identified in the Earth, indicating the concentric nature of its internal structure. The main of these boundaries are: the Mohorovicic surface at depths of 30-70 km on the continents and at depths of 5-10 km under the ocean floor; Wiechert-Gutenberg surface at a depth of 2900 km. These main boundaries divide our planet into three concentric shells - the geosphere:
The Earth's crust is the outer shell of the Earth located above the surface of Mohorovicic;
The Earth's mantle is an intermediate shell limited by the Mohorovicic and Wiechert-Gutenberg surfaces;
The Earth's core is the central body of our planet, located deeper than the Wiechert-Gutenberg surface.
In addition to the main boundaries, a number of secondary surfaces within geospheres are distinguished.
Earth's crust. This geosphere makes up a small fraction of the total mass of the Earth. Based on thickness and composition, three types of the earth’s crust are distinguished:
The continental crust is characterized by a maximum thickness reaching 70 km. It is composed of igneous, metamorphic and sedimentary rocks, which form three layers. The thickness of the upper layer (sedimentary) usually does not exceed 10-15 km. Below lies a granite-gneiss layer 10-20 km thick. In the lower part of the crust lies a balsat layer up to 40 km thick.
The oceanic crust is characterized by low thickness - decreasing to 10-15 km. It also consists of 3 layers. The upper, sedimentary, does not exceed several hundred meters. The second, balsate, with a total thickness of 1.5-2 km. The lower layer of oceanic crust reaches a thickness of 3-5 km. This type of earth's crust does not contain a granite-gneiss layer.
The crust of transitional regions is usually characteristic of the periphery of large continents, where marginal seas are developed and there are archipelagos of islands. Here, the continental crust is replaced by oceanic one and, naturally, in terms of structure, thickness and density of rocks, the crust of the transition areas occupies an intermediate place between the two types of crust indicated above.
Earth's mantle. This geosphere is the largest element of the Earth - it occupies 83% of its volume and makes up about 66% of its mass. In the composition of the mantle, a number of interfaces are distinguished, the main of which are surfaces located at depths of 410, 950 and 2700 km. According to the values of physical parameters, this geosphere is divided into two subshells:
Upper mantle (from the Mohorovicic surface to a depth of 950 km).
Lower mantle (from a depth of 950 km to the Wiechert-Gutenberg surface).
The upper mantle, in turn, is divided into layers. The upper layer, which lies from the Mohorovicic surface to a depth of 410 km, is called the Gutenberg layer. Inside this layer, a hard layer and an asthenosphere are distinguished. The earth's crust, together with the solid part of the Gutenberg layer, forms a single hard layer lying on the asthenosphere, which is called the lithosphere.
Below the Gutenberg layer lies the Golitsin layer. Which is sometimes called the middle mantle.
The lower mantle has a significant thickness, almost 2 thousand km, and consists of two layers.
Earth's core. The Earth's central geosphere occupies about 17% of its volume and accounts for 34% of its mass. In the section of the core, two boundaries are distinguished - at depths of 4980 and 5120 km. Therefore, it is divided into three elements:
Outer core - from the Wiechert-Gutenberg surface to 4980 km. This substance, which is under high pressure and temperature, is not a liquid in the usual sense. But it has some of its properties.
The transition shell is in the interval 4980-5120 km.
Subcore - below 5120 km. Possibly in a solid state.
The chemical composition of the Earth is similar to that of other terrestrial planets<#"justify">· lithosphere (crust and uppermost part of the mantle)
· hydrosphere (liquid shell)
· atmosphere (gas shell)
About 71% of the Earth's surface is covered with water, its average depth is approximately 4 km.
Earth's atmosphere:
more than 3/4 is nitrogen (N2);
approximately 1/5 is oxygen (O2).
Clouds, consisting of tiny droplets of water, cover approximately 50% of the planet's surface.
The atmosphere of our planet, like its interior, can be divided into several layers.
· The lowest and densest layer is called the troposphere. There are clouds here.
· Meteors ignite in the mesosphere.
· Auroras and many orbits of artificial satellites are inhabitants of the thermosphere. There are ghostly silvery clouds hovering there.
Hypotheses of the origin of the Earth. First cosmogonic hypotheses
A scientific approach to the question of the origin of the Earth and the Solar system became possible after the strengthening in science of the idea of material unity in the Universe. The science of the origin and development of celestial bodies - cosmogony - emerges.
The first attempts to provide a scientific basis for the question of the origin and development of the solar system were made 200 years ago.
All hypotheses about the origin of the Earth can be divided into two main groups: nebular (Latin “nebula” - fog, gas) and catastrophic. The first group is based on the principle of the formation of planets from gas, from dust nebulae. The second group is based on various catastrophic phenomena (collisions of celestial bodies, close passage of stars from each other, etc.).
One of the first hypotheses was expressed in 1745 by the French naturalist J. Buffon. According to this hypothesis, our planet was formed as a result of the cooling of one of the clumps of solar matter ejected by the Sun during a catastrophic collision with a large comet. J. Buffon's idea about the formation of the Earth (and other planets) from plasma was used in a whole series of later and more advanced hypotheses of the “hot” origin of our planet.
Nebular theories. Kant and Laplace hypothesis
Among them, of course, the leading place is occupied by the hypothesis developed by the German philosopher I. Kant (1755). Independently of him, another scientist - the French mathematician and astronomer P. Laplace - came to the same conclusions, but developed the hypothesis more deeply (1797). Both hypotheses are similar in essence and are often considered as one, and its authors are considered the founders of scientific cosmogony.
The Kant-Laplace hypothesis belongs to the group of nebular hypotheses. According to their concept, in the place of the Solar system there was previously a huge gas-dust nebula (dust nebula made of solid particles, according to I. Kant; gas nebula, according to P. Laplace). The nebula was hot and rotating. Under the influence of the laws of gravity, its matter gradually became denser, flattened, forming a core in the center. This is how the primary sun was formed. Further cooling and compaction of the nebula led to an increase in the angular velocity of rotation, as a result of which at the equator the outer part of the nebula separated from the main mass in the form of rings rotating in the equatorial plane: several of them were formed. Laplace cited the rings of Saturn as an example.
Cooling unevenly, the rings ruptured, and due to the attraction between the particles, the formation of planets orbiting the Sun occurred. The cooling planets were covered with a hard crust, on the surface of which geological processes began to develop.
I. Kant and P. Laplace correctly noted the main and characteristic features of the structure of the Solar system:
) the overwhelming majority of the mass (99.86%) of the system is concentrated in the Sun;
) the planets revolve in almost circular orbits and in almost the same plane;
) all planets and almost all their satellites rotate in the same direction, all planets rotate around their axis in the same direction.
A significant achievement of I. Kant and P. Laplace was the creation of a hypothesis based on the idea of the development of matter. Both scientists believed that the nebula had a rotational motion, as a result of which particles became compacted and the formation of planets and the Sun occurred. They believed that movement is inseparable from matter and is as eternal as matter itself.
The Kant-Laplace hypothesis has existed for almost two hundred years. Subsequently, its inconsistency was proven. Thus, it became known that the satellites of some planets, for example Uranus and Jupiter, rotate in a different direction than the planets themselves. According to modern physics, gas separated from the central body must dissipate and cannot form into gas rings, and later into planets. Other significant shortcomings of the Kant-Laplace hypothesis are the following:
It is known that the angular momentum in a rotating body always remains constant and is distributed evenly throughout the body in proportion to the mass, distance and angular velocity of the corresponding part of the body. This law also applies to the nebula from which the Sun and planets were formed. In the Solar System, the amount of motion does not correspond to the law of distribution of the amount of motion in the mass arising from one body. The planets of the Solar System concentrate 98% of the angular momentum of the system, and the Sun has only 2%, while the Sun accounts for 99.86% of the total mass of the Solar System.
If we add up the rotational moments of the Sun and other planets, then in calculations it turns out that the primary Sun rotated at the same speed with which Jupiter now rotates. In this regard, the Sun should have had the same compression as Jupiter. And this, as calculations show, is not enough to cause fragmentation of the rotating Sun, which, as Kant and Laplace believed, disintegrated due to excess rotation.
It has now been proven that a star with excess rotation breaks up into pieces rather than forming a family of planets. An example is spectral binary and multiple systems.
Catastrophic theories. Jeans conjecture
earth cosmogonic concentric origin
After the Kant-Laplace hypothesis in cosmogony, several more hypotheses for the formation of the Solar system were created.
The so-called catastrophic ones appear, which are based on an element of chance, an element of a happy coincidence:
Unlike Kant and Laplace, who “borrowed” from J. Buffon only the idea of the “hot” emergence of the Earth, the followers of this movement also developed the hypothesis of catastrophe itself. Buffon believed that the Earth and planets were formed due to the collision of the Sun with a comet; Chamberlain and Multon - the formation of planets is associated with the tidal influence of another star passing by the Sun.
As an example of a catastrophic hypothesis, consider the concept of the English astronomer Jeans (1919). His hypothesis is based on the possibility of another star passing near the Sun. Under the influence of its gravity, a stream of gas escaped from the Sun, which, with further evolution, turned into the planets of the solar system. The gas stream was shaped like a cigar. In the central part of this body rotating around the Sun, large planets were formed - Jupiter and Saturn, and at the ends of the “cigar” - the terrestrial planets: Mercury, Venus, Earth, Mars, Pluto.
Jeans believed that the passage of a star past the Sun, which caused the formation of the planets of the Solar System, explains the discrepancy in the distribution of mass and angular momentum in the Solar System. The star, which tore a gas stream from the Sun, gave the rotating “cigar” an excess of angular momentum. Thus, one of the main shortcomings of the Kant-Laplace hypothesis was eliminated.
In 1943, Russian astronomer N.I. Pariysky calculated that at a high speed of a star passing by the Sun, the gas prominence should have left along with the star. At the low speed of the star, the gas jet should have fallen onto the Sun. Only in the case of a strictly defined speed of the star could a gas prominence become a satellite of the Sun. In this case, its orbit should be 7 times smaller than the orbit of the planet closest to the Sun - Mercury.
Thus, the Jeans hypothesis, like the Kant-Laplace hypothesis, could not provide a correct explanation for the disproportionate distribution of angular momentum in the Solar System
The biggest drawback of this hypothesis is the fact of chance, the exclusivity of the formation of the family of planets, which contradicts the materialistic worldview and the available facts indicating the presence of planets in other stellar worlds.
In addition, calculations have shown that the convergence of stars in cosmic space is practically impossible, and even if this happened, a passing star could not give the planets movement in circular orbits.
Modern hypotheses
A fundamentally new idea lies in the hypotheses of the “cold” origin of the Earth. The most deeply developed meteorite hypothesis was proposed by the Soviet scientist O.Yu. Schmidt in 1944. Other hypotheses of “cold” origin include the hypotheses of K. Weizsäcker (1944) and J. Kuiper (1951), which are in many ways close to the theory of O. Yu. Schmidt, F. Foyle (England), A. Cameron (USA ) and E. Schatzman (France).
The most popular are the hypotheses about the origin of the solar system created by O.Yu. Schmidt and V.G. Fesenkov. Both scientists, when developing their hypotheses, proceeded from ideas about the unity of matter in the Universe, about the continuous movement and evolution of matter, which are its main properties, about the diversity of the world, due to various forms of existence of matter.
Hypothesis O.Yu. Schmidt
According to the concept of O.Yu. Schmidt, the Solar system was formed from an accumulation of interstellar matter captured by the Sun in the process of moving in cosmic space. The Sun moves around the center of the Galaxy, completing a full revolution every 180 million years. Among the stars of the Galaxy there are large accumulations of gas-dust nebulae. Based on this, O.Yu. Schmidt believed that the Sun, when moving, entered one of these clouds and took it with it. The rotation of the cloud in the strong gravitational field of the Sun led to a complex redistribution of meteorite particles by mass, density and size, as a result of which some of the meteorites, the centrifugal force of which turned out to be weaker than the force of gravity, were absorbed by the Sun. Schmidt believed that the original cloud of interstellar matter had some rotation, otherwise its particles would have fallen into the Sun.
The cloud turned into a flat, compacted rotating disk, in which, due to an increase in the mutual attraction of particles, condensation occurred. The resulting condensed bodies grew due to small particles joining them, like a snowball. During the process of cloud circulation, when particles collided, they began to stick together, form larger aggregates and join them - accretion of smaller particles falling into the sphere of their gravitational influence. In this way, planets and satellites orbiting around them were formed. The planets began to rotate in circular orbits due to the averaging of the orbits of small particles.
The earth, according to O.Yu. Schmidt, was also formed from a swarm of cold solid particles. The gradual heating of the Earth's interior occurred due to the energy of radioactive decay, which led to the release of water and gas, which were included in small quantities in the composition of solid particles. As a result, oceans and an atmosphere arose, which led to the emergence of life on Earth.
O.Yu. Schmidt, and later his students, gave a serious physical and mathematical substantiation of the meteorite model of the formation of the planets of the solar system. The modern meteorite hypothesis explains not only the peculiarities of the movement of planets (shape of orbits, different directions of rotation, etc.), but also their actually observed distribution of mass and density, as well as the ratio of planetary angular momentum to the solar one. The scientist believed that the existing discrepancies in the distribution of angular momentum of the Sun and the planets are explained by different initial angular momentum of the Sun and the gas-dust nebula. Schmidt calculated and mathematically substantiated the distances of the planets from the Sun and between themselves and found out the reasons for the formation of large and small planets in different parts of the Solar System and the difference in their composition. Through calculations, the reasons for the rotational motion of planets in one direction are substantiated.
The disadvantage of the hypothesis is that it considers the origin of the planets in isolation from the formation of the Sun, the defining member of the system. The concept is not without an element of chance: the capture of interstellar matter by the Sun. Indeed, the possibility of the Sun capturing a sufficiently large meteorite cloud is very small. Moreover, according to calculations, such capture is possible only with the gravitational assistance of a nearby star. The probability of a combination of such conditions is so insignificant that it makes the possibility of the Sun capturing interstellar matter an exceptional event.
Hypothesis V.G. Fesenkova
The work of astronomer V.A. Ambartsumyan, who proved the continuity of star formation as a result of condensation of matter from rarefied gas-dust nebulae, allowed academician V.G. Fesenkov to put forward a new hypothesis (1960) linking the origin of the Solar system with the general laws of matter formation in space space. Fesenkov believed that the process of planet formation is widespread in the Universe, where there are many planetary systems. In his opinion, the formation of planets is associated with the formation of new stars that arise as a result of the condensation of initially rarefied matter within one of the giant nebulae (“globules”). These nebulae were very rarefied matter (density of the order of 10 g/cm) and consisted of hydrogen, helium and a small amount of heavy metals. First, the Sun formed at the core of the “globule,” which was a hotter, more massive, and faster-rotating star than it is today. The evolution of the Sun was accompanied by repeated ejections of matter into the protoplanetary cloud, as a result of which it lost part of its mass and transferred a significant share of its angular momentum to the forming planets. Calculations show that with non-stationary ejections of matter from the depths of the Sun, the actually observed ratio of the moments of momentum of the Sun and the protoplanetary cloud (and therefore the planets) could have developed. The simultaneous formation of the Sun and planets is proven by the same age of the Earth and the Sun.
As a result of the compaction of the gas-dust cloud, a star-shaped condensation was formed. Under the influence of the rapid rotation of the nebula, a significant part of the gas-dust matter moved increasingly away from the center of the nebula along the equatorial plane, forming something like a disk. Gradually, the compaction of the gas-dust nebula led to the formation of planetary concentrations, which subsequently formed the modern planets of the Solar System. Unlike Schmidt, Fesenkov believes that the gas-dust nebula was in a hot state. His great merit is the substantiation of the law of planetary distances depending on the density of the medium. V.G. Fesenkov mathematically substantiated the reasons for the stability of the angular momentum in the Solar System by the loss of matter of the Sun when selecting matter, as a result of which its rotation slowed down. V.G. Fesenkov also argues in favor of the reverse motion of some satellites of Jupiter and Saturn, explaining this by the capture of asteroids by the planets.
Fesenkov attached great importance to the processes of radioactive decay of the isotopes K, U, Th and others, the content of which was then much higher.
To date, a number of options for radiotogenic heating of the subsoil have been theoretically calculated, the most detailed of which was proposed by E.A. Lyubimova (1958). According to these calculations, after one billion years, the temperature of the Earth's interior at a depth of several hundred kilometers reached the melting point of iron. Apparently, this time marks the beginning of the formation of the Earth's core, represented by metals - iron and nickel - that descended to its center. Later, with a further increase in temperature, the most fusible silicates began to melt from the mantle, which, due to their low density, rose upward. This process, studied theoretically and experimentally by A.P. Vinogradov, explains the formation of the earth’s crust.
It is also worth noting two hypotheses that developed towards the end of the 20th century. They considered the development of the Earth without affecting the development of the Solar system as a whole.
The earth was completely molten and, in the process of depleting internal thermal resources (radioactive elements), gradually began to cool. A hard crust has formed in the upper part. And as the volume of the cooled planet decreased, this crust broke, and folds and other relief forms formed.
There was no complete melting of matter on Earth. In a relatively loose protoplanet, local centers of melting formed (this term was introduced by Academician Vinogradov) at a depth of about 100 km.
Gradually, the amount of radioactive elements decreased, and the temperature of the LOP decreased. The first high-temperature minerals crystallized from the magma and fell to the bottom. The chemical composition of these minerals was different from the composition of the magma. Heavy elements were extracted from magma. And the residual melt was relatively enriched in light. After phase 1 and a further decrease in temperature, the next phase of minerals crystallized from the solution, also containing more heavy elements. This is how the gradual cooling and crystallization of the LOPs occurred. From the initial ultramafic composition of the magma, magma of basic balsic composition was formed.
A fluid cap (gas-liquid) formed in the upper part of the LOP. Balsate magma was mobile and fluid. It broke through from the LOPs and poured onto the surface of the planet, forming the first hard basalt crust. The fluid cap also broke through to the surface and, mixing with the remains of primary gases, formed the first atmosphere of the planet. The primary atmosphere contained nitrogen oxides. H, He, inert gases, CO, CO, HS, HCl, HF, CH, water vapor. There was almost no free oxygen. The temperature of the Earth's surface was about 100 C, there was no liquid phase. The interior of the rather loose protoplanet had a temperature close to the melting point. Under these conditions, heat and mass transfer processes inside the Earth proceeded intensively. They occurred in the form of thermal convection currents (TCFs). TCPs arising in the surface layers are especially important. Cellular thermal structures developed there, which at times were rebuilt into a single-cell structure. The ascending TCPs transmitted the impulse of motion to the surface of the planet (balsat crust), and a stretch zone was created on it. As a result of stretching, a powerful extended fault with a length of 100 to 1000 km is formed in the TKP uplift zone. They were called rift faults.
The temperature of the planet's surface and its atmosphere cools below 100 C. Water condenses from the primary atmosphere and the primary hydrosphere is formed. The Earth's landscape is a shallow ocean with a depth of up to 10 m, with individual volcanic pseudo-islands exposed during low tides. There was no permanent sushi.
With a further decrease in temperature, the LOPs completely crystallized and turned into hard crystalline cores in the bowels of a rather loose planet.
The surface cover of the planet was subject to destruction by aggressive atmosphere and hydrosphere.
As a result of all these processes, the formation of igneous, sedimentary and metamorphic rocks occurred.
Thus, hypotheses about the origin of our planet explain modern data on its structure and position in the solar system. And space exploration, launches of satellites and space rockets provide many new facts for practical testing of hypotheses and further improvement.
Literature
1. Questions of cosmogony, M., 1952-64
2. Schmidt O. Yu., Four lectures on the theory of the origin of the Earth, 3rd ed., M., 1957;
Levin B. Yu. Origin of the Earth. "Izv. Academy of Sciences of the USSR Physics of the Earth", 1972, No. 7;
Safronov V.S., Evolution of the preplanetary cloud and the formation of the Earth and planets, M., 1969; .
Kaplan S. A., Physics of Stars, 2nd ed., M., 1970;
Problems of modern cosmogony, ed. V. A. Ambartsumyan, 2nd ed., M., 1972.
Arkady Leokum, Moscow, “Julia”, 1992
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