Introduction
1. Hypotheses of the origin of the Earth and their justification
2. Formation of the inner shells of the Earth in the process of its geological evolution
2.1 The main stages of the evolution of the Earth
2.2 Inner shells of the Earth
3. The emergence of the Earth's atmosphere and hydrosphere and their role in the emergence of life
3.1 Hydrosphere
3.2 Atmosphere
Conclusion
Bibliography
Introduction
Planet Earth was formed about 4.6 billion years ago. There are many hypotheses about the formation of the planet. Modern hypotheses are based on the concept of planetary formation put forward by Kant and Laplace.
The modern appearance of the Earth is significantly different from the original. In its evolution, the Earth went through several stages, which are usually divided into eras, periods, etc. For example, we are now living in the Cenozoic era, which has already lasted 67 million years, which is not so much compared to other periods. In the course of evolution, the planet has undergone repeated changes. At present, considering the structure of the Earth, one can make sure that it is a series of spherical shells. The outermost shell is the gaseous atmosphere, then comes the liquid shell - the hydrosphere, which partially covers the bulk of the planet - the lithosphere.
The lithosphere and atmosphere are divided into a number of spherical layers, not identical in their physical properties. So the lithosphere consists of the earth's crust, mantle and core, the following layers are distinguished in the atmosphere: troposphere, stratosphere, mesosphere and thermosphere.
1. Hypotheses of the origin of the Earth and their justification
Modern hypotheses of the formation of the Earth and other planets Solar system based on the one advanced in the 18th century. I. Kant (Germany) and, independently of him, P. Laplace (France) of the concept of the formation of planets from dusty matter and a gas nebula, later this hypothesis was called Kant-Laplace. In the 20th century. this concept was developed by O. Yu. Schmidt (USSR), K. Weizsacker (Germany), F. Foyle (England), A. Cameron (USA) and E. Shatzman (France).
Kant and Laplace drew attention to the fact that the sun is hot, and the earth is cold and much smaller in size than the sun. All planets revolve in circles, in the same direction and in almost the same plane. This constitutes the main distinguishing features of the solar system.
Kant and Laplace argued that in nature everything is constantly changing and developing. Both the Earth and the Sun were not what they are now, and their constituent substance existed in a completely different form.
Laplace substantiated his hypothesis more convincingly. He believed that once there was no solar system, but there was a primary rarefied and incandescent gas nebula with a compaction in the center. It rotated slowly, and its dimensions were larger than the diameter of the planet farthest from the Sun now. The gravitational attraction of nebula particles to each other led to the contraction of the nebula and a decrease in its size. According to the law of conservation of angular momentum, when a rotating body is compressed, its rotation speed increases. Therefore, as the nebula rotated, a large number of particles at its equator (which rotated faster than at the poles) detached, or, more precisely, exfoliated from it. A rotating ring appeared around the nebula. At the same time, the nebula, spherical at first, due to the centrifugal flattened at the poles and became like a lens.
All the time, contracting and accelerating its rotation, the nebula gradually peeled off from itself ring by ring, which rotated in the same direction and in the same plane. The gas rings had density inhomogeneities. The greatest concentration in each of the rings gradually attracted the rest of the ring material. So each ring turned into one large ball of gas, rotating around its axis. After that, the same thing was repeated with it as with the huge primordial nebula: it turned into a relatively small sphere surrounded by rings, which again condensed into small bodies. The latter, having cooled down, became satellites of large gas balls orbiting the Sun and, after solidification, turned into planets. Most of the nebulae are concentrated in the center; it has not cooled down until now and has become the Sun.
Laplace's hypothesis was scientific, since it was based on the laws of nature, known from experience. However, after Laplace, new phenomena were discovered in the solar system that his theory could not explain. For example, it turned out that the planet Uranus rotates on its axis in the wrong direction, where the other planets rotate. The properties of gases and the features of the motion of the planets and their satellites were better studied. These phenomena also did not agree with Laplace's hypothesis and 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. 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, as a result of which a jet of gas was ejected from the surface layers of the Sun, from which the planets were subsequently formed. But the Jeans hypothesis, as well as the Kant-Laplace hypothesis, cannot explain the discrepancy in the distribution of the angular momentum between the planets and the Sun.
The famous Soviet scientist academician O. Yu Schmidt proposed a hypothesis, in the development of which astronomers, geophysicists, geologists and other scientists took part, and according to which the Earth and other planets have never been incandescent gaseous bodies like the Sun and stars, but should have been formed from cold particles of matter. These particles initially moved randomly. Then their orbits became circular and were located approximately in the same plane. In this case, the direction of rotation of the particles in any particular direction over time began to prevail, and, in the end, all the particles began to rotate in the same direction. As a result of the collision of particles during the initial disorderly motion, the energy of their motion was partially converted into heat and dissipated into space. Calculations showed that as a result of these processes, the spherical cloud gradually flattened and finally became similar in shape to a pancake. Further, the gravitational interaction led to the growth of larger particles by capturing small particles by them. Thus, most of the dust particles gathered into several giant lumps of matter, which became planets.
According to the estimates obtained by Schmidt, it took 6-7 billion years for the formation of the solar system, which agrees in order of magnitude with the data obtained as a result of isotopic analysis.
According to Schmidt's hypothesis, the Earth was never fiery liquid, and the heating of the inner region of the Earth occurred as a result of nuclear reactions of the decay of heavy elements that make up the original substance.
2. Formation of the inner shells of the Earth in the process of its geological evolution
2.1 The main stages of the evolution of the Earth
According to modern concepts, the history of the Earth is approximately 4.6 billion years old. Numerous results of the study of the earth's crust (the chemical composition and structure of rocks, their distribution over depth, the content of radioactive isotopes, the remains of fossil living organisms) made it possible to establish a picture of the formation and development of the planet, to determine the age of the biosphere.
The entire history of the Earth's existence is subdivided into time periods, each of which is characterized by certain physical, chemical, climatic conditions, as well as the stages of the evolution of living nature.
The time periods of the geochronological scale are subdivided into eons, eras, periods. The first, the earliest time period, called "katarchean" or "lunar period", corresponds to the formation of the Earth, its atmosphere, water environment. Life during the first 1-1.5 billion years did not exist in any form, since the corresponding physicochemical conditions had not yet emerged. At an early stage, intense tectonic processes took place, accompanied by a redistribution over the depth of the Earth chemical elements and connections. Nuclear decay reactions occurring in the center and deep layers of the planet contributed to the warming up of the Earth. The atmosphere was dominated by compounds of sulfur, chlorine, nitrogen, the oxygen content was hundreds of times less than now. The heavier elements moved towards the center of the Earth and then formed the core, the lighter ones towards the surface. Intensive volcanic and thunderstorm processes contributed to the formation of the aquatic environment - the first organic molecules began to form in it.
Geochronological scale 1
Archaea and Proterozoic are the two largest eras, during which life at the level of microorganisms began to form. These two eras are combined into "naderu" - cryptosis (time of latent life). The first multicellular organisms appeared at the very end of the Proterozoic about 600 million years ago.
Approximately 570 million years ago, when favorable conditions for life were practically formed on Earth, the rapid development of living organisms began. From that moment on, the "time of obvious life" came - phanerozoic. This segment of geological history is subdivided into 3 eras - Paleozoic, Mesozoic and Cenozoic. The last era, from the point of view of geo- and biology, continues to this day. It should be noted that the emergence and development of life on earth led to a significant change in the Earth's hard shell (lithosphere), hydrosphere and atmosphere, and the emergence of intelligent life (man) in a short time interval caused global changes in the evolution of the planet. The Mesozoic era is characterized by an active manifestation of magmatic activity, an intense process of mountain building. This era was dominated by dinosaurs.
Differences in the composition of rocks from one era to another, in turn, are due to abrupt changes in the natural, climatic and physical conditions on the planet. It was established that the climate on Earth changed many times, warming was replaced by sharp cold snaps, land was raised and lowered. Major space catastrophes also happened: collisions with meteorites, comets and asteroids. A large number of large meteorite craters have been discovered on Earth. The largest of them on the Yucatan Peninsula has a diameter of over 100 km; its age - 65 million years - practically coincides with the end of the Cretaceous and the beginning of the Paleogene period. Many paleontologists from this biggest disaster link the extinction of the dinosaurs.
Climate and temperature changes are largely due to astronomical factors: the tilt of the earth's axis (changed many times), disturbances of the giant planets, the activity of the Sun, the movement of the Solar system around the Galaxy. According to one of the hypotheses, abrupt climate changes occur every 210-215 million years (galactic year), when the solar system, revolving around the center of the Galaxy, passes through a cloud of gas and dust. This contributes to the weakening solar radiation and, as a consequence, cooling on the planet. At these moments, ice ages set in on Earth - polar caps appear and grow. The last ice age began about 5 million years ago and continues to this day. The Ice Age is characterized by periodic temperature fluctuations (once every 50 thousand years). During cold snaps (ice age), glaciers can spread from the poles to the equator up to 30-40 degrees. We are now living in the "interglacial" period of the Ice Age. The legacy of the Ice Age is the permafrost zone (in Russia, more than half of its territory).
2.2 Inner shells of the Earth
At present, as you know, the Earth has a core composed mainly of iron and nickel. Substances containing lighter elements (silicon, magnesium and others) gradually "floated up", forming the mantle and crust of the Earth. The lightest elements entered the composition of the oceans and the primary atmosphere of the Earth. The materials that make up the solid Earth are opaque and dense. Therefore, their research is possible only to depths that make up an insignificant part of the Earth's radius. The deepest drilled wells and currently available projects are limited to depths of 10-15 km, which is just over 0.1% of the radius. Therefore, information about the deep bowels of the Earth is obtained using only indirect methods. These include seismic, gravitational, magnetic, electrical, electromagnetic, thermal, nuclear and other methods 2. The most reliable of these is seismic. It is based on the observation of seismic waves that occur in the solid Earth during earthquakes. Seismic waves provide an opportunity to get an idea of internal structure Earth and about the change in the physical properties of the substance of the earth's interior with depth.
Seismic waves are of two types: longitudinal and transverse. In longitudinal waves, particles move along the direction, in transverse waves - perpendicular to this direction. The velocity of longitudinal waves is greater than that of transverse waves. When a seismic wave meets any interface, it is reflected and refracted. Observing seismic vibrations, it is possible to determine the depth of the boundaries at which the properties of rocks change, and the magnitude of the changes themselves.
Shear waves cannot propagate in a liquid medium; therefore, the presence of shear waves indicates that the lithosphere is solid down to great depths. However, starting from a depth of 3000 km, shear waves cannot propagate. Hence the conclusion: the inner part of the lithosphere forms a core, which is in a molten state. In addition, the core itself is still divided into two zones: an inner solid core and a liquid outer (layer between 2900 and 5100 km).
The hard shell of the Earth is also heterogeneous - it has a sharp interface at a depth of about 40 km. This boundary is called the Mohorovicic surface. The area above the surface of Mohorovich is called the crust, below the mantle.
The mantle extends to a depth of 2900 km. It is subdivided into 3 layers: upper, intermediate and lower. The upper layer, the asthenosphere, is characterized by a relatively low viscosity of the substance. The asthenosphere contains volcanic centers. A decrease in the melting temperature of the asthenosphere substance leads to the formation of magma, which can pour out onto the Earth's surface through cracks and channels of the earth's crust. The intermediate and lower layers are in a solid, crystalline state.
The upper layer of the earth is called crust and is subdivided into several layers. The uppermost layers of the earth's crust consist mainly of layers of sedimentary rocks formed by the deposition of various small particles, mainly in the seas and oceans. The remains of animals and plants that inhabited in the past are buried in these layers. Earth... The total thickness (thickness) of sedimentary rocks does not exceed 15-20 km.
The difference in the speed of propagation of seismic waves on the continents and on the ocean floor made it possible to conclude that there are two main types of the earth's crust on Earth: continental and oceanic.
The thickness of the continental crust is on average 30-40 km, under many mountains it reaches 80 km in places. Usually, two main layers are distinguished below sedimentary rocks: the upper one is “granite”, close in physical properties and composition to granite and the lower one, consisting of heavier rocks, “basalt” (it is assumed that it consists mainly of basalt). The thickness of each of these layers is on average 15-20 km. However, in many places it is not possible to establish the boundary between the granite and basalt layers.
The oceanic crust is much thinner (5-8 km). In composition and properties, it is close to that of the lower part of the basalt layer of the continents. But this type of crust is characteristic only of deep areas of the bottom of the oceans, not less than 4 thousand meters. At the bottom of the oceans there are areas where the crust has a structure of the continental or intermediate type.
3. The emergence of the Earth's atmosphere and hydrosphere and their role in the emergence of life
3.1 Hydrosphere
earth planet shell atmosphere hydrosphere
The hydrosphere is the totality of all water bodies of the Earth (oceans, seas, lakes, rivers, groundwater, swamps, glaciers, snow cover).
Most of the water is concentrated in the ocean, much less in the continental river network and groundwater. There are also large reserves of water in the atmosphere, in the form of clouds and water vapor. Over 96% of the volume of the hydrosphere are seas and oceans, about 2% - underground waters, about 2% - ice and snow, about 0.02% - surface waters sushi. Part of the water is in a solid state in the form of glaciers, snow cover and permafrost, representing the cryosphere 3. The bulk of the ice is located on dry land - mainly in Antarctica and Greenland. Its total mass is about 2.42 * 10 22 g. If This ice melted, then the level of the World Ocean would rise by about 60 m. In this case, 10% of the land would be flooded by the sea.
Surface waters occupy a relatively small share in the total mass of the hydrosphere.
The history of the formation of the hydrosphere
It is believed that when the Earth warms up, the crust, together with the hydrosphere and atmosphere, were formed as a result of volcanic activity - the release of lava, steam and gases from the inner parts of the mantle. It was in the form of steam that part of the water entered the atmosphere.
The value of the hydrosphere
The hydrosphere is in constant interaction with the atmosphere, earth's crust and biosphere. The circulation of water in the hydrosphere and its high heat capacity equalize climatic conditions at different latitudes. The hydrosphere supplies water vapor to the atmosphere; water vapor through infrared absorption creates a significant greenhouse effect , uplifting average temperature the surface of the Earth by about 40 ° C. The hydrosphere affects the climate in other ways as well. It stores large amounts of heat in summer and gradually releases it in winter, softening seasonal temperature fluctuations on the continents. It also transfers heat from equatorial regions to temperate and even polar latitudes.
Surface waters play a vital role in the life of our planet, being the main source of water supply, irrigation and water supply.
The presence of the hydrosphere played a decisive role in the origin of life on Earth. We now know that life originated in the oceans, and billions of years passed before land became habitable.
3.2 Atmosphere
The atmosphere is a shell of gas that surrounds the Earth and rotates with it as a whole. The atmosphere consists mainly of gases and various impurities (dust, water droplets, ice crystals, sea salts, combustion products). The concentration of gases that make up the atmosphere is practically constant, with the exception of water (H 2 O) and carbon dioxide (CO 2). The content of nitrogen by volume is 78.08%, oxygen - 20.95%, less argon, carbon dioxide, hydrogen, helium, neon and some other gases are contained. The lower part of the atmosphere also contains water vapor (up to 3% in the tropics), at an altitude of 20-25 km there is a layer of ozone, although its amount is small, but its role is very significant.
The history of the formation of the atmosphere.
The atmosphere was formed mainly from gases released by the lithosphere after the formation of the planet. Over billions of years, the Earth's atmosphere has undergone significant evolution under the influence of numerous physicochemical and biological processes: dissipation of gases into outer space, volcanic activity, dissociation (splitting) of molecules as a result of solar ultraviolet radiation, chemical reactions between atmospheric components and rocks, respiration, and metabolism of living organisms. So the modern composition of the atmosphere is significantly different from the primary, which took place 4.5 billion years ago, when the crust was formed. According to the most common theory, the Earth's atmosphere over time was in four different compositions. It originally consisted of light gases (hydrogen and helium) captured from interplanetary space. This is the so-called primary atmospheres (570-200 million years BC). At the next stage, active volcanic activity led to saturation of the atmosphere with gases other than hydrogen (hydrocarbons, ammonia, water vapor). This is how the secondary atmosphere was formed (200 million years ago - present day). The atmosphere was restorative. Further, the process of the formation of the atmosphere was determined by the following factors:
constant leakage of hydrogen into interplanetary space;
chemical reactions in the atmosphere under the influence of ultraviolet radiation, lightning discharges and some other factors.
Gradually, these factors led to the formation of a tertiary atmosphere, characterized by much less hydrogen and much more nitrogen and carbon dioxide (formed as a result of chemical reactions from ammonia and hydrocarbons).
With the appearance of living organisms on Earth, as a result of photosynthesis, accompanied by the release of oxygen and the absorption of carbon dioxide, the composition of the atmosphere began to change. Initially, oxygen was spent on the oxidation of reduced compounds - hydrocarbons, the ferrous form of iron contained in the oceans, etc. At the end of this stage, the oxygen content in the atmosphere began to grow. Gradually, a modern atmosphere with oxidizing properties was formed.
During the Phanerozoic, the composition of the atmosphere and the oxygen content underwent changes. Thus, during periods of coal accumulation, the oxygen content in the atmosphere significantly exceeded the current level. The carbon dioxide content may have increased during periods of intense volcanic activity. Recently, man has also begun to influence the evolution of the atmosphere. The result of his activities was a constant significant increase in the content of carbon dioxide in the atmosphere due to the combustion of hydrocarbon fuels.
The structure of the atmosphere.
The atmosphere has a layered structure. The troposphere, stratosphere, mesosphere and thermosphere are distinguished. The troposphere accounts for about 80% of the mass of the atmosphere, the stratosphere - about 20%; the mass of the mesosphere is no more than 0.3%, the thermosphere is less than 0.05% of the total mass of the atmosphere.
The troposphere is the lower, most studied layer of the atmosphere, with a height in the polar regions of 8 - 10 km, in temperate latitudes up to 10 - 12 km, at the equator - 16 - 18 km. The troposphere contains about 80-90% of the entire mass of the atmosphere and almost all water vapor. In the troposphere, physical processes take place that determine this or that weather. All transformations of water vapor take place in the troposphere. Clouds are formed in it and precipitation, cyclones and anticyclones are formed, turbulent and convective mixing is very strongly developed.
Above the troposphere is the stratosphere. The stratosphere is characterized by constant or increasing temperature with altitude and exceptional dryness of the air, there is almost no water vapor. The processes in the stratosphere have practically no effect on the weather. The stratosphere is located at an altitude of 11 to 50 km. A slight change in temperature in the layer of 11-25 km (the lower layer of the stratosphere) and its increase in the layer 25-40 km from -56.5 to 0.8 ° C (upper layer of the stratosphere) are characteristic. Having reached a value of about 0 ° C at an altitude of about 40 km, the temperature remains constant up to an altitude of about 55 km. This region of constant temperature is called the stratopause and is the boundary between the stratosphere and the mesosphere. It is in the stratosphere that the ozone layer ("ozone layer") is located (at an altitude of 15-20 to 55-60 km), which determines the upper limit of life in the biosphere.
An important component of the stratosphere and mesosphere is O 3, which is formed as a result of photochemical reactions most intensively at an altitude of ~ 30 km. The total mass of O 3 at normal pressure would be a layer 1.7-4.0 mm thick, but even this is sufficient to absorb the UV radiation of the Sun, which is destructive for life.
The next layer above the stratosphere is the mesosphere. The mesosphere begins at an altitude of 50 km and extends up to 80-90 km. The air temperature drops to an altitude of 75-85 km to -88 ° С. The upper boundary of the mesosphere is the mesopause, where the temperature minimum is located, above the temperature begins to rise again. Next, a new layer begins, which is called the thermosphere. Its temperature rises rapidly, reaching 1000 - 2000 ° C at an altitude of 400 km. Above 400 km, the temperature hardly changes with altitude. Air temperature and density are highly dependent on the time of day and year, as well as on solar activity. During the years of maximum solar activity, the temperature and air density in the thermosphere are significantly higher than in the years of minimum.
Next is the exosphere. Gas in the exosphere is very rarefied, and from here comes the leakage of its particles into interplanetary space (dissipation). Further, the exosphere gradually passes into the so-called near-space vacuum, which is filled with highly rarefied particles of interplanetary gas, mainly hydrogen atoms. But this gas is only a fraction of the interplanetary matter. The other part is made up of dust-like particles of cometary and meteoric origin. In addition to extremely rarefied dust-like particles, electromagnetic and corpuscular radiation of solar and galactic origin penetrates into this space.
The meaning of the atmosphere.
The atmosphere supplies us with the oxygen we need to breathe. Already at an altitude of 5 km above sea level, an untrained person develops oxygen starvation and without adaptation, the person's working capacity is significantly reduced. This is where the physiological zone of the atmosphere ends.
Dense layers of air - troposphere and stratosphere - protect us from the damaging effects of radiation. With sufficient rarefaction of air, at altitudes of more than 36 km, an intense effect on the body has ionizing radiation- primary cosmic rays; at altitudes of more than 40 km, the ultraviolet part of the solar spectrum, which is dangerous for humans, operates.
Ozone in the upper atmosphere serves as a kind of shield that protects us from the action of ultraviolet radiation from the Sun. Without this shield, the development of life on land in its modern forms would hardly be possible.
Conclusion
Planet Earth was formed about 4.6 billion years ago and went through several stages of evolution. During these periods, the surface of the planet was constantly changing: the formation of the planet's relief took place, a water shell appeared - a hydrosphere, a gas shell - an atmosphere. The emergence of the hydrosphere and atmosphere was the beginning of the emergence of life on the planet. So it is in aquatic environment the first living organisms were born, the appearance of the atmosphere contributed to their emergence on land. And today earthquakes, volcanic eruptions constantly occur on the Earth, the Earth's surface is constantly influenced not only by internal processes, but also by external ones (erosion under the influence of wind, water, glaciers, etc.), human activities also have a huge impact - this suggests that our planet continues to evolve, and in a few thousand years or more, its appearance and state may change on a large scale.
Astronomy Mathematics education she ... Earth due to the fact that after its education to the present day biosphere planets... allows life to develop on these planets. Planet Land like other space ...
Characteristic planets Land Four closest to the sun planets are called planets type Of the earth, Unlike planets-giants - Jupiter, Saturn ... by accident. It is associated with history education and development planets... Pluto, still little studied, is close ...
Scientists (Shklovsky, 1984, et al.) Associate the beginning of the formation of our Universe with the Big Bang about 12 billion years ago, which, of the only elementary nuclear particles and photons that existed in outer space before that, gave rise to a huge mass of the lightest elements - hydrogen and helium. possibly also other light elements - lithium, beryllium, boron. Immediately after the explosion, these elements existed in the form of a more or less homogeneous hydrogen-helium plasma, that is, an ionized gas with a temperature of about 4000 ° C with an average negligible density of 3000 particles per 1 cm3. The radius of the plasma cloud was initially about 15 million light years, but as a result of the Big Bang, the Universe is rapidly expanding, and its modern diameter is estimated at 20 billion light years, i.e., light moving at a speed of about 300 thousand km / s, will fly the distance from one edge of the starry world visible to us to the other edge in 20 billion years - so incredibly huge are the dimensions of our Universe.
From this simplest hydrogen-helium plasma, in the course of its further evolution, a whole huge variety of chemical substances... The main mechanism of this evolution, accompanied by the continuous complication of the Universe, was the focal cooling of the initially homogeneous plasma, which generated certain areas of gravitational condensation of matter in it. As a result, the plasma disintegrated into huge clumps, from which later clusters of galaxies were formed, then the galaxies themselves and then stellar and planetary-stellar systems, the formation of which continues at the present time.
With the appearance of stars, the further evolution of the chemical composition of the Universe began. Inside stars, light chemical elements were transformed into other, heavier, currently existing elements due to thermonuclear fusion - the fusion of nuclei of lighter elements, their combustion in the interiors of stars and during the final explosions of fairly large supernovae (Taylor, 1975). With such explosions, the The dispersed chemical elements were thrown into outer space, and then they became part of the stars of a new generation, that is, the process of the formation of elements was multiple.
This formation of elements took place only in stars with a critical mass of at least 0.3 times the mass of our Sun. With a smaller mass, cosmic bodies remain at the planetary stage of development and emit only the thermal energy of their gravitational compression; with a greater mass in their depths, the development of thermonuclear reactions with the formation of new chemical elements becomes possible. These reactions are accompanied by the release of energy, which prevents the compression of stars and ensures their luminosity.
The synthesis of these elements is currently taking place in the bowels of our Sun, which was formed together with the surrounding planetary system about 5 billion years ago. The sun is an ordinary small star (yellow dwarf). There are several billion such stars in our galaxy. All of them change little over time, referring to the type of long-lived stars, in contrast to more massive, rapidly evolving stars with short lifetimes. In stellar evolution, young stars arise by concentrating the matter of gas-dust nebulae that formed in the interiors of stars of earlier generations, so that they include more and more heavy chemical elements that have arisen as a result of nuclear fusion in the interiors and during explosions of stars of previous generations. The sun, in the photosphere of which 75 chemical elements are found, inherited the chemical composition of cosmic matter from the period of the previous stellar evolution.
Directly the formation of the solar system and planet Earth according to modern concepts, for example, in accordance with the cometary hypothesis of A. A. Marakushev (1992), proceeded as follows. At first, there was a gas-dust nebula in the form of a giant disk-shaped rotating cloud, consisting of small dusty iron-silicate particles and gases - hydrogen and water. As the temperature in this cloud decreased, the gases began to turn into a solid ice state and freeze onto iron-silicate dust grains, increasing the size of solid particles with the formation of comet-like ice particles. In the latter, more than 90% of the substance is ice of water or hydrogen composition, and the rest is small iron-silicate inclusions. This is the composition of typical comets. Subsequently, cometary matter, present in the form of chaotically moving, colliding particles, began to concentrate in the form of condensations, maximum in volume in the center of the nebula - in the place of the modern Sun, and smaller ones along the periphery - in the place of modern planets. In these condensations, the gravitational attraction of small particles by larger ones took place and their subsequent growth into larger comets, asteroids and further to the planets and the Sun. This process is called accretion.
The largest condensation was the Sun in the center of the protosol - nebula, where a very large stellar mass of matter was concentrated, which, at its concentration, contributed to the release of a large amount of heat due to the gravitational compression of masses during accretion. This heat turned out to be enough to start the development of thermonuclear reactions of burning hydrogen and helium, as a result of which the Sun acquired a high temperature and luminosity like a star, influencing the surrounding planets with its light and heat.
When initially scattered cometary particles were pulled together into solid planets, for example, the Earth, and these particles fell onto its surface, the thermal accretionary energy of gravitational pulling was released without thermonuclear reactions. Due to the small mass of the planet, this only led to its warming up to a molten state and stratification into a fluid hydrogen shell and an iron-silicate core, which, in turn, was further stratified into an iron-nickel core and a silicate shell by specific gravity. Maintaining high temperature contributed, in particular, this outer fluid shell, which, like a fur coat, prevented the removal of heat into outer space, released during the compression and compaction of particles falling on the Earth. As a result of melting and stratification, the planet acquired a regular spherical shape. The speed of the Earth's rotation at this time accelerated due to the concentration of heavier masses in the core, which allowed centrifugal forces to throw out part of the molten material outside the planet and thus form asteroids, meteorites and its satellite - the Moon. Subsequently, the hydrogen fluid shell of the Earth underwent surface degassing under the influence of solar luminosity and disappeared in outer space, exposing the iron-silicate molten skeleton of the Earth, where, from that moment, the geological processes of the formation of the earth's crust began and, as it cooled, its own atmosphere.
With the cooling of the molten Earth, the beginning of the formation of the earth's crust is associated, which is a relatively thin (560 km) hard shell, which is only 1/200 of the radius of the globe in thickness. The earth's crust is underlain by a mantle about 3000 km thick; from a depth of 120-150 km, the so-called astheno - spheral layer with increased plasticity of rocks begins.
An increase in the density of rocks is observed from top to bottom into the interior of the Earth. The earth's crust consists of three shells (Fig. 20). The upper sedimentary layer with a density of 2.2-2.5 g / cm3 is composed of various sedimentary rocks formed by deposition in marine conditions or on land. Its thickness is from the first meters to 20 km. Under it lies a granite-metamorphic (or simply granite) layer with a density of 2.4-2.7 g / cm3, formed by igneous rocks of predominantly granitoid felsic composition, gneisses, crystalline schists. The layer thickness usually does not exceed 25 km. The lower part of the section of the earth's crust is composed of a basalt layer with a thickness of up to 20 km and a density of 2.7-2.9 g / cm3. It is formed by igneous rocks of basaltic and gabbro composition and their metamorphosed analogs.
The rocks of the mantle are even denser - 2.9-3.2 g / cm3. They are presumably represented by ultrabasic rocks (periotites, dunites) or rocks of pyroxene-garnet composition (eclogites).
The increase in density is associated with a corresponding increase in the amount of heavier elements (iron, calcium) in the rocks and a corresponding decrease in the amount of light elements (primarily silicon, which moves to the upper horizons of the earth's crust).
There are two main types of the structure of the earth's crust - continental and oceanic. The first is developed within the continents and large islands, and the second - in the depressions of the oceans.
A feature of the continental crust is the increased thickness of all three layers, and primarily the lightest granite and sedimentary. Therefore, continents are elevated areas earth surface, rising and floating like icebergs above the water surface, only in this case the role of water is played by the viscous asthenosphere of the mantle. The earth's crust reaches its greatest thickness under the highest mountain systems - the Himalayas, Andes, the Caucasus, Tien Shan, Pamir, i.e., the height is isostatically balanced by the corresponding thickness of the lighter crust.
In the oceans, the earth's crust is thin, there is no granite layer, the sedimentary layer is composed of deep-water siliceous-clayey and siliceous-carbonate deposits, and the basaltic layer is composed of basaltic lavas.
In addition to these two main types of the earth's crust, transitional types are distinguished - mid-oceanic, with reduced thickness
Basalt and sedimentary layers, suboceanic with a thick sedimentary layer and subcontinental with a thin granite layer.
The change of crustal layers occurs within the continental slope. Towards the ocean floor and the basins of the marginal seas, the granite layer is thinning and pinching out under the continental slope. Areas of distribution of suboceanic and subcontinental types of the earth's crust spatially gravitate towards the periphery The Pacific, forming an area of vast ocean margins. This area consists of basins of the marginal seas, deep-sea trenches and island arcs separating them. It is she who is considered as the standard of areas where the transformation of the oceanic crust into the continental - the modern geosynclinal area is currently taking place.
In accordance with the geosynclinal theory of the formation of the earth's crust, the formation of large areas of land - continents - currently protruding above the surface of the oceans - occurs through the transformation of the oceanic crust into continental in the course of the geosynclinal process, in which two stages are distinguished: the geosynclinal proper and the orogenic. During the first, the earth's surface is predominantly submerged below ocean level to rather large depths with a simultaneous intense outpouring of basic and intermediate lavas (basalts and andesites), intrusion of basic and ultrabasic intrusions (peridotites, dunites, diabases), deposition of thick deep-water strata on the seabed siliceous, siliceous-carbonate, flysch, jasper, slate sediments. This is now happening on the outskirts of the Pacific Ocean, and in particular in the Kamchatka region and Kuril Islands and adjacent areas of the ocean. During the second stage, the uplift of geosynclinal areas, mountain building, strong collapse, folding and metamorphism of the previously formed sedimentary-volcanic strata and the widespread development of coarse-detrital deposits (molasses) in the depressions between the growing mountain uplifts; the most important feature is the introduction of large felsic intrusions (granites), i.e., the lightest igneous rocks in terms of specific gravity.
The saturation of these areas of the earth's crust with the lightest facet-like rocks leads to its isostatic uplift and mountain building. The mountain ranges then collapse as a result of surface weathering; their debris is carried out to adjacent parts of the ocean; they align, turning into platform-aligned land areas. Then, along the outskirts, the next cycle of geosynclinal development develops, ending with the
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By digging another platform area of the continent, growing to the first, and so on (Fig. 21).
The sequence of their formation in the history of the Earth is as follows. After the completion of the melting of the Earth and the formation of its iron-nickel core and outer silicate shell (4.2-4.6 billion years) ago, the surface began to cool and a crust of solid rocks - protokors - began to form. It is assumed that it had the composition of anorthosite or eucrite (anorthosite gabbro with plagioclase of the composition anorthite and pyroxene), formed in the process of magmatic differentiation of the melt.
The stage of the early existence of the earth's protokor was distinguished by the grandiose development of volcanic phenomena. Whole seas of basaltic lavas poured out onto the earth's surface as magma rose through cracks in the earth's crust. Later, the crust became thicker and volcanic eruptions of basaltic lavas concentrated along the faults, where fissure eruptions took place at this time, huge volcanic cones and explosion craters were formed, similar to those that we now observe on the Moon, where this initial stage is believed to have been preserved. During this so-called lunar stage, a basalt protocore, i.e., oceanic, was formed. At the end of it, the first sialic (i.e., alumino-silicon) rocks of felsic composition, granitoids, began to form.
Rice. 21. The main structural elements continents (according to M.V. Muratov, 1974, with changes) 1 - ancient platforms (1 - East European, 2 - Siberian, 3 - Tarim - sky, 4 - North China, 5 - South China, 6 - North -American, 7 - North African, 8 - South African, 9 - Arabian, 10 - Indo - Stan, 11 - Australian, 12 - South American, 13 - Brazilian, 14 - Antarctic); 2-4 - geosynclinal folded belts: 2 - Late Proterozoic folded areas of the Small belts, which underwent folding and granitization during the Dalslandic, Grenville (1200-900 Ma) and Baikal, Katangian, Brazilian, Cadomian, Vindian (700-500 Ma) ) eras; 3 - areas of the Great Fold Belts, which turned into young platforms (Epibaikalian, Epigercyn, Epimesozoic); 4 - parts of the Greater geosynclinal fold belts that have retained their mobility and are Cenozoic and modern geosynclinal areas; 5 - basins of inland and marginal seas within geosynclinal areas; 6 - deep-water troughs; 7-9 - elements of the structure of the ocean floor: 7 - boundaries of the deep parts of the ocean floor, 8 - ocean shafts, 9 - mid-ocean ridges; 10 - major faults; 11 - boundaries of the Pacific Ocean depression (andesite "line")
The lunar stage on Earth lasted for a relatively short time, until the surface of the primary crust and the lower layers of the atmosphere cooled to 100 ° C, i.e., until the time when water in the form of liquid began to fill the depressions on the Earth's surface. The first water basins were formed - seas, lakes, rivers. The processes of intense weathering and erosion of the primary crust, the transfer of debris by water currents and the deposition of sediments at the bottom of reservoirs, where they were interbedded with volcanic lavas and tuffs, began. From this period, the formation of the face of the Earth began under the action of internal forces that lifted, bent and broke the earth's crust and caused the activity of volcanoes and external forces that destroyed, erased the traces of these deep processes and covered the surface of the Earth with a cover of sedimentary rocks.
The Early Archean stage is considered as the stage of the formation of the Earth's water envelope and the beginning of the formation of the continental crust. The first continents formed on certain territories of modern continents in the form of often isometric or slightly elongated massifs - ancient shields. The beginning of their formation is due to the fact that these areas, which formed the lower forms of the Earth's relief in regions with the thinnest crust, were first covered with water, at their bottom the accumulation of sediments began due to the drift of weathering products, destruction of coastal land areas and volcanic processes.
Here I have a new, it seems, no one has yet expressed, idea. But what if it was these primary seawater bodies, which at first covered individual areas of the Earth's surface, that contributed to the creation of primary geosynclinal systems in their place? Water has a very low thermal conductivity, and it, like a fur coat, covered areas of the earth's crust, contributing to the maintenance of high temperatures in these areas. In addition, water penetrated into the earth's crust or, at least, delayed the outflow from it, as a hydro-barrier, thereby contributing to the widespread development of metasomatic granitization processes, because the thickness of the earth's crust was still very small. The latter factor could also contribute to the prolonged subsidence of these areas under the influence of the weight of the water mass itself and the marine sediments accumulating here, precisely because the protocore was the thinnest here.
The composition of the aquatic environment at the beginning of the Archean differed significantly from the modern one, since gaseous products released by volcanoes were dissolved in the water of the early Archean oceans: hydrochloric (HCl), hydrofluoric (HF) and boric (H3BO3) acids, hydrogen sulfide (H2S), carbon dioxide (CO2) , methane (CH4) and other hydrocarbons. Due to this, the water was essentially an acid, with a pH close to 1-2, and silica was dissolved in it. In the atmosphere at the beginning of the Archean, carbon dioxide and ammonia (ammonia - NH3) predominated, and HCl, H2804, CH4 were also present. The surface temperature at this time (3.53.0 billion years ago) was 65-80 ° C.
By the end of the Early Archean, the composition of seawater had changed significantly. The acids dissolved in the water of the seas were gradually neutralized, being exposed to the action of silicates of sedimentary deposits and carbonates of K, Na, Ca, Mg, which were formed on the land surface during the weathering of minerals of volcanic rocks under the influence of carbon dioxide atmosphere. The resulting various carbonates entered seawater and reacted with acids dissolved in it, in particular with hydrochloric acid, forming chlorides. As a result, the acidity of the sea water dropped, the water acquired the character of a chloride solution. At the same time, the composition of the gases in the atmosphere also changed. Although it still consisted mainly of ammonia and methane, in the upper layers, under the influence of oxygen (supplied by the first organisms and plants), the process of oxidation and release of nitrogen from ammonia, which gradually became the main gas of the atmosphere, could begin.
Subsequently, in the seas, there was a transformation of chloride water into chloride-carbonate, which was associated with a more intensive drift from land of dissolved carbonates, which were formed as a result of chemical weathering on the earth's surface. Carbonates not only neutralized the remains of strong acids, but also led to the formation of carbonate sediments. As a result, along with sandy-clayey sediments and products of volcanic activity, carbonate deposits - dolomites and limestones - began to form on the bottom of the seas and oceans in the second half of the Early Archean. Also, there was an enhanced deposition of chemogenic silica and iron oxides with the formation of silts consisting of alternating thin layers of silica and ferruginous minerals, subsequently transformed into ferruginous quartzites - jaspilites, which make up the largest modern deposits of iron ores.
Volcanic sedimentary strata of the Lower Archean reach enormous thickness (10-12 km) and then undergo metamorphism and folding. This was accompanied, or even, more precisely, associated with the processes of granitization of the formed sedimentary rocks and underlying areas of the earth's crust. Metasomatism and granitization led to the formation of granite melts and their penetration into the overlying strata with the formation of intrusive bodies. Towards the end of the Early Archean, granitization manifested itself over large areas composed of dislocated sedimentary rocks. The resulting granite bodies rose upward in the form of huge granite domes, causing deformation of the host metamorphic rocks. The latter also acquired a dome-shaped occurrence, forming granite-gneiss domes.
Thus, at the end of the Early Archean, as a result of the processes of granitization and granite magmatism, a thick granite-metamorphic layer with continental type the earth's crust in some part of the territory of modern continents, forming their cores - ancient shields protruding above the water. And modern oceanic areas, on the contrary, were flooded. sea water and so they exist in large part to this day.
In the Late Archean and Early Proterozoic (3.00-1.65 billion years ago), on the outskirts of ancient shields, the development of the first typical geosynclinal regions begins, where the earth's crust subsides, massifs, metamorphism, folding and uplift of these areas - mountain building and the formation of the continental crust.
Shallow and subaerial sediments and volcanic rocks were deposited on the platform areas that already existed at that time, which did not experience strong folding during mountain building in neighboring geosynclinal systems and are represented by subhorizontal weakly metamorphosed volcanogenic - sedimentary rocks.
As a result of these processes, large platform areas of rigid stabilization were formed in the contours of modern continents.
In the subsequent Late Proterozoic stage (1.65-0.58 billion years ago), new large geosynclinal belts arose on the outskirts of the platform areas - the Pacific, Mediterranean, Atlantic, Ural-Mongolian and Arctic, the development of which led to an ever greater expansion of the continental crust. an increase in areas of mainland land. During this period, in the composition of sedimentary rocks, the deposition of carbonate rocks - limestones and dolomites - increased especially sharply. This is due to a change in the composition of the atmosphere due to the appearance of oxygen in it, caused by the photosynthetic activity of the blue-green algae that appeared at that time. Sulfur and hydrogen sulfide released during volcanic processes in the presence of oxygen formed sulfates, which displaced CO2 from seawater into sediment. Moreover, along with purely chemical phenomena, organogenic limestones began to play an important role due to the binding of carbonates by microalgae.
The geosynclinal belts that arose at that time completed their development, i.e., the orogenic stage, by folding and granitization, which manifested themselves in different time... The sections of these belts, which turned into folded areas at the end of the Riphean, are called Baikalids, in the middle of the Cambrian - Salairids, in the middle of the Paleozoic - Caledonids, at the end of the Paleozoic - Hercynides, in the middle of the Mesozoic - Cimmerids, in the Neogene - Alpids. They grew in many cases successively from ancient platforms towards oceanic regions.
In accordance with the main stages of development of geosynclinal regions, the Riphean stage of the earth's crust is called Baikal, the Early Paleozoic - Caledonian, Late Paleozoic - Hercynian, etc. Accordingly, young platforms with a Baikal folded basement are called Epibaikalian, Hercynian - Epigercynian, etc. All young platforms are part of geosynclinal fold belts, representing areas of the platform regime, characterized as areas of stable uplift or slow subsidence-uplifts without signs of shearing of the strata. Therefore, the platform cover is composed of gently sloping rock strata, and the underlying basement is composed of crumpled folded rocks.
Geosynclinal development continues at the present time on the borders of the continents with the Pacific Ocean - the Pacific Belt, characterized by intense volcanism, earthquakes, the formation of deep-sea depressions and chains of islands. In the future, the stage of mountain building will take place here, and these areas will become new accreted edge parts of the platforms.
Here the development of the earth's crust was characterized from the perspective of the most detailed theory, the so-called doctrine of geosynclines. There is another concept of tectonics of lithospheric plates, or a new global tectonics, which began to develop recently, in the early 1960s. It assumes the existence of rigid lithospheric plates in the earth's crust, which "float" over the plastic asthenospheric layer of the earth's mantle. In the rift valleys of mid-oceanic ridges, for example, the Mid-Atlantic, the process of stretching and spreading of plates is constantly taking place due to the rise and spread of viscous mantle matter in the asthenosphere. Basalt lavas erupt through the cracks from below, solidifying in the form of powerful dikes, which, like wedges, burst the adjacent lithospheric plates and displace them horizontally in different directions. Here, in the so-called spreading zones, the oceanic crust is thus built up. As a result of the emergence of new excess crust, lithospheric plates are displaced sideways from the mid-ocean ridge to the edges of the oceans and here they move under the neighboring continental lithospheric plates in the Zavaritsky-Benioff zones (the so-called subduction zones, for example, in the region of Kamchatka and the Kuril Islands). Moving under the adjacent one, each plate plunges into the asthenosphere and thereby eliminates the excess crust. Underthrusting is accompanied by heating of the plate edges, melting of the lithosphere, active andesite volcanism, and high seismic activity. The layers of the sedimentary layer seem to be "scraped off" from the plate, which plunges into the asthenosphere, and crumpled into folds on the oceanic side of the deep-sea trench.
In conclusion, let us note some ideas in cosmology about the formation of our Universe. What happened before the Big Bang, which led to the formation of the Earth and humanity, and what will happen after it? Academician A. D. Sakharov proposed a model of a "many-sheeted universe" (see. Science and life. - 1991. - No. 6), according to which the Big Bang was preceded by the compression of the previous Universe; after the maximum compression of our Universe, there will again be a Big Bang, that is, if we use the image proposed by A. D. Sakharov, the pages of the endless book of life are always flipping through. It follows from the second law of thermodynamics that the radius of the Universe increases from cycle to cycle. Consequently, there was once the very first cycle in which the universe had a minimum radius. What happened before this cycle?
Academician A. D. Sakharov suggested that at the beginning of the first cycle, time is reversed. In other words, up to this moment the same thing happens as after it, but only in the opposite order. Since when time reverses, all processes change direction, the inhabitants of each Universe (if any) live in the firm belief that time flows in the only possible direction - from the past to the future.
However, why are the parameters of our world exactly what they are? Why does space have three dimensions, and not two or ten, why the electron charge is exactly 1.6021892x10-19 coulomb? Scientists offer the hypothesis of the Megaverse, that is, the assumption that a huge number of different worlds with different conditions (in particular, with a different number of spatial dimensions or with several axes of time) were formed simultaneously. Our study is available that the only world, in which the existence of intelligent protein life is possible (anthropic principle).
Academician A.D.Sakharov proposed a hypothesis according to which a highly organized mind, developing billions of billions of years during a cycle, finds a way to transmit in encoded form some of the most valuable part of the information it has to its heirs in the following cycles, separated from this cycle in time by a period superdense compression and Big Bangs. An analogy is the transmission by living beings from generation to generation of genetic information, compressed and encoded in the chromosomes of the nucleus of a fertilized cell.
PLANET EARTH: EDUCATION AND DEVELOPMENT
Introduction
1. Formation of the planet Earth.
2. Formation of the World Ocean and Land.
3. The era of glaciation.
4. Eras of folding, state of the art... 5. The device of earth plates.
6. Volcanoes.
Conclusion
List of used literature
Introduction
Second half of the 20th century was marked by indisputable achievements in the study of not only the Earth, but all the planets of the solar system. The decisive factors were advances in technology and technology. For the first time in its history, mankind has managed to look at the Earth from the outside, visit the Moon, obtain detailed images of all planets, photograph asteroids, study meteorites and substantiate their belonging to some planets, for example, to Mars. Thanks to the invention of the echo sounder and satellite observations, researchers have gained a complete picture of the topography of the ocean floor.
Deep drilling on land and deep in the oceans and seas made it possible to gain an idea of the structure of sedimentary oceanic strata and to pass the Konrad surface on the Baltic shield.
Diving into the depths of the oceans and lakes, in particular, Lake Baikal, led to the discovery of the century - the discovery of "working factories" of ore, the so-called. black smokers. Paleomagnetology gave us the opportunity to reconstruct the movement of continental plates and prove the growth of the ocean floor. A detailed study of the sedimentary cover of the oceans led to a completely new concept of sedimentation, especially biogenic. The invention of microprobes and other devices for accurate diagnostics of minerals and their chemical and isotopic compositions opened up unprecedented possibilities in petrology.
In 1944, an article was published on the "Meteorite theory of the origin of the Earth and planets", which laid the foundation for numerous studies on the development of the theory of the formation of the Earth and planets from solid particles of a rotating gas-dust cloud captured by the Sun. In 1949, Four Lectures on the Theory of the Origin of the Earth were published.
Harold (Harold) Clayton URI (USA) physicist and physicochemist and G. Suess for the first time used chemical data when considering the origin and evolution of the solar system, rejected the theory of the formation of the Earth and planets from the initial molten matter. He was one of the first to consider the thermal theory of the formation of planets, believing that they arose as cold objects by accretion (gravitational capture and subsequent fall onto a protoplanetary embryo).
In 1957, the International Symposium "The Emergence of Life on Earth" was held. It is believed that the Earth was formed about 4.6 billion years ago as a result of the concentration of cold (10-20K) matter of the gas and dust nebula and the collision of solid cosmic formations (planetozimals). The oldest sedimentary rocks are 3960 million years old.
The flowering of the protozoa
Late Archean
The appearance of soils, green algae - eukaryotes, hydroid polyps (multicellular); the appearance of the first heterotrophic organisms (animals), both in the sea and on land.
The heyday of ancient life
Prothero - Zoey
The evolutionary trunk of the most ancient karyotes is divided into several branches, from which multicellular plants, fungi and multicellular animals arose. Life becomes a geological factor, that is, the formation of the biosphere has begun. The result of the vital activity of organisms is the formation of the overwhelming majority of minerals, both on land and on the ocean floor.
The flowering of ancient life
Paleozoic
By the beginning of the Paleozoic, four more kingdoms of living nature had already formed: prokaryotes (pellets), fungi, green plants and animals. The flourishing of skeletal invertebrates (Cambrian) and the appearance of the first vertebrates (Silurian). The flowering of fish (Devonian) in the seas and woody vegetation on land (Carboniferous). The emergence of animals on land in the Devonian led to the emergence and further flourishing of terrestrial - aquatic (amphibians), the progenitors of reptiles.
Basic
The reptiles have reached enormous diversity and have inhabited all land and seas and have adapted to fly. Dinosaurs become the masters of sushi. The emergence and development of angiosperms is one of the largest events in the history of life on Earth. The emergence of primitive mammals and birds.
Flourishing mammals - melting (new life)
Cenozoic
The flourishing of flowering plants, insects, birds and mammals. The earth is periodically exposed to giant glaciers. The emergence of the ancestors of modern people.
The emergence of reason
From great apes to modern humans. This is only the beginning of the longest stage in the evolution of living matter, since the new era should naturally pass into the newest - the era of the noosphere, and only after that into the era of intelligent population of the Cosmos. The further stage of evolution is still problematic to predict.
So, 3.8 billion years ago (only a few hundred million years after the formation of the planet), life was already in full swing on Earth, that is, more than a billion years earlier than it was assumed until now.
At the same time, the level of our ignorance about the planet Earth is still very high. And as we progress in our knowledge about it, the number of issues that remain unresolved does not diminish. We began to understand that the processes taking place 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 it is now possible to predict volcanic eruptions with a high degree of probability. Many geological processes are still difficult to explain and even more so to forecast.
Figure 1 shows our Earth as it was seen by astronauts from space. They noticed how welcoming and at the same time lonely our Earth seemed. This view from space, as well as research conducted on Earth, have enriched our understanding of planet Earth.
Rice. 1. Earth from space
Changes in the shape of the Earth have been accumulating for tens of millions of years. The preferential expansion of the Earth to the side Southern hemisphere is clearly demonstrated in the figures of South America, Africa, Australia, etc., the tips of the wedges of which are directed to the South Pole.
The history of the Earth is composed of two successive events, two parts.
The first event: the formation of the Earth's body from the material of the exploded Star. If the construction period passed relatively quickly (5-10 million years), then it took 100-200 million years to get out of the state of shock after a grand catastrophe - the time it took to enter the autonomous stage of development. There was a pressure test on a small loose planet. Its own warmth was accumulating.
The original size of the Earth can be imagined by putting together the Archean lands, which today are scattered in small tiles across its entire surface. The initial appearance of a not quite round planet was determined by large and small differences in altitude with gentle and steep transitions to one another without horizontal plains.
The primordial body of the Earth was composed of crushed, repeatedly ground material from the stellar archean. The small planet represented a continuous breccia, with small qualitative changes in depth, determined mainly by the increasingly later approach of material from the formation zones of Jupiter, Saturn, Uranus and Neptune.
The main composition of the primary Earth is anorthosite, which is also typical for the Moon. Powerful deposits of ferruginous quartzites in the seas of the Precambrian are evidence of the richness of the primary material in iron compounds (throughout the entire volume of the Earth). Iron is present in the form of small particles and in a dispersed state (as on the Moon).
The huge amount of maghemite in the north of Siberia indicates a large component of iron in the body of the Earth, which cannot but be related to the formation of the Earth's magnetic field and the Siberian magnetic anomaly. In quantitative terms, iron, like other metals, should be distributed over the terrestrial planets in the order of increasing distances from Mercury to the asteroid belt, which is associated with the impact-velocity differentiation of matter.
Water. The abundance of water on the bodies of the solar system can be traced everywhere. Both planets and satellites are literally flooded with it. Water is found in the atmospheres of stars. In another case, water is found in a disk of gas and dust orbiting a star. There is more and more water on the bodies of the terrestrial planets with distance from the Sun. The early Earth was saturated with water from the center to the surface. There is even more water on Mars and in the Asteroid Belt.
The water component is an integral part of all bodies in the solar system with the exception of Mercury and, probably, Venus.
Homogeneous sphere of the early Earth. As a direct indication of the homogeneous composition of not only early, but also modern earth(along the horizon) is the constancy of the 3He / 4He ratio along the entire length of the mid-oceanic ridges of the world ocean 60,000 km long (the equator is 40,000 km long). Solar helium 3He (helium-3) is released from the Earth's mantle simultaneously with the terrestrial 4He (helium-4). The same is happening throughout the Pacific Rim.
The nature of the appearance of solar helium in the earth's mantle is quite obvious. The presence of diamonds in the Earth's mantle is also quite obvious. Diamonds were formed when the Star exploded under a monstrous pressure of about a trillion atmospheres. (At the center of our Sun, in a calm state, 220 billion atm.). Naturally, diamonds are older than the Earth, as an established body. At the same time, 2 diamonds with an age of 9 billion years were discovered. It must be assumed that these diamonds were formed before the explosion, the rest of their mass - during the explosion. The age of the most ancient diamonds suggests that the exploding Star was at least 9 billion years old.
The core of the Earth. There was no iron-nickel core in the center of the Earth and is not present. The modern core is compressed breccia from known rocks under a pressure of about 4 million atm. In the center of the Earth, weightlessness and iron, even molten, cannot rush there in any way. Iron should be in the area of maximum gravity and should be a hollow sphere with a wall of a certain thickness. According to many indications, such a sphere was in the core of the exploding Star, inside which a nuclear explosion took place.
All minerals in ancient lands are of stellar origin. On the basis of uranium deposits, established only in ancient lands, the assumption arises that the explosion of the Star was nuclear.
The heating of the earth's interior occurred on the basis of radioactive stellar material. Its especially powerful manifestations are associated with trap magmatism.
This is how the first part of the history of the Earth developed.
Part one is stellar.
Part two is earthly.
The second part begins with the moment when, after a long silent run around the Sun, the Earth suddenly shuddered and there was an underground rumble from a volcano erupting upward.
Heart of the Earth - the heat engine started working. The earthly part of History began. The conditions for the formation of Life were laid.
Rice. 2 The structure of the Earth
As the Earth compacted, water began to appear on the surface, forming small bodies of water. At perihelion, the orbits both water and the earth warmed up to high temperatures. The first heat centers appeared in the zones of increased accumulation of radioactive material. V different places planets gushing volcanoes arose, magnificent examples of which are demonstrated in our time on Io, the nearest large moon of Jupiter.
Everything that happens on Io is a copy of the Earth's past: its original appearance, and immature volcanoes, and the first weak lava flows and hot water... Looking at the erupting volcanoes and at the surface of the satellite, one can accurately write the early history of the Earth.
2. Formation of the World Ocean and Land.
The age of the Earth is 5 - 7 billion years. All planets go through the stage of an incandescent body, the temperature on the Earth's surface at that time was more than 4000 degrees Celsius. When the temperature dropped and became less than 100 degrees Celsius, the water in the primary atmosphere of the Earth formed the world's oceans. There was no oxygen in the primary atmosphere, the atmosphere was "reducing". It contained water vapor, ammonia, hydrogen sulfide, methane, carbon dioxide, hydrogen.
Most of the Earth's surface is occupied by the World (361.1 million km2; 70.8%); land is 149.1 million km2 (29.2%) and forms six continents and islands.
According to the most common hypothesis, the Earth arose from a rotating incandescent gas nebula, which, gradually cooling and contracting, reached a fiery liquid state, and then a crust formed on it. The state of the earth's crust is determined by the forces of stress and deformation caused by the cooling and compression of the inner mass of the Earth.
According to another theory put forward at the beginning of our century by American scientists and, the Earth was originally a mass of gas erupted under the action of tidal forces from the surface of the Sun. At the same time, small particles of gas were released, which, rapidly condensing, turned into solids called planetesimals. With great gravity, earth mass attracted them.
Thus, the Earth reached its present size due to the growth process, and not as a result of compression, as the first hypothesis states.
Almost all hypotheses agree that the formation of oceanic basins was caused by two main reasons: firstly, the redistribution of rocks of various densities that occurred during the solidification of the earth's crust, and, secondly, the interaction of forces in the bowels of the shrinking Earth, which caused revolutionary changes in the surface relief.
An original hypothesis of the origin of continents and oceans is associated with the name of the Austrian geologist Alfred Lothar Wegener. The scientist believed that at some point in the history of the Earth, a uniform layer of sial had accumulated on one side. This is how the continent of Pangea arose. Wegener suggested that this mass of sial was adhered to the surface of a denser layer of sima. As the sial began to disintegrate, the horizontal movement of the continents caused the leading edges of the sial to bend. This may explain the origin of such high coastal mountain ranges as the Andes and Rocky Mountains.
Although the origin of the oceanic basins is still a mystery, the picture of how they were filled with water and how the oceans appeared and disappeared in the geological past of the Earth can be imagined more or less accurately.
After the formation of the earth's crust, its surface began to cool rapidly, since the heat it received from the bowels of the Earth did not sufficiently compensate for the loss of heat radiated into space. As it cooled, the water vapor that surrounded the Earth formed a cloud cover. When the temperature dropped to the point where moisture turned into water, the first rains fell.
The rains that have been pouring down to the surface of the Earth for centuries were the main source of water that filled the oceanic trenches. The sea, therefore, was the brainchild of the atmosphere, which in turn was gaseous ancient earth... Part of the water came from the bowels of the Earth.
The process of erosion, or erosion, began to operate on the Earth. This process has had a profound impact on the evolution of land and sea. The outlines of the seas, and with them the outlines of the oceans, were constantly changing. As a result of erosion and movement of the earth's crust, new seas were created, and the bottom of the old ones rose and turned into dry land.
As, due to the gradual loss of heat, the molten bowels of the Earth decreased in volume, horizontal compression of the crust occurred, which was deformed. Folded mountain ranges and crustal subsidence arose.
As a result of repeated cycles of compression and weakening, the outlines of large oceanic basins have undergone significant changes.
The outlines of the World Ocean in the first period of the Paleozoic era - the Cambrian, whose age is almost 500 million years, were completely different from the modern ones. The Pacific Ocean, which may have been a scar on the earth's crust, was almost the same shape as it is now. However, other oceans conquered large areas now occupied by land.
At present, on all continents of our planet, areas of the so-called Archean shield have been discovered, probably representing the remains of the most ancient land areas.
As it turned out, within these zones, the rocks composing the crust are close to 4 billion years old: Africa, Greenland, Karelia and Ukraine - 3.5 billion years; Siberia - 3.8-4.0 billion years; Northern Canada- up to 4 billion years; Western Australia - 4.1 billion years; Antarctica and South Africa- up to 4 billion years.
Thus, in general, the continental crust is about 4 billion years old and this issue is no longer discussed by scientists. It means only from this moment it is possible to speak about the possibility of proto-life on Earth. About 500-600 million years after the formation of the Earth (4.5 billion years ago), violent processes of metamorphization and the formation of basalts and granites took place on its surface.
3. The era of glaciation.
"The rocks keep evidence of the period of the main ice age, the first, the existence of which has been firmly proven" ... "Why was thermal equilibrium established on Earth? ...".
From the time of the first revolutions of fragmental matter after the explosion and up to the Mesozoic (240 million years), the Earth was formed, and then it was in a negative temperature annual balance, that is, it was always in conditions of glaciation. In the final stage, it is especially powerful and long lasting in the Carboniferous-Permian period, after which 240 million years ago an unprecedented melting of the global glacier and the advance of melt water on land began, ending in the greatest transgression in the Cretaceous period. This is a special and unique phenomenon in the history of the Earth.
With the initial eccentricity of the earth's orbit e = 0.253, about 2/3 of the year the Earth was in the glaciation regime. Taking into account spring and autumn, there were about 40 days left for the summer. The hot summer was short due to the rapid passage of the Earth's perihelion of its orbit at a high speed of 39 km / s, with a decrease in its aphelion to 23 km / s. Most of the time the Earth was in the freezing mode than in the thawing ash.
As the planet warmed up internally and water was added, more and more of it, evaporating in the hot summer, rose upward, spreading on both sides of the equator into the polar regions, where powerful streams of rain and snow fell, building up the ice shell of the Earth. The addition of the global glacier took hundreds of millions of years. However, in a relatively narrow equatorial strip, conditions have always existed for the emergence of life, as soon as the Earth "acquired" its own water in open basins. On the young, primordial Earth, when the elements of substances were not yet united by links of interactions, the necessary combinations for the production of an organic medium were given much easier than today.
The beginning of the global melting of the global glacier is associated with a decrease in the eccentricity of the earth's orbit. The cold aphelion approached the Sun so much that a positive temperature regime of the atmosphere was established (thermal equilibrium). For this reason, the expected next glaciation in the Jurassic period did not take place, glaciation that could no longer be. From the very beginning of its formation, there has been no change of seasons on Earth. This period of time in its history was distinguished by a clear distribution of temperature latitudinal bands parallel to the equator.
Extremely large and extremely low temperatures arisen, naturally, in the equatorial band and in the polar regions. However, even at the equator alone, the temperature varied over a wide range of +145 to 0 ° С. at the subsolar point, since at an eccentricity of the orbit e = 0.253, the Earth approached the Sun to 112 million km and moved away to 188 million km (today, respectively, no closer than 147 million km and no further than 152 million km).
In aphelion, the Earth froze to death not only because of the great distance from the Sun, but also because of the increase in the transit time of the second half of the ellipse due to the slowing down of the orbital speed. As the inclination of the earth's orbit decreased, at first the seasons with cold winters and hot summers became more and more contrasting, without which the Earth cannot be imagined, and in the memory of mankind it is associated with the once and for all eternal order in nature.
4. Epochs of folding, current state.
The eras of folding and mountain building are characterized by the following features:
The widespread development of mountain building movements in geos. areas of swaying movements on platforms;
Manifestation of powerful intrusive and then effusive magmatism;
Rise of platform margins adjacent to epiogeosynclinal areas, regression of epicontinental seas and complication of land relief;
Continentalization of climates, calming climatic conditions, increased zoning, expansion of deserts and the emergence of areas of continental glaciation (in the mountains and near the platforms).
Deteriorating conditions for development organic world, resulting in the extinction of the dominant and highly specialized forms and the emergence of new ones.
Compression of the continental crust, which occurs during the collision of lithospheric plates, leads to the emergence of extended belts of folded mountains. The rocks composing them are either crumpled into folds of two types (convex ridge anticlines and concave grooved synclines), or some blocks of rocks are thrust over others along a system of faults. In the central and southern parts Appalachian Mountains North America both types meet tectonic structures- fault deformations in the east, in the geological province of Blue Ridge (most common in the west of North Carolina), and folded - in the west, in the geological province of the Valleys and Ridges (these structures are best expressed in the territory of Pennsylvania, West Virginia and in the east of Tennessee) ... The compression that led to the emergence of these structures occurred at the end of the Paleozoic era, ca. 250 million years ago, when the African plate collided with the North American plate. Tectonic processes under the influence of which are formed folded mountains are called orogenic.
Two and a half billion years ago, the ancient platforms finished their formation and, since then, have remained practically unchanged. These include East European, Siberian, East Chinese and others.
So, the ancient platforms, like ice floes, drifted, and now they are drifting at a speed of 2-3 to 10 cm per year, on the surface of the semi-liquid mantle of the Earth, surrounded by smaller formations similar to ice sludge. In the zones of collision of platforms, the earth's crust bends, crumples into folds, and cracks. Along the cracks, geologists call them tectonic faults, molten magma rises, and volcanoes begin to operate. Note that volcanoes usually form away from the collision line of the platforms along which the main ridges are located (Fig. 3 and 4).
Rice. 3. Collision of platforms and subsidence of the earth's crust at the 1st stage of the folding epoch.
Rice. 4. The emergence of mountains. II stage of folding.
They are confined to faults separating the intact part of the platform from the part involved in subsidence. So, for example, Elbrus, Kazbek, Ararat, Aragats, volcanoes are located Of the Far East... After sagging, in the collision zone of the platforms, mountain ranges are formed.
Experts call the collision zones of the platforms geosynclinal fold belts of the Earth. It is within these belts that mountain building takes place. Let's take a look at the map of the book on geography (Fig. 5).
Rice. 5. Ancient platforms and geosynclinal regions of Eurasia.
For example, the well-known Alpine fold belt. It runs from Spain through the Alps, Dolomites, Carpathians, Crimea, Caucasus, Pamir, Himalayas, Hindu Kush, Kara-Korum. Or the Ural-Mongolian belt, it stretches from Novaya Zemlya through the Urals, Tien Shan, Altai, part of the Sayan Mountains. Fold belts divide either platforms (Alpine, Ural-Mongolian) or continental and oceanic plates (Pacific belt).
The thickness of the earth's crust varies from place to place. Under the ancient platforms, it is 15-20 kilometers, under mountain ranges much bigger. Mountains, like icebergs, rise above the Earth's surface, but at the same time their bases sink deeper into the mantle. Under the Caucasus, with an average altitude of 2.5 to 3.5 kilometers, the thickness of the earth's crust reaches 30-40 kilometers. Under the Tien Shan at heights of 5-6 kilometers, the thickness of the earth's crust reaches 70-80 kilometers. But under the oceans, where the load is much less, the thickness of the rocks also decreases. Here it ranges from 4 to 15 kilometers (Fig. 6).
Rice. 6. The thickness of the earth's crust beneath the main geological structures.
Active mountain building does not take place constantly and not along the entire length of the folded belts. The periods of mountain building, they are called epochs of folding, appear in different parts of the belts at different times. Mountains in the era of folding are formed in two stages. On the first, platforms collide. The monstrous energy of their movement I maneuvers in the collision zone to the sagging of the earth's crust. Why sagging? Because it is easier for rocks displaced from the collision zone to overcome the buoyancy (Archimedean) force of the liquid mantle than the force of gravity. Tectonic faults appear along the edges of the resulting troughs. Molten magma is squeezed out along them, forming numerous volcanoes and entire lava fields. Such fields can be seen, for example, in Armenia or in India on the Deccan plateau.
Sagging occurs very slowly, several centimeters per year, and continues for thousands and millions of years. The deflections are filled with seawater. In shallow warm seas living organisms reproduce actively. Dying off, they form with their skeletons and shells kilometer-long strata of sedimentary rocks: limestones, marls, etc. But the energy of the colliding platforms has been exhausted. The counter movement stops, and the subsidence of the earth's crust also stops. The second stage of mountain building begins.
Under the action of the buoyancy force, the rocks submerged in the mantle slowly rise, the layers collapse and the formation of mountain ranges and intermontane depressions. When all forces are balanced, mountain building stops and the era of folding ends. The area is stabilizing, turning into a young platform.
Then, or rather at the same time, the mountains begin to collapse. Fragments of rocks are carried by water to their foot in intermontane depressions and foredeeps. Over time (millions of years!), They can completely disappear under the sediments, and subsequent geological processes can turn them into smooth plains. Such destroyed mountains are hidden, for example, under the steppe spaces Crimean peninsula... However, the life of the fold belt does not end there. A new stage may begin in its history, capable of destroying the results of past eras or supplementing existing mountains with new ones, as happened in the Caucasus, where the ridges located north of the Main Caucasian ridge belong to an earlier era.
Other mechanisms of mountain building are also possible. For example, due to hydration and swelling of rocks, the Zaalaysky ridge at a rate of about 2 centimeters per year comes to the Alai Valley, an intermontane depression separating the Pamir and Pamir-Alai. As the Earth cools, the thickness of its crust increases, and, consequently, the volume of rocks. The earth, as it were, slowly swells, which naturally leads to geological cataclysms. In some places, continental plates collide with oceanic ones; in these areas, deep-sea depressions and island arcs are formed. This is how the Lake Baikal region and the Pacific depressions were formed. However, for us to understand the essence of the matter, it is enough to consider platform collisions. We emphasize once again that real processes in the earth's crust are much more complicated, and the above diagram serves only as a rough analogy.
Within the limits of young platforms, under the influence of the same Archimedean force, shifts of individual blocks can occur (Fig. 7), which also leads to the formation of mountains. So, for example, the Pobeda Peak area arose in the Central Tien Shan.
Rice. 7. Shift of crustal blocks (formation of mountains) within the young platform.
For example, we give a table of mountains of folded regions.
table 2
Mountains of folded regions
|
The era of folding |
Basic landforms |
Tectonic structure |
Relative age |
|
|
Proterozoic |
Baikal |
Yenisei ridge |
blocky, folded-blocky |
Revived (in the Neogene-Quaternary) |
|
Paleozoic |
caledonian |
Western Sayan |
||
|
Hercynian |
Ural mountains |
|||
|
Mesozoic |
Mesozoic |
Byrranga mountains |
||
|
Cenozoic |
alpine and pacific |
Caucasus mountains |
folded |
Young (originated in the Neogene-Quaternary) |
The areas where mountain formation is taking place in our time are mainly located within the Pacific belt (ring) on the coast around the Pacific Ocean. Mountain building also did not complete within the Mediterranean or Alpine fold belt. The Caucasus, the Pamirs and the Himalayas continue to develop. Evidence of this is the latest earthquake in northern Italy, in the Belgrade region.
5. The device of earth plates.
From the surface of the Earth to its center, approximately 6380 km. This distance is more than 600 times greater than the depth of the deepest ocean trench, the height of the most high mountain or the thickness of the troposphere. It turns out that that part of our planet with which we are in direct contact is negligible compared to its inaccessible depths. Human curiosity, however, cannot be limited to what is available. Exploring the outer layers of the earth's firmament, shaking the Earth with directed explosions and drawing conclusions based on the open laws of nature, people have formed an idea of the internal "structure" of the Earth.
It is assumed that when approaching its center, the temperature increases (it is in the center ° С, as on the surface of the Sun), the density of matter and the pressure of the outer layers. At such a high temperature, all known substances would have to melt. But the incredibly high pressure prevents melting. Therefore, it is likely that the Earth in the section has the following structure.
Above is a solid earth crust 3-5 km thick under the oceans and up to 80 km under the continents. It differs not only in thickness, but also in composition and age. Therefore, scientists distinguish two types of crust - oceanic and continental. Below, to a depth of about 2900 km, is the mantle. The substance of this layer is in a state not found on the surface of the Earth. It is neither solid nor liquid, it can mix very slowly under the influence of internal heat, like semolina on a stove. In the upper part of the mantle there is a very thin layer of matter, rather liquid than solid. This layer is called the asthenosphere (weakened sphere). The Earth's core is hidden under the mantle. Its upper part, experiencing a slightly lower pressure, is in a liquid state, and its lower part is in a solid state.
Rice. 8. Internally, the "structure" of the earth.
The layers of the Earth differ in their properties. The most important for us is the upper part of the Earth - the lithosphere is separated from the lower by a thin layer of melted rocks - the asthenosphere, which allows the lithosphere to slide over the Earth's surface.
The asthenosphere allows the layers above it to glide across the planet's surface, and the upper layers behave differently than the deeper ones. Therefore, these upper layers, including the earth's crust and the upper part of the mantle, received a special name - lithosphere (stone shell).
Rice. 9. Map of the movement of lithospheric plates.
Map of movement of lithospheric plates (arrows show the direction of movement of lithospheric plates, yellow - seismic zones, triangles - volcanoes). The lithosphere is split into several large plates that slowly move along the surface of the Earth. In some places the slabs abut each other, in others they dive one under the other, in others they disperse in different directions.
Geological studies using modern instruments have shown that the earth's crust consists of about 20 small and large plates or platforms that are constantly changing their location on the planet.
These wandering tectonic plates of the earth's crust are 60 to 100 km thick and, like ice floes, then sinking.
The places where they touch each other (faults, seams) are the main causes of earthquakes: here the earth's ground almost never remains calm.
However, the edges of the tectonic plates are not smoothly polished. They have enough roughness and scratches, there are sharp edges and cracks, ribs and gigantic protrusions that cling to each other like the teeth of a zipper. When the slabs move, their edges remain in place, because they cannot change their position. Over time, this leads to enormous stresses in the earth's crust. At some point, the edges cannot withstand the growing pressure: protruding, tightly adhered sections break off and, as it were, catch up with their slab.
There are 3 types of interaction of lithospheric plates: they either move apart or collide, one advances on the other, or one moves along the other. This movement is not constant, but intermittent, that is, it occurs sporadically due to their mutual friction. Every sudden movement, every dash can be marked by an earthquake.
Below the asthenosphere, as we have already said, the mantle is in constant, but very slow motion. Part of the mantle, heated in the depths of the earth to a very high temperature, expands and tends upward. And in its place the cooled upper layers fall. These movements carry along the lithosphere, splitting it into pieces and forcing the formed plates to move in different directions along the surface of the planet. They occur extremely slowly, at a rate of several centimeters per year. But scientists have learned to notice insignificant changes and from them guess the past of the Earth and even predict its future.
Back at the beginning of the XX century. German geophysicist Alfred Wegener, studying a map of the world, noticed that the shapes of some continents resemble parts of a disassembled mosaic. For example, the east ledge South America would be inserted into the trough of Africa, where the Gulf of Guinea is now located. So there was an assumption that these continents were once a single whole. And at the moment America and Africa are moving apart, increasing the Atlantic Ocean.
However, the earth's crust is not rubbery and cannot stretch to fill the ocean. Compensation for the lack of material occurs in the middle Atlantic Ocean... Here, matter from the depths of the earth rises to the surface, solidifies and forms a new oceanic crust. If in some places of the planet the earth's crust is formed, in others it should disappear. Otherwise, the Earth would have to continuously increase, which does not happen.
Rice. 10 The structure of the volcano
Where lithospheric plates abut each other, the earth's crust is squeezed upward, forming mountains. This is how, for example, the Himalayas arose. Here the Indo-Australian plate abuts the Eurasian one, and on the border of the Indian subcontinent appeared the highest mountain system the world. Moreover, the Himalayas continue to grow, as the movement of the lithospheric plates has not yet changed.
When slabs collide, they can behave differently: one slab dives under the other. Then, instead of mountains, deep faults of the earth's surface are formed. This occurs off the coast of the Pacific Ocean, where a number of the deepest oceanic trenches are located.
The gases escaping from the ground create a channel - it is called a volcanic vent - and throw chunks of rock high up. Falling to the ground, these stones make a neat mountain - the cone of a volcano.
6. Volcanoes.
According to scientists, it was with the help of volcanoes that the formation of the earth's crust, air and water took place. This means that volcanoes played a crucial role in the origin of life on Earth.
At present, most researchers have accepted the developing point of view about the mantle feeding of volcanoes. This conclusion is based, on the one hand, on the effect of screening of seismic waves by magma chambers, and on the other, on the results of petrochemical, petrological, geochemical studies and, in particular, on the ratio of strontium and neodymium isotopes in volcanic rocks.
Volcanoes, in the figurative expression of the famous German naturalist Alexander Humboldt "safety valves of the Earth", are a surface reflection of the deep processes that took place and are occurring in the Earth's mantle. Since a direct study of the deep horizons of the earth's crust and upper mantle is now and in the near foreseeable future impossible, volcanoes are still one of the main sources of information about the depths of the Earth.
This information is collected mainly in the analysis of volcanic rocks, but it can be substantially supplemented by establishing patterns of spatial distribution of volcanoes.
"Volcanism is a phenomenon due to which, during geological history, the outer shells of the Earth - crust, hydrosphere and atmosphere, that is, the habitat of living organisms - the biosphere were formed."
This opinion is expressed by the majority of volcanologists, but this is far from the only idea of the development of the geographic envelope.
Volcanism covers all phenomena associated with the eruption of magma to the surface. When magma is deep in the earth's crust under high pressure, all of its gas components remain in a dissolved state. As the magma moves to the surface, the pressure decreases, gases begin to be released, as a result, the magma poured onto the surface is significantly different from the original. To emphasize this difference, magma poured onto the surface is called lava. The eruption process is called eruptive activity.
Volcanic eruptions are not the same, depending on the composition of the eruption products. In some cases, eruptions proceed calmly, gases are released without large explosions, and liquid lava flows freely onto the surface. In other cases, eruptions are very violent, accompanied by powerful gas explosions and squeezing out or outpouring of relatively viscous lava. The eruptions of some volcanoes consist only in grandiose gas explosions, as a result of which colossal clouds of gas and water vapor, saturated with lava, rise to great heights.
According to modern concepts, volcanism is an external, so-called effusive form of magmatism - a process associated with the movement of magma from the interior of the Earth to its surface. At a depth of 50 to 350 km, in the thickness of our planet, foci of molten matter - magma are formed.
Along the areas of crushing and faults of the earth's crust, magma rises and pours out to the surface in the form of lava (differs from magma in that it contains almost no volatile components, which are separated from magma when pressure drops and go into the atmosphere.
In places of eruption, lava sheets, flows, volcanoes-mountains, composed of lavas and their dispersed particles - pyroclasts appear.
Effusive magmatism or volcanism is the outpouring of lava on the Earth's surface, the release of gases or the release of debris by an explosion of gases.
Depending on the amount of gases, their composition and temperature, the following occurs:
a) change in lava - effusion (slow release of gases, T ° C - high);
b) explosive eruption - explosion (rapid gas evolution, boiling, T ° C - high);
c) slow boiling of magma - extrusion (viscous magma, T ° C - high).
Distinguish between liquid, solid and gaseous products of volcanic eruptions.
1) Gaseous (volatile): water vapor, carbon dioxide (CO2), carbon monoxide (CO), nitrogen (N2), sulfur dioxide (SO2), sulfur oxide (SO), gaseous sulfur (S2), hydrogen (H2), ammonia (NH3), hydrogen chloride (HCl), hydrogen fluoride (HF), hydrogen sulfide (H2S), methane (CH4), boric acid (H3BO3), chlorine (Cl), argon (Ar), converted H2O and CO2. Chlorides of alkali metals and iron are also present. The composition of gases and their concentration depend on temperature and on the type of the earth's crust, so they can vary within a single volcano.
2) Liquid volcanic products are lava released to the surface.
Rice. 11 Volcanoes
The nature of effusive eruptions, the shape and length of lava flows are determined by the chemical composition, viscosity, temperature, and volatile matter content.
The most common are basalt lavas, with temperatures up to 1100 - 1200 ° C, low viscosity, V currents = 60 km / h (they form lava rivers or sheets).
Basalts flowing out in underwater conditions form pillow lavas. This occurs in the rift zones of the mid-oceanic ridges.
Viscous, low-temperature lavas (andesites, dacites, rhyolites), forming short and powerful flows, are comparatively less widespread. Cool quickly on the surface.
3) Solid volcanic products are formed during exclusive explosive eruptions. In this case, volcanic bombs (solidified ejections of liquid lava), 6 cm in size and more, are formed. Accumulations of volcanic bombs - agglomerates.
Lapikki ("ball") - sizes 1 - 5 cm. Smaller products of release - volcanic sand, ash and dust. The latter is carried over thousands of kilometers. The volcano Krakatoa (between the island of Sumatra and the island of Java in the Sunda Strait), having erupted in 1883, threw out the finest dust, which bypassed the entire globe in the upper atmosphere.
Explosions crush and eject already hardened volcanic rocks and spray liquid lava, forming tuffs, the size of which is from 1 to 2 parts of a mm.
There are 2 main types of volcanoes: central and linear.
Volcanoes of the central type are cone-shaped or dome-shaped hills, folded volcanic eruptions, several thousand meters high.
At the tops there are bowl-shaped depressions - craters that connect to a magma chamber located at a depth of 80 km. and more in the upper mantle, through the vent. Debris and lava ejected during the eruption build up a cone. Lakes are often confined to craters. During the eruption, mud flows are formed, leading to catastrophic destruction.
Crater ancient volcano, destroyed as a result of exogenous processes, inside which there are several younger cones, up to 2 - 3 tens of kilometers. across is called a caldera. By genesis, calderas are distinguished:
· Explosive, formed during explosive eruptions;
· Caldera collapse or subsidence, due to the collapse of the roof of the underground cavity, from where the emulsion of magma was suddenly ejected and partial subsidence of the ejected lava;
· Erosional - formed as a result of exogenous processes during a long period of rest of the volcano;
· Mixed - both endogenous and exogenous processes took part in their formation.
Volcanoes of linear or fractured type - have extended supply channels
Basalt liquid lava is usually poured out, forming blankets. Splash shafts (lavas), flat cones, and lava fields are formed along the cracks.
If the magma is acidic, acidic extrusion rolls and masses are formed.
Conclusion
Answering the question, when did life appear on Earth, we received a rather convincing answer - 3.8-4.0 billion years ago. At the same time, there is every reason to assume that the Earth 4 billion years ago was already finally formed as a planet and even acquired and retained a secondary atmosphere with its gravitational field.
It can be considered proven (with a high degree of probability) that the Earth, like other planets of the solar system, during this period received from the Cosmos a significant supply of "bio-building material" for life, in the form of protein "semi-finished products" and the simplest forms of organisms.
And then, apparently, the evolution of life on Earth was characterized by a tendency to a gradual acceleration with a certain alternation of relatively short periods of aromorphoses (morphophysiological progress - the emergence in the course of evolution of signs that increase the level of organization of living beings) and subsequent long periods of idioadaptation (particular adaptations of the living world, allowing master the specific conditions of the environment).
The Earth as a planet has taken place since the Proterozoic, a geological era that began 1 billion 800 million years ago.
Until this moment, geologists do not know a single geometrically correct structure, not even a line, on the Earth's surface.
From the Proterozoic, not only individual traces of the "infancy" of the planet (for example, zones of geological activity, linearly elongated on a planetary scale), but also the system of distribution of continents and oceans, in which many famous researchers of the planet over the past hundred years (L. Green , R. Owen, SchLalleman, A. Lapparan, T. Arldt and others) quite naturally "saw" the outline of the tetrahedron frame - the simplest correct body consisting of four triangular faces.
After the Proterozoic, several more geological eras followed, characterized by significant changes in the tectonics of the planet, which, according to the famous scientist, "indicates some kind of cardinal change in the processes at depth." Science has given its name to each of these most significant stages of the restructuring of the planet's "face": Proterozoic, Paleozoic, Mesozoic, Cenozoic. According to the IDES hypothesis, "a cardinal change in processes at depth" these geological eras were provided by the corresponding stages of the Geocrystal evolution: tetrahedron, cube, octahedron, icosahedron, that is, with a gradual complication and a greater degree of approximation to the ball.
It is assumed that the era of the Cenozoic ended only a few millennia ago (this is consistent with the current prevailing scientific point of view). And the onset of a new geological stage was predetermined by the overgrowth of the Geocrystal from the form of an icosahedron to the form of a dodecahedron.
What follows from this? It follows that only a few millennia ago, fundamental changes took place in the mechanism of movement of the planet's matter as a result of the reprofiling of the functions of the frameworks of the icosahedron and dodecahedron. The "growth" framework has become the "nutrition" framework and vice versa. The centers of ancient cultures and civilizations flourishing in the ascending "nodes" turned out to be in the descending ones. And the descending "nodes" of the earth's surface tend to lower the relief, following the turn of the subcrustal currents of the asthenosphere towards the descending branch of the stream.
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Introduction
2. Formation of the inner shells of the Earth in the process of its geological evolution
2.1 The main stages of the evolution of the Earth
2.2 Inner shells of the Earth
3. The emergence of the Earth's atmosphere and hydrosphere and their role in the emergence of life
3.1 Hydrosphere
3.2 Atmosphere
Conclusion
Bibliography
Introduction
Planet Earth was formed about 4.6 billion years ago. There are many hypotheses about the formation of the planet. Modern hypotheses are based on the concept of planetary formation put forward by Kant and Laplace.
The modern appearance of the Earth is significantly different from the original. In its evolution, the Earth went through several stages, which are usually divided into eras, periods, etc. For example, we are now living in the Cenozoic era, which has already lasted 67 million years, which is not so much compared to other periods. In the course of evolution, the planet has undergone repeated changes. At present, considering the structure of the Earth, one can make sure that it is a series of spherical shells. The outermost shell is the gaseous atmosphere, then comes the liquid shell - the hydrosphere, which partially covers the bulk of the planet - the lithosphere.
The lithosphere and atmosphere are divided into a number of spherical layers, not identical in their physical properties. So the lithosphere consists of the earth's crust, mantle and core, the following layers are distinguished in the atmosphere: troposphere, stratosphere, mesosphere and thermosphere.
1. Hypotheses of the origin of the Earth and their justification
Modern hypotheses of the formation of the Earth and other planets of the solar system are based on the one put forward in the 18th century. I. Kant (Germany) and, independently of him, P. Laplace (France) of the concept of the formation of planets from dusty matter and a gas nebula, later this hypothesis was called Kant-Laplace. In the 20th century. this concept was developed by O. Yu. Schmidt (USSR), K. Weizsacker (Germany), F. Foyle (England), A. Cameron (USA) and E. Shatzman (France).
Kant and Laplace drew attention to the fact that the sun is hot, and the earth is cold and much smaller in size than the sun. All planets revolve in circles, in the same direction and in almost the same plane. This constitutes the main distinguishing features of the solar system.
Kant and Laplace argued that in nature everything is constantly changing and developing. Both the Earth and the Sun were not what they are now, and their constituent substance existed in a completely different form.
Laplace substantiated his hypothesis more convincingly. He believed that once there was no solar system, but there was a primary rarefied and incandescent gas nebula with a compaction in the center. It rotated slowly, and its dimensions were larger than the diameter of the planet farthest from the Sun now. The gravitational attraction of nebula particles to each other led to the contraction of the nebula and a decrease in its size. According to the law of conservation of angular momentum, when a rotating body is compressed, its rotation speed increases. Therefore, as the nebula rotated, a large number of particles at its equator (which rotated faster than at the poles) detached, or, more precisely, exfoliated from it. A rotating ring appeared around the nebula. At the same time, the nebula, spherical at first, due to the centrifugal flattened at the poles and became like a lens.
All the time, contracting and accelerating its rotation, the nebula gradually peeled off from itself ring by ring, which rotated in the same direction and in the same plane. The gas rings had density inhomogeneities. The greatest concentration in each of the rings gradually attracted the rest of the ring material. So each ring turned into one large ball of gas, rotating around its axis. After that, the same thing was repeated with it as with the huge primordial nebula: it turned into a relatively small sphere surrounded by rings, which again condensed into small bodies. The latter, having cooled down, became satellites of large gas balls orbiting the Sun and, after solidification, turned into planets. Most of the nebulae are concentrated in the center; it has not cooled down until now and has become the Sun.
Laplace's hypothesis was scientific, since it was based on the laws of nature, known from experience. However, after Laplace, new phenomena were discovered in the solar system that his theory could not explain. For example, it turned out that the planet Uranus rotates on its axis in the wrong direction, where the other planets rotate. The properties of gases and the features of the motion of the planets and their satellites were better studied. These phenomena also did not agree with Laplace's hypothesis and had to be abandoned.
The famous Soviet scientist academician O. Yu Schmidt proposed a hypothesis, in the development of which astronomers, geophysicists, geologists and other scientists took part, and according to which the Earth and other planets have never been incandescent gaseous bodies like the Sun and stars, but should have been formed from cold particles of matter. These particles initially moved randomly. Then their orbits became circular and were located approximately in the same plane. In this case, the direction of rotation of the particles in any particular direction over time began to prevail, and, in the end, all the particles began to rotate in the same direction. As a result of the collision of particles during the initial disorderly motion, the energy of their motion was partially converted into heat and dissipated into space. Calculations showed that as a result of these processes, the spherical cloud gradually flattened and finally became similar in shape to a pancake. Further, the gravitational interaction led to the growth of larger particles by capturing small particles by them. Thus, most of the dust particles gathered into several giant lumps of matter, which became planets.
According to the estimates obtained by Schmidt, it took 6-7 billion years for the formation of the solar system, which agrees in order of magnitude with the data obtained as a result of isotopic analysis.
According to Schmidt's hypothesis, the Earth was never fiery liquid, and the heating of the inner region of the Earth occurred as a result of nuclear reactions of the decay of heavy elements that make up the original substance.
2. Formation of the inner shells of the Earth in the process of its geological evolution
2.1 The main stages of the evolution of the Earth
According to modern concepts, the history of the Earth is approximately 4.6 billion years old. Numerous results of the study of the earth's crust ( chemical composition and the structure of rocks, their distribution in depth, the content of radioactive isotopes, the remains of fossil living organisms) made it possible to establish a picture of the formation and development of the planet, to determine the age of the biosphere.
The entire history of the Earth's existence is subdivided into time periods, each of which is characterized by certain physical, chemical, climatic conditions, as well as stages of the evolution of living nature.
The time periods of the geochronological scale are subdivided into eons, eras, periods. The first, the earliest time period, called "katarchean" or "lunar period", corresponds to the formation of the Earth, its atmosphere, water environment. Life during the first 1-1.5 billion years did not exist in any form, since the corresponding physicochemical conditions had not yet emerged. At an early stage, intense tectonic processes took place, accompanied by the redistribution of chemical elements and compounds throughout the depth of the Earth. Nuclear decay reactions occurring in the center and deep layers of the planet contributed to the warming up of the Earth. The atmosphere was dominated by compounds of sulfur, chlorine, nitrogen, the oxygen content was hundreds of times less than now. The heavier elements moved towards the center of the Earth and then formed the core, the lighter ones towards the surface. Intensive volcanic and thunderstorm processes contributed to the formation of the aquatic environment - the first organic molecules began to form in it.
Archaea and Proterozoic are the two largest eras, during which life at the level of microorganisms began to form. These two eras are combined into "naderu" - cryptosis (time of latent life). The first multicellular organisms appeared at the very end of the Proterozoic about 600 million years ago.
Approximately 570 million years ago, when favorable conditions for life were practically formed on Earth, the rapid development of living organisms began. From that moment on, the "time of obvious life" came - phanerozoic. This segment of geological history is subdivided into 3 eras - Paleozoic, Mesozoic and Cenozoic. The last era, from the point of view of geo- and biology, continues to this day. It should be noted that the emergence and development of life on earth led to a significant change in the Earth's hard shell (lithosphere), hydrosphere and atmosphere, and the emergence of intelligent life (man) in a short time interval caused global changes in the evolution of the planet. The Mesozoic era is characterized by an active manifestation of magmatic activity, an intense process of mountain building. This era was dominated by dinosaurs.
Differences in the composition of rocks from one era to another, in turn, are due to abrupt changes in the natural, climatic and physical conditions on the planet. It was established that the climate on Earth changed many times, warming was replaced by sharp cold snaps, land was raised and lowered. Major space catastrophes also happened: collisions with meteorites, comets and asteroids. A large number of large meteorite craters have been discovered on Earth. The largest of them on the Yucatan Peninsula has a diameter of over 100 km; its age - 65 million years - practically coincides with the end of the Cretaceous and the beginning of the Paleogene period. Many paleontologists associate the extinction of dinosaurs with this major catastrophe.
Climate and temperature changes are largely due to astronomical factors: the tilt of the earth's axis (changed many times), disturbances of the giant planets, the activity of the Sun, the movement of the Solar system around the Galaxy. According to one of the hypotheses, abrupt climate changes occur every 210-215 million years (galactic year), when the solar system, revolving around the center of the Galaxy, passes through a cloud of gas and dust. This contributes to the weakening of solar radiation and, as a result, cooling of the planet. At these moments, ice ages set in on Earth - polar caps appear and grow. The last ice age began about 5 million years ago and continues to this day. The Ice Age is characterized by periodic temperature fluctuations (once every 50 thousand years). During cold snaps (ice age), glaciers can spread from the poles to the equator up to 30-40 degrees. We are now living in the "interglacial" period of the Ice Age. The legacy of the Ice Age is the permafrost zone (in Russia, more than half of its territory).
2.2 Inner shells of the Earth
At present, as you know, the Earth has a core composed mainly of iron and nickel. Substances containing lighter elements (silicon, magnesium and others) gradually "floated up", forming the mantle and crust of the Earth. The lightest elements entered the composition of the oceans and the primary atmosphere of the Earth. The materials that make up the solid Earth are opaque and dense. Therefore, their research is possible only to depths that make up an insignificant part of the Earth's radius. The deepest drilled wells and currently available projects are limited to depths of 10-15 km, which is just over 0.1% of the radius. Therefore, information about the deep bowels of the Earth is obtained using only indirect methods. These include seismic, gravitational, magnetic, electrical, electromagnetic, thermal, nuclear and other methods. The most reliable of these is seismic. It is based on the observation of seismic waves that occur in the solid Earth during earthquakes. Seismic waves make it possible to get an idea of the internal structure of the Earth and the change in the physical properties of the substance of the earth's interior with depth.
Seismic waves are of two types: longitudinal and transverse. In longitudinal waves, particles move along the direction, in transverse waves - perpendicular to this direction. The velocity of longitudinal waves is greater than that of transverse waves. When a seismic wave meets any interface, it is reflected and refracted. Observing seismic vibrations, it is possible to determine the depth of the boundaries at which the properties of rocks change, and the magnitude of the changes themselves.
Shear waves cannot propagate in a liquid medium; therefore, the presence of shear waves indicates that the lithosphere is solid down to great depths. However, starting from a depth of 3000 km, shear waves cannot propagate. Hence the conclusion: the inner part of the lithosphere forms a core, which is in a molten state. In addition, the core itself is still divided into two zones: an inner solid core and a liquid outer (layer between 2900 and 5100 km).
The hard shell of the Earth is also heterogeneous - it has a sharp interface at a depth of about 40 km. This boundary is called the Mohorovicic surface. The area above the surface of Mohorovich is called the crust, below the mantle.
The mantle extends to a depth of 2900 km. It is subdivided into 3 layers: upper, intermediate and lower. The upper layer, the asthenosphere, is characterized by a relatively low viscosity of the substance. The asthenosphere contains volcanic centers. A decrease in the melting temperature of the asthenosphere substance leads to the formation of magma, which can pour out onto the Earth's surface through cracks and channels of the earth's crust. The intermediate and lower layers are in a solid, crystalline state.
The top layer of the earth is called the earth's crust and is subdivided into several layers. The uppermost layers of the earth's crust consist mainly of layers of sedimentary rocks formed by the deposition of various small particles, mainly in the seas and oceans. The remains of animals and plants that inhabited the earth in the past are buried in these layers. The total thickness (thickness) of sedimentary rocks does not exceed 15-20 km.
The difference in the speed of propagation of seismic waves on the continents and on the ocean floor made it possible to conclude that there are two main types of the earth's crust on Earth: continental and oceanic.
The oceanic crust is much thinner (5-8 km). In composition and properties, it is close to that of the lower part of the basalt layer of the continents. But this type of crust is characteristic only of deep areas of the bottom of the oceans, not less than 4 thousand meters. At the bottom of the oceans there are areas where the crust has a structure of the continental or intermediate type.
3. The emergence of the Earth's atmosphere and hydrosphere and their role in the emergence of life
3.1 Hydrosphere
earth planet shell atmosphere hydrosphere
The hydrosphere is the totality of all water bodies of the Earth (oceans, seas, lakes, rivers, groundwater, swamps, glaciers, snow cover).
Most of the water is concentrated in, much less - in the continental network and. There are also large reserves of water and water vapor. Over 96% of the volume of the hydrosphere is made up of seas and oceans, about 2% is groundwater, about 2% is ice and snow, and about 0.02% is surface water on land. Part of the water is in a solid state in the form, representing itself. The bulk of the ice is located on dry land - mainly in Antarctica and Greenland. Its total mass is about 2.42 * 10 22 g. If This ice melted, then the level of the World Ocean would rise by about 60 m. In this case, 10% of the land would be flooded by the sea.
Surface waters occupy a relatively small share in the total mass of the hydrosphere.
The history of the formation of the hydrosphere
It is believed that when the Earth warms up, the crust, together with the hydrosphere and atmosphere, were formed as a result of volcanic activity - the release of lava, steam and gases from the inner parts of the mantle. It was in the form of steam that part of the water entered the atmosphere.
The value of the hydrosphere
The hydrosphere is in constant interaction with,. The circulation of water in the hydrosphere and its high heat capacity equalize climatic conditions at different latitudes. The hydrosphere supplies water vapor to the atmosphere; water vapor through infrared absorption creates a significant greenhouse effect , raising the average temperature of the Earth's surface by about 40 ° C. The hydrosphere affects the climate in other ways as well. It stores large amounts of heat in summer and gradually releases it in winter, softening seasonal temperature fluctuations on the continents. It also transfers heat from equatorial regions to temperate and even polar latitudes.
Surface waters play a vital role in the life of our planet, being the main source of water supply, irrigation and water supply.
The presence of the hydrosphere played a decisive role in the origin of life on Earth. We now know that life originated in the oceans, and billions of years passed before land became habitable.
3.2 Atmosphere
The atmosphere is a shell of gas that surrounds the Earth and rotates with it as a whole. The atmosphere consists mainly of gases and various impurities (dust, water droplets, ice crystals, sea salts, combustion products). The concentration of gases that make up the atmosphere is practically constant, with the exception of water (H 2 O) and carbon dioxide (CO 2). The content of nitrogen by volume is 78.08%, oxygen - 20.95%, less argon, carbon dioxide, hydrogen, helium, neon and some other gases are contained. The lower part of the atmosphere also contains water vapor (up to 3% in the tropics), at an altitude of 20-25 km there is a layer of ozone, although its amount is small, but its role is very significant.
The history of the formation of the atmosphere.
The atmosphere was formed mainly from gases released by the lithosphere after the formation of the planet. Over billions of years, the Earth's atmosphere has undergone significant evolution under the influence of numerous physicochemical and biological processes: dissipation of gases into outer space, volcanic activity, dissociation (splitting) of molecules as a result of solar ultraviolet radiation, chemical reactions between atmospheric components and rocks, respiration, and metabolism of living organisms. So the modern composition of the atmosphere is significantly different from the primary, which took place 4.5 billion years ago, when the crust was formed. According to the most common theory, the Earth's atmosphere over time was in four different compositions. Initially, it consisted of light gases ( hydrogen and helium) captured from interplanetary space. This is the so-called primary atmospheres (570-200 million years BC). At the next stage, active volcanic activity led to saturation of the atmosphere with gases other than hydrogen (hydrocarbons, ammonia , steam). This is how the secondary atmosphere was formed (200 million years ago - present day). The atmosphere was restorative. Further, the process of the formation of the atmosphere was determined by the following factors:
Constant leakage of hydrogen into interplanetary space ;
· Chemical reactions occurring in the atmosphere under the influence of ultraviolet radiation, lightning discharges and some other factors.
Gradually, these factors led to the formation of a tertiary atmosphere, characterized by much less hydrogen and much more nitrogen and carbon dioxide (formed as a result of chemical reactions from ammonia and hydrocarbons).
With the advent on Earth living organisms, as a result photosynthesis accompanied by the release of oxygen and the absorption of carbon dioxide, the composition of the atmosphere began to change. Initially, oxygen was spent on the oxidation of reduced compounds - hydrocarbons, sour form gland contained in the oceans, etc. At the end of this stage, the oxygen content in the atmosphere began to grow. Gradually, a modern atmosphere with oxidizing properties was formed.
During phanerozoic the composition of the atmosphere and the oxygen content underwent changes. Thus, during periods of coal accumulation, the oxygen content in the atmosphere significantly exceeded the current level. The carbon dioxide content may have increased during periods of intense volcanic activity. Recently, the evolution of the atmosphere began to be influenced and Human... The result of his activities was a constant significant increase in the content of carbon dioxide in the atmosphere due to the combustion of hydrocarbon fuels.
The structure of the atmosphere.
The troposphere is the lower, most studied layer of the atmosphere, with a height in the polar regions of 8 - 10 km, in temperate latitudes up to 10 - 12 km, at the equator - 16 - 18 km. The troposphere contains about 80-90% of the entire mass of the atmosphere and almost all water vapor. In the troposphere, physical processes take place that determine this or that weather. All transformations of water vapor take place in the troposphere. Clouds are formed in it and precipitation, cyclones and anticyclones are formed, turbulent and convective mixing is very strongly developed.
Above the troposphere is the stratosphere. The stratosphere is characterized by constant or increasing temperature with altitude and exceptional dryness of the air, there is almost no water vapor. The processes in the stratosphere have practically no effect on the weather. The stratosphere is located at an altitude of 11 to 50 km. A slight change in temperature in the layer of 11-25 km (the lower layer of the stratosphere) and its increase in the layer 25-40 km from -56.5 to 0.8 ° C (upper layer of the stratosphere) are characteristic. Having reached a value of about 0 ° C at an altitude of about 40 km, the temperature remains constant up to an altitude of about 55 km. This area of constant temperature is called and is the boundary between the stratosphere and the mesosphere. It is in the stratosphere that the layer is located ozonosphere("Ozone layer") (at an altitude of 15-20 to 55-60 km), which defines the upper limit of life in the biosphere.
An important component of the stratosphere and mesosphere is formed as a result of photochemical reactions most intensively at an altitude of ~ 30 km. The total mass of O 3 at normal pressure would be a layer with a thickness of 1.7-4.0 mm, but even this is enough to absorb life-destructive Uv- radiation from the sun.
The next layer above the stratosphere is the mesosphere. The mesosphere begins at an altitude of 50 km and extends up to 80-90 km. The air temperature drops to an altitude of 75-85 km to -88 ° С. The upper boundary of the mesosphere is the mesopause, where the temperature minimum is located, above the temperature begins to rise again. Next, a new layer begins, which is called the thermosphere. Its temperature rises rapidly, reaching 1000 - 2000 ° C at an altitude of 400 km. Above 400 km, the temperature hardly changes with altitude. Air temperature and density are highly dependent on the time of day and year, as well as on solar activity. During the years of maximum solar activity, the temperature and air density in the thermosphere are significantly higher than in the years of minimum.
Next is the exosphere. The gas in the exosphere is very rarefied, and from here there is a leak of its particles into interplanetary space (). Further, the exosphere gradually passes into the so-called near-space vacuum, which is filled with highly rarefied particles of interplanetary gas, mainly hydrogen atoms. But this gas is only a fraction of the interplanetary matter. Another part is made up of dust-like particles of cometary and meteoric origin. In addition to extremely rarefied dust-like particles, electromagnetic and corpuscular radiation of solar and galactic origin penetrates into this space.
The meaning of the atmosphere.
The atmosphere supplies us with the oxygen we need to breathe. Already at an altitude of 5 km above sea level, an untrained person develops oxygen starvation and without adaptation, the person's working capacity is significantly reduced. This is where the physiological zone of the atmosphere ends.
Dense layers of air - troposphere and stratosphere - protect us from the damaging effects of radiation. With sufficient rarefaction of air, at altitudes of more than 36 km, ionizing radiation - primary cosmic rays - has an intense effect on the body; at altitudes of more than 40 km, the ultraviolet part of the solar spectrum, which is dangerous for humans, operates.
Ozone in the upper atmosphere serves as a kind of shield that protects us from the action of ultraviolet radiation from the Sun. Without this shield, the development of life on land in its modern forms would hardly be possible.
Conclusion
Planet Earth was formed about 4.6 billion years ago and went through several stages of evolution. During these periods, the surface of the planet was constantly changing: the formation of the planet's relief took place, a water shell appeared - a hydrosphere, a gas shell - an atmosphere. The emergence of the hydrosphere and atmosphere was the beginning of the emergence of life on the planet. So it was in the aquatic environment that the first living organisms were born, the appearance of the atmosphere contributed to their emergence on land. And today earthquakes, volcanic eruptions constantly occur on the Earth, the Earth's surface is constantly influenced not only by internal processes, but also by external ones (erosion under the influence of wind, water, glaciers, etc.), human activities also have a huge impact - this suggests that our planet continues to evolve, and in a few thousand years or more, its appearance and state may change on a large scale. The processes considered above, which began with the formation of our planet, continue to this day, and affect, one way or another, on existence ...
