Shape, size and structure of the globe
The earth has a complex configuration. Its shape does not correspond to any of the regular geometric shapes. Speaking about the shape of the globe, it is believed that the figure of the Earth is limited by an imaginary surface that coincides with the surface of the water in the World Ocean, conditionally extended under the continents in such a way that a plumb line at any point on the globe is perpendicular to this surface. This shape is called a geoid, i.e. a form unique to the Earth.
The study of the shape of the Earth has a rather long history. The first assumptions about the spherical shape of the Earth belong to the ancient Greek scientist Pythagoras (571-497 BC). However, scientific evidence of the sphericity of the planet was given by Aristotle (384-322 BC), who was the first to explain the nature of lunar eclipses as the shadow of the Earth.
In the 18th century, I. Newton (1643-1727) calculated that the rotation of the Earth causes its shape to deviate from an exact sphere and gives it some flattening at the poles. The reason for this is centrifugal force.
Determining the size of the Earth has also occupied the minds of mankind for a long time. For the first time, the size of the planet was calculated by the Alexandrian scientist Eratosthenes of Cyrene (about 276-194 BC): according to his data, the radius of the Earth is about 6290 km. In 1024-1039 AD Abu Reyhan Biruni calculated the radius of the Earth, which turned out to be equal to 6340 km.
For the first time, an accurate calculation of the shape and size of the geoid was made in 1940 by A.A. Izotov. The figure he calculated was named after the famous Russian surveyor F.N. Krasovsky, the Krasovsky ellipsoid. These calculations showed that the figure of the Earth is a triaxial ellipsoid and differs from an ellipsoid of revolution.
According to measurements, the Earth is a ball flattened at the poles. The equatorial radius (semi-major axis of the ellipslide - a) is equal to 6378 km 245 m, the polar radius (semi-minor axis - b) is 6356 km 863 m. The difference between the equatorial and polar radii is 21 km 382 m. Compression of the Earth (ratio of the difference between a and b to a) is (a-b)/a=1/298.3. In cases where greater accuracy is not required, the average radius of the Earth is taken to be 6371 km.
Modern measurements show that the surface of the geoid slightly exceeds 510 million km, and the volume of the Earth is approximately 1.083 billion km. The determination of other characteristics of the Earth - mass and density - is carried out on the basis of the fundamental laws of physics. Thus, the mass of the Earth is 5.98 * 10 tons. The average density value turned out to be 5.517 g/cm.
General structure of the Earth
To date, according to seismological data, about ten interfaces have been identified in the Earth, indicating the concentric nature of its internal structure. The main of these boundaries are: the Mohorovicic surface at depths of 30-70 km on the continents and at depths of 5-10 km under the ocean floor; Wiechert-Gutenberg surface at a depth of 2900 km. These main boundaries divide our planet into three concentric shells - the geosphere:
The Earth's crust is the outer shell of the Earth located above the surface of Mohorovicic;
The Earth's mantle is an intermediate shell limited by the Mohorovicic and Wiechert-Gutenberg surfaces;
The Earth's core is the central body of our planet, located deeper than the Wiechert-Gutenberg surface.
In addition to the main boundaries, a number of secondary surfaces within geospheres are distinguished.
Earth's crust. This geosphere makes up a small fraction of the total mass of the Earth. Based on thickness and composition, three types of the earth’s crust are distinguished:
The continental crust is characterized by a maximum thickness reaching 70 km. It is composed of igneous, metamorphic and sedimentary rocks, which form three layers. The thickness of the upper layer (sedimentary) usually does not exceed 10-15 km. Below lies a granite-gneiss layer 10-20 km thick. In the lower part of the crust lies a balsat layer up to 40 km thick.
The oceanic crust is characterized by low thickness - decreasing to 10-15 km. It also consists of 3 layers. The upper, sedimentary, does not exceed several hundred meters. The second, balsate, with a total thickness of 1.5-2 km. The lower layer of oceanic crust reaches a thickness of 3-5 km. This type of earth's crust does not contain a granite-gneiss layer.
The crust of transitional regions is usually characteristic of the periphery of large continents, where marginal seas are developed and there are archipelagos of islands. Here, the continental crust is replaced by oceanic one and, naturally, in terms of structure, thickness and density of rocks, the crust of the transition areas occupies an intermediate place between the two types of crust indicated above.
Earth's mantle. This geosphere is the largest element of the Earth - it occupies 83% of its volume and makes up about 66% of its mass. The mantle contains a number of interfaces, the main of which are surfaces located at depths of 410, 950 and 2700 km. According to the values of physical parameters, this geosphere is divided into two subshells:
Upper mantle (from the Mohorovicic surface to a depth of 950 km).
Lower mantle (from a depth of 950 km to the Wiechert-Gutenberg surface).
The upper mantle, in turn, is divided into layers. The upper layer, which lies from the Mohorovicic surface to a depth of 410 km, is called the Gutenberg layer. Inside this layer, a hard layer and an asthenosphere are distinguished. The earth's crust, together with the solid part of the Gutenberg layer, forms a single hard layer lying on the asthenosphere, which is called the lithosphere.
Below the Gutenberg layer lies the Golitsin layer. Which is sometimes called the middle mantle.
The lower mantle has a significant thickness, almost 2 thousand km, and consists of two layers.
Earth's core. The central geosphere of the Earth occupies about 17% of its volume and accounts for 34% of its mass. In the section of the core, two boundaries are distinguished - at depths of 4980 and 5120 km. Therefore, it is divided into three elements:
Outer core - from the Wiechert-Gutenberg surface to 4980 km. This substance, which is under high pressure and temperature, is not a liquid in the usual sense. But it has some of its properties.
The transition shell is in the interval 4980-5120 km.
Subcore - below 5120 km. Possibly in a solid state.
The chemical composition of the Earth is similar to that of other terrestrial planets<#"justify">· lithosphere (crust and uppermost part of the mantle) · hydrosphere (liquid shell) · atmosphere (gas shell) About 71% of the Earth's surface is covered with water, its average depth is approximately 4 km. Earth's atmosphere: more than 3/4 is nitrogen (N2); approximately 1/5 is oxygen (O2). Clouds, consisting of tiny droplets of water, cover approximately 50% of the planet's surface. The atmosphere of our planet, like its interior, can be divided into several layers. · The lowest and densest layer is called the troposphere. There are clouds here. · Meteors ignite in the mesosphere. · Auroras and many orbits of artificial satellites are inhabitants of the thermosphere. There are ghostly silvery clouds hovering there. Hypotheses of the origin of the Earth. First cosmogonic hypotheses A scientific approach to the question of the origin of the Earth and the Solar system became possible after the strengthening in science of the idea of material unity in the Universe. The science of the origin and development of celestial bodies - cosmogony - emerges. The first attempts to provide a scientific basis for the question of the origin and development of the solar system were made 200 years ago. All hypotheses about the origin of the Earth can be divided into two main groups: nebular (Latin “nebula” - fog, gas) and catastrophic. The first group is based on the principle of the formation of planets from gas, from dust nebulae. The second group is based on various catastrophic phenomena (collisions of celestial bodies, close passage of stars from each other, etc.). One of the first hypotheses was expressed in 1745 by the French naturalist J. Buffon. According to this hypothesis, our planet was formed as a result of the cooling of one of the clumps of solar matter ejected by the Sun during a catastrophic collision with a large comet. J. Buffon's idea about the formation of the Earth (and other planets) from plasma was used in a whole series of later and more advanced hypotheses of the “hot” origin of our planet. Nebular theories. Kant and Laplace hypothesis Among them, of course, the leading place is occupied by the hypothesis developed by the German philosopher I. Kant (1755). Independently of him, another scientist - the French mathematician and astronomer P. Laplace - came to the same conclusions, but developed the hypothesis more deeply (1797). Both hypotheses are similar in essence and are often considered as one, and its authors are considered the founders of scientific cosmogony. The Kant-Laplace hypothesis belongs to the group of nebular hypotheses. According to their concept, in the place of the Solar system there was previously a huge gas-dust nebula (dust nebula made of solid particles, according to I. Kant; gas nebula, according to P. Laplace). The nebula was hot and rotating. Under the influence of the laws of gravity, its matter gradually became denser, flattened, forming a core in the center. This is how the primary sun was formed. Further cooling and compaction of the nebula led to an increase in the angular velocity of rotation, as a result of which at the equator the outer part of the nebula separated from the main mass in the form of rings rotating in the equatorial plane: several of them were formed. Laplace cited the rings of Saturn as an example. Cooling unevenly, the rings ruptured, and due to the attraction between the particles, the formation of planets orbiting the Sun occurred. The cooling planets were covered with a hard crust, on the surface of which geological processes began to develop. I. Kant and P. Laplace correctly noted the main and characteristic features of the structure of the Solar system: ) the overwhelming majority of the mass (99.86%) of the system is concentrated in the Sun; ) the planets revolve in almost circular orbits and in almost the same plane; ) all planets and almost all their satellites rotate in the same direction, all planets rotate around their axis in the same direction. A significant achievement of I. Kant and P. Laplace was the creation of a hypothesis based on the idea of the development of matter. Both scientists believed that the nebula had a rotational motion, as a result of which particles became compacted and the formation of planets and the Sun occurred. They believed that movement is inseparable from matter and is as eternal as matter itself. The Kant-Laplace hypothesis has existed for almost two hundred years. Subsequently, its inconsistency was proven. Thus, it became known that the satellites of some planets, for example Uranus and Jupiter, rotate in a different direction than the planets themselves. According to modern physics, gas separated from the central body must dissipate and cannot form into gas rings, and later into planets. Other significant shortcomings of the Kant-Laplace hypothesis are the following: It is known that the angular momentum in a rotating body always remains constant and is distributed evenly throughout the body in proportion to the mass, distance and angular velocity of the corresponding part of the body. This law also applies to the nebula from which the Sun and planets were formed. In the Solar System, the amount of motion does not correspond to the law of distribution of the amount of motion in the mass arising from one body. The planets of the Solar System concentrate 98% of the angular momentum of the system, and the Sun has only 2%, while the Sun accounts for 99.86% of the total mass of the Solar System. If we add up the rotational moments of the Sun and other planets, then in calculations it turns out that the primary Sun rotated at the same speed with which Jupiter now rotates. In this regard, the Sun should have had the same compression as Jupiter. And this, as calculations show, is not enough to cause fragmentation of the rotating Sun, which, as Kant and Laplace believed, disintegrated due to excess rotation. It has now been proven that a star with excess rotation breaks up into pieces rather than forming a family of planets. An example is spectral binary and multiple systems. Catastrophic theories. Jeans conjecture earth cosmogonic concentric origin After the Kant-Laplace hypothesis in cosmogony, several more hypotheses for the formation of the Solar system were created. The so-called catastrophic ones appear, which are based on an element of chance, an element of a happy coincidence: Unlike Kant and Laplace, who “borrowed” from J. Buffon only the idea of the “hot” emergence of the Earth, the followers of this movement also developed the hypothesis of catastrophe itself. Buffon believed that the Earth and planets were formed due to the collision of the Sun with a comet; Chamberlain and Multon - the formation of planets is associated with the tidal influence of another star passing by the Sun. As an example of a catastrophic hypothesis, consider the concept of the English astronomer Jeans (1919). His hypothesis is based on the possibility of another star passing near the Sun. Under the influence of its gravity, a stream of gas escaped from the Sun, which, with further evolution, turned into the planets of the solar system. The gas stream was shaped like a cigar. In the central part of this body rotating around the Sun, large planets were formed - Jupiter and Saturn, and at the ends of the “cigar” - the terrestrial planets: Mercury, Venus, Earth, Mars, Pluto. Jeans believed that the passage of a star past the Sun, which caused the formation of the planets of the Solar System, explains the discrepancy in the distribution of mass and angular momentum in the Solar System. The star, which tore a gas stream from the Sun, gave the rotating “cigar” an excess of angular momentum. Thus, one of the main shortcomings of the Kant-Laplace hypothesis was eliminated. In 1943, Russian astronomer N.I. Pariysky calculated that at a high speed of a star passing by the Sun, the gas prominence should have left along with the star. At the low speed of the star, the gas jet should have fallen onto the Sun. Only in the case of a strictly defined speed of the star could a gas prominence become a satellite of the Sun. In this case, its orbit should be 7 times smaller than the orbit of the planet closest to the Sun - Mercury. Thus, the Jeans hypothesis, like the Kant-Laplace hypothesis, could not provide a correct explanation for the disproportionate distribution of angular momentum in the Solar System In addition, calculations have shown that the convergence of stars in cosmic space is practically impossible, and even if this happened, a passing star could not give the planets movement in circular orbits. Modern hypotheses A fundamentally new idea lies in the hypotheses of the “cold” origin of the Earth. The most deeply developed meteorite hypothesis was proposed by the Soviet scientist O.Yu. Schmidt in 1944. Other hypotheses of “cold” origin include the hypotheses of K. Weizsäcker (1944) and J. Kuiper (1951), which are in many ways close to the theory of O. Yu. Schmidt, F. Foyle (England), A. Cameron (USA ) and E. Schatzman (France). The most popular are the hypotheses about the origin of the solar system created by O.Yu. Schmidt and V.G. Fesenkov. Both scientists, when developing their hypotheses, proceeded from ideas about the unity of matter in the Universe, about the continuous movement and evolution of matter, which are its main properties, about the diversity of the world, due to various forms of existence of matter. Hypothesis O.Yu. Schmidt According to the concept of O.Yu. Schmidt, the Solar system was formed from an accumulation of interstellar matter captured by the Sun in the process of moving in space. The Sun moves around the center of the Galaxy, completing a full revolution every 180 million years. Among the stars of the Galaxy there are large accumulations of gas-dust nebulae. Based on this, O.Yu. Schmidt believed that the Sun, when moving, entered one of these clouds and took it with it. The rotation of the cloud in the strong gravitational field of the Sun led to a complex redistribution of meteorite particles by mass, density and size, as a result of which some of the meteorites, the centrifugal force of which turned out to be weaker than the force of gravity, were absorbed by the Sun. Schmidt believed that the original cloud of interstellar matter had some rotation, otherwise its particles would have fallen into the Sun. The cloud turned into a flat, compacted rotating disk, in which, due to an increase in the mutual attraction of particles, condensation occurred. The resulting condensed bodies grew due to small particles joining them, like a snowball. During the process of cloud circulation, when particles collided, they began to stick together, form larger aggregates and join them - accretion of smaller particles falling into the sphere of their gravitational influence. In this way, planets and satellites orbiting around them were formed. The planets began to rotate in circular orbits due to the averaging of the orbits of small particles. The earth, according to O.Yu. Schmidt, was also formed from a swarm of cold solid particles. The gradual heating of the Earth's interior occurred due to the energy of radioactive decay, which led to the release of water and gas, which were included in small quantities in the composition of solid particles. As a result, oceans and an atmosphere arose, which led to the emergence of life on Earth. O.Yu. Schmidt, and later his students, gave a serious physical and mathematical justification for the meteorite model of the formation of the planets of the Solar System. The modern meteorite hypothesis explains not only the peculiarities of the movement of planets (shape of orbits, different directions of rotation, etc.), but also their actually observed distribution of mass and density, as well as the ratio of planetary angular momentum to the solar one. The scientist believed that the existing discrepancies in the distribution of angular momentum of the Sun and the planets are explained by different initial angular momentum of the Sun and the gas-dust nebula. Schmidt calculated and mathematically substantiated the distances of the planets from the Sun and between themselves and found out the reasons for the formation of large and small planets in different parts of the Solar System and the difference in their composition. Through calculations, the reasons for the rotational motion of planets in one direction are substantiated. The disadvantage of the hypothesis is that it considers the origin of the planets in isolation from the formation of the Sun, the defining member of the system. The concept is not without an element of chance: the capture of interstellar matter by the Sun. Indeed, the possibility of the Sun capturing a sufficiently large meteorite cloud is very small. Moreover, according to calculations, such capture is possible only with the gravitational assistance of a nearby star. The probability of a combination of such conditions is so insignificant that it makes the possibility of the Sun capturing interstellar matter an exceptional event. Hypothesis V.G. Fesenkova The work of astronomer V.A. Ambartsumyan, who proved the continuity of star formation as a result of condensation of matter from rarefied gas-dust nebulae, allowed academician V.G. Fesenkov to put forward a new hypothesis (1960) linking the origin of the Solar system with the general laws of matter formation in space space. Fesenkov believed that the process of planet formation is widespread in the Universe, where there are many planetary systems. In his opinion, the formation of planets is associated with the formation of new stars that arise as a result of the condensation of initially rarefied matter within one of the giant nebulae (“globules”). These nebulae were very rarefied matter (density of the order of 10 g/cm) and consisted of hydrogen, helium and a small amount of heavy metals. First, the Sun formed at the core of the “globule,” which was a hotter, more massive, and faster-rotating star than it is today. The evolution of the Sun was accompanied by repeated ejections of matter into the protoplanetary cloud, as a result of which it lost part of its mass and transferred a significant share of its angular momentum to the forming planets. Calculations show that with non-stationary ejections of matter from the depths of the Sun, the actually observed ratio of the moments of momentum of the Sun and the protoplanetary cloud (and therefore the planets) could have developed. The simultaneous formation of the Sun and planets is proven by the same age of the Earth and the Sun. As a result of the compaction of the gas-dust cloud, a star-shaped condensation was formed. Under the influence of the rapid rotation of the nebula, a significant part of the gas-dust matter moved increasingly away from the center of the nebula along the equatorial plane, forming something like a disk. Gradually, the compaction of the gas-dust nebula led to the formation of planetary concentrations, which subsequently formed the modern planets of the Solar System. Unlike Schmidt, Fesenkov believes that the gas-dust nebula was in a hot state. His great merit is the substantiation of the law of planetary distances depending on the density of the medium. V.G. Fesenkov mathematically substantiated the reasons for the stability of the angular momentum in the Solar System by the loss of matter of the Sun when selecting matter, as a result of which its rotation slowed down. V.G. Fesenkov also argues in favor of the reverse motion of some satellites of Jupiter and Saturn, explaining this by the capture of asteroids by the planets. Fesenkov attached great importance to the processes of radioactive decay of the isotopes K, U, Th and others, the content of which was then much higher. To date, a number of options for radiotogenic heating of the subsoil have been theoretically calculated, the most detailed of which was proposed by E.A. Lyubimova (1958). According to these calculations, after one billion years, the temperature of the Earth's interior at a depth of several hundred kilometers reached the melting point of iron. Apparently, this time marks the beginning of the formation of the Earth's core, represented by metals - iron and nickel - that descended to its center. Later, with a further increase in temperature, the most fusible silicates began to melt from the mantle, which, due to their low density, rose upward. This process, studied theoretically and experimentally by A.P. Vinogradov, explains the formation of the earth's crust. It is also worth noting two hypotheses that developed towards the end of the 20th century. They considered the development of the Earth without affecting the development of the Solar system as a whole. The earth was completely molten and, in the process of depleting internal thermal resources (radioactive elements), gradually began to cool. A hard crust has formed in the upper part. And as the volume of the cooled planet decreased, this crust broke, and folds and other relief forms formed. There was no complete melting of matter on Earth. In a relatively loose protoplanet, local centers of melting formed (this term was introduced by Academician Vinogradov) at a depth of about 100 km. Gradually, the amount of radioactive elements decreased, and the temperature of the LOP decreased. The first high-temperature minerals crystallized from the magma and fell to the bottom. The chemical composition of these minerals was different from the composition of the magma. Heavy elements were extracted from magma. And the residual melt was relatively enriched in light. After phase 1 and a further decrease in temperature, the next phase of minerals crystallized from the solution, also containing more heavy elements. This is how the gradual cooling and crystallization of the LOPs occurred. From the initial ultramafic composition of the magma, magma of basic balsic composition was formed. A fluid cap (gas-liquid) formed in the upper part of the LOP. Balsate magma was mobile and fluid. It broke through from the LOPs and poured onto the surface of the planet, forming the first hard basalt crust. The fluid cap also broke through to the surface and, mixing with the remains of primary gases, formed the first atmosphere of the planet. The primary atmosphere contained nitrogen oxides. H, He, inert gases, CO, CO, HS, HCl, HF, CH, water vapor. There was almost no free oxygen. The temperature of the Earth's surface was about 100 C, there was no liquid phase. The interior of the rather loose protoplanet had a temperature close to the melting point. Under these conditions, heat and mass transfer processes inside the Earth proceeded intensively. They occurred in the form of thermal convection currents (TCFs). TCPs arising in the surface layers are especially important. Cellular thermal structures developed there, which at times were rebuilt into a single-cell structure. The ascending TCPs transmitted the impulse of motion to the surface of the planet (balsat crust), and a stretch zone was created on it. As a result of stretching, a powerful extended fault with a length of 100 to 1000 km is formed in the TKP uplift zone. They were called rift faults. The temperature of the planet's surface and its atmosphere cools below 100 C. Water condenses from the primary atmosphere and the primary hydrosphere is formed. The Earth's landscape is a shallow ocean with a depth of up to 10 m, with individual volcanic pseudo-islands exposed during low tides. There was no permanent sushi. With a further decrease in temperature, the LOPs completely crystallized and turned into hard crystalline cores in the bowels of a rather loose planet. The surface cover of the planet was subject to destruction by aggressive atmosphere and hydrosphere. As a result of all these processes, the formation of igneous, sedimentary and metamorphic rocks occurred. Thus, hypotheses about the origin of our planet explain modern data on its structure and position in the solar system. And space exploration, launches of satellites and space rockets provide many new facts for practical testing of hypotheses and further improvement. Literature 1. Questions of cosmogony, M., 1952-64 2. Schmidt O. Yu., Four lectures on the theory of the origin of the Earth, 3rd ed., M., 1957; Levin B. Yu. Origin of the Earth. "Izv. Academy of Sciences of the USSR Physics of the Earth", 1972, No. 7; Safronov V.S., Evolution of the preplanetary cloud and the formation of the Earth and planets, M., 1969; . Kaplan S. A., Physics of Stars, 2nd ed., M., 1970; Problems of modern cosmogony, ed. V. A. Ambartsumyan, 2nd ed., M., 1972. Arkady Leokum, Moscow, “Julia”, 1992
In modern astronomy, the concept has been accepted cold initial state of planets, which, under the influence of electromagnetic and gravitational forces, were formed as a result of the combination of solid particles of the gas-dust cloud surrounding the Sun. The protoplanetary nebula consisted of dense interstellar material that could have been formed as a result of the explosion of a relatively nearby supernova, which accelerated the process of gas condensation.
The pressure level in the protoplanetary cloud was such that the gas material condensed directly into solid particles, bypassing the liquid form. At some point, the density of the gas turned out to be so high that compactions formed in it. Colliding with each other, the gas clumps continued to compress and become denser, forming the so-called preplanetary bodies.
The formation of preplanetary bodies lasted tens of thousands of years. The collision of these bodies with each other led to the fact that the largest of them began to increase in size even more, as a result of which planets were formed, including our Earth.
Early history of the Earth includes three phases of evolution: accretion (birth); melting of the outer sphere of the globe; primary cortex (lunar phase).
Accretion phase represented a continuous fall onto the growing Earth of an increasing number of large bodies, enlarged in flight during collisions with each other, as well as as a result of the attraction of more distant small particles to them. In addition, the largest objects fell to the Earth - planetesimals, reaching many kilometers in diameter. During the accretion phase, the Earth acquired approximately 95% of its present mass. This took about 17 million years (although some researchers increase this period to 400 million years). At the same time, the Earth remained a cold cosmic body, and only at the end of this phase, when extremely intense bombardment of large objects began, did strong heating and then complete melting of the planet’s surface matter occur.
The phase of melting of the outer sphere of the globe occurred between 4-4.6 billion years ago. At this time, a planetary chemical differentiation of matter occurred, which led to the formation of the central core of the Earth and the mantle enveloping it. Later the earth's crust formed.
In this phase, the Earth's surface was an ocean of heavy molten mass with gases escaping from it. Small and large cosmic bodies continued to rapidly fall into it, causing bursts of heavy liquid. Hanging over the hot ocean was a sky completely covered with thick clouds, from which not a drop of water could fall.
Moon Phase - the time of cooling of the molten matter of the Earth as a result of the radiation of heat into space and the weakening of meteorite bombardment. This is how the primary crust of basaltic composition was formed. At the same time, the formation of the granite layer of the continental crust occurred. True, the mechanism of this process is still not clear. During the lunar phase, there was a gradual cooling of the Earth's surface from the melting point of basalts, which ranged from 800-1000 to 100 °C.
When the temperature dropped below 100 °C, all the water that covered the Earth fell out of the atmosphere. As a result, surface and groundwater runoff formed, and bodies of water appeared, including the primary ocean.
It arose about 4600 million years ago. Since then, its surface has constantly changed under the influence of various processes. The earth apparently formed several million years after a colossal explosion in space. The explosion created a huge amount of gas and dust. Scientists believe that its particles, colliding with each other, united into giant clumps of hot matter, which over time turned into the existing planets.
According to scientists, the Earth arose after a colossal cosmic explosion. The first continents probably formed from molten rock flowing to the surface from vents. As it solidified, it made the earth's crust thicker. Oceans could have formed in the lowlands from droplets contained in volcanic gases. The original one probably consisted of the same gases.
It is thought that the Earth was at first incredibly hot, with a sea of molten rocks on the surface. About 4 billion years ago, the Earth began to slowly cool and split into several layers (see right). The heaviest rocks sank deep into the bowels of the Earth and formed its core, remaining unimaginably hot. Less dense matter formed a series of layers around the core. On the surface itself, molten rocks gradually hardened, forming a solid crust covered with many volcanoes. The molten rock, bursting to the surface, froze, forming the earth's crust. Low areas were filled with water.
Earth today
Although the earth's surface seems solid and unshakable, changes are still taking place. They are caused by various kinds of processes, some of which destroy the earth's surface, while others recreate it. Most changes occur extremely slowly and are detected only by special devices. It takes millions of years for a new mountain range to form, but a powerful volcanic eruption or a monstrous earthquake can transform the surface of the Earth in a matter of days, hours and even minutes. In 1988, an earthquake in Armenia that lasted about 20 seconds destroyed buildings and killed more than 25,000 people.
Structure of the Earth
In general, the Earth has the shape of a ball, slightly flattened at the poles. It consists of three main layers: crust, mantle and core. Each layer is formed by different types of rocks. The picture below shows the structure of the Earth, but the layers are not to scale. The outer layer is called the earth's crust. Its thickness is from 6 to 70 km. Beneath the crust is the upper layer of the mantle, formed by hard rock. This layer, together with the crust, is called and has a thickness of about 100 km. The part of the mantle underlying the lithosphere is called the asthenosphere. It is approximately 100 km thick and is likely composed of partially molten rocks. the mantle varies from 4000°C near the core to 1000″C in the upper part of the asthenosphere. The lower mantle probably consists of solid rock. The outer core is composed of iron and nickel, apparently molten. The temperature of this layer can reach 55СТГС. The temperature of the subcore can be above 6000'C. It is solid due to the colossal pressure of all the other layers. Scientists believe that it consists mainly of iron (more about this in the article ““).
Until now, the main theory of the origin of the cradle of humanity is considered to be the Big Bang theory. According to astronomers, an infinitely long time ago, a huge hot ball existed in outer space, whose temperature was millions of degrees. As a result of the chemical reactions that took place inside the fiery sphere, an explosion occurred that scattered a huge number of tiny particles of matter and energy in space. Initially, these particles had too high a temperature. Then the Universe cooled down, the particles were attracted to each other, accumulating in one space. Lighter elements were attracted to heavier ones, which arose as a result of the gradual cooling of the Universe. This is how galaxies, stars, and planets were formed.
To support this theory, scientists cite the structure of the Earth, whose inner part, called the core, consists of heavy elements - nickel and iron. The core, in turn, is covered with a thick mantle of hot rocks, which are lighter. The surface of the planet, in other words, the earth's crust, seems to float on the surface of molten masses, being the result of their cooling.
Creation of living conditions
Gradually, the globe cooled, creating increasingly dense areas of soil on its surface. The volcanic activity of the planet in those days was quite active. As a result of magma eruptions, a huge amount of various gases were released into space. The lightest ones, such as helium and hydrogen, instantly evaporated. Heavier molecules remained above the surface of the planet, attracted by its gravitational fields. Under the influence of external and internal factors, vapors of emitted gases became a source of moisture, and the first precipitation appeared, which played a key role in the emergence of life on the planet.
Gradually, internal and external metamorphoses led to the diversity of the landscape to which humanity has long been accustomed:
- mountains and valleys were formed;
- seas, oceans and rivers appeared;
- A certain climate developed in each area, which gave impetus to the development of one or another form of life on the planet.
The opinion that the planet is calm and that it is finally formed is incorrect. Under the influence of endogenous and exogenous processes, the surface of the planet is still being formed. Through his destructive management, man contributes to the acceleration of these processes, which leads to the most catastrophic consequences.
The history of our planet still holds many mysteries. Scientists from various fields of natural science have contributed to the study of the development of life on Earth.
Our planet is believed to be about 4.54 billion years old. This entire time period is usually divided into two main stages: Phanerozoic and Precambrian. These stages are called eons or eonothema. Eons, in turn, are divided into several periods, each of which is distinguished by a set of changes that occurred in the geological, biological, and atmospheric state of the planet.
- Precambrian, or cryptozoic is an eon (time period in the development of the Earth), covering about 3.8 billion years. That is, the Precambrian is the development of the planet from the moment of formation, the formation of the earth’s crust, the proto-ocean and the emergence of life on Earth. By the end of the Precambrian, highly organized organisms with a developed skeleton were already widespread on the planet.
The eon includes two more eonothems - catarchaean and archaean. The latter, in turn, includes 4 eras.
1. Katarhey- this is the time of the formation of the Earth, but there was no core or crust yet. The planet was still a cold cosmic body. Scientists suggest that during this period there was already water on Earth. The Catarchaean lasted about 600 million years.
2. Archaea covers a period of 1.5 billion years. During this period, there was no oxygen on Earth yet, and deposits of sulfur, iron, graphite, and nickel were being formed. The hydrosphere and atmosphere were a single vapor-gas shell that enveloped the globe in a dense cloud. The sun's rays practically did not penetrate through this curtain, so darkness reigned on the planet. 2.1 2.1. Eoarchaean- This is the first geological era, which lasted about 400 million years. The most important event of the Eoarchean was the formation of the hydrosphere. But there was still little water, the reservoirs existed separately from each other and did not yet merge into the world ocean. At the same time, the earth's crust becomes solid, although asteroids are still bombarding the earth. At the end of the Eoarchean, the first supercontinent in the history of the planet, Vaalbara, formed.
2.2 Paleoarchean- the next era, which also lasted approximately 400 million years. During this period, the Earth's core is formed and the magnetic field strength increases. A day on the planet lasted only 15 hours. But the oxygen content in the atmosphere increases due to the activity of emerging bacteria. Remains of these first forms of Paleoarchean life have been found in Western Australia.
2.3 Mesoarchean also lasted about 400 million years. During the Mesoarchean era, our planet was covered by a shallow ocean. The land areas were small volcanic islands. But already during this period the formation of the lithosphere begins and the mechanism of plate tectonics begins. At the end of the Mesoarchean, the first ice age occurs, during which snow and ice first formed on Earth. Biological species are still represented by bacteria and microbial life forms.
2.4 Neoarchaean- the final era of the Archean eon, the duration of which is about 300 million years. Colonies of bacteria at this time form the first stromatolites (limestone deposits) on Earth. The most important event of the Neoarchean was the formation of oxygen photosynthesis.
II. Proterozoic- one of the longest time periods in the history of the Earth, which is usually divided into three eras. During the Proterozoic, the ozone layer appears for the first time, and the world ocean reaches almost its modern volume. And after the long Huronian glaciation, the first multicellular life forms appeared on Earth - mushrooms and sponges. The Proterozoic is usually divided into three eras, each of which contained several periods.
3.1 Paleo-Proterozoic- the first era of the Proterozoic, which began 2.5 billion years ago. At this time, the lithosphere is fully formed. But the previous forms of life practically died out due to an increase in oxygen content. This period was called the oxygen catastrophe. By the end of the era, the first eukaryotes appear on Earth.
3.2 Meso-Proterozoic lasted approximately 600 million years. The most important events of this era: the formation of continental masses, the formation of the supercontinent Rodinia and the evolution of sexual reproduction.
3.3 Neo-Proterozoic. During this era, Rodinia breaks up into approximately 8 parts, the superocean of Mirovia ceases to exist, and at the end of the era, the Earth is covered with ice almost to the equator. In the Neoproterozoic era, living organisms for the first time begin to acquire a hard shell, which will later serve as the basis of the skeleton.
III. Paleozoic- the first era of the Phanerozoic eon, which began approximately 541 million years ago and lasted about 289 million years. This is the era of the emergence of ancient life. The supercontinent Gondwana unites the southern continents, a little later the rest of the land joins it and Pangea appears. Climatic zones begin to form, and the flora and fauna are represented mainly by marine species. Only towards the end of the Paleozoic did land development begin and the first vertebrates appeared.
The Paleozoic era is conventionally divided into 6 periods.
1. Cambrian period lasted 56 million years. During this period, the main rocks are formed, and a mineral skeleton appears in living organisms. And the most important event of the Cambrian is the emergence of the first arthropods.
2. Ordovician period- the second period of the Paleozoic, which lasted 42 million years. This is the era of the formation of sedimentary rocks, phosphorites and oil shale. The organic world of the Ordovician is represented by marine invertebrates and blue-green algae.
3. Silurian period covers the next 24 million years. At this time, almost 60% of living organisms that existed before die out. But the first cartilaginous and bony fishes in the history of the planet appear. On land, the Silurian is marked by the appearance of vascular plants. Supercontinents are moving closer together and forming Laurasia. By the end of the period, ice melted, sea levels rose, and the climate became milder.
4. Devonian period is characterized by the rapid development of diverse life forms and the development of new ecological niches. The Devonian covers a time period of 60 million years. The first terrestrial vertebrates, spiders, and insects appear. Sushi animals develop lungs. Although, fish still predominate. The flora kingdom of this period is represented by propferns, horsetails, mosses and gosperms.
5. Carboniferous period often called carbon. At this time, Laurasia collides with Gondwana and a new supercontinent Pangea appears. A new ocean is also formed - Tethys. This is the time of the appearance of the first amphibians and reptiles.
6. Permian period- the last period of the Paleozoic, ending 252 million years ago. It is believed that at this time a large asteroid fell on Earth, which led to significant climate change and the extinction of almost 90% of all living organisms. Most of the land is covered with sand, and the most extensive deserts appear that have ever existed in the entire history of the development of the Earth.
IV. Mesozoic- the second era of the Phanerozoic eon, which lasted almost 186 million years. At this time, the continents acquired almost modern outlines. A warm climate contributes to the rapid development of life on Earth. Giant ferns disappear and are replaced by angiosperms. The Mesozoic is the era of dinosaurs and the appearance of the first mammals.
The Mesozoic era is divided into three periods: Triassic, Jurassic and Cretaceous.
1. Triassic period lasted just over 50 million years. At this time, Pangea begins to break apart, and the internal seas gradually become smaller and dry out. The climate is mild, the zones are not clearly defined. Almost half of the land's plants are disappearing as deserts spread. And in the kingdom of fauna the first warm-blooded and land reptiles appeared, which became the ancestors of dinosaurs and birds.
2. Jurassic covers a span of 56 million years. The Earth had a humid and warm climate. The land is covered with thickets of ferns, pines, palms, and cypresses. Dinosaurs reign on the planet, and numerous mammals were still distinguished by their small stature and thick hair.
3. Cretaceous period- the longest period of the Mesozoic, lasting almost 79 million years. The separation of the continents is almost ending, the Atlantic Ocean is significantly increasing in volume, and ice sheets are forming at the poles. An increase in the water mass of the oceans leads to the formation of a greenhouse effect. At the end of the Cretaceous period, a catastrophe occurs, the causes of which are still not clear. As a result, all dinosaurs and most species of reptiles and gymnosperms became extinct.
V. Cenozoic- this is the era of animals and homo sapiens, which began 66 million years ago. At this time, the continents acquired their modern shape, Antarctica occupied the south pole of the Earth, and the oceans continued to expand. Plants and animals that survived the disaster of the Cretaceous period found themselves in a completely new world. Unique communities of life forms began to form on each continent.
The Cenozoic era is divided into three periods: Paleogene, Neogene and Quaternary.
1. Paleogene period ended approximately 23 million years ago. At this time, a tropical climate reigned on Earth, Europe was hidden under evergreen tropical forests, only deciduous trees grew in the north of the continents. It was during the Paleogene period that mammals developed rapidly.
2. Neogene period covers the next 20 million years of the planet's development. Whales and bats appear. And, although saber-toothed tigers and mastodons still roam the earth, the fauna is increasingly acquiring modern features.
3. Quaternary period began more than 2.5 million years ago and continues to this day. Two major events characterize this time period: the Ice Age and the emergence of man. The Ice Age completely completed the formation of the climate, flora and fauna of the continents. And the appearance of man marked the beginning of civilization.
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