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Earth — description of the planet

Earth

What if our earth is the hell of some other planet? (C) Aldous Huxley

Earth (original article in RussianЗемля) — is the third largest planet in the Solar[horo] system from the Sun. The earth became the place where organic life originated and developed.

Shape, size, and movement of the Earth

In shape, the Earth is close to an ellipsoid, flattened at the poles and stretched in the Equatorial zone. The average radius of the Earth is 6371.032 kilometers, polar-6356.777 km, Equatorial - 6378.160 km. the Mass of the Earth is 5.9761024 kg, the average density is 5518 kg/cubic meters. the Earth moves around the Sun at an average speed of 29.765 km/s in an elliptical, close to circular orbit (eccentricity 0.0167); the average distance from the Sun is 149.6 million kilometers, the period of one orbit is 365.24 solar days. The rotation of the Earth around its own axis occurs with an average angular velocity of 7.29211510-5 rad/s, which approximately corresponds to a period of 23 hours 56 minutes 4.1 seconds. The linear velocity of the Earth's surface at the equator is about 465 m/s. the axis of rotation is inclined to the plane of the Ecliptic at an angle of 66 33 '22". This inclination and the annual rotation of the Earth around the Sun determine the extremely important change of seasons for The earth's climate, and its own rotation - the change of day and night. The rotation of the Earth due to tidal influences is steadily slowing down (although very slowly — by 0.0015 s per century). There are also small irregular variations in the length of the day.

The position of the geographical poles changes with a period of 434 days with an amplitude of 0.36". In addition, there are small seasonal movements of them. The earth's surface area is 510.2 million km2, of which approximately 70.8% is in the world's oceans. Its average depth is about 3.8 km, the maximum (Mariana trench in the Pacific ocean) is 11.022 km; the volume of water is 1370 million km3, the average salinity is 35 g/l. Land is 29.2%, respectively, and forms six continents and Islands. It rises above sea level at an average of 875 m; the highest altitude (the peak of jomolungma in the Himalayas) is 8848 meters. Mountains on the planet occupy more than 1/3 of the land surface. Deserts cover about 20% of the land surface, savannas and woodlands-about 20%, forests-about 30%, glaciers-more than 10%. More than 10% of the land is occupied by agricultural land.

According to modern cosmogonic concepts, the Earth was formed about 4.6-4.7 billion years ago from a protoplanetary cloud captured by the attraction of the Sun. The formation of the first, most ancient of the studied rocks took 100-200 million years. About 3.5 billion years ago, conditions favorable for the emergence of life emerged. Homo sapiens ("Homo sapiens") as a species appeared about half a million years ago, and the formation of the modern type of man is attributed to the time of the retreat of the first glacier, that is, about 40 thousand years ago. The Earth has a single satellite, the Moon[horo]. Its orbit is close to a circle with a radius of about 384400 km.

On June 19, 240 BC, the Greek scientist Eratosthenes of Cyrene calculated the length of the earth's Meridian for the first time in the world.

On January 8, 1851, the French physicist Jean Bernard Leon Foucault proved that the Earth rotates on its axis.

Internal structure of the Earth

Internal structure of the Earth

Core (shown in red);

Mantle (brown);

Earth's crust (yellow); O

Oceans (blue).

The main role in the study of the internal structure of the Earth is played by seismic methods based on the study of the propagation of elastic waves (both longitudinal and transverse) in its thickness that occur during seismic events — natural earthquakes and explosions. Based on these studies, the Earth is conventionally divided into three regions: the crust, the mantle, and the core (in the center). The outer layer-the crust-has an average thickness of about 35 km. the Main types of the earth's crust are continental (mainland) and oceanic; in the transition zone from the mainland to the ocean, an intermediate type of crust is developed. The thickness of the crust varies quite widely: the oceanic crust (taking into account the water layer) has a thickness of about 10 km, while the thickness of the continental crust is ten times greater.

Surface deposits occupy a layer about 2 km thick. Below them is a granite layer (20 km thick on continents), and below it is about 14 km (both on continents and in oceans) basalt layer (lower crust). Average densities are: 2.6 g/cm3 at the Earth's surface, 2.67 g/cm3 at granite, and 2.85 g/cm3 at basalt.

The earth's mantle, also called the silicate shell, extends to a depth of approximately 35 to 2885 km. It is separated from the crust by a sharp boundary (the so-called Mohorovich boundary, or "Moho"), deeper than which the velocities of both longitudinal and transverse elastic seismic waves, as well as the mechanical density, increase abruptly. Densities in the mantle increase as the depth increases from about 3.3 to 9.7 g/cm3.

Extensive lithospheric plates are located in the crust and (partially) in the mantle. Their age-old movements not only determine the drift of continents, which significantly affects the appearance of the Earth, but are also related to the location of seismic zones on the planet.

Another discovered by seismic methods border (border Gutenberg) between the mantle and outer core is at a depth of 2775 km On it, the speed of longitudinal waves drops from 13.6 km/s (mantle) to 8.1 km/s (in the core), and the shear velocity decreases from 7.3 km/s to zero. The latter means that the outer core is liquid. According to modern concepts, the outer core consists of sulfur (12%) and iron (88%). Finally, at depths of more than 5120 km, seismic methods detect the presence of a solid inner core, which accounts for 1.7% of the Earth's mass. Presumably, this is an iron-Nickel alloy (80% Fe, 20% Ni).

Among the many chemical elements that make up the Earth, there are also radioactive ones. Their decay, as well as gravitational differentiation (moving denser substances to the Central, and less dense ones to the peripheral regions of the planet) lead to the release of heat. The temperature in the Central part of the Earth is about 5000 C. the Maximum surface temperature is close to 60 C (in the tropical deserts of Africa and North America[ru]), and the minimum is about -90 C (in the Central regions of Antarctica).

The pressure increases monotonously with a depth of 0 to 3.61 GPA. Heat from the earth's interior is transferred to its surface due to thermal conductivity and convection.

The density in the center of the Earth is about 12.5 g/cm3.

Diagram of the Solar system

Solar system

Above the ground

The earth is surrounded by an atmosphere. Its lower layer (the troposphere) extends on average to a height of 14 km; the processes occurring here play a crucial role in shaping the weather on the planet. The temperature in the troposphere drops with increasing altitude. The layer from 14 to 50-55 km is called the stratosphere; here the temperature increases with increasing altitude. Even higher (up to about 80-85 km) is the mesosphere, above which silvery clouds are observed (usually at an altitude of about 85 km). For biological processes on Earth, the ozonosphere is of great importance — the ozone layer located at an altitude of 12 to 50 km. The area above 50-80 km is called the ionosphere. Atoms and molecules in this layer are intensively ionized by solar radiation, in particular, ultraviolet radiation. If it were not for the ozone layer, radiation flows would reach The earth's surface, causing destruction in the living organisms there. Finally, at distances of more than 1,000 km, the gas is so sparse that collisions between molecules cease to play a significant role, and the atoms are ionized by more than half. At an altitude of about 1.6 and 3.7 earth radii are the first and second radiation belts.

The gravitational field of the Earth is described with high accuracy by Newton's law of universal gravitation. The acceleration of free fall over the Earth's surface is determined by both the gravitational and centrifugal force caused by The earth's rotation. The dependence of the free fall acceleration on latitude is approximated by the formula g=9.78031 (1+0.005302 sin2) m/c2, where m is the mass of the body.

The earth also has magnetic and electric fields. The magnetic field above the Earth's surface consists of a constant (or changing quite slowly) "main" and variable parts; the latter is usually referred to as variations of the magnetic field. The main magnetic field has a structure close to the dipole. The magnetic dipole moment of the Earth, equal to 7.981025 units of SGSM, is directed approximately opposite to the mechanical one, although at present the magnetic poles are slightly shifted in relation to the geographical ones. Their position, however, changes with time, and although these changes are quite slow, over geological periods of time, according to paleomagnetic data, even magnetic inversions, that is, inversions of polarity, are detected. The magnetic field strengths at the North and South magnetic poles are equal to 0.58 and 0.68 E, respectively, and at the geomagnetic equator — about 0.4 E.

The electric field above the Earth's surface has an average intensity of about 100 V/m and is directed vertically downward — this is the so-called "clear weather field", but this field experiences significant (both periodic and irregular) variations.

Geophysics - the physics of the Earth - is relatively young. Everything that happens in the bowels of our planet has not yet been fully studied.

History of research the Initial phase

The most ancient cartographic images of the Earth were created in Egypt and Babylonia in the 3-1 Millennium BC. In the 7th century BC, maps were made on clay tablets in Mesopotamia. Purely speculative ideas about the surrounding world are contained in the sources left by the peoples of the Ancient East. However, during this period, ideas about the Earth were mostly determined by myths and legends.

Early antiquity (6th-1st centuries BC.)

The greatest achievements in this period were achieved by scientists of Ancient Greece, who sought to give an idea of the Earth as a whole. The first attempt to create a map of the entire Earth was made by Anaximander, according to whom the Earth is a cylinder (surrounded by a celestial sphere), around the sea basin there is land, in turn, surrounded by a water ring. One of the first geographical works — "land Description" of hecateus of Miletus was accompanied, apparently, by a geographical map on which, in addition to Europe and Asia, the seas known to the ancient Greeks were shown: the Mediterranean, the Black, the Azov, the Caspian, and the Red. Hecateus first introduced the concept of the oikumen. Between 350 and 320 BC, Piteas (PYTHEAS) reached the shores of Western Europe, discovering the British and Irish Islands. To him belongs the correct observation of the connection of the tides in the ocean with the movements of the moon.

The assumption that the Earth is spherical seems to have been made by Pythagoras for the first time. Experienced navigators, the ancient Greeks, noticed that when the ship approaches the observer, the sails are first visible and only then the entire ship, which indicates the sphericity of the planet. In the development of these ideas, Heraclitus proposed the idea of the earth's rotation around its axis. In 340 BC. in the book" About the sky", Aristotle gave evidence of the earth's spherical shape: during lunar eclipses, the Earth always casts a round shadow on the moon, and the North star is located higher above the horizon in the Northern regions than in the southern ones. After estimating the difference in the apparent position of the Polar star in Greece and Egypt, Aristotle calculated the length of the equator, which, however, was about twice as large as the real one.

For the first time, Eratosthenes determined the diameter of the globe fairly accurately based on a simple experiment — the difference in the height of the Sun in the cities of Siena and Alexandria, lying on the same midday line, and the distance between them. The measurement was performed during the summer solstice, the calculated diameter length differed from the actual one only by 75 kilometers. The geometrical principles that he used, formed the basis of the degree measurement of the Earth. Almost all the works of this scientist have not been preserved, they are known from the works of later Greek authors.

In the 2nd century BC, ancient Greek scientists introduced the concepts of geographical latitude and longitude, developed the first map projections that showed a grid of Parallels and meridians, and proposed methods for determining the relative position of points on the earth's surface.

Ancient scientists paid attention to the change of the Earth's surface over time as a result of the action of water and internal forces of the Earth, especially volcanic processes. These ideas later formed the basis of the geological concepts of neptunism (see also about Neptune in mythology) and plutonism.

Late antiquity (1-2 centuries)

In the first decades of the 1st century, the idea of a spherical Earth was established. The level of knowledge about the surrounding world of this period is characterized by the outstanding work of Pliny the Elder "Natural history" in 37 books, containing information on geography, meteorology, botany, Mineralogy, as well as history and art.

A peculiar result of geographical knowledge of antiquity is the "Geography" of Strabo in 17 books, where the Caucasus and the Bosporan Kingdom are described in some detail. The book was intended to serve as a practical guide for generals, navigators, and merchants, and therefore contained numerous household and historical information. Strabo suggested that several continents and Islands probably lie in the unknown ocean between the Western tip of Europe and East Asia. It is possible that this assumption was known to Christopher Columbus[ru].

In the 2nd century, Ptolemy in the work "Geography" gave a summary of geographical information, including a map of the world and 16 regions of the Earth. He has already suggested the Central position of the Earth in the Universe (the geocentric system of the world). During this period, along with ideas based on the discoveries of scientists, travelers, and merchants, legends were spread about unknown or disappeared regions and countries, such as Atlantis.

Middle ages (late 8th-14th centuries)

In the 8-10 centuries, the Vikings, who made conquests, discovered Greenland and were the first Europeans to reach North America (the so-called country of Vinland, Markland, Heluland). In the 9th-11th centuries, studies of lands unknown to Europeans by Arab scholars and travelers (Masudi, muqaddasi, yakubi) became an important source for the study of the East. Biruni was the first in the Middle East to suggest that the Earth moves around the Sun. He gave many interesting topographical and geographical observations for his time, as well as geological and mineralogical information. In the 12th-13th centuries. the travels of PLANO Carpini and Marco Polo provided an insight into Central, Eastern, and southern Asia.

Great geographical discoveries (15th-mid-17th centuries)

The improvement of devices that allowed navigating the ocean (compass, log, astrolabe), the creation of nautical charts, as well as the need for new trade links, contributed to the Great geographical discoveries. The results of these discoveries finally clarified the question of the earth's spherical shape, which was directly proved by the circumnavigation of the world by Fernand Magellan in the early 16th century. The voyages of Christopher Columbus, Vasco da Gama, Amerigo Vespucci and other navigators in the world ocean, and the travels of Russian explorers in North Asia allowed us to establish the contours of continents, as well as describe most of the earth's surface, the animal and plant world of the Earth. At the same time, the heliocentric system of the world proposed by the Polish scientist Nikolai Nikolaevich Copernicus marked the beginning of a new era in natural science.

On April 20, 1910, Halley's comet came as close as possible to Earth.

Section of the earth's surface with a vertical plane

The Section Of The Earth

The scientific phase of the study of the Earth

First period (17th-mid-19th centuries)

This historical stage is characterized by a wide use of physical, mathematical and instrumental methods. Isaac Newton's discovery of the law of universal gravitation in the second half of the 17th century led to the idea that the Earth is not a perfect ball, but a flattened spheroid at the poles. Based on assumptions about the internal structure of the Earth and based on the law of universal gravitation, Newton and Christian Huygens gave a theoretical estimate of the size of the compression of the earth's spheroid and obtained such different results that there were doubts about the validity of the hypothesis about the earth's spheroid. To disperse them, the Paris Academy of Sciences in the first half of the 18th century sent expeditions to the circumpolar regions of the Earth-in Peru and Lapland, where degree measurements were performed, confirming the validity of the idea of the spheroidicity of the Earth and the law of universal gravity.

Rene Descartes and Gottfried Wilhelm Leibniz first considered the Earth as a developing cosmic body that was initially in a molten state and then cooled, becoming covered with solid crust. The molten Earth was enveloped in vapors, which then thickened and created the world's ocean, its waters partially went into underground voids, creating land. Robert Hooke, Georg Wilhelm Richman, and others associated the appearance of mountains on Earth with earthquakes or volcanic activity. Mikhail Vasilyevich Lomonosov[ru], a Russian natural scientist of world significance, also explained the formation of mountains by "underground heat".

The discoveries, research, and ideas of the 17th and first half of the 19th centuries set the stage for the emergence of a complex of Earth Sciences. The most important of them is, in particular, the discovery of the English physicist and doctor[ru] William Hilbert, which consists in the fact that the Earth is in the first approximation an elementary magnet. Lomonosov suggested that the value of gravity on the earth's surface is determined by the internal structure of the planet. He was also one of the first to attempt to measure variations in the acceleration of gravity, and together with the Russian physicist Georg Wilhelm Richman, he studied atmospheric electricity. During the same period, the pendulum theory was developed, on the basis of which fairly accurate definitions of gravity were made, and meteorological instruments were developed for measuring wind speed, precipitation, and air humidity. German naturalist Alexander Humboldt found that the intensity of earth's magnetism changes with latitude, decreasing from the pole to the equator, and developed ideas about the natural distribution of vegetation on the Earth's surface (latitude and altitude zoning). He was one of the first to observe the magnetic storm and summarized the accumulated data on the structure of the Earth by the first quarter of the 19th century. To study the passage of seismic waves in the earth, mallet carried out the first artificial earthquake in 1851 (exploding gunpowder and observing the propagation of vibrations on the surface of mercury in a vessel). In 1897, Emil Wichert, based on the results of studying the composition of meteorites and the distribution of density in the bowels of the planet, identified the earth's metal core and stone shell in the Earth. During this period, it was possible to determine the relative age of rocks from the remains of flora and fauna that remained in them, which later allowed us to build a geochronological scale, carry out paleoreconstructions of the position of continents and oceans in different geological epochs, and study the history of the geological development of the Earth.

Second period (mid-late 19th century)

At this time, there was a deepening of knowledge about the structure of our planet on the basis of developing magnetic, gravimetric, seismic, electrical and radiometric methods of Geophysics. The contract hypothesis is widely accepted among geologists. In 1855, the English astronomer Airey suggested the equilibrium state of the earth's crust (isostasis), which was confirmed in the 20th century when studying the deep structure of mountains, when it was found that higher mountains have deeper roots.

The third period (the first half of the 20th century)

The beginning of the century was marked by major successes in the study of the polar regions of the Earth. In 1909, American Explorer Robert Edwin Peary reached the North pole, and in 1911, Norwegian polar Explorer and Explorer Roald Amundsen reached the South pole. Norwegian, Belgian, French, and Russian[ru] travelers surveyed the circumpolar regions, compiled descriptions and maps of them. Later, a systematic study of these areas was started with the help of Antarctic research stations and North pole drifting observatories. In the first half of the 20th century, thanks to further improvement of geophysical methods and, especially, seismology, fundamental data on the deep structure of the Earth were obtained. In 1909, the Yugoslav geophysicist and seismologist Andrei Mokhorovich identified a planetary boundary that is the sole of the earth's crust. In 1916, one of the founders of seismology, Russian physicist and geophysicist, seismologist Boris Borisovich Golitsyn fixed the boundary of the upper mantle, and in 1926, American geophysicist Beno Gutenberg established the presence of a seismic waveguide (asthenosphere) in it. The same scientist determined the position and depth of the boundary between The earth's mantle and the core. In 1935, the American seismologist Charles Francis Richter introduced the concept of earthquake magnitude and developed the Richter scale together with Gutenberg in 1941-1945. Later, based on seismological and gravimetric data, a model of The earth's internal structure was developed, which remains virtually unchanged to this day.

The beginning of the 20th century was marked by the emergence of a hypothesis that was destined to play a key role in the Earth Sciences in the future. F. Taylor (1910), followed by Alfred Lothar Wegener (1912), expressed the idea of horizontal movements of continents over long distances (continental drift), which was confirmed in the 1960s after the discovery of a global system of mid-ocean ridges in the oceans, encircling the entire globe and sometimes coming to land (Rift world system). It was also found that the earth's crust under the oceans is fundamentally different from the continental crust, and the power of precipitation on the bottom increases from the crests of ridges to their periphery. Anomalies of the magnetic field of the ocean bed were mapped, which have an amazing, symmetrical structure relative to the axes of the ridges. All these and other results served as the basis for a return to the ideas of continental drift, but in a new form-plate tectonics, which remains the leading theory in the Earth Sciences.

A significant amount of new information, especially about the structure of the atmosphere, was obtained as a result of studies of global geophysical processes during maximum solar activity, conducted within the framework of the International geophysical year (1957-1958) by scientists from 67 countries.

The fourth period (the second half of the 20th century)

The development of methods for radiometric Dating of rocks in the 2nd half of the 20th century allowed us to clarify the age of our planet. Intensive development of satellite Geophysics has begun. Based on satellite measurements, the structure of the magnetosphere was studied, as well as the presence of radiation belts around the Earth. In the late 1970s, significant progress was made in the study of the geoid using geodesic satellites (GEOS-3) equipped with high-precision radar altimeters. Along with satellite geodesy, methods for studying atmospheric processes from satellites-satellite meteorology-have been widely developed, which has significantly increased the accuracy of weather forecasts.

Since 1968, an international program of deep-sea drilling in The world's oceans has been conducted, about 2,000 wells have been drilled, and more than 182 km of core has been obtained. This made it possible to significantly advance the understanding of tectonic structure, paleooceanography, and sedimentation of ocean basins. On the continents, the study of the deep structure of the Earth is carried out using ultra-deep drilling, which reached a depth of more than 12 km in 1984 (Kola super-deep well).

Habitable deep-sea vehicles were used to study the maximum depths of the ocean. In 1960, the Swiss J. Piccard and the American D. Walsh in the bathyscaphe "Trieste" reached the bottom of the Mariana trench — the deepest place in The world ocean (11022 meters). Since the 1980s and 90s, underwater vehicles with a human on Board have been widely used to perform geological, hydrological and biological observations in the depths of the ocean.

With 1980-90s developing geophysical imaging, which is built seismic sections of the lower and upper mantle, which together with geothermal and other geophysical data allowed the qualitative and quantitative modeling of mantle convection — circulation movement of mantle material.

Launches of interplanetary spacecraft to Mercury[horo], Mars[horo], Venus[horo] (see also about Venus from mythology), as well as to more distant planets also allowed to deepen knowledge about the structure and evolution of the Earth on the basis of comparative study of planets (comparative planetology). The obtained data together with information about the structure of the earth's crust and deep interior of the planet was the basis for the development of models of the Earth, since its formation from the protoplanetary cloud. (V. I. Grigoriev, E. G. Mirlin).

On July 23, 2019, the Belarusian newspaper Zvyazda published a large article devoted to the problems of near-space industrialization - "Baron Munchausen's Pigtail to face planet Earth" (pdf-file 900 KB) - which tells about the project of Anatoly Yunitskiy[ru] General Planetary vehicle (OTS) — an astroengineered transport system that implements the "Baron Munchausen principle" - the use of the system's internal forces to overcome earth's gravity.

Songs about the Earth

Before it's too late — performed by Kobzon, Muz. Pakhmutova
Native land — Lev Valeryanovich Leshchenko

Earth Day

Earth day is an international holiday, celebrated on the initiative of the United Nations. In the calendar of international holidays, there are two Earth Days — March 20 is celebrated on the day of the vernal equinox, and the second-on April 22. The first has a peacemaking and humanistic orientation, the second — environmental.

The date of March 20 was chosen and officially approved in 1971 by the United Nations for Earth Day precisely because this time falls on the day of the vernal equinox, when the biological rhythm of the planet changes, and it goes to a new round of its development, when there is an awakening of nature and its renewal. The UN address reads: "Earth Day is a special time that is intended to draw the attention of all people to the awareness of planet Earth as their common home, to feel our all-earth community and mutual dependence on each other."

The founder of this Day is considered to be a famous American public figure John Morton, who in the 1840s launched a campaign to plant trees and shrubs, as part of the program of respect for the environment of every citizen of the country. And when he became Secretary Of the territory of Nebraska, in 1872, he proposed setting a day that would be dedicated to gardening. So there was a tree Day, which immediately became very popular.

During the first Day, residents of the state planted about a million trees, and soon their initiative turned into a social movement. Starting in 1970, the meaning of the holiday expanded to the General idea of environmental protection, and a new name appeared — Earth Day, which became nationwide. In 1971, the United Nations officially adopted this holiday, and it subsequently became a worldwide holiday, receiving more and more international support every year.

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