Planet of the solar system earth.
Four centuries of hard work of scientists - astronomers, mathematicians, physicists, who performed the finest observations, deep theoretical studies, were needed to find out the features of the planetary system and, to some extent, the nature of the planetary bodies closest to the Earth.
We see our Earth among nine large planets revolving around the Sun. They are located by distance from the Sun in the following order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto. The first five have been known since ancient times. Uranus was "accidentally" discovered by Herschel in 1781. The existence of Neptune was discovered in 1846 (and before that it was theoretically predicted). In 1930, Pluto was also discovered near the theoretically calculated place.
The paths of the planets deviate from circles - these are slightly elongated elliptical curves. The planets move according to Kepler's laws - faster near perihelion- the point of the orbit closest to the Sun, slower - near aphelion. The periods of revolution depend on the average distances - on the semi-axis of the orbit: P = a 3/2. Astronomers measure distances in the solar system in astronomical units. The astronomical unit is the average distance of the Earth from the Sun. It is equal to 149.6 million km.
The sizes of the planets have been measured, their masses have been determined. For some planets, it is established how they rotate around their axes. Table 1 provides some important information about the planets and individual moons.
The earth, therefore, is indeed an average planet both in position relative to the sun and in size. Venus, for example, is only slightly smaller. The rotation of Mars on its axis is very similar to the rotation of the Earth; it determines the change of seasons of the year and the position of climatic zones on the earth's surface. Jupiter is a giant planet. It is 11 times larger than the Earth in diameter and 318 times larger in mass. A curious anomaly is the distant Pluto, which has not passed even one-eighth of its orbit around the Sun since its discovery. Pluto is almost the same size as Mercury, and many astronomers consider it a body that escaped after some kind of catastrophe from the Neptune system.
An interesting problem is the satellites of the planets. So far, 31 satellites have been discovered. Seven of them are large. Such satellites are the Moon or Ganymede (near Jupiter) or Titan (near Saturn). They are almost the size of Mercury and only slightly smaller than Pluto or Mars. The rest of the satellites are small. Their diameters are measured only in hundreds, tens or even several kilometers.
Saturn is surrounded by many small moons and masses of gas and ice, which together form a ring visible around the planet even with small telescopes. Apparently, a similar ring, only much weaker, is also found in Jupiter.
A lot of cosmic boulders and stones make up the family of asteroids and meteoroids. Astronomers already know more than 1,600 minor planets and countless stones, which, often meeting the Earth, fall on its surface in the form of meteorites. Flying at cosmic speeds of tens of kilometers per second through the earth's atmosphere, they form the phenomena of fireballs and meteors. Studying these phenomena, examining meteorites in laboratories, scientists establish the nature and origin of numerous small bodies that "clog" interplanetary space. Their number is very large, and the total mass apparently approaches the mass of the Earth. All minor planets and many meteoroids move in elliptical orbits and belong to the solar system.
There are even more comets in the solar system moving in both short periodic and very elongated orbits. It takes 30 million years for the comet to reach the limits of the solar system (the limits of the sphere of action of the Sun), that is, to pass 150,000 astronomical units and return to the Sun again. The hazy heads and tails of comets are made up of gas and dust produced by the evaporation of "contaminated" ices found in cometary nuclei. Comets are relatively recently formed bodies that still retain a large amount of frozen gases.
The sun controls, thanks to the force of its attraction, the movement of planets and comets, cosmic boulders and an infinite number of dust particles - meteor particles. It also has other effects on the planets and small bodies of the solar system.
The sun is a star like "billions of stars shining in the night sky.
Having determined the distance to the Sun, astronomers were convinced that its dimensions are indeed colossal. Although in the sky the apparent diameter of the Sun is equal to the lunar one or even slightly less, the distance to the Sun (149.6 million km, or 1 astronomical unit) is 400 times greater than the distance of the Moon from the Earth; therefore, the same number of times the Sun must be larger than the Moon. If the lunar diameter is 3.5 thousand km, then the size of the Sun is 1400 thousand km, 109 times larger than that of the Earth.
By measuring the amount of energy coming from the Sun and the strength of its light, scientists found the temperature of its surface, reaching 6000 °, and made sure that the Sun is a giant hot gas ball, in mass (i.e., the amount of matter) 330,000 times greater than Earth and almost 7/10 times the total mass of all the major planets.
The sun plays a decisive role in all processes on Earth, and therefore its study is not only of theoretical but also of great practical importance.
A continuous service of the Sun has been created, which, with the help of optical solar telescopes, as well as radio telescopes, conducts observations of processes on the solar surface. Registration and study of sunspots - giant electromagnetic vortices in the solar atmosphere are underway. Their dimensions sometimes exceed tens and hundreds of thousands of kilometers; the strength of magnetic fields in spots that astronomers have learned to measure often exceeds thousands of gauss (Gauss is a unit of strength magnetic field). Above the bright surface of the Sun - photosphere- layers of more rarefied, hot gases are located chromosphere. They often rise from the surface in the form prominences to a height of hundreds of thousands of kilometers. In the chromosphere and even in the upper parts of the Sun's atmosphere - solar corona, clearly visible during full solar eclipses, grandiose whirlwinds and storms are played out.
These processes are controlled by powerful electromagnetic forces arising in the ionized solar matter - in the solar plasma.
The rays of the solar corona are streams of solar matter - corpuscular streams, consisting mainly of the nuclei of atoms (mainly of the nuclei of hydrogen atoms - protons) and electrons.
With special attention Explosions on the Sun are studied, leading to flashes of ultraviolet and X-ray radiation, to the ejection of solar corpuscles and a huge amount of hard cosmic particles. About 30 years ago, scientists discovered that the Sun is a source of radio waves. Now, at many observatories in the world, special radio telescopes continuously monitor the Sun and register its radiation at meter, centimeter and millimeter waves. The data obtained in the form of records reveal a picture of powerful processes taking place on the solar surface. When giant explosions occur in sunspot regions, astronomers can determine the speeds of solar matter from bursts of radio emission, reaching tens and even hundreds of thousands of kilometers per second. At a speed close to the speed of light, particles of cosmic rays rush. Arising from solar explosions, fast cosmic particles permeate interplanetary space.
The root cause of solar radiation and all processes on the Sun, apparently, is atomic (thermonuclear) energy generated inside the Sun. At a temperature of 13-20 million degrees in the bowels of the Sun, hydrogen is converted into helium, and part of the intra-atomic energy is released. It turns out to be enough to support high temperature stars for millions and billions of years.
Astronomers and physicists are working hard to unravel the nature of solar flares. Some researchers believe that the movement of charged solar matter (ionized gas) in a magnetic field can cause compression of flows, leading to explosions. Academician V. A. Ambartsumyan admits that explosions occur as a result of the release of matter from the central regions, which is in a superdense "pre-stellar" state, onto the surface of the Sun. The transition from a superdense state to a state of ordinary rarefied, heated gas should lead to explosions. In some stars, these explosions take on the scale of grandiose cosmic catastrophes.
Without clarifying the nature of solar processes, it is impossible to understand the features of the Earth, since the Sun plays a decisive role in the life of the Earth and other planets closest to us. The sun emits a huge amount of light, heat, radio waves, charged particles. In a second, the Sun wastes energy reaching hundreds of billions of billions of kilowatts, i.e., more than a thousand times more than what could be obtained by burning all reserves hard coal, which are on Earth. Of this energy, the Earth receives only one two-billionth part, but even this amounts to tens of thousands of millions of kilowatts.
The life of plants and animals is supported and developed by the energy of the Sun. At the same time, the processes of solar activity - ultraviolet radiation from the Sun, corpuscular streams escaping from the solar surface - determine many features of phenomena on Earth. The state of the radiation belts around the Earth and fluctuations of the earth's magnetic field depend on them. Streams of hard ultraviolet radiation and charged particles ionize the upper layers of our atmosphere and determine the conditions for the propagation of radio waves, the conditions for radio communication on the earth's surface.
Excitation in the upper atmosphere (ionosphere) is transmitted to the lower layers, to the troposphere, where all weather phenomena are played out.
The giant water cycle caused by solar energy- the evaporation of ocean waters and the transfer of water vapor and water droplets by winds - depends to some extent on the rhythm of solar activity. That is why the 11-year cycle of solar activity affects the growth of trees and plants. However, far from all aspects of this connection between solar processes and phenomena on Earth have been elucidated. And not only astronomers, but also geophysicists, specialists in the atmosphere and hydrosphere, ice, terrestrial currents and other phenomena, as well as biologists, physicists, radio physicists and space explorers are intensively studying all manifestations of solar influences.
Abstract on the topic
"Earth is a planet in the solar system"
1. The structure and composition of the solar system. Two groups of planets
2. Terrestrial planets. Earth-Moon system
3. Earth
4. Ancient and modern explorations of the Earth
5. Exploring the Earth from space
6. Origin of life on earth
7. Earth's only satellite is the Moon
Conclusion
1. The structure and composition of the solar system. two groups of planets.
Our Earth is one of the 8 major planets revolving around the Sun. It is in the Sun that the main part of the matter of the solar system is concentrated. The mass of the Sun is 750 times the mass of all the planets and 330,000 times the mass of the Earth. Under the influence of the force of its attraction, the planets and all other bodies of the solar system move around the sun.
The distances between the Sun and the planets are many times greater than their size, and it is almost impossible to draw such a diagram that would observe a single scale for the Sun, planets and the distances between them. The diameter of the Sun is 109 times larger than the Earth, and the distance between them is about the same number of times the diameter of the Sun. In addition, the distance from the Sun to the last planet of the solar system (Neptune) is 30 times greater than the distance to the Earth. If we depict our planet as a circle with a diameter of 1 mm, then the Sun will be at a distance of about 11 m from the Earth, and its diameter will be about 11 cm. The orbit of Neptune will be shown as a circle with a radius of 330 m. Therefore, they usually give not a modern diagram of the solar system, but only drawing from the book of Copernicus "On the circulation of the celestial circles" with other, very approximate proportions.
By physical characteristics the major planets are divided into two groups. One of them - the planets of the terrestrial group - is the Earth and similar Mercury, Venus and Mars. The second includes the giant planets: Jupiter, Saturn, Uranus and Neptune. Until 2006, Pluto was considered the largest planet farthest from the Sun. Now, together with other objects of similar size - long-known large asteroids (see § 4) and objects discovered on the outskirts of the solar system - it is among the dwarf planets.
The division of the planets into groups can be traced by three characteristics (mass, pressure, rotation), but most clearly by density. Planets belonging to the same group differ insignificantly in density, while the average density of terrestrial planets is approximately 5 times greater than the average density of giant planets (see Table 1).
Most of the mass of the terrestrial planets is in solid matter. The Earth and other terrestrial planets are composed of oxides and other heavy compounds. chemical elements A: iron, magnesium, aluminum and other metals, as well as silicon and other non-metals. The four most abundant elements in the solid shell of our planet (lithosphere) - iron, oxygen, silicon and magnesium - account for over 90% of its mass.
The low density of the giant planets (for Saturn it is less than the density of water) is explained by the fact that they consist mainly of hydrogen and helium, which are mainly in gaseous and liquid states. The atmospheres of these planets also contain hydrogen compounds - methane and ammonia. Differences between the planets of the two groups arose already at the stage of their formation (see § 5).
Of the giant planets, Jupiter is best studied, on which, even in a small school telescope, numerous dark and light stripes are visible, stretching parallel to the planet's equator. This is what cloud formations look like in its atmosphere, the temperature of which is only -140 ° C, and the pressure is about the same as at the surface of the Earth. The reddish-brown color of the bands is apparently due to the fact that, in addition to the ammonia crystals that form the basis of the clouds, they contain various impurities. The images taken by spacecraft show traces of intense and sometimes persistent atmospheric processes. So, for over 350 years, an atmospheric vortex, called the Great Red Spot, has been observed on Jupiter. In the earth's atmosphere, cyclones and anticyclones exist on average for about a week. Atmospheric currents and clouds have been recorded by spacecraft on other giant planets, although they are less developed than on Jupiter.
Structure. It is assumed that as it approaches the center of the giant planets, due to an increase in pressure, hydrogen should pass from a gaseous to a gaseous state, in which its gaseous and liquid phases coexist. At the center of Jupiter, the pressure is millions of times greater than Atmosphere pressure that exists on Earth, and hydrogen acquires properties characteristic of metals. In the depths of Jupiter, metallic hydrogen, together with silicates and metals, forms a core, which is approximately 1.5 times larger in size and 10–15 times larger in mass than the Earth.
Weight. Any of the giant planets exceeds in mass all the terrestrial planets combined. The largest planet in the solar system - Jupiter is larger than the largest planet of the terrestrial group - the Earth by 11 times in diameter and more than 300 times in mass.
Rotation. The differences between the planets of the two groups are also manifested in the fact that the giant planets rotate faster around the axis, and in the number of satellites: there are only 3 satellites for 4 terrestrial planets, more than 120 for 4 giant planets. All these satellites consist of the same substances, like the planets of the terrestrial group - silicates, oxides and sulfides of metals, etc., as well as water (or water-ammonia) ice. In addition to numerous craters of meteorite origin, tectonic faults and cracks in their crust or ice cover have been found on the surface of many satellites. The discovery of about a dozen active volcanoes on the closest satellite to Jupiter, Io, turned out to be the most surprising. This is the first reliable observation of terrestrial-type volcanic activity outside our planet.
In addition to satellites, giant planets also have rings, which are clusters of small bodies. They are so small that they cannot be seen individually. Due to their circulation around the planet, the rings appear to be continuous, although both the surface of the planet and the stars shine through the rings of Saturn, for example. The rings are located in close proximity to the planet, where large satellites cannot exist.
2. Planets of the terrestrial group. Earth-Moon system
Due to the presence of a satellite, the Moon, the Earth is often called a double planet. This emphasizes both the commonality of their origin and the rare ratio of the masses of the planet and its satellite: the Moon is only 81 times smaller than the Earth.
Sufficiently detailed information will be given about the nature of the Earth in subsequent chapters of the textbook. Therefore, here we will talk about the rest of the planets of the terrestrial group, comparing them with ours, and about the Moon, which, although it is only a satellite of the Earth, by its nature belongs to planetary-type bodies.
Despite the common origin, the nature of the moon is significantly different from the earth, which is determined by its mass and size. Due to the fact that the force of gravity on the surface of the Moon is 6 times less than on the surface of the Earth, it is much easier for gas molecules to leave the Moon. Therefore, our natural satellite is devoid of a noticeable atmosphere and hydrosphere.
The absence of an atmosphere and slow rotation around the axis (a day on the Moon is equal to an Earth month) lead to the fact that during the day the surface of the Moon heats up to 120 ° C, and cools down to -170 ° C at night. Due to the absence of an atmosphere, the lunar surface is subject to constant “bombardment” by meteorites and smaller micrometeorites that fall on it at cosmic speeds (tens of kilometers per second). As a result, the entire Moon is covered with a layer of finely divided substance - regolith. As described by American astronauts who have been on the Moon, and as photographs of the traces of lunar rovers show, in terms of its physical and mechanical properties (particle sizes, strength, etc.), regolith is similar to wet sand.
When large bodies fall on the surface of the Moon, craters up to 200 km in diameter are formed. Craters meter and even centimeter in diameter are clearly visible in the panoramas of the lunar surface obtained from spacecraft.
Under laboratory conditions, samples of rocks delivered by our automatic stations "Luna" and American astronauts who visited the Moon on the Apollo spacecraft were studied in detail. This made it possible to obtain more complete information than in the analysis of the rocks of Mars and Venus, which was carried out directly on the surface of these planets. Lunar rocks are similar in composition to terrestrial rocks such as basalts, norites, and anorthosites. The set of minerals in lunar rocks is poorer than in terrestrial, but richer than in meteorites. Our satellite does not have and never had a hydrosphere or an atmosphere of the same composition as on Earth. Therefore, there are no minerals that can be formed in the aquatic environment and in the presence of free oxygen. Lunar rocks are depleted in volatile elements compared to terrestrial ones, but they are distinguished by an increased content of iron and aluminum oxides, and in some cases titanium, potassium, rare earth elements and phosphorus. No signs of life, even in the form of microorganisms or organic compounds, have been found on the Moon.
The light areas of the Moon - the "continents" and the darker ones - the "seas" differ not only in appearance, but also in relief, geological history and chemical composition material that covers them. On the younger surface of the "seas", covered with solidified lava, there are fewer craters than on the older surface of the "continents". In various parts of the Moon, such relief forms as cracks are noticeable, along which the crust is shifted vertically and horizontally. In this case, only fault-type mountains are formed, and there are no folded mountains, so typical for our planet, on the Moon.
The absence of erosion and weathering processes on the Moon allows us to consider it a kind of geological reserve, where for millions and billions of years all the landforms that have arisen during this time have been preserved. Thus, the study of the Moon makes it possible to understand the geological processes that took place on Earth in the distant past, of which no traces remain on our planet.
3. Earth.
Earth is the third planet from the Sun in the solar system. It revolves around the star at an average distance of 149.6 million km over a period of 365.24 days.
The Earth has a satellite - the Moon, which revolves around the Sun at an average distance of 384,400 km. The inclination of the earth's axis to the plane of the ecliptic is 66033`22``. The period of rotation of the planet around its axis is 23 hours 56 minutes 4.1 seconds. Rotation around its axis causes the change of day and night, and the tilt of the axis and circulation around the Sun - the change of seasons. The shape of the Earth is a geoid, approximately a triaxial ellipsoid, a spheroid. The average radius of the Earth is 6371.032 km, equatorial - 6378.16 km, polar - 6356.777 km. Surface area the globe 510 million km², volume - 1.083 * 1012 km², average density 5518 kg / m³. The mass of the Earth is 5976 * 1021 kg.
The earth has magnetic and electric fields. The gravitational field of the Earth determines its spherical shape and the existence of the atmosphere. According to modern cosmogonic concepts, the Earth was formed about 4.7 billion years ago from the gaseous matter scattered in the protosolar system. As a result of the differentiation of matter, the Earth, under the influence of its gravitational field, under the conditions of heating of the earth's interior, arose and developed various in chemical composition, state of aggregation and physical properties shells - geospheres: core (in the center), mantle, earth's crust, hydrosphere, atmosphere, magnetosphere. The composition of the Earth is dominated by iron (34.6%), oxygen (29.5%), silicon (15.2%), magnesium (12.7%). The earth's crust, mantle and inner part of the core are solid (the outer part of the core is considered liquid). From the surface of the Earth to the center, pressure, density and temperature increase.
The pressure in the center of the planet is 3.6 * 1011 Pa, the density is about 12.5 * 103 kg / m³, the temperature ranges from 50000ºС to 60000ºС.
The main types of the earth's crust are continental and oceanic; in the transition zone from the mainland to the ocean, an intermediate crust is developed.
Most of the Earth is occupied by the World Ocean (361.1 million km²; 70.8%), the land is 149.1 million km² (29.2%), and forms six continents and islands. It rises above the world ocean level by an average of 875 m (the highest height is 8848 m - Mount Chomolungma), mountains occupy more than 1/3 of the land surface. Deserts cover about 20% of the land surface, forests - about 30%, glaciers - over 10%. The average depth of the world ocean is about 3800 m (the greatest depth is 11020 m - the Mariana Trench (trough) in pacific ocean). The volume of water on the planet is 1370 million km³, the average salinity is 35 g/l. The atmosphere of the Earth, the total mass of which is 5.15 * 1015 tons, consists of air - a mixture of mainly nitrogen (78.08%) and oxygen (20.95%), the rest is water vapor, carbon dioxide, as well as inert and other gases. The maximum land surface temperature is 570º-580º C (in the tropical deserts of Africa and North America), the minimum is about -900º C (in the central regions of Antarctica). The formation of the Earth and the initial stage of its development belong to pregeological history. The absolute age of the most ancient rocks is over 3.5 billion years. The geological history of the Earth is divided into two unequal stages: the Precambrian, which occupies approximately 5/6 of the entire geological chronology (about 3 billion years) and the Phanerozoic, covering the last 570 million years.
About 3-3.5 billion years ago, as a result of the natural evolution of matter, life arose on Earth, and the development of the biosphere began. The totality of all living organisms inhabiting it, the so-called living matter of the Earth, had a significant impact on the development of the atmosphere, hydrosphere and sedimentary shell. A new factor that has a powerful influence on the biosphere is the production activity of man, who appeared on Earth less than 3 million years ago. The high growth rate of the world's population (275 million people in 1000, 1.6 billion people in 1900 and about 6.3 billion people in 1995) and the increasing influence of human society on natural environment put forward the problems of rational use of all natural resources and nature protection.
4. Ancient and modern studies of the Earth.
For the first time, the ancient Greek mathematician and astronomer Eratosthenes managed to obtain fairly accurate dimensions of our planet in the 1st century BC (an accuracy of about 1.3%). Eratosthenes discovered that at noon on the longest day of summer, when the Sun is at its highest in the sky of Aswan and its rays fall vertically, in Alexandria at the same time the Sun's zenith distance is 1/50 of a circle. Knowing the distance from Aswan to Alexandria, he was able to calculate the radius of the Earth, which, according to his calculations, was 6290 km. An equally significant contribution to astronomy was made by the Muslim astronomer and mathematician Biruni, who lived in the 10th-11th century AD. e. Despite the fact that he used the geocentric system, he was able to quite accurately determine the size of the Earth and the inclination of the equator to the ecliptic. The sizes of the planets, although they were determined by him, but with a big error; the only size he determined relatively accurately is the size of the moon.
In the 15th century, Copernicus put forward the heliocentric theory of the structure of the world. The theory, as is known, had no development for quite a long time, as it was persecuted by the church. The system was finally refined by I. Kepler at the end of the 16th century. Kepler also discovered the laws of planetary motion and calculated the eccentricities of their orbits, theoretically created a model of a telescope. Galileo, who lived somewhat later than Kepler, constructed a telescope with a magnification of 34.6 times, which allowed him to estimate even the height of the mountains on the moon. He also discovered a characteristic difference when observing stars and planets through a telescope: the clarity of the appearance and shape of the planets was much greater, and he also discovered several new stars. For almost 2000 years, astronomers believed that the distance from the Earth to the Sun is equal to 1200 Earth distances, i.e. making a mistake about 20 times! For the first time, these data were specified only at the end of the 17th century as 140 million km, i.e. with an error of 6.3% by the astronomers Cassini and Richet. They also determined the speed of light as 215 km / s, which was a significant breakthrough in astronomy, since they previously believed that the speed of light was infinite. Around the same time, Newton discovered the law of universal gravitation, and the decomposition of light into a spectrum, which marked the beginning of spectral analysis several centuries later.
The Earth seems to us so huge, so reliable and means so much to us that we do not notice her secondary position in the family of planets. The only weak consolation is that the Earth is the largest of the terrestrial planets. In addition, it has an atmosphere of medium power, a significant part of the earth's surface is covered with a thin heterogeneous layer of water. And around it revolves a majestic satellite, the diameter of which is equal to a quarter of the earth's diameter. However, these arguments are hardly sufficient to support our cosmic conceit. Tiny in astronomical terms, the Earth is our home planet and therefore deserves the most careful study. After the painstaking and hard work of dozens of generations of scientists, it was irrefutably proven that the Earth is not at all the “center of the universe”, but the most ordinary planet, i.e. cold ball moving around the sun. According to Kepler's laws, the Earth revolves around the Sun at a variable speed in a slightly elongated ellipse. It is closest to the sun in early January, when winter reigns in the Northern Hemisphere, and farthest away in early July, when we have summer. The difference in the distance of the Earth from the Sun between January and July is about 5 million km. Therefore, winters in the northern hemisphere are slightly warmer than in the southern, and summers, on the contrary, are slightly cooler. This is most clearly felt in the Arctic and Antarctica. The ellipticity of the Earth's orbit has only an indirect and very insignificant influence on the nature of the seasons. The reason for the change of seasons lies in the tilt of the earth's axis. The axis of rotation of the Earth is located at an angle of 66.5º to the plane of its movement around the Sun. For most practical problems, it can be assumed that the Earth's axis of rotation always moves in space parallel to itself. In fact, the axis of rotation of the Earth describes on celestial sphere a small circle, making one complete revolution in 26 thousand years. In the next hundreds of years, the north pole of the world will be located not far from the Polar Star, then it will begin to move away from it, and the name of the last star in the handle of the Ursa Minor bucket - Polaris - will lose its meaning. In 12 thousand years, the celestial pole will approach the brightest star in the northern sky - Vega from the constellation Lyra. The described phenomenon is called the precession of the Earth's axis of rotation. The phenomenon of precession was already discovered by Hipparchus, who compared the positions of the stars in the catalog with the star catalog of Aristillus and Timocharis compiled long before him. Comparison of catalogs indicated to Hipparchus the slow movement of the axis of the world.
There are three outer shells of the Earth: the lithosphere, hydrosphere and atmosphere. The lithosphere is understood as the upper solid cover of the planet, which serves as the bed of the ocean, and on the continents coincides with the land. The hydrosphere is groundwater, the waters of rivers, lakes, seas and, finally, the oceans. Water covers 71% of the entire surface of the Earth. The average depth of the World Ocean is 3900 m.
5. Exploring the Earth from space
Man first appreciated the role of satellites in monitoring the state of agricultural land, forests and other natural resources of the Earth only a few years after the onset of the space age. The beginning was laid in 1960, when with the help of meteorological satellites "Tiros" map-like outlines of the globe were obtained, lying under the clouds. These first black-and-white TV images gave very little insight into human activity, and yet it was a first step. Soon new technical means were developed that made it possible to improve the quality of observations. Information was extracted from multispectral images in the visible and infrared (IR) regions of the spectrum. The first satellites designed to make the most of these opportunities were the Landsat. For example, the Landsat-D satellite, the fourth in a series, observed the Earth from an altitude of more than 640 km using advanced sensitive instruments, which allowed consumers to receive much more detailed and timely information. One of the first areas of application of images of the earth's surface was cartography. In the pre-satellite era, maps of many areas, even in the developed regions of the world, were inaccurate. The Landsat images have corrected and updated some of the existing maps of the United States. In the mid-70s, NASA, the ministry Agriculture The United States decided to demonstrate the capabilities of the satellite system in forecasting the most important wheat crop. Satellite observations, which turned out to be extremely accurate, were later extended to other agricultural crops. The use of satellite information has revealed its undeniable advantages in assessing the volume of timber in the vast territories of any country. It became possible to manage the process of deforestation and, if necessary, to give recommendations on changing the contours of the deforestation area from the point of view of the best preservation of the forest. Satellite images also made it possible to quickly assess the boundaries of forest fires, especially the “crown-shaped” ones that are characteristic of the western regions of North America, as well as the regions of Primorye and southern regions of Eastern Siberia in Russia.
Of great importance for humanity as a whole is the ability to observe almost continuously over the expanses of the World Ocean. It is above the depths of ocean water that monstrous forces are born of hurricanes and typhoons, bringing numerous victims and destruction to the inhabitants of the coast. Early warning to the public is often critical to saving the lives of tens of thousands of people. Determining the stocks of fish and other seafood is also of great practical importance. Ocean currents often curve, change course and size. For example, El Nino, a warm current in a southerly direction off the coast of Ecuador in some years can spread along the coast of Peru up to 12º S. When this happens, plankton and fish die in huge numbers, causing irreparable damage to the fisheries of many countries, including Russia. Large concentrations of unicellular marine organisms increase the mortality of fish, possibly due to the toxins they contain. Satellite observation helps to identify the “whims” of such currents and provide useful information to those who need it. According to some estimates by Russian and American scientists, the fuel savings, combined with the "extra catch" due to the use of information from satellites obtained in the infrared range, yield an annual profit of $ 2.44 million. The use of satellites for survey purposes has facilitated the task of plotting the course of ships .
6. The emergence of life on Earth
The emergence of living matter on Earth was preceded by a rather long and complex evolution of the chemical composition of the atmosphere, which ultimately led to the formation of a number of organic molecules. These molecules later served as a kind of “bricks” for the formation of living matter. According to modern data, the planets are formed from a primary gas-dust cloud, the chemical composition of which is similar to the chemical composition of the Sun and stars, their initial atmosphere consisted mainly of the simplest compounds of hydrogen - the most common element in space. Most of all there were molecules of hydrogen, ammonia, water and methane. In addition, the primary atmosphere should have been rich in inert gases - primarily helium and neon. At present, there are few noble gases on Earth, since they once dissipated (evaporated) into interplanetary space, like many hydrogen-containing compounds. However, a decisive role in establishing the composition of the earth's atmosphere was played by plant photosynthesis, in which oxygen is released. It is possible that some, and perhaps even significant, amount organic matter was brought to Earth by meteorites and possibly even comets. Some meteorites are quite rich in organic compounds. It is estimated that over 2 billion years meteorites could bring to Earth from 108 to 1012 tons of such substances. Also, organic compounds can occur in small quantities as a result of volcanic activity, meteorite impacts, lightning, due to the radioactive decay of some elements. There are fairly reliable geological data indicating that already 3.5 billion years ago the Earth's atmosphere was rich in oxygen. On the other hand, the age of the earth's crust is estimated by geologists at 4.5 billion years. Life must have originated on Earth before the atmosphere became rich in oxygen, since the latter is mainly a product of the vital activity of plants. According to a recent estimate by the American specialist in planetary astronomy Sagan, life on Earth arose 4.0-4.4 billion years ago. The mechanism of the complication of the structure of organic substances and the appearance in them of the properties inherent in living matter has not yet been sufficiently studied. But it is already clear that such processes last for billions of years.
Any complex combination of amino acids and other organic compounds is not yet a living organism. It can, of course, be assumed that under some exceptional circumstances, somewhere on Earth, a certain “praDNA” arose, which served as the beginning of all living things. This is hardly the case if the hypothetical “praDNA” was similar to the modern one. The fact is that modern DNA itself is completely helpless. It can function only in the presence of enzyme proteins. To think that purely by chance, by “shaking up” individual proteins - polyatomic molecules, such a complex machine as “praDNA” and the complex of protein-enzymes necessary for its functioning could arise - this means believing in miracles. However, it can be assumed that DNA and RNA molecules originated from a more primitive molecule. For the first primitive living organisms formed on the planet, high doses of radiation can be a mortal danger, since mutations will occur so quickly that natural selection will not keep up with them.
The following question deserves attention: why does life on Earth not arise from non-living matter in our time? This can only be explained by the fact that the previously arisen life will not give an opportunity for a new birth of life. Microorganisms and viruses will literally eat the first sprouts of new life. We cannot completely exclude the possibility that life on Earth arose by chance. There is another circumstance that may be worth paying attention to. It is well known that all “living” proteins consist of 22 amino acids, while more than 100 amino acids are known in total. It is not entirely clear how these acids differ from their other “brothers”. Is there some deep connection between the origin of life and this amazing phenomenon? If life on Earth arose by chance, then life in the Universe is a rare phenomenon. For a given planet (like, for example, our Earth), the emergence of a special form of highly organized matter, which we call "life", is an accident. But in the vast expanses of the universe, life arising in this way should be a natural phenomenon. It should be noted once again that the central problem of the emergence of life on Earth - the explanation of the qualitative leap from "non-living" to "living" - is still far from clear. No wonder one of the founders of modern molecular biology, Professor Crick, at the Byurakan Symposium on the Problem of Extraterrestrial Civilizations in September 1971, said: “We do not see a path from the primordial soup to natural selection. It can be concluded that the origin of life is a miracle, but this only testifies to our ignorance.”
8. The only satellite of the Earth is the Moon.
Gone are the days when people believed that the mysterious forces of the moon influenced their everyday life. But the Moon does have a variety of influences on the Earth, which are due to the simple laws of physics and, above all, dynamics. The most amazing feature of the motion of the Moon is that the speed of its rotation around its axis coincides with the average angular velocity of revolution around the Earth. Therefore, the Moon always faces the Earth with the same hemisphere. Since the Moon is the nearest celestial body, its distance from the Earth is known with the greatest accuracy, up to several centimeters from measurements using lasers and laser rangefinders. The smallest distance between the centers of the Earth and the Moon is 356,410 km. longest distance The moon from the Earth reaches 406,700 km, and the average distance is 384,401 km. The Earth's atmosphere bends the rays of light to such an extent that the entire Moon (or the Sun) can be seen even before sunrise or after sunset. The fact is that the refraction of light rays entering the atmosphere from airless space is about 0,
5º, i.e. equal to the apparent angular diameter of the moon.
Thus, when the upper edge of the true Moon is just below the horizon, the entire Moon is visible above the horizon. Another surprising result was obtained from tidal experiments. It turns out that the Earth is an elastic ball. Prior to these experiments, it was commonly believed that the Earth was viscous, like molasses or molten glass; with slight distortions, it would probably have to keep them or slowly return to its original form under the action of weak restoring forces. Experiments have shown that the Earth as a whole is given tidal forces and immediately returns to its original form after the cessation of their action. Thus, the Earth is not only harder than steel, but also more resilient.
Conclusion
We got acquainted with state of the art our planet. The future of our planet, and indeed the entire planetary system, if nothing unforeseen happens, seems clear. The probability that the established order of the planets will be disturbed by some wandering star is small, even within a few billion years.
In the near future, one should not expect strong changes in the flow of solar energy. It is likely that ice ages will repeat. A person is able to change the climate, but in doing so, he can make a mistake. The continents will rise and fall in subsequent epochs, but we hope that the processes will be slow. Massive meteorite impacts are possible from time to time. But basically, the planet Earth will retain its modern appearance.
The Earth is the third planet from the Sun and the largest of the terrestrial planets. However, it is only the fifth largest planet in terms of size and mass in the solar system, but, surprisingly, the densest of all the planets in the system (5.513 kg / m3). It is also noteworthy that the Earth is the only planet in the solar system that people themselves did not name after a mythological creature - its name comes from the old English word"ertha" which means soil.
It is believed that the Earth formed somewhere around 4.5 billion years ago, and is currently the only known planet where life is possible in principle, and the conditions are such that life is literally teeming on the planet.
Throughout human history, humans have sought to understand their home planet. However, the learning curve turned out to be very, very difficult, with lots of mistakes made along the way. For example, even before the existence of the ancient Romans, the world was understood as flat, not spherical. Second good example is the belief that the sun revolves around the earth. It wasn't until the sixteenth century, thanks to the work of Copernicus, that people learned that the earth was actually just a planet revolving around the sun.
Perhaps the most important discovery regarding our planet in the last two centuries is that the Earth is both a common and a unique place in the solar system. On the one hand, many of its characteristics are rather ordinary. Take, for example, the size of the planet, its internal and geological processes: its internal structure is almost identical to the other three terrestrial planets in the solar system. Almost the same geological processes that form the surface take place on Earth, which are characteristic of similar planets and many planetary satellites. However, with all this, the Earth has just a huge number of absolutely unique characteristics that strikingly distinguish it from almost all the planets of the terrestrial group known today.
One of the necessary conditions for the existence of life on Earth without a doubt is its atmosphere. It is composed of approximately 78% nitrogen (N2), 21% oxygen (O2) and 1% argon. It also contains very small amounts of carbon dioxide (CO2) and other gases. It is noteworthy that nitrogen and oxygen are necessary for the creation of deoxyribonucleic acid (DNA) and the production of biological energy, without which life cannot exist. In addition, the oxygen present in the ozone layer of the atmosphere protects the surface of the planet and absorbs harmful solar radiation.
It is curious that a significant amount of oxygen present in the atmosphere is created on Earth. It is formed as a by-product of photosynthesis, when plants convert carbon dioxide from the atmosphere into oxygen. Essentially, this means that without plants, the number carbon dioxide in the atmosphere would be much higher, and the oxygen level would be much lower. On the one hand, if the level of carbon dioxide rises, it is likely that the Earth will suffer from the greenhouse effect as on. On the other hand, if the percentage of carbon dioxide becomes even slightly lower, then a decrease in the greenhouse effect would lead to a sharp cooling. Thus, the current level of carbon dioxide contributes to an ideal range of comfortable temperatures from -88°C to 58°C.
When observing the Earth from space, the first thing that catches your eye is the oceans of liquid water. In terms of surface area, the oceans cover approximately 70% of the Earth, which is one of the most unique features of our planet.
Like the Earth's atmosphere, the presence of liquid water is a necessary criterion for sustaining life. Scientists believe that for the first time life on Earth arose 3.8 billion years ago and it was in the ocean, and the ability to move on land appeared in living beings much later.
Planetologists explain the presence of oceans on Earth in two ways. The first of these is the Earth itself. There is an assumption that during the formation of the Earth, the atmosphere of the planet was able to capture large volumes of water vapor. Over time, the planet's geological mechanisms, primarily its volcanic activity, released this water vapor into the atmosphere, after which, in the atmosphere, this vapor condensed and fell to the planet's surface in the form of liquid water. Another version suggests that the comets that fell on the Earth's surface in the past were the source of water, the ice that prevailed in their composition and formed the reservoirs existing on Earth.
Land surface
Despite the fact that most of the Earth's surface is located under its oceans, the "dry" surface has many distinctive features. When comparing the Earth with other solid bodies in the solar system, its surface is strikingly different, since it does not have craters. According to planetary scientists, this does not mean that the Earth has escaped numerous impacts of small cosmic bodies, but rather indicates that evidence of such impacts has been erased. There may be many geological processes responsible for this, but the two most important are weathering and erosion. It is believed that in many respects it was the dual impact of these factors that influenced the erasure of traces of craters from the face of the Earth.
So weathering breaks surface structures into smaller pieces, not to mention the chemical and physical means of weathering. An example of chemical weathering is acid rain. An example of physical weathering is the abrasion of river beds caused by rocks contained in running water. The second mechanism, erosion, is essentially the impact on the relief by the movement of particles of water, ice, wind or earth. Thus, under the influence of weathering and erosion, impact craters on our planet were “erased”, due to which some relief features were formed.
Scientists also identify two geological mechanisms that, in their opinion, helped shape the surface of the Earth. The first such mechanism is volcanic activity - the process of release of magma (molten rock) from the bowels of the Earth through gaps in its crust. Perhaps it was due to volcanic activity that the earth's crust was changed and islands were formed (the Hawaiian Islands are a good example). The second mechanism determines mountain building or the formation of mountains as a result of compression of tectonic plates.
Structure of the planet Earth
Like other terrestrial planets, the Earth consists of three components: core, mantle and crust. Science now believes that the core of our planet consists of two separate layers: an inner core of solid nickel and iron, and an outer core of molten nickel and iron. At the same time, the mantle is a very dense and almost completely solid silicate rock - its thickness is approximately 2850 km. The crust is also composed of silicate rocks and the difference is in its thickness. While continental ranges of crust are 30 to 40 kilometers thick, oceanic crust is much thinner, only 6 to 11 kilometers.
Another distinguishing feature of the Earth relative to other terrestrial planets is that its crust is divided into cold, rigid plates that rest on the hotter mantle below. In addition, these plates are in constant motion. Along their boundaries, as a rule, two processes are carried out at once, known as subduction and spreading. During subduction, two plates come into contact producing earthquakes and one plate runs over the other. The second process is separation, when two plates move away from each other.
Orbit and rotation of the Earth
The Earth takes approximately 365 days to make a complete orbit around the Sun. The length of our year is related to a large extent to the average orbital distance of the Earth, which is 1.50 x 10 to the power of 8 km. At this orbital distance, it takes on average about eight minutes and twenty seconds for sunlight to reach the Earth's surface.
With an orbital eccentricity of .0167, the Earth's orbit is one of the most circular in the entire solar system. This means that the difference between the Earth's perihelion and aphelion is relatively small. As a result of such a small difference, the intensity of sunlight on Earth remains almost the same all year round. However, the position of the Earth in its orbit determines this or that season.
The tilt of the Earth's axis is approximately 23.45°. At the same time, the Earth takes twenty-four hours to complete one revolution around its axis. This is the fastest rotation among the terrestrial planets, but slightly slower than all gas planets.
In the past, the Earth was considered the center of the universe. For 2000 years, ancient astronomers believed that the Earth was static, and that other celestial bodies traveled in circular orbits around it. They came to this conclusion by observing the apparent movement of the Sun and planets when viewed from the Earth. In 1543, Copernicus published his heliocentric model of the solar system, in which the sun is at the center of our solar system.
Earth is the only planet in the system not named after mythological gods or goddesses (the other seven planets in the solar system were named after Roman gods or goddesses). This refers to the five planets visible to the naked eye: Mercury, Venus, Mars, Jupiter and Saturn. The same approach with the names of the ancient Roman gods was used after the discovery of Uranus and Neptune. The very same word "Earth" comes from the old English word "ertha" meaning soil.
Earth is the densest planet in the solar system. The density of the Earth is different in each layer of the planet (the core, for example, is denser than the earth's crust). The average density of the planet is about 5.52 grams per cubic centimeter.
The gravitational interaction between the Earth and causes the tides on the Earth. It is believed that the Moon is blocked by the tidal forces of the Earth, so its period of rotation coincides with the Earth's and it always faces our planet with the same side.
Our planet Earth is inimitable and unique, despite the fact that planets have also been discovered around a number of other stars. Like other planets in the solar system, Earth formed from interstellar dust and gases. Its geological age is 4.5-5 billion years. Since the beginning of the geological stage, the surface of the Earth has been divided into mainland ledges and ocean trenches. A special granite-metamorphic layer was formed in the earth's crust. When gases were released from the mantle, the primary atmosphere and hydrosphere were formed.
The natural conditions on Earth turned out to be so favorable that with a billion years since the formation of the planet on it life appeared. The emergence of life is due not only to the peculiarities of the Earth as a planet, but also to its optimal distance from the Sun ( about 150 million km). For planets closer to the Sun, the flow of solar heat and light is too great and heats their surfaces above the boiling point of water. Planets more distant than Earth receive too little solar heat and are too cool. The planets, the mass of which is much less than the Earth's, the gravitational force is so small that it does not provide the ability to hold a sufficiently powerful and dense atmosphere.
During the existence of the planet, its nature has changed significantly. Tectonic activity periodically intensified, the size and shape of land and oceans changed, cosmic bodies fell on the surface of the planet, and ice sheets repeatedly appeared and disappeared. However, these changes, although they influenced the development of organic life, did not significantly disturb it.
The uniqueness of the Earth is associated with the presence of a geographical shell that arose as a result of the interaction of the lithosphere, hydrosphere, atmosphere and living organisms.
In the observable part of outer space, another celestial body similar to the Earth has not yet been discovered.
Earth, like other planets in the solar system, has spherical shape. The ancient Greeks were the first to talk about sphericity ( Pythagoras ). Aristotle , watching lunar eclipses, noted that the shadow cast by the Earth on the Moon always has a rounded shape, which prompted the scientist to think about the sphericity of the Earth. Over time, this idea was substantiated not only by observations, but also by accurate calculations.
At the end 17th century Newton proposed the polar compression of the Earth due to its axial rotation. Measurements of the lengths of meridian segments near the poles and the equator, carried out in the middle XVIII century proved the "oblateness" of the planet at the poles. It was determined that The equatorial radius of the Earth is 21 km longer than its polar radius. Thus, of the geometric bodies, the figure of the Earth most of all resembles ellipsoid of revolution , not a ball.
As evidence of the sphericity of the Earth, they often cite circumnavigations, an increase in the range of the visible horizon with height, etc. Strictly speaking, these are only proofs of the convexity of the Earth, and not its sphericity. 
The scientific proof of sphericity is images of the Earth from space, geodetic measurements on the Earth's surface and lunar eclipses.
As a result of changes carried out in various ways, the main parameters of the Earth were determined:
middle radius - 6371 km;
equatorial radius - 6378 km;
polar radius - 6357 km;
circumference of the equator 40,076 km;
surface area - 510 million km 2;
weight - 5976 ∙ 10 21 kg.
Earth- the third planet from the Sun (after Mercury and Venus) and the fifth largest among the other planets of the solar system (Mercury is about 3 times smaller than the Earth, and Jupiter is 11 times larger). The Earth's orbit is in the shape of an ellipse. The maximum distance between the earth and the sun is 152 million km, minimum - 147 million km.
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