The Earth's crust, along with the upper part of the mantle, are the main components of the lithosphere (the solid shell of the Earth). The earth's crust is characterized by large irregularities on land, and in some places its thickness can reach seventy kilometers. We are talking primarily about mountain ranges. Scientists calculate the thickness based on the speed of propagation of seismic waves.
The difference in the structure of the earth's crust had a direct impact on the formation of continents, their existence and relative location. Researchers are confident that several million years ago our planet looked completely different, and the movement of lithospheric plates gradually formed the current location of the continents. For the first time, the famous German geographer Alfred Weneger was able to formulate a scientific theory about continental drift.
It is known that for quite a long time man could not accurately determine the content of chemical substances in the earth’s crust. However, with the development of science, it became known that the earth’s crust contains the most oxygen at a depth of up to sixteen kilometers.
Oxygen makes up about fifty percent of the total weight. Aluminum ranks second - about seven to eight percent. Potassium, calcium, magnesium, sodium in general make up just over ten percent of the total mass.
It turns out that in ancient times attempts were also made to study the geological structure of the earth's crust, although the methods were quite primitive when compared with today. For example, Diodorus Siculus wrote that “the workers were able to find very brilliant veins thanks to the properties of the earth.” It was about gold.
The movement of the earth's crust is of considerable interest. In particular, several million years ago India was part of the African continent. However, the movement of the earth’s crust led to the fact that it simply broke off and, after completing a small arc, “crashed” into Eurasia. The collision led to the formation of the Himalayas. By the way, some scientists are of the opinion that perhaps another piece will break off from Africa.
Continental crust
Its overall thickness varies greatly depending on elevation changes, bark structure and other factors. The continental crust is usually divided into several layers:
- The uppermost one is presented in the form of sedimentary rocks. It can reach fifteen kilometers;
- Just below there is a granite layer. It received its name due to the fact that the rocks composing it are similar in many of their qualities to granite. The average thickness of this layer varies from five to fifteen kilometers;
- The thickness of the basalt layer varies even more (it ranges from 10 to 35 kilometers).
That is, the average thickness of the continental (or mainland) crust can reach 30-70 kilometers.
Oceanic crust
The absence of a granite layer is the main difference between the oceanic crust. It is for this reason that its thickness is small and varies from six to fifteen kilometers. Another significant difference is the high basalt content. Scientists were able to prove that most of the rocks of the oceanic crust were formed a very long time ago - about three billion years ago.
Modern experts believe that it was the oceanic crust that appeared first. Then folds began to appear in it (modern mountain ranges). Their formation occurred under the influence of processes that were observed inside the earth. Thus, the thickness of the crust gradually increased, which led to the formation of the continental crust - this is how the first continents appeared.
The state of rest is unknown to our planet. This applies not only to external, but also to internal processes that occur in the bowels of the Earth: its lithospheric plates are constantly moving. True, some parts of the lithosphere are quite stable, while others, especially those located at the junctions of tectonic plates, are extremely mobile and constantly shake.
Naturally, people could not ignore such a phenomenon, and therefore throughout their history they studied and explained it. For example, in Myanmar there is still a legend that our planet is entwined with a huge ring of snakes, and when they begin to move, the earth begins to shake. Such stories could not satisfy inquisitive human minds for long, and in order to find out the truth, the most curious drilled into the ground, drew maps, built hypotheses and made assumptions.
The concept of lithosphere contains the hard shell of the Earth, consisting of the earth's crust and a layer of softened rocks that make up the upper mantle, the asthenosphere (its plastic composition allows the plates that make up the earth's crust to move along it at a speed of 2 to 16 cm per year). It is interesting that the upper layer of the lithosphere is elastic, and the lower layer is plastic, which allows the plates to maintain balance when moving, despite constant shaking.
During numerous studies, scientists came to the conclusion that the lithosphere has a heterogeneous thickness, and largely depends on the terrain under which it is located. So, on land its thickness ranges from 25 to 200 km (the older the platform, the larger it is, and the thinnest is located under young mountain ranges).
But the thinnest layer of the earth’s crust is under the oceans: its average thickness ranges from 7 to 10 km, and in some regions of the Pacific Ocean it even reaches five. The thickest layer of crust is located at the edges of the oceans, the thinnest is located under the mid-ocean ridges. Interestingly, the lithosphere has not yet fully formed, and this process continues to this day (mainly under the ocean floor).
What is the earth's crust made of?
The structure of the lithosphere under the oceans and continents is different in that there is no granite layer under the ocean floor, since the oceanic crust was subjected to melting processes many times during its formation. Common to the oceanic and continental crust are such layers of the lithosphere as basalt and sedimentary.
Thus, the earth's crust consists mainly of rocks that are formed during the cooling and crystallization of magma, which penetrates into the lithosphere along cracks. If the magma was not able to seep to the surface, then it formed coarse-crystalline rocks such as granite, gabbro, diorite, due to its slow cooling and crystallization.
But the magma, which managed to get out due to rapid cooling, formed small crystals - basalt, liparite, andesite.
As for sedimentary rocks, they were formed in the Earth's lithosphere in different ways: clastic rocks appeared as a result of the destruction of sand, sandstones and clay, chemical rocks were formed due to various chemical reactions in aqueous solutions - these are gypsum, salt, phosphorites. Organic ones were formed by plant and calcareous residues - chalk, peat, limestone, coal.
Interestingly, some rocks appeared due to a complete or partial change in their composition: granite was transformed into gneiss, sandstone into quartzite, limestone into marble. According to scientific research, scientists have been able to establish that the lithosphere consists of:
- Oxygen – 49%;
- Silicon – 26%;
- Aluminum – 7%;
- Iron – 5%;
- Calcium – 4%
- The lithosphere contains many minerals, the most common being spar and quartz.
As for the structure of the lithosphere, there are stable and mobile zones (in other words, platforms and folded belts). On tectonic maps you can always see the marked boundaries of both stable and dangerous territories. First of all, this is the Pacific Ring of Fire (located along the edges of the Pacific Ocean), as well as part of the Alpine-Himalayan seismic belt (Southern Europe and the Caucasus).
Description of platforms
A platform is an almost motionless part of the earth's crust that has gone through a very long stage of geological formation. Their age is determined by the stage of formation of the crystalline foundation (granite and basalt layers). Ancient or Precambrian platforms on the map are always located in the center of the continent, young ones are either at the edge of the continent or between Precambrian platforms.
Mountain fold region
The folded mountain area was formed during the collision of tectonic plates located on the mainland. If mountain ranges were formed recently, increased seismic activity is recorded near them and they are all located along the edges of lithospheric plates (younger massifs belong to the Alpine and Cimmerian stages of formation). Older areas related to ancient, Paleozoic folding can be located both on the edge of the continent, for example, in North America and Australia, and in the center - in Eurasia.
It is interesting that scientists determine the age of folded mountain areas based on the youngest folds. Since mountain building occurs continuously, this makes it possible to determine only the time frame of the stages of development of our Earth. For example, the presence of a mountain range in the middle of a tectonic plate indicates that a boundary once passed there.
Lithospheric plates
Despite the fact that ninety percent of the lithosphere consists of fourteen lithospheric plates, many disagree with this statement and draw their own tectonic maps, saying that there are seven large and about ten small ones. This division is quite arbitrary, since with the development of science, scientists either identify new plates, or recognize certain boundaries as non-existent, especially when it comes to small plates.
It is worth noting that the largest tectonic plates are very clearly visible on the map and they are:
- The Pacific is the largest plate on the planet, along the boundaries of which constant collisions of tectonic plates occur and faults form - this is the reason for its constant decrease;
- Eurasian - covers almost the entire territory of Eurasia (except for Hindustan and the Arabian Peninsula) and contains the largest part of the continental crust;
- Indo-Australian - it includes the Australian continent and the Indian subcontinent. Due to constant collisions with the Eurasian plate, it is in the process of breaking;
- South American - consists of the South American continent and part of the Atlantic Ocean;
- North American - consists of the North American continent, part of northeastern Siberia, the northwestern part of the Atlantic and half of the Arctic oceans;
- African - consists of the African continent and the oceanic crust of the Atlantic and Indian oceans. Interestingly, the plates adjacent to it move in the opposite direction from it, so the largest fault on our planet is located here;
- Antarctic plate – consists of the continent of Antarctica and nearby oceanic crust. Due to the fact that the plate is surrounded by mid-ocean ridges, the remaining continents are constantly moving away from it.
Movement of tectonic plates
Lithospheric plates, connecting and separating, constantly change their outlines. This allows scientists to put forward the theory that about 200 million years ago the lithosphere had only Pangea - a single continent, which subsequently split into parts, which began to gradually move away from each other at a very low speed (on average about seven centimeters per year ).
There is an assumption that, thanks to the movement of the lithosphere, in 250 million years a new continent will form on our planet due to the unification of moving continents.
When the oceanic and continental plates collide, the edge of the oceanic crust is subducted under the continental crust, while on the other side of the oceanic plate its boundary diverges from the adjacent plate. The boundary along which the movement of lithospheres occurs is called the subduction zone, where the upper and subducting edges of the plate are distinguished. It is interesting that the plate, plunging into the mantle, begins to melt when the upper part of the earth’s crust is compressed, as a result of which mountains are formed, and if magma also erupts, then volcanoes.
In places where tectonic plates come into contact with each other, zones of maximum volcanic and seismic activity are located: during the movement and collision of the lithosphere, the earth's crust is destroyed, and when they diverge, faults and depressions are formed (the lithosphere and the Earth's topography are connected to each other). This is the reason that the Earth's largest landforms—mountain ranges with active volcanoes and deep-sea trenches—are located along the edges of tectonic plates.
Relief
It is not surprising that the movement of lithospheres directly affects the appearance of our planet, and the diversity of the Earth’s relief is amazing (relief is a set of irregularities on the earth’s surface that are located above sea level at different heights, and therefore the main forms of the Earth’s relief are conventionally divided into convex (continents) , mountains) and concave - oceans, river valleys, gorges).
It is worth noting that land occupies only 29% of our planet (149 million km2), and the lithosphere and topography of the Earth consists mainly of plains, mountains and lowlands. As for the ocean, its average depth is slightly less than four kilometers, and the lithosphere and topography of the Earth in the ocean consists of continental shallows, coastal slope, ocean floor and abyssal or deep-sea trenches. Most of the ocean has a complex and varied topography: there are plains, basins, plateaus, hills, and ridges up to 2 km high.
Lithosphere problems
The intensive development of industry has led to the fact that man and the lithosphere have recently begun to get along extremely poorly with each other: the pollution of the lithosphere is acquiring catastrophic proportions. This happened due to the increase in industrial waste in combination with household waste and fertilizers and pesticides used in agriculture, which negatively affects the chemical composition of the soil and living organisms. Scientists have calculated that about one ton of garbage is generated per person per year, including 50 kg of hard-to-degrade waste.
Today, pollution of the lithosphere has become an urgent problem, since nature is not able to cope with it on its own: the self-cleaning of the earth’s crust occurs very slowly, and therefore harmful substances gradually accumulate and, over time, negatively affect the main culprit of the problem - humans.
Internal structure of the Earth. It is customary to divide the Earth's body into three main parts - the lithosphere (the earth's crust), the mantle and the core.
Lithosphere - the upper shell of the “solid” Earth, including the earth’s crust and the upper part of the underlying upper mantle of the Earth.
Earth's crust- the upper shell of the “solid” Earth. The thickness of the earth's crust ranges from 5 km (under the oceans) to 75 km (under the continents).
Distinguish continental And oceanic the earth's crust. There are 3 layers in the continental crust: sedimentary, granite, and basalt. Granite and basalt layers are so named because they contain rocks similar in physical properties to granite and basalt.
The oceanic one differs from the continental one in the absence of a granite layer and a significantly smaller thickness (from 5 to 10 km).
The position of the layers in the continental crust indicates different times of its formation. The basalt layer is the oldest, the granite layer is younger than it, and the youngest is the upper, sedimentary layer, which is still developing today. Each layer of crust was formed over a long period of geological time.
Rocks- the main substance that makes up the earth's crust. A solid or loose compound of minerals. Based on their origin, rocks are divided into three groups:
- igneous
- are formed as a result of the solidification of magma in the thickness of the earth's crust or on the surface. Highlight:
- A) intrusive(formed in the thickness of the earth's crust, for example, granites);
- b) effusive(formed by the outpouring of magma onto the surface, for example, basalts).
- sedimentary
— are formed on the surface of land or in bodies of water as a result of the accumulation of destruction products of pre-existing rocks of various origins. Sedimentary rocks cover about 75% of the surface of the continents. Among the sedimentary rocks are:
- A) clastic— formed from various minerals and rock fragments during their transport and redeposition (by flowing water, wind, glacier). For example: crushed stone, pebbles, sand, clay; the largest fragments are boulders and blocks;
- b) chemical— are formed from water-soluble substances (potassium salt, table salt, etc.);
- V) organic(or biogenic) - consist of the remains of plants and animals or of minerals formed as a result of the vital activity of organisms (limestone-shell rock, chalk, fossil coals);
- metamorphic — are obtained by changing other types of rocks under the influence of heat and pressure in the depths of the earth’s crust (quartzite, marble).
Minerals- natural mineral formations in the earth’s crust of inorganic and organic origin, which, at a given level of technological and economic development, can be used in the economy in their natural form or after appropriate processing. Minerals are classified according to many criteria. For example, they distinguish between solid (coal, metal ores), liquid (oil, mineral waters) and gaseous (combustible natural gases) minerals.
According to composition and features of use usually distinguished:
- a) fossil fuels - coal, oil, natural gas, oil shale, peat;
- b) metallic - ores of ferrous, non-ferrous, noble and other metals;
- c) non-metallic minerals - limestone, rock salt, gypsum, mica, etc.
Sometimes by origin There are two groups: ore And nonmetallic(sedimentary) minerals. The characteristics of the distribution of minerals on Earth are closely related to their origin.
Lithospheric plates- large rigid blocks of the Earth's lithosphere, bounded by seismically and tectonically active fault zones.
The plates, as a rule, are separated by deep faults and move through the viscous layer of the mantle relative to each other at a speed of 2-3 cm per year. Where continental plates converge, they collide and mountain belts are formed. When the continental and oceanic plates interact, the plate with the oceanic crust is pushed under the plate with the continental crust, resulting in the formation of deep-sea trenches and island arcs.
The movement of lithospheric plates is associated with the movement of matter in the mantle. In certain parts of the mantle there are powerful flows of heat and matter rising from its depths to the surface of the planet.
Rift- a huge fault in the earth’s crust, formed during its horizontal stretching (i.e., where flows of heat and matter diverge).
In rifts, magma outflows, new faults, horsts, and grabens arise. Mid-ocean ridges are formed.
Mid-ocean ridges- powerful underwater mountain structures within the ocean floor, most often occupying a middle position. Near mid-ocean ridges, lithospheric plates move apart and young basaltic oceanic crust appears. The process is accompanied by intense volcanism and high seismicity.
Continental rift zones are, for example, the East African Rift System, the Baikal Rift System. Rifts, like mid-ocean ridges, are characterized by seismic activity and volcanism.
Plate tectonics is a hypothesis that suggests that the lithosphere is broken into large plates that move horizontally through the mantle. Near mid-ocean ridges, lithospheric plates move apart and grow due to material rising from the bowels of the Earth; in deep-sea trenches, one plate moves under another and is absorbed by the mantle. Fold structures are formed where plates collide.
Seismic belts of the Earth. The moving areas of the Earth are the boundaries of lithospheric plates (places of their rupture and divergence, collision), i.e. these are rift zones on land, as well as mid-ocean ridges and deep-sea trenches in the ocean. These areas experience frequent volcanic eruptions and earthquakes. This is explained by the emerging tension in the earth's crust and indicates that the process of formation of the earth's crust in these zones is intensively ongoing at the present time.
Thus, zones of modern volcanism and high seismic activity (i.e., the spread of earthquakes) coincide with faults in the earth's crust.
Regions where earthquakes occur are called seismic.
External and internal forces that change the surface of the Earth. Relief- a set of irregularities on the earth's surface. The formation of relief is simultaneously influenced by external and internal forces, giving rise to many geological processes.
Processes that change the Earth's surface are divided into two groups:
- internal processes - tectonic movements, earthquakes, volcanism. The source of energy for these processes is the internal energy of the Earth;
- external processes - weathering (physical, chemical, biological), wind activity, surface flowing water activity, glacier activity. The source of energy is solar heat.
Internal processes of relief formation (endogenous). Tectonic movements- mechanical movements of the earth's crust caused by forces acting in the earth's crust and mantle. Lead to significant changes in relief. Tectonic movements vary in form, depth and causes. Tectonic movements are divided into oscillatory (slow vibrations of the earth's crust), folded and discontinuous (formation of cracks, grabens, horsts). Based on time, they are distinguished as ancient (before the Cenozoic folding), newest (starting from the Neogene period) and modern. The newest and modern ones are sometimes combined into Neo-Quaternary movements.
Neogene-Quaternary movements of the earth's crust. These include tectonic processes of the Neogene-Quaternary period (the last 30 million years), which covered all geostructures and determined the basic appearance of the modern relief. In modern times, the movements of many previously formed large landforms continue - hills and mountain ranges rise, and certain parts of the lowlands descend and are filled with sediment.
Earthquakes. Earthquakes called tremors of the earth's surface caused by natural causes.
There are about 100,000 earthquakes on Earth during the year, or about 300 per day. Earthquakes usually occur quickly, within a few seconds or even fractions of seconds. The area within the Earth's interior within which an earthquake occurs is called the source of the earthquake, its center is hypocenter, and the projection of the hypocenter onto the Earth’s surface is epicenter. The sources of earthquakes can be located at depths from 20-30 km to 500-600 km. The most powerful earthquakes had a focal depth of 10-15 to 20-25 km. Earthquakes with a deep source are usually not very destructive on the surface.
The strength of earthquakes is determined on a 12-point scale. One point indicates the weakest earthquake, the strongest, 10-12 points, have catastrophic consequences. Earthquakes are recorded by special instruments - seismographs. The science that studies the causes of earthquakes, their consequences, the connection of earthquakes with tectonic processes and the possibility of their prediction is called seismology.
One of the main tasks is earthquake prediction, that is, forecasting where, when and what strength an earthquake will occur. This can be determined using a seismic zoning map.
Seismic zoning— dividing the territory into regions according to their seismic activity, assessing and displaying on maps the potential seismic hazard, which must be taken into account during earthquake-resistant construction.
In Russia, strong earthquakes are possible in the Baikal region, Kamchatka, the Kuril Islands, and Southern Siberia.
In Russia, seismic zones include Kamchatka, the Kuril Islands, Sakhalin, the Baikal region, Altai, Sayan Mountains, the Caucasus and Crimea.
The world is divided into the Pacific seismic belt, which surrounds the Pacific Ocean, and the Mediterranean, which runs from the Atlantic Ocean through Central Asia to the Pacific. The active seismic belt passing through East Africa, the Red Sea, Tien Shan, the Baikal basin, and the Stanovoy Range is much younger.
Thus, most earthquakes are confined to the margins of lithospheric plates, to the places of their interaction. There is a significant connection between earthquakes and volcanism.
Volcanism- a set of processes and phenomena associated with the outpouring of magma onto the earth's surface.
Magma- molten material of rocks and minerals, a mixture of many components. Magma always contains volatile substances: water vapor, carbon dioxide, hydrogen sulfide, etc. The emergence and movement of magma is determined by the internal energy of the Earth.
Volcanism can be:
- 1) internal(intrusive) - the movement of magma inside the earth's crust leads to the formation of laccoliths - underdeveloped forms of volcanoes in which magma did not reach the earth's surface, but invaded through cracks and channels into the thickness of sedimentary rocks, lifting them. Sometimes the upper sedimentary cover above the laccoliths is washed away, exposing the laccolith's core of solidified magma on the surface. Laccoliths are known in the vicinity of Pyatigorsk (Mount Mashuk), in the Crimea (Mount Ayudag);
- 2) external(effusive) - movement of magma with its release to the surface. Magma that has erupted onto the surface and has lost a significant portion of its gases is called lava.
Volcanoes- geological formations, usually having a cone- or dome-shaped shape, composed of eruption products. In their central part there is a channel through which these products are released. Less commonly, modern volcanoes have the appearance of cracks through which volcanic products erupt from time to time.
Modern volcanoes are common where intense movements of the earth's crust occur:
- Pacific volcanic ring.
- Mediterranean-Indonesian belt.
- Atlantic belt.
In addition, volcanic activity also occurs in rift zones and mid-ocean ridges.
External processes of relief formation (exogenous). Weathering- the process of destruction of rocks at their location under the influence of temperature fluctuations, chemical interaction with water, as well as the action of animals and plants.
Depending on what exactly caused the destruction process, weathering is distinguished between physical, chemical and organic.
Wind activity. Aeolian processes(as the geological activity of the wind is called) are most developed where there is no or poorly developed vegetation cover. The wind, carrying loose sediments, is capable of creating various forms of relief: blowing basins, sand ridges, hills, including crescent-shaped ones - dunes.
Activity of surface flowing waters. Surface water creates forms of erosion (erosive) and sediment accumulation (accumulative). The formation of these landforms occurs simultaneously: if there is erosion in one place, there must be deposition in another. There are two forms of destructive activity of flowing waters: planar washout and erosion. Geological activity flat flush lies in the fact that rain and melt water flowing down the slope pick up small weathering products and carry them down. Thus, the slopes are flattened, and the products of the washout are increasingly deposited below. Under erosion, or linear erosion, understand the destructive activity of water streams flowing in a certain channel. Linear erosion leads to the dissection of slopes by ravines and river valleys.
Ravine- a linearly elongated pothole with steep, unturfed slopes.
river valley- a linearly elongated depression at the bottom of which there is a constant water flow.
In lowland rivers, as a rule, there are steps (river terraces) on the slopes, indicating the incision of the river. Each terrace was a valley bottom into which a river had cut. This is evidenced by river sediments covering the terraces or completely composing them. River sediments are called alluvial deposits, or alluvium. Rivers transport large amounts of different materials, depositing them in the delta.
Glacier activity. Glaciers form where snow that falls during the winter does not melt completely in the summer.
There are two types of glaciers:
- mountain
- continental (or integumentary).
Mountain glaciers are found on high mountains with sharp, jagged peaks. Glaciers here lie in various depressions on the slopes or move along valleys, like an icy river. In the mountains there are snow line- the height above which the snow does not completely melt even in summer. The height of the snow line depends on the geographical latitude of the place, the amount of precipitation, the nature and position of the mountain slopes.
Mainland glaciers are developed in the polar regions (Antarctica, Novaya Zemlya, Greenland, etc.). All the unevenness of the relief is buried under the ice here. The ice of cover glaciers moves from the center to the edges.
An accumulation of debris (boulders, pebbles, sand, clay) carried and deposited by glaciers is called moraine.
During the general melting of a stationary glacier, all the material contained in it is projected onto the underlying surface, and extensive moraine plains, mostly hilly. If the edge of a glacier lingers in one place for a long time, course-moraine shafts And ridges. Sandy plains called outwash, are formed by glacier meltwater flows carrying fine clastic material.
There is a number of factual data indicating that periods of glaciation have been observed repeatedly in the history of the Earth. The main centers of glaciations in Eurasia were the Scandinavian Mountains, Novaya Zemlya, and the Northern Urals. For example, glaciers descended to the East European Plain from the Scandinavian Mountains and the Polar Urals, and to the West Siberian Plain - from the Polar Urals, the Putorana and Byrranga mountains. To the North Siberian Lowland and to the northern part of the Central Siberian Plateau - from the Byrranga and Putorana mountains.
Shapes of the earth's surface. Plains- vast areas of land with a flat or hilly surface, having different heights relative to the level of the World Ocean.
Plains, depending on the nature of the relief, can be flat(West Siberian, US Coastal Plains, etc.) and hilly(East European, Kazakh small hills).
Depending on the height at which the plains are located, they are divided into:
- lowlands - having an absolute height of no more than 200 m;
- hills - located at an altitude of no higher than 500 m;
- plateaus - above 500 m.
Mountains- certain areas of the land surface,
rising above the level of the World Ocean above 500 m and having a dissected topography with steep slopes and clearly visible peaks. Depending on the height, mountains are divided into low (up to 1000 m), medium (from 1000 to 2000 m) and high - above 2000 m.
Highlands- vast mountainous areas, including individual ridges, intermountain depressions, and small plateaus. The difference in heights in the highlands does not reach a large value.
Tectonic structures- a set of structural forms of the earth's crust. Elementary structural forms are layers, folds, cracks, etc. The largest are platforms, plates, geosynclines, etc. The formation of tectonic structures occurs as a result of tectonic movements.
Platform- the most stable section of the lithosphere, which has a two-tier structure - a folded crystalline base at the bottom and a sedimentary cover at the top. Shields— places where the crystalline foundation of the platform reaches the surface (for example, the Baltic Shield, Anabar Shield).
Stove is called a platform whose foundation is deeply hidden under the sedimentary cover (West Siberian Plate). Platforms are divided into ancient ones - with a foundation of Precambrian age (for example, East European, Siberian) and young - with a foundation of Paleozoic and Mesozoic age (for example, Scythian, West Siberian, Turanian). Ancient platforms form the cores of continents. Young platforms are located along the periphery of ancient platforms or between them.
In relief, the platforms are usually expressed as plains. Although mountain-building phenomena (platform activation) are also possible. The reason may be mountain building occurring near the platform, or the ongoing pressure of lithospheric plates.
Marginal deflection- a linearly elongated deflection that occurs between the platform and a folded mountain structure. The marginal troughs are filled with products of the destruction of mountains and adjacent platforms.
Folded areas, unlike platforms, are mobile sections of the earth's crust that have experienced mountain building. Folded areas in the relief are expressed by mountains of different ages. Folded regions and mountains are usually formed in places where lithospheric plates collide.
In the history of the Earth there were several eras of intensifying folding processes - eras of mountain building. The foundation of ancient platforms, for example, was formed during the Precambrian folding era. Then there were the Baikal, Caledonian, Hercynian, Mesozoic, and Cenozoic folding eras, in each of which mountains were formed. So, for example, the mountains of the Baikal region were formed during the era of the Baikal and Early Caledonian folding, the Urals - in the Hercynian, the Verkhoyansk Range - in the Mesozoic, and the mountains of Kamchatka - in the Cenozoic. The era of Cenozoic folding continues to this day, as evidenced by earthquakes and volcanic eruptions.
In this video lesson, everyone will be able to study the topic “Structure of the Earth.” Users will learn about how the earth's crust is studied, what properties it has, and what layers our planet consists of. The teacher will talk about the structure of the Earth, how it was studied at different times.
2. Mantle.
As we move deeper into the Earth, temperature and pressure increase. At the center of the Earth there is a core, its radius is about 3500 km, and the temperature is more than 4500 degrees. The core is surrounded by a mantle, its thickness is about 2900 km. Above the mantle is the earth's crust, its thickness ranges from 5 km (under the oceans) to 70 km (under mountain systems). The earth's crust is the hardest shell. The mantle substance is in a special plastic state; this substance can flow slowly under pressure.
Rice. 1. Internal structure of the Earth ()
Earth's crust- the upper part of the lithosphere, the outer hard shell of the Earth.
The earth's crust is made up of rocks and minerals.
Rice. 2. Structure of the Earth and the earth’s crust ()
There are two types of earth's crust:
1. Continental (it consists of sedimentary, granite and basalt layers).
2. Oceanic (it consists of sedimentary and basalt layers).
Rice. 3. Structure of the earth's crust ()
The mantle accounts for 67% of the Earth's total mass and 87% of its volume. The upper and lower mantle are distinguished. The mantle material can move under pressure. Internal heat from the mantle is transferred to the earth's crust.
The core is the deepest part of the Earth. There is an outer liquid core and an inner solid core.
Most of the earth's crust is covered by the waters of oceans and seas. The continental crust is much larger than the oceanic crust and has three layers. The upper part of the earth's crust is heated by the sun's rays. At a depth of more than 20 meters, the temperature practically does not change, and then increases.
The most accessible part for human study is the upper part of the earth's crust. Sometimes deep wells are made to study the internal structure of the earth's crust. The deepest well is more than 12 km deep. Help study the earth's crust and mines. In addition, the internal structure of the Earth is studied using special instruments, methods, images from space and sciences: geophysics, geology, seismology.
Homework
Paragraph 16.
1. What parts does the Earth consist of?
References
Main
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Literature for preparing for the State Exam and the Unified State Exam
1. Geography: initial course. Tests. Textbook manual for 6th grade students. - M.: Humanite. ed. VLADOS center, 2011. - 144 p.
2. Tests. Geography. 6-10 grades: Educational and methodological manual / A.A. Letyagin. - M.: LLC "Agency "KRPA "Olympus": "Astrel", "AST", 2001. - 284 p.
Materials on the Internet
1. Federal Institute of Pedagogical Measurements ().
2. Russian Geographical Society ().
4. 900 children's presentations and 20,000 presentations for schoolchildren ().
Our Earth consists of many layers piled on top of each other. However, what we know best is the earth's crust and lithosphere. This is not surprising - after all, we not only live on them, but also draw from the depths most of the natural resources available to us. But the upper shells of the Earth still preserve millions of years of history of our planet and the entire solar system.
Lithosphere and crust - 2 in 1
These two concepts appear so often in the press and literature that they have entered the everyday vocabulary of modern man. Both words are used to refer to the surface of the Earth or another planet - however, there is a difference between the concepts, based on two fundamental approaches: chemical and mechanical.
Chemical aspect - earth's crust
If you divide the Earth into layers based on differences in chemical composition, the top layer of the planet will be the earth's crust. This is a relatively thin shell, ending at a depth of 5 to 130 kilometers below sea level - the oceanic crust is thinner, and the continental crust, in mountainous areas, is thickest. Although 75% of the crust's mass consists only of silicon and oxygen (not pure, bound in different substances), it has the greatest chemical diversity of all layers of the Earth.
The wealth of minerals also plays a role - various substances and mixtures created over billions of years of the planet’s history. The Earth's crust contains not only "native" minerals that were created by geological processes, but also massive organic heritage, such as oil and coal, as well as alien, meteorite inclusions.
Physical aspect - lithosphere
Based on the physical characteristics of the Earth, such as hardness or elasticity, we will get a slightly different picture - the interior of the planet will be enveloped by the lithosphere (from the Greek lithos, “rocky, hard” and “sphaira” sphere). It is much thicker than the earth's crust: the lithosphere extends up to 280 kilometers deep and even covers the upper solid part of the mantle!
The characteristics of this shell fully correspond to the name - it is the only solid layer of the Earth, besides the inner core. Strength, however, is relative - the Earth's lithosphere is one of the most mobile in the solar system, which is why the planet has changed its appearance more than once. But significant compression, curvature and other elastic changes require thousands of years, if not more.
An interesting fact is that the planet may not have a surface crust. Thus, the surface of Mercury is its solidified mantle; The planet closest to the Sun lost its crust a long time ago as a result of numerous collisions.
To summarize, the Earth's crust is the upper, chemically diverse part of the lithosphere, the hard shell of the Earth. Initially they had almost the same composition. But when only the underlying asthenosphere and high temperatures affected the depths, the hydrosphere, atmosphere, meteorite remains and living organisms actively participated in the formation of minerals on the surface.
Lithospheric plates
Another feature that distinguishes the Earth from other planets is the diversity of different types of landscapes on it. Of course, air and water played an incredibly important role, which we will talk about a little later. But even the basic forms of the planetary landscape of our planet differ from the same Moon. The seas and mountains of our satellite are pits from bombardment by meteorites. And on Earth they were formed as a result of hundreds and thousands of millions of years of movement of lithospheric plates.
You've probably already heard about plates - these are huge stable fragments of the lithosphere that drift along the fluid asthenosphere, like broken ice on a river. However, there are two main differences between the lithosphere and ice:
1. The gaps between the plates are small, and are quickly closed due to the molten substance erupting from them, and the plates themselves are not destroyed by collisions.
2. Unlike water, there is no constant flow in the mantle, which could set a constant direction of movement for the continents.
Thus, the driving force behind the drift of lithospheric plates is the convection of the asthenosphere, the main part of the mantle - hotter flows from the earth's core rise to the surface when cold ones fall back down. Considering that the continents differ in size, and the topography of their lower side mirrors the irregularities of the upper side, they also move unevenly and inconsistently.
Main plates
Over billions of years of movement of lithospheric plates, they repeatedly merged into supercontinents, after which they separated again. In the near future, in 200–300 million years, the formation of a supercontinent called Pangea Ultima is also expected. We recommend watching the video at the end of the article - it clearly shows how lithospheric plates have migrated over the past several hundred million years. In addition, the strength and activity of continental movement is determined by the internal heating of the Earth - the higher it is, the more the planet expands, and the faster and freer the lithospheric plates move. However, since the beginning of the Earth's history, its temperature and radius have been gradually decreasing.
An interesting fact is that plate drift and geological activity do not necessarily have to be powered by the internal self-heating of the planet. For example, Io, a moon of Jupiter, has many active volcanoes. But the energy for this is not provided by the satellite’s core, but by gravitational friction with Jupiter, due to which Io’s interior heats up.
The boundaries of lithospheric plates are very arbitrary - some parts of the lithosphere sink under others, and some, like the Pacific plate, are completely hidden under water. Geologists today count 8 main plates that cover 90 percent of the entire Earth's area:
1. Australian
2. Antarctic
3. African
4. Eurasian
5. Hindustan
6. Pacific
7. North American
8. South American
Such a division appeared recently - for example, the Eurasian plate, 350 million years ago, consisted of separate parts, during the merger of which the Ural Mountains, one of the oldest on Earth, were formed. Scientists to this day continue to study faults and the ocean floor, discovering new plates and clarifying the boundaries of old ones.
Geological activity
Lithospheric plates move very slowly - they creep over each other at a speed of 1–6 cm/year, and move away by a maximum of 10–18 cm/year. But it is the interaction between the continents that creates the geological activity of the Earth, noticeable on the surface - volcanic eruptions, earthquakes and the formation of mountains always occur in the contact zones of lithospheric plates.
However, there are exceptions - so-called hot spots, which can also exist deep in lithospheric plates. In them, molten flows of asthenosphere matter break upward, melting the lithosphere, which leads to increased volcanic activity and regular earthquakes. Most often, this happens near those places where one lithospheric plate creeps onto another - the lower, depressed part of the plate sinks into the Earth's mantle, thereby increasing the pressure of magma on the upper plate. However, now scientists are inclined to believe that the “drowned” parts of the lithosphere are melting, increasing pressure in the depths of the mantle and thereby creating upward flows. This can explain the anomalous distance of some hot spots from tectonic faults.
An interesting fact is that shield volcanoes, characterized by their flat shape, often form in hot spots. They erupt many times, growing due to flowing lava. This is also a typical alien volcano format. The most famous of them is the Olympus volcano on Mars, the highest point on the planet - its height reaches 27 kilometers!
Oceanic and continental crust of the Earth
Plate interactions also result in the formation of two different types of crust - oceanic and continental. Since the oceans, as a rule, are the junctions of different lithospheric plates, their crust is constantly changing - being broken or absorbed by other plates. At the site of faults, direct contact occurs with the mantle, from where hot magma rises. As it cools under the influence of water, it creates a thin layer of basalts, the main volcanic rock. Thus, the oceanic crust is completely renewed every 100 million years - the oldest areas, which are located in the Pacific Ocean, reach a maximum age of 156–160 million years.
Important! The oceanic crust is not all of the earth’s crust that is under water, but only its young sections at the junction of continents. Part of the continental crust is under water, in the zone of stable lithospheric plates.
The continental crust, on the contrary, is located in stable areas of the lithosphere - its age in some areas exceeds 2 billion years, and some minerals were born along with the Earth! The absence of active destructive processes allowed the development of a thick layer of sedimentary rocks, as well as the preservation of layers from different eras of the planet’s development. This also made it possible to create metamorphic substances - minerals formed due to the exposure of sedimentary or igneous rocks to unusual conditions. Diamonds are prime examples of such minerals.
Lithosphere and crust of the Earth in astronomy
Studying the Earth rarely happens just like that - often the searches of scientists have a very clear practical goal. This is especially relevant in the study of the lithosphere: at the junctions of lithospheric plates, whole placers of ores and valuable minerals come out, for the extraction of which in another place it would be necessary to drill a many-kilometer well. Much data about the earth's crust was obtained thanks to the oil field - in the search for oil and gas deposits, scientists learned a lot about the internal mechanisms of our planet.
Therefore, it is not for nothing that astronomers strive for a detailed study of the crust of other planets - its outlines and appearance reveal the entire internal structure of a space object. For example, on Mars, volcanoes are very high and erupt repeatedly, while on Earth they constantly migrate, appearing periodically in new places. This indicates that on Mars there is no such active movement of lithospheric plates as on Earth. Together with the absence of a magnetic field, the stability of the lithosphere became the main evidence of the stopping of the red planet’s core and the gradual cooling of its interior.
spacegid.com/li…
