Tectonic plates and their movement. Life and plate tectonics of planet earth Speed ​​of movement of tectonic plates

Plate tectonics

Definition 1

A tectonic plate is a moving part of the lithosphere that moves on the asthenosphere as a relatively rigid block.

Note 1

Plate tectonics is the science that studies the structure and dynamics of the earth's surface. It has been established that the upper dynamic zone of the Earth is fragmented into plates moving along the asthenosphere. Plate tectonics describes the direction in which lithospheric plates move and how they interact.

The entire lithosphere is divided into larger and smaller plates. Tectonic, volcanic and seismic activity occurs at the edges of plates, leading to the formation of large mountain basins. Tectonic movements can change the topography of the planet. At the point of their connection, mountains and hills are formed, at the points of divergence, depressions and cracks in the ground are formed.

Currently, the movement of tectonic plates continues.

Movement of tectonic plates

Lithospheric plates move relative to each other at an average speed of 2.5 cm per year. As plates move, they interact with each other, especially along their boundaries, causing significant deformations in the earth's crust.

As a result of the interaction of tectonic plates with each other, massive mountain ranges and associated fault systems were formed (for example, the Himalayas, Pyrenees, Alps, Urals, Atlas, Appalachians, Apennines, Andes, San Andreas fault system, etc.).

Friction between plates causes most of the planet's earthquakes, volcanic activity and the formation of ocean pits.

Tectonic plates contain two types of lithosphere: continental crust and oceanic crust.

A tectonic plate can be of three types:

• continental plate,
• oceanic plate,
• mixed slab.

Theories of tectonic plate movement

In the study of the movement of tectonic plates, special merit belongs to A. Wegener, who suggested that Africa and the eastern part of South America were previously a single continent. However, after a fault that occurred many millions of years ago, parts of the earth’s crust began to shift.

According to Wegener's hypothesis, tectonic platforms with different weights and having a rigid structure, were placed on a plastic asthenosphere. They were in an unstable state and moved all the time, as a result of which they collided, overlapped each other, and zones of moving apart plates and joints were formed. In places of collisions, areas with increased tectonic activity were formed, mountains were formed, volcanoes erupted and earthquakes occurred. The displacement occurred at a rate of up to 18 cm per year. Magma penetrated into the faults from the deep layers of the lithosphere.

Some researchers believe that the magma that came to the surface gradually cooled and formed a new bottom structure. The unused earth's crust, under the influence of plate drift, sank into the depths and again turned into magma.

Wegener's research affected the processes of volcanism, the study of stretching of the surface of the ocean floor, as well as the viscous-liquid internal structure of the earth. The works of A. Wegener became the foundation for the development of the theory of lithospheric plate tectonics.

Schmelling's research proved the existence of convective movement within the mantle leading to the movement of lithospheric plates. The scientist believed that the main reason for the movement of tectonic plates is thermal convection in the planet’s mantle, during which the lower layers of the earth’s crust heat up and rise, and the upper layers cool and gradually sink.

The main position in the theory of plate tectonics is occupied by the concept of geodynamic setting, a characteristic structure with a certain relationship of tectonic plates. In the same geodynamic setting, the same type of magmatic, tectonic, geochemical and seismic processes are observed.

The theory of plate tectonics does not fully explain the relationship between plate movements and processes occurring deep within the planet. A theory is needed that could describe the internal structure of the earth itself, the processes occurring in its depths.

Positions of modern plate tectonics:

• the upper part of the earth's crust includes the lithosphere, which has a fragile structure, and the asthenosphere, which has a plastic structure;
• the main reason for plate movement is convection in the asthenosphere;
• the modern lithosphere consists of eight large tectonic plates, about ten medium plates and many small ones;
• small tectonic plates are located between large ones;
• igneous, tectonic and seismic activity is concentrated at plate boundaries;
• The movement of tectonic plates obeys Euler's rotation theorem.

Types of tectonic plate movements

Highlight Various types movements of tectonic plates:

• divergent movement - two plates diverge, and an underwater mountain range or chasm in the ground forms between them;
• convergent movement - two plates converge and a thinner plate moves under a larger plate, resulting in the formation of mountain ranges;
• sliding movement - plates move in opposite directions.

Depending on the type of movement, divergent, convergent and sliding tectonic plates are distinguished.

Convergence leads to subduction (one plate sits on top of another) or collision (two plates crush to form mountain ranges).

Divergence leads to spreading (the separation of plates and the formation of ocean ridges) and rifting (the formation of a break in the continental crust).

The transform type of movement of tectonic plates involves their movement along a fault.

Figure 1. Types of tectonic plate movements. Author24 - online exchange of student work

In the process of the formation and then the development of geology as a science, many hypotheses were proposed, each of which, from one position or another, examined and explained either individual problems or a complex of problems relating to the development of the earth’s crust or the Earth as a whole. These hypotheses are called geotectonic. Some of them, due to lack of convincingness, quickly lost their significance in science, while others turned out to be more durable, again until new facts and ideas accumulated, which served as the basis for new hypotheses that were more appropriate to the given stage of development of science. Despite the great successes achieved in the study of the structure and development of the earth's crust, none of the modern hypotheses and theories (even recognized ones) are able to explain with sufficient reliability and fully all the conditions for the formation of the earth's crust.

The first scientific hypothesis, the uplift hypothesis, was formulated in the first half of the 19th century. based on the ideas of Plutonists about the role of the internal forces of the Earth, which played a positive role in the fight against the erroneous ideas of Neptunists. In the 50s XIX century it was replaced by a more reasonable at that time hypothesis of contraction (compressed), set forth by the French scientist Elie de Beaumont. The contraction hypothesis was based on Laplace's cosmogonic hypothesis, which, as is known, recognized the primary hot state of the Earth and its subsequent gradual cooling.

The essence of the contraction hypothesis is that the cooling of the Earth causes its compression with a subsequent decrease in its volume. As a result, the earth's crust, which hardened before the planet's inner zones, is forced to shrink, resulting in the formation of folded mountains.

In the second half of the 19th century. American scientists J. Hall and J. Deng formulated the doctrine of geosynclines - special mobile zones of the earth's crust that over time turn into folded mountain structures. This teaching significantly strengthened the position of the contraction hypothesis. However, by the beginning of the 20th century. in connection with the acquisition of new data about the Earth, this hypothesis began to lose its significance, since it was unable to explain the periodicity of mountain-building movements and magmatism processes, ignored extension processes, etc. In addition, ideas arose in science about the formation of the planet from cold particles , which deprived the hypothesis of its main support.

At the same time, the doctrine of geosynclines continued to be supplemented and developed. In this regard, a great contribution was made by Soviet scientists A.D. Arkhangelsky, N.S. Shatsky, M.V. Muratov and others. Along with the ideas about mobile zones - geosynclines and on the basis of them at the end of the 19th century. and especially since the beginning of the 20th century. the doctrine of relatively stable continental areas - platforms - began to develop; Among the domestic scientists who developed this teaching, we must first of all name A. P. Karpinsky, A. D. Arkhangelsky, N. S. Shatsky, A. A. Bogdanov, A. L. Yanshin.

The doctrine of geosynclines and platforms has become firmly established in geological science and remains important to this day. However, it still does not have a solid theoretical basis.

The desire to supplement and eliminate shortcomings in the contraction hypothesis or, conversely, to completely replace it led to the emergence during the first half of the 20th century. a number of new geotectonic hypotheses. Let's note some of them.

Pulsation hypothesis. It is based on the idea of ​​alternating processes of compression and expansion of the Earth - processes that are very characteristic of the Universe as a whole. M.A. Usov and V.A. Obruchev, who developed this hypothesis, associated folding, thrusts, and the introduction of acidic intrusions with compression phases, and the appearance of cracks in the earth’s crust and the outpouring of mainly basic lavas along them with expansion phases.

Hypothesis of differentiation of subcrustal substance and migration of radioelements. Under the influence of gravitational differentiation and radiogenic heating, periodic melting of liquid components from the atmosphere occurs, which entails ruptures of the earth's crust, volcanism, mountain building and other phenomena. One of the authors of this hypothesis is the famous Soviet scientist V.V. Belousov.

Continental drift hypothesis. It was outlined in 1912 by the German scientist A. Wegener and is fundamentally different from all other hypotheses. Based on the principles of mobilism - recognition of significant horizontal movements of vast continental masses. Most of the hypotheses were based on the principles of fixism - the recognition of a stable, fixed position of individual parts of the earth's crust relative to the underlying mantle (such as the hypotheses of contraction, differentiation of subcrustal matter and migration of radioelements, etc.).

According to the ideas of A. Wegener, the granite layer of the earth’s crust “floats” on the basalt layer. Under the influence of the rotation of the Earth, it turned out to be collected into a single continent, Pangea. At the end of the Paleozoic era (about 200-300 million years ago), Pangea was fragmented into separate blocks and their drift began until they occupied their present position. Under the influence of the drift of blocks of North and South America to the west, the Atlantic Ocean arose, and the resistance that these continents experienced as they moved along the basalt layer contributed to the emergence of mountains such as the Andes and the Cordillera. For the same reasons, Australia and Antarctica moved apart and moved south, etc.

A. Wegener saw confirmation of his hypothesis in the similarity of the contours and geological structure of the coasts on both sides of the Atlantic Ocean, in the similarity of fossil organisms of continents far removed from each other, in the different structure of the earth's crust within the oceans and continents.

The appearance of A. Wegener's hypothesis aroused great interest, but it faded away relatively quickly, since it was not able to explain many phenomena, and most importantly, the possibility of continental movement along the basalt layer. Nevertheless, as we will see below, mobilist views, but on a completely new basis, were revived and received widespread recognition in the second half of the 20th century.

Rotation hypothesis. It occupies a separate place among geotectonic hypotheses, since it sees the manifestation of tectonic processes on Earth under the influence of extraterrestrial causes, namely the attraction of the Moon and the Sun, causing solid tides in the earth's crust and mantle, slowing down the rotation of the Earth and changing its shape. The consequence of this is not only vertical, but also horizontal movements of individual blocks of the earth's crust. The hypothesis is not widely accepted because absolute majority Scientists believe that tectogenesis is the result of the manifestation of the internal forces of the Earth. At the same time, the influence of extraterrestrial causes on the formation of the earth’s crust obviously also needs to be taken into account.

The theory of new global tectonics, or lithospheric plate tectonics. Since the beginning of the second half of the 20th century. Extensive geological and geophysical studies of the bottom of the World Ocean began. Their result was the emergence of completely new ideas about the development of the oceans, such as, for example, the spreading of lithospheric plates and the formation of young oceanic crust in rift valleys, the formation of continental crust in zones of underthrust of lithospheric plates, etc. These ideas led to the revival of mobilist ideas in geological science and to the emergence of a new theory global tectonics, or tectonics of lithospheric plates.

The new theory is based on the idea that the entire lithosphere (i.e., the earth’s crust together with the upper layer of the mantle) is divided by narrow tectonically active zones into separate rigid plates moving along the asthenosphere (a plastic layer in the upper mantle). Active tectonic zones, characterized by high seismicity and volcanism, are rift zones of mid-ocean ridges, systems of island arcs and deep ocean trenches, and rift valleys on continents. In the rift zones of mid-ocean ridges, plates move apart and new oceanic crust forms, and in deep-sea trenches, some plates move under others and continental crust forms. A collision of plates is also possible - the formation of the Himalayan folded zone is considered to be the result of this phenomenon.

There are seven large lithospheric plates and a slightly larger number of small ones. These plates received the following names: 1) Pacific, 2) North American, 3) South American, 4) Eurasian, 5) African, 6) Indo-Australian and 7) Antarctic. Each of them consists of one or more continents or parts thereof and oceanic crust, with the exception of the Pacific Plate, which consists almost entirely of oceanic crust. Simultaneously with the horizontal movements of the plates, their rotations also occurred.

The movement of lithospheric plates, according to this theory, is caused by convective flows of matter in the mantle, generated by the heat released during the radioactive decay of elements and gravitational differentiation of matter in the bowels of the Earth. However, the evidence for thermal convection in the mantle, according to many scientists, is insufficient. This also applies to the possibility of oceanic plates plunging into the mantle to great depths and a number of other positions. The surface expression of convective movement is the rift zones of mid-ocean ridges, where the relatively warmer mantle, rising to the surface, undergoes melting. It pours out in the form of basaltic lavas and hardens. Then basaltic magma reintroduces itself into these frozen rocks and pushes older basalts in both directions. This happens many times. At the same time, the ocean floor is growing and expanding. This process is called spreading. The rate of growth of the ocean floor ranges from a few mm to 18 cm per year.

Other boundaries between lithospheric plates are convergent, that is, the earth's crust in these areas is absorbed. Such zones were called subduction zones. They are located along the edges of the Pacific Ocean and in the east of the Indian Ocean. The heavy and cold oceanic lithosphere, approaching the thicker and lighter continental lithosphere, goes under it, as if diving. If two oceanic plates come into contact, the older one sinks because it is heavier and colder than the younger plate.

The zones where subduction occurs are morphologically expressed as deep-sea trenches, and the subducting oceanic cold and elastic lithosphere itself is well established from seismic tomography data. The plunging angle of oceanic plates varies, up to vertical, and the plates can be traced to the boundary of the upper and lower mantles at a depth of approximately 670 km.

When the ocean plate begins to bend sharply as it approaches the continental plate, stress arises in it, which, when released, provokes earthquakes. Hypocenters or earthquake foci clearly mark the friction boundary between two plates and form an inclined seismofocal zone, plunging beneath the continental lithosphere to depths of 700 km. These zones are called Benioff zones, after the American seismologist who studied them.

The sinking of the oceanic lithosphere leads to other important consequences. When the lithosphere reaches a depth of 100–200 km in the area high temperatures and pressure, fluids are released from it - special superheated mineral solutions that cause the melting of rocks of the continental lithosphere and the formation of magma chambers that feed chains of volcanoes developed parallel to deep-sea trenches on active continental margins.

Thus, on the active continental margin, due to subduction, highly dissected topography, high seismicity and vigorous volcanic activity are observed.

In addition to the phenomenon of subduction, there is the so-called obduction, that is, the thrust of the oceanic lithosphere onto the continental one, an example of which is the huge tectonic cover on the eastern edge of the Arabian Peninsula, composed of typical oceanic crust.

Mention should also be made of collision, or collisions, two continental plates, which, due to the relative lightness of the material composing them, cannot sink under each other, but collide, forming a folded mountain belt with a very complex internal structure.

The main principles of lithospheric plate tectonics are the following:

1.The first prerequisite Plate tectonics is the division of the upper part of the solid Earth into two shells that differ significantly in rheological properties (viscosity) - a rigid and brittle lithosphere and a more plastic and mobile asthenosphere. As already mentioned, these two shells are distinguished using seismological or magnetotelluric data.

2.Second position Plate tectonics, to which it owes its name, is that the lithosphere is naturally divided into a limited number of plates—currently seven large and the same number of small ones. The basis for identifying them and drawing boundaries between them is the location of earthquake foci.

3.Third position Plate tectonics concerns the nature of their mutual movements. There are three types of such movements and, accordingly, boundaries between plates: 1) divergent boundaries, along which plates move apart - spreading; 2) convergent boundaries, on which there is a convergence of plates, usually expressed by the subduction of one plate under another; if an oceanic plate moves under a continental plate, this process is called subduction, if the oceanic plate moves over the continental plate - obduction; if two continental plates collide, also usually with one moving under the other, - collision; 3)transform boundaries, along which horizontal sliding of one plate occurs relative to another along the plane of a vertical transform fault.

In nature, boundaries of the first two types predominate.

At divergent boundaries, in spreading zones, there is a continuous birth of new ocean crust; therefore these boundaries are also called constructive. This crust is moved by the asthenospheric current towards subduction zones, where it is absorbed at depth; this gives grounds to call such boundaries destructive.

Fourth position plate tectonics lies in the fact that during their movements the plates obey the laws of spherical geometry, or rather Euler's theorem, according to which any movement of two conjugate points on a sphere occurs along a circle drawn relative to an axis passing through the center of the Earth.

5.Fifth position Plate tectonics states that the volume of oceanic crust absorbed in subduction zones is equal to the volume of crust emerging in spreading zones.

6.Sixth position plate tectonics sees the main cause of plate movement in the mantle convection. This convection in the classic 1968 model. is purely thermal and general mantle, and the way it affects lithospheric plates is that these plates, which are in viscous adhesion with the asthenosphere, are carried away by the flow of the latter and move like a conveyor belt from the spreading axes to the subduction zones. In general, the scheme of mantle convection, leading to a plate tectonic model of lithosphere movements, is that under the mid-ocean ridges there are ascending branches of convective cells, under subduction zones there are descending ones, and in the interval between the ridges and trenches, under the abyssal plains and continents there are horizontal ones segments of these cells.

The theory of new global tectonics, or lithospheric plate tectonics, is especially popular abroad: it is also recognized by many Soviet scientists, who do not limit themselves to general recognition, but work hard to clarify its main provisions, complementing, deepening and developing them. The Soviet mobility scientist A.V. Paves, developing this theory, came, however, to the conclusion that giant rigid lithospheric plates do not exist at all, and the lithosphere, due to the fact that it is penetrated by horizontal, inclined and vertical moving zones, consists of separate plates (“litoplastins”) moving differentially. This is a significantly new look at one of the main but controversial provisions of this theory.

Let us note that a certain part of mobile scientists (both foreign and domestic) in their views show an extremely negative attitude towards the classical doctrine of geosynclines in fact, they completely reject it, not taking into account the fact that many of the provisions of this doctrine are based on reliable facts and observations established and carried out during geological studies of the continents.

Obviously, the most correct way in creating a truly global theory of the Earth is not opposition, but the identification of unity and interconnection between everything positive reflected in the classical doctrine of geosynclines, and everything new that is revealed in the theory of new global tectonics.

When viewed from space, it is not at all obvious that the Earth is teeming with life. To understand that it is here, you need to get close enough to the planet. But even from space our planet still seems alive. Its surface is divided into seven continents, which are washed by huge oceans. Below these oceans, in the invisible depths of our planet, there is also life.

A dozen cold, hard plates slide slowly over the hot inner mantle, diving under each other and occasionally colliding. This process, called plate tectonics, is one of the defining characteristics of planet Earth. People mainly feel it when earthquakes occur and volcanoes erupt.

But plate tectonics is responsible for something more important than earthquakes and eruptions. New research suggests that Earth's tectonic activity may have important for the other defining feature of our planet: life. Our Earth has a moving, ever-transforming outer crust, and this may be the main reason why the Earth is so amazing and no other planet can match its abundance.

One and a half billion years before the Cambrian explosion, back in the Archean era, there was almost no oxygen on Earth that we breathe now. Algae had already begun to use photosynthesis to produce oxygen, but most of this oxygen was consumed by iron-rich rocks, which used the oxygen to convert themselves into rust.

According to research published in 2016, plate tectonics initiated a two-step process that led to higher oxygen levels. In the first stage, subduction caused the Earth's mantle to change and produce two types of crust - oceanic and continental. The continental version had fewer iron-rich minerals and more quartz-rich rocks, which do not pull oxygen from the atmosphere.

Then, over the next billion years—from 2.5 billion years ago to 1.5 billion years ago—the rocks pumped carbon dioxide into the air and oceans. The extra carbon dioxide helped the algae, which produced even more oxygen—enough to eventually cause the Cambrian explosion.

Tectonic plates on other planets

So tectonics is important for life?

The problem is that we have one sample. We have one planet, one place with water and a sliding outer crust, one place that is teeming with life. Other planets or moons may have activity that resembles Earth's tectonics, but it is not like what we see on Earth.

The Earth will eventually cool so much that plate tectonics will weaken, and the planet will eventually become frozen. New supercontinents will grow and disappear before this happens, but at some point the earthquakes will stop. Volcanoes will be turned off forever. The earth will die like... Whether any forms of life will inhabit it by this time is a question.

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 form mountain belts . 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.

More than 90% of the Earth's surface is covered 13 -th largest lithospheric plates.

Rift– a huge fracture in the earth's crust, formed during its horizontal stretching (i.e., where the flows of heat and matter diverge). In rifts, magma outflows, new faults, horsts, and grabens arise. Mid-ocean ridges form.

First continental drift hypothesis (i.e. horizontal movement of the earth's crust) put forward at the beginning of the twentieth century A. Wegener. Created on its basis lithospheric theory t. According to this theory, the lithosphere is not a monolith, but consists of large and small plates “floating” on the asthenosphere. The boundary areas between lithospheric plates are called seismic belts - these are the most “restless” areas of the planet.

The earth's crust is divided into stable (platforms) and mobile areas (folded areas - geosynclines).

- 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- a hypothesis suggesting that the lithosphere is divided 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.

According to modern plate theories The entire lithosphere is divided into separate blocks by narrow and active zones - deep faults - moving in the plastic layer of the upper mantle relative to each other at a speed of 2-3 cm per year. These blocks are called lithospheric plates.

The peculiarity of lithospheric plates is their rigidity and ability, in the absence of external influences, to maintain their shape and structure unchanged for a long time.

Lithospheric plates are mobile. Their movement along the surface of the asthenosphere occurs under the influence of convective currents in the mantle. Individual lithospheric plates can move apart, move closer together, or slide relative to each other. In the first case, tension zones with cracks along the boundaries of the plates appear between the plates, in the second - compression zones, accompanied by the pushing of one plate onto another (thrusting - obduction; thrusting - subduction), in the third - shear zones - faults along which sliding of neighboring plates occurs .

Where continental plates converge, they collide and mountain belts are formed. This is how, for example, the Himalaya mountain system arose on the border of the Eurasian and Indo-Australian plates (Fig. 1).

Rice. 1. Collision of continental lithospheric plates

When the continental and oceanic plates interact, the plate with the oceanic crust moves under the plate with the continental crust (Fig. 2).

Rice. 2. Collision of continental and oceanic lithospheric plates

As a result of the collision of continental and oceanic lithospheric plates, deep-sea trenches and island arcs are formed.

The divergence of lithospheric plates and the resulting formation of the oceanic crust is shown in Fig. 3.

The axial zones of mid-ocean ridges are characterized by rifts(from English rift - crevice, crack, fault) - a large linear tectonic structure of the earth's crust hundreds, thousands in length, tens and sometimes hundreds of kilometers wide, formed mainly during horizontal stretching of the crust (Fig. 4). Very large rifts are called rift belts, zones or systems.

Since the lithospheric plate is a single plate, each of its faults is a source of seismic activity and volcanism. These sources are concentrated within relatively narrow zones along which mutual movements and friction of adjacent plates occur. These zones are called seismic belts. Reefs, mid-ocean ridges and deep-sea trenches are mobile regions of the Earth and are located at the boundaries of lithospheric plates. This indicates that the process of formation of the earth's crust in these zones is currently occurring very intensively.

Rice. 3. Divergence of lithospheric plates in the zone among the oceanic ridge

Rice. 4. Rift formation scheme

Most of the faults of lithospheric plates occur at the bottom of the oceans, where the earth’s crust is thinner, but they also occur on land. The largest fault on land is located in eastern Africa. It stretches for 4000 km. The width of this fault is 80-120 km.

Currently, seven of the largest plates can be distinguished (Fig. 5). Of these, the largest in area is the Pacific, which consists entirely of oceanic lithosphere. As a rule, the Nazca plate, which is several times smaller in size than each of the seven largest ones, is also classified as large. At the same time, scientists suggest that in fact the Nazca plate is much more bigger size, than we see it on the map (see Fig. 5), since a significant part of it went under the neighboring plates. This plate also consists only of oceanic lithosphere.

Rice. 5. Earth's lithospheric plates

An example of a plate that includes both continental and oceanic lithosphere is, for example, the Indo-Australian lithospheric plate. The Arabian plate consists almost entirely of continental lithosphere.

The theory of lithospheric plates is important. First of all, it can explain why there are mountains in some places on Earth and plains in others. Using the theory of lithospheric plates, it is possible to explain and predict catastrophic phenomena that occur at plate boundaries.

Rice. 6. The shapes of the continents really seem compatible.

Continental drift theory

The theory of lithospheric plates originates from the theory of continental drift. Back in the 19th century. many geographers have noted that when looking at a map, one can notice that the coasts of Africa and South America seem compatible when approaching (Fig. 6).

The emergence of the hypothesis of continental movement is associated with the name of the German scientist Alfred Wegener(1880-1930) (Fig. 7), who most fully developed this idea.

Wegener wrote: “In 1910, the idea of ​​​​moving continents first occurred to me... when I was struck by the similarity of the outlines of the coasts on both sides of the Atlantic Ocean.” He suggested that in the early Paleozoic there were two large continents on Earth - Laurasia and Gondwana.

Laurasia was the northern continent, which included the territories of modern Europe, Asia without India and North America. The southern continent - Gondwana united the modern territories of South America, Africa, Antarctica, Australia and Hindustan.

Between Gondwana and Laurasia there was the first sea - Tethys, like a huge bay. The rest of the Earth's space was occupied by the Panthalassa Ocean.

About 200 million years ago, Gondwana and Laurasia were united into a single continent - Pangea (Pan - universal, Ge - earth) (Fig. 8).

Rice. 8. The existence of a single continent of Pangea (white - land, dots - shallow sea)

About 180 million years ago, the continent of Pangea again began to separate into its component parts, which mixed on the surface of our planet. The division occurred as follows: first Laurasia and Gondwana reappeared, then Laurasia split, and then Gondwana split. Due to the split and divergence of parts of Pangea, oceans were formed. The Atlantic and Indian oceans can be considered young oceans; old - Quiet. The Arctic Ocean became isolated as landmass increased in the Northern Hemisphere.

Rice. 9. Location and directions of continental drift during the Cretaceous period 180 million years ago

A. Wegener found many confirmations of the existence of a single continent of the Earth. He found the existence of remains of ancient animals—listosaurus—in Africa and South America especially convincing. These were reptiles, similar to small hippopotamuses, that lived only in freshwater bodies of water. This means swimming huge distances on the salty sea ​​water they couldn't. He found similar evidence in the plant world.

Interest in the hypothesis of continental movement in the 30s of the 20th century. decreased somewhat, but was revived again in the 60s, when, as a result of studies of the relief and geology of the ocean floor, data were obtained indicating the processes of expansion (spreading) of the oceanic crust and the “diving” of some parts of the crust under others (subduction).