Composition of the earth's lithosphere. The thinnest layer of the planet

It is carried out by reducing the viscosity of rocks, increasing their electrical conductivity, and also due to the speed with which seismic waves propagate. The lithosphere has different thicknesses on land and under the oceans. Its average value is 25-200 km for land and 5-100 km for.

95% of the lithosphere consists of igneous magma rocks. Granites and granitoids are the predominant rocks on the continents, while basalts are such rocks.

The lithosphere is the environment for all known mineral resources and is also the subject of human activity. Changes in the lithosphere have an impact on the environment.

Soils are one of the components of the upper parts of the earth's crust. They are of great importance to humans. They are an organo-mineral product, which is the result of thousands of years of activity of various organisms, as well as factors such as air, water, sunlight and heat. The thickness of the soil, especially in comparison with the thickness of the lithosphere itself, is relatively small. In different regions it ranges from 15-20 cm to 2-3 m.

Soils appeared along with the emergence of living matter. Further they developed, they were influenced by the activity of microorganisms, plants and animals. The bulk of all microorganisms and organisms existing in the lithosphere are concentrated in the soil at a depth of several meters.

The lithosphere is the outer shell of the Earth made of relatively solid material: the earth's crust and the upper layer of the mantle. The term “” was coined by the American scientist Burrell in 1916, but at that time this concept meant only the solid rocks that make up the earth’s crust - the mantle was no longer considered part of this shell. Later, the upper sections of this layer of the planet (up to several tens of kilometers wide) were included: they border on the so-called asthenosphere, which is characterized by low viscosity and high temperature, at which substances already begin to melt.

The thickness varies in different parts of the Earth: beneath its layer can be from five kilometers thick - under the deepest places, and near the coast it already rises to 100 kilometers. Beneath the continents, the lithosphere extends up to two hundred kilometers deep.

In the past, it was believed that the lithosphere had a monolithic structure and did not break into parts. But this assumption has long been refuted - this one consists of several plates that move along the plastic mantle and interact with each other.

Hydrosphere

As the name suggests, the hydrosphere is the shell of the Earth consisting of water, or rather, all the water on the surface of our planet and under the Earth: oceans, seas, rivers and lakes, as well as groundwater. Ice and water in a gaseous state or steam are also part of the water shell. The hydrosphere consists of more than one and a half billion cubic kilometers of water.

Water covers 70% of the Earth's surface, most of it in the World Ocean - almost 98%. Only one and a half percent is allocated to ice at the poles, and the rest is rivers, lakes, reservoirs, and groundwater. Fresh water makes up only 0.3% of the entire hydrosphere.

The hydrosphere owes its appearance to

Lithosphere of the Earth literally means “stone shell”. This is one of the shells of the planet, formed by solid components. Let's consider what the lithosphere consists of and what the planet needs from it.

1. What it is?
2. What is the lithosphere formed by?
3. How do plates move?
4. Ecological situation
5. What have we learned?
6. Evaluation of the report

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• Test on the topic

What it is?

The planet's lithosphere is the covering layer formed by the upper part of the mantle and the earth's crust. This definition was given in 1916 by scientist Burrell. It is located on a softer layer - the asthenosphere. The lithosphere completely covers the entire planet. The thickness of the upper hard shell is not the same in different areas. On land, the thickness of the shell is 20-200 km, in the oceans - 10-100 km. An interesting fact is the presence of the Mohorovicic surface. This is a conditional boundary separating layers with different seismic activity. Here there is an increase in the density of the lithosphere matter. This surface completely repeats the earth's topography.

Rice. 1. Structure of the lithosphere

What is the lithosphere formed by?

The development of the lithosphere has occurred since the formation of the planet. The solid shell of the earth is formed mainly by igneous and sedimentary rocks. In the course of various studies, the approximate composition of the lithosphere was established:

• oxygen;
• silicon;
• aluminum;
• iron;
• calcium;
• microelements.

The outer layer of the lithosphere is called the earth's crust. This is a relatively thin shell, no more than 80 km thick. The greatest thickness is observed in mountainous areas, the smallest in lowland areas. The earth's crust on continents consists of three layers - sedimentary, granite and basalt. In the oceans, the crust is formed by two layers - sedimentary and basalt; there is no granite layer.

Many planets have crust, but only Earth has differences between oceanic and continental crust.

The main part of the lithosphere is located under the crust. It consists of separate blocks - lithospheric plates. These plates move slowly along a softer shell - the asthenosphere. The processes of plate movement are studied by the science of tectonics.

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There are seven largest slabs.

• Pacific . This is the largest lithospheric plate. Along its boundaries, collisions with other plates and the formation of faults constantly occur.
• Eurasian . Covers the entire continent of Eurasia, with the exception of India.
• Indo-Australian . Occupies Australia and India. Constantly collides with the Eurasian plate.
• South American . It forms the continent of South America and part of the Atlantic Ocean.
• North American . It contains the continent of North America, part of Eastern Siberia, part of the Atlantic and Arctic oceans.
• African . Forms Africa, parts of the Indian and Atlantic oceans. The boundary between the plates is the largest here, as they move in different directions.
• Antarctic . Forms Antarctica and adjacent parts of the oceans.

Rice. 2. Lithospheric plates

How do plates move?

The laws of the lithosphere also include features of the movement of lithospheric plates. They constantly change their shape, but this happens so slowly that a person is not able to notice it. It is assumed that 200 million years ago there was only one continent on the planet - Pangea. As a result of some internal processes, it was separated into separate continents, the boundaries of which pass through the places where the earth’s crust split. A sign of plate movement today can be a gradual warming of the climate.

Since the movement of lithospheric plates does not stop, some scientists suggest that in a few million years the continents will once again unite into one continent.

What natural phenomena are associated with plate movement? In the places where they collide, the boundaries of seismic activity pass - when the plates hit each other, an earthquake begins, and if this happened in the ocean, then a tsunami.

The movements of the lithosphere are also responsible for the formation of the planet's topography. The collision of lithospheric plates leads to the crushing of the earth's crust, resulting in the formation of mountains. Underwater ridges appear in the ocean, and deep-sea trenches appear in places where plates diverge. The relief also changes under the influence of the air and water shells of the planet - the hydrosphere and atmosphere.

Rice. 3. Due to the movement of lithospheric plates, mountains are formed

Ecological situation

One example of the connection between the biosphere and the lithosphere is the active influence of human actions on the shell of the planet. The rapidly developing industry leads to the fact that the lithosphere is completely polluted. Chemical and radiation waste, toxic chemicals, and hard-to-decompose garbage are buried in the soil. The influence of human activity has a noticeable effect on the relief.

What have we learned?

We learned what the lithosphere is and how it was formed. They found that the lithosphere consists of several layers, and its thickness varies in different parts of the planet. The components of the lithosphere are various metals and trace elements. The movement of lithospheric plates causes earthquakes and tsunamis. The state of the lithosphere is greatly influenced by anthropogenic impacts.

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The lithosphere is the rocky shell of the Earth. From the Greek “lithos” - stone and “sphere” - ball

The lithosphere is the outer solid shell of the Earth, which includes the entire Earth's crust with part of the Earth's upper mantle and consists of sedimentary, igneous and metamorphic rocks. The lower boundary of the lithosphere is unclear and is determined by a sharp decrease in the viscosity of rocks, a change in the speed of propagation of seismic waves and an increase in the electrical conductivity of rocks. The thickness of the lithosphere on continents and under the oceans varies and averages 25 - 200 and 5 - 100 km, respectively.

Let us consider in general terms the geological structure of the Earth. The third planet beyond the distance from the Sun, Earth, has a radius of 6370 km, an average density of 5.5 g/cm3 and consists of three shells - bark, mantle and and. The mantle and core are divided into internal and external parts.

The Earth's crust is the thin upper shell of the Earth, which is 40-80 km thick on the continents, 5-10 km under the oceans and makes up only about 1% of the Earth's mass. Eight elements - oxygen, silicon, hydrogen, aluminum, iron, magnesium, calcium, sodium - form 99.5% of the earth's crust.

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.

On continents, the crust is three-layered: sedimentary rocks cover granite rocks, and granite rocks overlie basaltic rocks. Under the oceans the crust is “oceanic”, of a two-layer type; sedimentary rocks simply lie on basalts, there is no granite layer. There is also a transitional type of the earth's crust (island-arc zones on the margins of the oceans and some areas on continents, for example the Black Sea).

The earth's crust is thickest in mountainous regions(under the Himalayas - over 75 km), the average - in the areas of the platforms (under the West Siberian Lowland - 35-40, within the borders of the Russian Platform - 30-35), and the smallest - in the central regions of the oceans (5-7 km). The predominant part of the earth's surface is the plains of the continents and the ocean floor.

The continents are surrounded by a shelf - a shallow strip with a depth of up to 200 g and an average width of about 80 km, which, after a sharp steep bend of the bottom, turns into a continental slope (the slope varies from 15-17 to 20-30°). The slopes gradually level out and turn into abyssal plains (depths 3.7-6.0 km). The oceanic trenches have the greatest depths (9-11 km), the vast majority of which are located on the northern and western edges of the Pacific Ocean.

The main part of the lithosphere consists of igneous igneous rocks (95%), among which granites and granitoids predominate on the continents, and basalts in the oceans.

Blocks of the lithosphere - lithospheric plates - move along a relatively plastic asthenosphere. The section of geology on plate tectonics is devoted to the study and description of these movements.

To designate the outer shell of the lithosphere, the now obsolete term sial was used, derived from the name of the main rock elements Si (Latin: Silicium - silicon) and Al (Latin: Aluminum - aluminum).

Lithospheric plates

It is worth noting that the largest tectonic plates are very clearly visible on the map and they are:

• Pacific- 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 the 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 in the lithosphere

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 ).

This is interesting! 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.

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.

The upper layer of the lithosphere is the earth's crust; it is the most heterogeneous solid shell of the Earth. The chemical composition of the earth's crust and its structure are heterogeneous (Table 9).
The earth's crust is composed of rocks of various types and origins. Their distribution in general can be presented as follows: sedimentary rocks - 9.2%; metamorphic rocks - 20.0%; igneous rocks - 70.8%.

Table 8 - Chemical composition of the earth's crust (according to Vronsky, Voitkevich, 1997)

Mineral composition

The earth's crust - the upper solid layer of our planet - originally arose as a product of the melting of mantle material, which in the further course of geological history turned out to be significantly processed in the biosphere under the influence of air, water, and the activity of living organisms. During this transformation, a mineral and chemical difference was established between sedimentary and igneous rocks, consisting of the following (Vronsky, Voitkevich, 1997): The ratio of oxide iron to ferrous iron (FerO3: FeO) in sedimentary and igneous rocks has the opposite meaning. Oxide iron predominates in sedimentary rocks. This is due to the fact that sedimentary rocks were formed in the biosphere in the presence of free oxygen, which led to the oxidation of huge masses of iron, as well as other polyvalent chemical elements. The sodium content in sedimentary rocks is significantly reduced (almost 3 times) compared to igneous rocks with almost the same potassium content. This is apparently due to the fact that sodium under biosphere conditions is easily leached by natural waters and carried into the ocean, where it accumulates in pelagic ocean sediments. Sedimentary rocks are more enriched in HgO and CO2, which, as components, are found in igneous rocks in rather small concentrations. Sedimentary rocks contain varying amounts of organic carbon, which is usually not found in deep-seated igneous rocks. Organic compounds in sedimentary rocks are products of photosynthesis and biomineralization that have occurred in the Earth's biosphere since time immemorial.
During the development of the Earth, the geological cycle of rocks occurs (Fig. 12).
Figure 12 - Geological cycle of the Earth’s rocks according to the ideas of J. Hetton (Vronsky, Voitkevich, 1997)

When fresh sediments remain at depth for a long time, their compaction begins - the transition to typical rocks. This transition is associated with a process called diagenesis. Diagenesis itself is a physicochemical stage of sediment equilibration, which was originally a nonequilibrium physicochemical system. This system was watered and enriched with organic matter as well as living bacteria. Under such conditions, organisms absorb oxygen from the silt water and create a reducing environment. Reduction of oxides of polyvalent metals occurs. Silt waters often dissolve solid phases and lead to redistribution of matter. Secondary minerals appear, sometimes determining the cementation of clastic material with the formation of sandstones, conglomerates, and breccias.
With the immersion of sedimentary strata into deeper horizons, into the region of elevated temperatures and pressures, recrystallization of matter occurs, which is characteristic of metamorphism. Metamorphic processes are very diverse in the form of manifestation and the nature of the transformation of rocks. The main types of metamorphism are: regional, contact, dynamometamorphism and hydrothermal metamorphism. Regional metamorphism is the most common. Its products are schistose rocks - crystalline schists and gneisses. Contact metamorphism usually occurs as a result of the interaction of normal sedimentary rocks with hot magma and its exudates. In this case, skarns (at the contact with limestones) and hornfels (at the contact with sandy clay rocks), devoid of layering, are formed.
Ultrametamorphism occupies a special place in the formation of deep rocks. This is a high temperature process that results in the formation of a liquid molten phase. In this case, the process of remelting occurs of solid rocks that were not previously in a state of melt. Granitization is associated with this process - the transformation of the chemical and mineral composition of rocks towards granite. With the widespread and intensive development of anatexis processes, magma is revived, producing on the surface those rocks that are again subject to weathering and thus the cycle of geological circulation is completed.

General characteristics of the lithosphere.

The term "lithosphere" was proposed in 1916 by J. Burrell and until the 60s. twentieth century was synonymous with the earth's crust. Then it was proven that the lithosphere also includes the upper layers of the mantle up to several tens of kilometers thick.

IN lithosphere structure mobile areas (folded belts) and relatively stable platforms are distinguished.

Lithosphere thickness varies from 5 to 200 km. Under the continents, the thickness of the lithosphere varies from 25 km under young mountains, volcanic arcs and continental rift zones to 200 or more kilometers under the shields of ancient platforms. Under the oceans, the lithosphere is thinner and reaches a minimum of 5 km under the mid-ocean ridges; on the periphery of the ocean, gradually thickening, it reaches a thickness of 100 km. The lithosphere reaches its greatest thickness in the least heated areas, and its least in the hottest ones.

Based on the response to long-term loads in the lithosphere, it is customary to distinguish upper elastic and lower plastic layer. Also, at different levels in tectonically active areas of the lithosphere, horizons of relatively low viscosity can be traced, which are characterized by low velocities of seismic waves. Geologists do not exclude the possibility of some layers slipping relative to others along these horizons. This phenomenon is called stratification lithosphere.

The largest elements of the lithosphere are lithospheric plates with dimensions in diameter of 1–10 thousand km. Currently, the lithosphere is divided into seven main and several minor plates. Boundaries between plates are carried out along zones of greatest seismic and volcanic activity.

Boundaries of the lithosphere.

Upper part of the lithosphere borders the atmosphere and hydrosphere. The atmosphere, hydrosphere and upper layer of the lithosphere are in a strong relationship and partially penetrate each other.

Lower boundary of the lithosphere located above asthenosphere– a layer of reduced hardness, strength and viscosity in the upper mantle of the Earth. The boundary between the lithosphere and asthenosphere is not sharp - the transition of the lithosphere to the asthenosphere is characterized by a decrease in viscosity, a change in the speed of seismic waves and an increase in electrical conductivity. All these changes occur due to an increase in temperature and partial melting of the substance. Hence the main methods for determining the lower boundary of the lithosphere - seismological And magnetotelluric.

) and tough the upper part of the mantle. Layers of the lithosphere are separated from each other Mohorovic border. Let us take a closer look at the parts into which the lithosphere is divided.

Earth's crust. Structure and composition.

Earth's crust- part of the lithosphere, the uppermost of the solid shells of the Earth. The earth's crust accounts for 1% of the total mass of the Earth (see Physical characteristics of the Earth in numbers).

The structure of the earth's crust varies between continents and beneath the oceans, as well as in transition regions.

The continental crust is 35-45 km thick, in mountainous areas up to 80 km. For example, under the Himalayas - over 75 km, under the West Siberian Lowland - 35-40 km, under the Russian Platform - 30-35.

The continental crust is divided into layers:

- Sedimentary layer- a layer covering the upper part of the continental crust. Consists of sedimentary and volcanic rocks. In some places (mainly on the shields of ancient platforms) the sedimentary layer is absent.

- granite layer– a conventional name for a layer where the speed of propagation of longitudinal seismic waves does not exceed 6.4 km/sec. Consists of granites and gneisses - metamorphic rocks whose main minerals are plagioclase, quartz and potassium feldspar.

- Basalt layer - a conventional name for a layer where the speed of propagation of longitudinal seismic waves is in the range of 6.4 - 7.6 km/sec. Composed of basalts, gabbro ( igneous intrusive rock of mafic composition) and highly metamorphosed sedimentary rocks.

Layers of the continental crust can be crushed, torn and displaced along the fault line. Granite and basalt layers are often separated Conrad surface, which is characterized by a sharp jump in the speed of seismic waves.

Oceanic crust has a thickness of 5-10 km. The smallest thickness is characteristic of the central regions of the oceans.

The oceanic crust is divided into 3 layers :

- Marine sediment layer – thickness less than 1 km. In some places it is completely absent.

- Middle layer or "second" - a layer with a propagation speed of longitudinal seismic waves from 4 to 6 km/sec – thickness from 1 to 2.5 km. It consists of serpentine and basalt, possibly with an admixture of sedimentary rocks.

- The lowest layer or "oceanic" – the speed of propagation of longitudinal seismic waves is in the range of 6.4-7.0 km/sec. Made of gabbro.

Also distinguished transitional type of earth's crust. It is typical for island-arc zones on the margins of the oceans, as well as for some parts of continents, for example, in the Black Sea region.

Earth's surface mainly represented by the plains of continents and the ocean floor. The continents are surrounded by a shelf - a shallow strip with a depth of up to 200 g and an average width of about 80 km, which, after a sharp steep bend of the bottom, turns into a continental slope (the slope varies from 15-17 to 20-30°). The slopes gradually level out and turn into abyssal plains (depths 3.7-6.0 km). The oceanic trenches, located mainly in the northern and western parts of the Pacific Ocean, have the greatest depths (9-11 km).

Mohorovicic boundary (surface)

The lower boundary of the earth's crust passes along the Mohorovicic boundary (surface)– a zone in which a sharp jump in seismic wave velocities occurs. Longitudinal from 6.7-7.6 km/sec to 7.9-8.2 km/sec, and transverse – from 3.6-4.2 km/sec to 4.4-4.7 km/sec .

This same area is characterized by a sharp increase in the density of the substance - from 2.9-3 to 3.1-3.5 t/m³. That is, at the Mohorovicic boundary, the less elastic material of the earth's crust is replaced by the more elastic material of the upper mantle.

The presence of the Mohorovicic surface has been established for the entire globe at a depth of 5-70 km. Apparently, this boundary separates layers with different chemical compositions.

The surface of Mohorovicic follows the relief of the earth's surface, being its mirror image. It is higher under the oceans, lower under the continents.

The Mohorovicic surface (abbreviated Moho) was discovered in 1909 by the Croatian geophysicist and seismologist Andrej Mohorovicic and named after him.

Upper mantle

Upper mantle– the lower part of the lithosphere, located under the earth’s crust. Another name for the upper mantle is substrate.

The speed of propagation of longitudinal seismic waves is about 8 km/sec.

Lower boundary of the upper mantle passes at a depth of 900 km (when dividing the mantle into upper and lower) or at a depth of 400 km (when dividing it into upper, middle and lower).

Relatively composition of the upper mantle there is no clear answer. Some researchers, based on the study of xenoliths, believe that the upper mantle has an olivine-pyroxene composition. Others believe that the material of the upper mantle is represented by garnet peridotites with an admixture of eclogite in the upper part.

The upper mantle is not homogeneous in composition and structure. There are zones of reduced seismic wave velocities in it, and differences in the structure under different tectonic zones are also observed.

Isostasia.

Phenomenon isostasy was discovered when studying gravity at the foot of mountain ranges. Previously, it was believed that such massive structures, such as the Himalayas, should increase the force of gravity of the Earth. However, research carried out in the mid-19th century disproved this theory - the force of gravity on the surface of the entire earth's surface remains the same.

It was found that large unevenness of the relief is compensated, balanced by something at depth. The thicker the section of the earth's crust, the deeper it is buried in the material of the upper mantle.

Based on the discoveries made, scientists came to the conclusion that the earth's crust tends to balance at the expense of the mantle. This phenomenon is called isostasy.

Isostasy can sometimes be disrupted due to tectonic forces, but over time the earth's crust still returns to equilibrium.

Based on gravimetric studies, it has been proven that most of the earth's surface is in a state of equilibrium. M.E. Artemyev studied the phenomenon of isostasy on the territory of the former USSR.

The phenomenon of isostasy can be clearly seen using the example of glaciers. Under the weight of powerful ice sheets four or more kilometers thick, the earth’s crust under Antarctica and Greenland “sank”, falling below ocean level. In Scandinavia and Canada, which relatively recently became free of glaciers, a rise in the earth's crust is observed.

The chemical compounds that make up the elements of the earth's crust are called minerals . Rocks are formed from minerals.

Main types of rocks:

Igneous;

Sedimentary;

Metamorphic.

The lithosphere is predominantly composed of igneous rocks. They account for about 95% of the total material of the lithosphere.

The composition of the lithosphere on continents and beneath the oceans varies significantly.

The lithosphere on continents consists of three layers:

Sedimentary rocks;

Granite rocks;

Basalt.

The lithosphere under the oceans has two layers:

Sedimentary rocks;

Basalt rocks.

The chemical composition of the lithosphere is represented mainly by only eight elements. These are oxygen, silicon, hydrogen, aluminum, iron, magnesium, calcium and sodium. These elements account for about 99.5% of the earth's crust.

Table 1. Chemical composition of the earth's crust at depths of 10 - 20 km.