Punjab Edusat Society Production

                            SUBJECT      : GEOGRAPHY
                            CLASS  ...
• Seismological Evidences
       Define Primary, Secondary and Surface Waves
       Discuss the constitution of the Eart...
Sources of Knowledge about the Interior of Earth

There are few direct as well as some indirect evidences about the struct...
and 3.5 at different places. The average density of the whole earth is about 5.5.
It is generally estimated therefore, tha...
Cut to Anchor 6
Apart from artificial sources that we discussed earlier, the various theories
related to the origin of the...
Tidal hypothesis: The core of the earth should be in liquid state because
the earth has been taken to have been formed fro...
Anchor pulls the relevant super

                          Natural Sources-Seismology

Do you know what is meant by Seismo...
Cut to MM 7

VO 7
Seismic waves follow curved path which indicates that there are variations of
density inside the earth. ...
properties, density and composition prevailing there. Surface layer of rock has a
much lower density compared to the inner...
(2) Asthenosphere: .It is just below the lithosphere. As per its name, it is neither
too solid nor too hard or rigid. Its ...
this basis of changes in the velocity of seismic waves, we can divide the interior
of the earth into three zones of varyin...
Between the lower mantle and the core lies a further discontinuity at a depth of
2,900 km, at which the density increases ...
Our knowledge about the interior of the earth is based upon indirect scientific
evidences i.e. grouped into three categori...
65%
80%

Q5.
      What is the lithosphere composed of?
      The continental and oceanic crust
      The crust and upperm...
A. P wave
B. an S wave
C. surface wave
D. All of the Above

Q11. Which region in the Earth consists primarily of solid iro...
16
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Geo ba i_interior of earth

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Geo ba i_interior of earth

  1. 1. Punjab Edusat Society Production SUBJECT : GEOGRAPHY CLASS : BA PART I CHAPTER : EARTH TOPIC : INTERIOR OF THE EARTH Cut to MM 1: Montage showing Solar System and then focusing Earth and its various life forms, upcoming mountains, sea floor spreading, earthquake structure, volcanic eruption and then close up of interior earth (Capsule Solar System, Biosphere, Plate tectonics and Mt building, Earthquake, Structure of Volcano, VO 1: Our Earth holds a prominent place in the Solar System. This planet is unique because of the availability of life on it. Manifold changes have been taking place on its surface like formation of mountains, spreading of sea floor, natural disasters like earthquake and volcanic eruptions. This gives us immense evidences that extensive forces are acting from within the earth and bringing these changes. In order to understand the nature of these changes, let’s explore the inside earth. Cut to ANCHOR 1: Hello Students! Welcome to today’s module-Interior of the Earth. You all must have got a fair idea after seeing the visuals that the elementary knowledge of constitution of the Earth is necessary to understand the nature of changes taking place on the Earth’s surface. Could you ponder over the thought that what constitutes the interior of the earth? What is the nature of the surface of the earth? Or why is it that when Volcano erupts it emits hot, molten lava? We are going to unfold reasons to all these queries. But first of all, let me share with you the learning objectives for today’s lesson. Cut to our hi-tech board on which the following SUPER appears: LEARNING OBJETIVES Upon completion of the module, the learner will be able to-  Explain the structure of the Earth  List an overview of the layers of the Earth  Discuss the physical state of the Earth’s interior  List the density and pressure of the Earth’s interior  Give an account of temperature of the Earth’s interior  Describe the various evidences regarding the constitution of the Earth’s interior • Artificial Sources • Theories from the Origin of the earth 1
  2. 2. • Seismological Evidences  Define Primary, Secondary and Surface Waves  Discuss the constitution of the Earth’s interior as postulated by – Suess, Daly, Jeffrey and Arthur Holmes  Describe the constitution of Earth’s interior on the basis of Recent Views  Describe the features of each layer of the Earth i.e., Crust, Mantle and Core  Write a short note on Sial, Sima, Nife, Moho Discontinuity, Wiechert- Gutenberg Discontinuity, Earth Crust, Mantle and Core Cut to our hi-tech board on which the following SUPER appears: Introduction Cut to ANCHOR 2: “Interior of the Earth”- Do you know students? This topic has been of great interest among geographers and scientist since ancient times. When Jules Verne wrote ‘Journey to the Centre of the Earth’ in 1864, there were many conflicting theories about the nature of the Earth’s interior. Some geologist thought that the earth contained a highly compressed ball of gases while some suspected that it was made of separate shells, each made of a different material. Today, well over a century later, there is little direct evidence to tell us what the earth is made up of. So our knowledge about the interior of the earth is based upon indirect scientific evidences. Before we discuss about the various evidences, let me give you all an overview of the structure of the Earth. Anchor pulls the relevant super An Overview of the Layers of the Earth The Earth is divided into different layers like a giant onion, each with its own particular characteristics. Take a look at the slides to see the visual on structure of the Earth. Cut to MM 2 VO 2: Layers of the Earth The planet Earth is made up of three main shells: the very thin, brittle Crust, the Mantle, and the Core; the mantle and core are each divided into two parts i.e. upper mantle and lower mantle and outer core and inner core. Although the core and mantle are about equal in thickness, the core actually forms only 15 percent of the Earth's volume, whereas the mantle occupies 84 percent. The crust makes up the remaining 1 percent. Thus, the solid crust on which we live is no thicker in relation to the Earth than an egg shell. Cut to Anchor 3: Anchor pulls the relevant super 2
  3. 3. Sources of Knowledge about the Interior of Earth There are few direct as well as some indirect evidences about the structure of the Earth. As regards physical conditions, direct evidence is available from mines, which do not extend beyond a depth of 4km. So our knowledge about the interior of the earth is based upon indirect scientific evidences. These sources may be classified into three groups: On Board Activity 1 Evidences about Interior Earth Artificial Evidences from the theories of the Origin of Earth Natural Sources Density Vulcanicity Pressure Seismology Temperature Anchor pulls the super on the screen Density of different Shells of the Earth When we look at the density of different shells of the Earth, the basic principle that governs the arrangement of layers is a simple one based on flotation. If oil, water and glycerine are poured into a beaker, they will arrange themselves in three layers. The lightest liquid oil will be at the top followed by water and glycerine. In the same way, the different materials that make up the Earth float one above the other, even though some of the components are solid. Three centuries ago, the English scientist Isaac Newton calculated, from his studies of planets and the force of gravity, that the average density of the Earth is twice that of surface rocks and therefore that the Earth's interior must be composed of much denser material. Our knowledge of what's inside the Earth has improved immensely since Newton's time, but his estimate of the density remains essentially unchanged. Let’s find out the density of different layers of the earth Cut to MM 3 VO 3 Density It is commonly believed that the outer thinner part of the earth is composed of sedimentary rocks with an average density of 2.7. Just below this, there is the second layer of igneous rocks with an average density ranging between 3.0 3
  4. 4. and 3.5 at different places. The average density of the whole earth is about 5.5. It is generally estimated therefore, that the density of the core of the earth is around 11.0. Thus, the density of the core is highest in all parts of the Earth. Cut to Anchor 4 As we saw in the visual that the density of the core is the highest, it bears a great relation with the pressure inside the Earth. Take a look at the slides to know the state of pressure within the Earth. Cut to MM 4 VO 4 Pressure The weight and pressure of rocks increases with increasing depth. Hence the density of rocks also increases with increasing depth. Thus, earlier it was believed that the high density of the core of the earth is due to very high pressure prevailing there because of the weight of the overlying rocks. Now according to second opinion, the core of the earth is itself composed of heavy metallic materials of high density like Nickel and Iron. Cut to Anchor 5 Thus it is estimated that the pressure at the centre of the earth is 30-40 lakh times the atmospheric pressure. It is due to high pressure inside the earth that the phenomena of volcanoes and earthquakes occur. Anchor pulls the relevant super Temperature You all are aware of volcanic activity and the occurrence of hot springs. These are very much indicative of high temperatures prevailing in the interior of the earth. On the basis of findings of deep mining, temperature increases from the surface of the Earth downward at the rate of 2 to 3 degree Celsius for every 100 metres of descent. The rise in temperature is the result of internal forces, disintegration of radioactive substances, chemical reaction and other sources keeping the interior hot. Thus, the rate of increase in temperature is now considered to be variable and there is no uniform increase from the surface to the centre of the earth. Cut to MM 5 VO 5 As like pressure, the temperature also increases with increasing depth. The Core records a temperature of 2000 degree Celsius. The high temperature prevailing in the interior indicates the liquid or perhaps gaseous conditions prevailing at greater depths. But at the same time there is a tremendous increase in the pressure of overlying layers on earth’s interior. Thus even under extremely high temperature towards the central part of the earth, the liquid nature of the core has acquired the properties of a solid and is probably in a plastic state. 4
  5. 5. Cut to Anchor 6 Apart from artificial sources that we discussed earlier, the various theories related to the origin of the Earth also presents evidences regarding the state of interior Earth. Anchor pulls the relevant super Theories of the Origin of the Earth Various scholars of different fields have put forward different hypothesis and theories related to the origin of the Earth. They have assumed the original form of the Earth to be in solid or liquid or gaseous state. According to the Planetesimal hypothesis proposed by Thomas Chamberlin and Forest Moulton in 1905, the planets of the Solar System have emerged from an encounter between the Sun and another star. In this scenario, the gravity of the passing star tears a series of bolts from the solar surface. Bolts coming from the side nearer the star are thrown out to distances while those from the far side of the Sun are ejected less violently. The outer part is expanded and cooled into a huge cloud of solid particles spread out in a disk rotating about the Sun in a plane determined by the motion of the passing star. Thus, the views of Planetesimals can be summarised as On Board Activity Planetesimal hypothesis: Earth originated due to accretion and aggregation of solid dust particles known as planetesimals. Based on this, the core of the earth should be in solid state. Cut to Anchor 7 Now, according to James Jeans and Harold Jeffreys, the propounder of Tidal hypothesis, the origin of the solar system is a result of a close encounter between the Sun and a second star. However, they differed significantly from the planetesimal hypothesis. As a result of a detailed mathematical analysis, Jeans concluded in 1916 that the tidal interaction between the Sun and a passing star would raise tides on the Sun resulting in the loss of a single cigar-shaped filament of hot gas, rather than separate streams of gas as in the Chamberlin and Moulton scenario. This hot gas would then condense directly into the planets instead of going through a planetesimal stage. The central section of the "cigar" would give rise to the largest planets – Jupiter and Saturn – while the tapering ends would provide the substance for the smaller worlds. Thus, the views of Tidal hypothesis can be summarised as: On Board Activity 5
  6. 6. Tidal hypothesis: The core of the earth should be in liquid state because the earth has been taken to have been formed from the tidal materials ejected from the primitive Sun. Cut to Anchor 8 Apart from Tidal and Planetesimal hypothesis, there is one more hypothesis that became very popular during the 18th century called as Nebular hypothesis proposed by Kant and Laplace. According to Kant, great cloud of gas and dust, called as nebula, begins to collapse because the gravitational force overcomes the forces associated with gas pressure that would like to expand it. Thus, the views of Tidal hypothesis can be summarised as: On Board Activity Nebular Hypothesis: According to this, the core of the earth should be in gaseous state. This view was suggested by Laplace. Cut to Anchor 9 Based on the different hypothesis, it can be presumed that the Earth, along with the other planets, is believed to have been born 4.5 billion years ago as a solidified cloud of dust and gases left over from the creation of the Sun. For perhaps 500 million years, the interior of Earth stayed solid and relatively cool. The main ingredients, according to the best available evidence, were iron and silicates, with small amounts of other elements, some of them being radioactive. As millions of years passed, energy released by radioactive decay—mostly of uranium, thorium, and potassium—gradually heated Earth, melting some of its constituents. The iron melted before the silicates, and, being heavier, sank towards the centre. Now we move on to the natural sources of interior earth. Anchor pulls the relevant super Natural Sources-Vulcanicity This natural phenomenon of volcanoes has been a great source of study for the scientists to decipher the structure of the earth. Some scientists believe on the basis of upwelling and spread of hot and liquid lava on the Earth’s surface during volcanic eruption that there is at least such a layer below the Earth’s surface which is in liquid state. Such molten layer has been termed as Magma Chamber which supplies magma and lava during volcanic eruptions. So on the basis of these postulation, it may be inferred that some part of the earth should be in liquid state. But on the other hand the increasing pressure increases the melting point of rocks. Therefore, in spite of very high temperature prevailing therein the inner part of the Earth may not be in molten state owing to excessive weight and pressure exerted by the overlying layers. But due to the fracturing and faulting in the crustal surface, the melting point of the underlying rocks is reduced and thus the rocks are instantaneously melted because required degree of high temperature is already present there. Thus, vulcanicity does not seem to be a valid source of evidence for determining the interior of the Earth. 6
  7. 7. Anchor pulls the relevant super Natural Sources-Seismology Do you know what is meant by Seismology? It is the science that studies the behaviour of seismic waves. These seismic waves are recorded with the help of an instrument known as Seismograph.It is believed that seismology is the only source which provides us sound information about the composition of the earth’s interior. You all must be acquainted with the structure of an earthquake. The place of the occurrence of an earthquake is called focus and the place which experiences the waves is located on the earth surface. What has been discovered through scientific studies is the fact that there is change in the course and the velocity of the waves on crossing the boundaries of different zones inside the earth. Their behaviour vary from one medium to another i.e. in solid they behave in one way, while in liquid in another way. These earthquake waves are of three types: On Board Activity Primary or Longitudinal waves, Secondary waves and Long waves or Surface waves. Cut to Anchor 10 Take a look at the slides to observe the characteristics of each: Anchor pulls the relevant super Primary Waves Cut to MM 6 VO 6 Primary waves or P waves are like sound waves in which the movement of the particles is in the direction of the propagation of the waves. They travel with fastest speed through solid materials. Though they also pass through liquids but their speed is slowed down. Their average velocity is 8km/sec. Secondary Waves or S waves are like light waves where particles move at right angles to the rays. They can travel through solids only and they disappear in liquids. Their average velocity is 4km/sec. Long waves or Lwaves refer to up and down or side to side motion of the Earth surface. They affect only the surface of the earth and die out at smaller depths. These waves cover longest distances of all the earthquake waves. They are most violent and destructive. Their velocity is only 3km/sec Cut to Anchor 11 Now you will be noticing from the given visuals the behavior of earthquake wave while they pass through the interior of the earth. Take a look at the slides. 7
  8. 8. Cut to MM 7 VO 7 Seismic waves follow curved path which indicates that there are variations of density inside the earth. Primary waves and Secondary waves are recorded only up to Mantle. The velocity also increases with increasing depth. Secondary waves are totally absent in the core of the earth. It appears from this observation that the core is in liquid state which is located at the depth of more than 2,900 km from the Earth’s surface and surrounds the nucleus of the earth. P Waves passes through the Core but is refracted at various angles based on the density of rocks. The area between the zone of P and S waves is called as the Shadow Zone specifying it does not receive any waves. Cut to Anchor 12 As you saw the behaviour of seismic waves in the visuals, it is apparent that earthquake waves are bent, like light passing through a piece of glass, when they traverse rock boundaries with different densities. If the waves hit the boundary at a low angle, they are reflected instead. Waves from distant earthquakes emerge steeply through the crust while those from earthquakes nearby emerge at shallow angles. By knowing these angles, the velocities at which the waves emerge, their times of arrival and distances travelled, geophysicist have been able to compute the positions and densities of the earth’s different shells. On the above bases, it can be summed up that compressional or P waves cause the rock particles through which they pass to shake back and forth in the direction of the wave. While Shear waves or Secondary waves make the particles vibrate at right angles to the direction of their passage. Neither types of seismic waves physically move the particles; instead it merely travels through them. It is L waves that produce the most violent shocks. The Richter scale is used to measure the magnitude of earthquakes. The scale of magnitudes is so arranged that each unit on the scale is equivalent to 30 times the energy released by the previous unit. A magnitude of 2 is hardly felt, while a magnitude of 7 is the lower limit of an earthquake that has a devastating effect over a large area. It is thus obvious that seismology is the only source, which provides us authentic information about the composition of the Earth’s interior. In the light of this, the nature and properties of the composition of the interior of the earth may be successfully obtained on the basis of the study of various aspects of seismic waves. Cut to Anchor 13 So that was all about the sources of knowledge related to the interior of the earth. Keeping these evidences in view, we can derive conclusions regarding the composition of earth in general. As we come to know that the temperature and pressure inside the earth, the velocity and the path followed by earthquake waves tell us of varying physical 8
  9. 9. properties, density and composition prevailing there. Surface layer of rock has a much lower density compared to the inner layers. As regards chemical composition, the crust is made up of silicates of lighter metals and mantle is a layer of mixed metals and silicates. Different geologists and geographer such as Edward Suess, R.A. Daly, Jeffrey and Arthur Holmes have postulated their ideas about the structure of the earth interior in the light of chemical composition and layers. So let’s starts with Suess’s opinion about the constitution of earth’s interior. Anchor pulls the SUPER: Constitution of the Earth’s interior according to Suess Cut to MM 8: Relevant capsule VO 8: Edward Suess has thrown light on the chemical composition of the earth’s interior. He has identified three zones of different matter below the outer thin sedimentary cover i.e. Crust. SIAL: it is located just below the outer sedimentary cover. The layer is dominated by silica and aluminum called as (SIAL=SI+AL). The average density of this layer is 2.9. SIMA: it is located just below the SIAL layer. This layer is composed of basalt and is the source of magma and lava during volcanic eruptions. Silica and magnesium are the dominant constituents. Average density ranges between 2.9 to 4.7. NIFE: it is located just below the SIMA layer. This is the lowermost layers of the interior earth. This layer is composed of nickel (NI) and ferrium or iron (Fe). These metals constitute the term NIFE. It is, thus apparent that this layer is made of heavy metals which are responsible for very high density from 11 to 12. Cut to ANCHOR 14: So far we came to know that the earth can be sub-divided into different layers or zones from its surface to its core. In 1940, R.A. daly has divided the interior of the earth in four layers. Let us see the opinion of this geographer. Anchor pulls the SUPER: Constitution of the Earth’s interior according to R.A.Daly Cut to MM 9: Relevant capsule VO 9: (1) Lithosphere: - Daly named the outer zone or the surface of the earth as Lithosphere. It is rigidly solid and made up of sedimentary rocks with its depth about 80 kilometers. Average density is 3.0 and the thickness is 1600 km. 9
  10. 10. (2) Asthenosphere: .It is just below the lithosphere. As per its name, it is neither too solid nor too hard or rigid. Its average depth is about 360 kilometers. (3) Mesosphere: Mesosphere is just below the Asthenosphere. It is relatively more rigid, hard and solid than Asthenosphere. Its depth is about 2400 kilometers. (4) Centrosphere: - It starts just below mesosphere and extends up to the interior core of the earth. It is made of iron and is in solid state. Here the density of the rocks being the maximum, the Centrosphere gets firm and the rocks happen to be of crystalline material. Cut to ANCHOR 15: Anchor pulls the SUPER: Constitution of the Earth’s interior according to Harold Jeffrey Now we move on to another view put forward by Harold Jeffereys who has identified four layers of the interior earth in the light of seismic waves. Let’s get the knowledge from the visual. Cut to MM 10: VO 10: (1) Outer Layer:-It is made up of sedimentary rocks. (2) Second Layer: - It is composed of granite rocks. (3) Third or intermediate layer: It is made of diorite rocks. (4) Fourth Layer:-It is made up of peridotite rocks. Cut to Anchor 16: Another renowned scientist or geographer Arthur Holmes has recognized two major layers of the earth on the basis of the composition of the interior of the earth. Let’s identify them. Cut to MM 11 VO 11: Crust: the upper layer of earth is termed as crust which is composed of whole of the SIAL and the upper portion of SIMA. Substratum: the second layer is termed as substratum. It includes the lower portion of SIMA. Cut to ANCHOR 17: So we came to know different geographer’s or scientist’s views about the composition and layers of the interior earth. It appears from foregoing discussion that there is difference of opinions about the number, thickness and various properties of layers of the earth. Due to this confusion these aforesaid views became obsolete. The scientific study and analysis of various aspects of seismic waves of natural and man-induced earthquakes have enabled the scientist to unravel the mystery of the earth’s interior and put forward the recent views. On 10
  11. 11. this basis of changes in the velocity of seismic waves, we can divide the interior of the earth into three zones of varying properties such as Crust, Mantle and Core. Let’s explore their features. Crust Cut to MM 12: VO 12: The upper layer of the earth is known as earth crust. It occupies not much of the mass. We can further sub-divide the earth's crust in three parts on the basis of its thickness and composition. (i) Continental Crust: - As we know that Earth Crust is mostly found in Continental areas. We can have three layers in it. It is also known as SIAL with the combination of Silicon (SI) and Aluminum (AL). The uppermost layer is of Sedimentary Rocks whereas second layer is of Granite rocks which are just below the sedimentary rocks. Igneous and Metamorphic rocks are found in this layer. The lower most layer of the Earth crust i.e. the basic layer is of Basaltic materials. Discontinuity separating the layers of Granite and Basalt is termed as Conard discontinuity. (ii) Oceanic Crust: - It also has two layers. The upper layer is made up of sedimentary rocks while the lower layer is composed of Basaltic material. It is called SIMA with the combination of Silicon (SI) and Magnesium (MA). (ii) Transitional Crust: - It is present in between Continental and Oceanic parts. It is mainly present in such continental coastal regions as abounds in coastal oceans and islands. The crust is separated from the mantle by a sudden change of density which shows up a good reflecting plane for earthquake waves. This plane is known as Mohorovicic discontinuity. Cut to Anchor 18: The layer of mantle lies below the crust. The mantle, which contains more iron, magnesium, and calcium than the crust, is hotter and denser because the temperature and pressure inside the Earth increases with depth. As a comparison, the mantle might be thought of as the white of a boiled egg. Let’s study its features. MANTLE Cut MM 13: VO13: The depth of mantle is 2900 km inside the earth. On the basis of changes in the velocities of seismic waves and density mantle is divided into upper mantle from Moho discontinuity to the depth of 700 km and lower mantle from 700 km to 2900 km depth. 11
  12. 12. Between the lower mantle and the core lies a further discontinuity at a depth of 2,900 km, at which the density increases from 5.5 to 10g/cm3. This is called Gutenberg discontinuity as per the name of scientist Weichert Gutenberg. It helps to separate Mantle and Core. Here S-waves become invisible and velocity of P waves also decreases. Cut to Anchor 19: Unlike the yolk of an egg, however, the Earth's core is actually made up of two distinct parts: a 2,200 km-thick liquid outer core and a 1,250 km-thick solid inner core. As the Earth rotates, the liquid outer core spins, creating the Earth's magnetic field. Take a look at the visuals to observe the features of core. CORE Cut to MM 14: VO 14: The core, the deepest and most inaccessible zone of the earth, extends from the lower boundary of the mantle at the depth of 2900 km to the center of the earth up to 6371 km. Core is made of metallic materials mainly iron and nickel. The core is further divided into two sub-zones such as outer zone and inner or transitional zone. Let’s classify these two zones according to their depth. (a) Outer Core: - It extends from 2900 km i.e. Wiechert-Gutenberg discontinuity to the depth of 5150 km. In other words, keeping in mind the nature of the seismic waves, it can be said to be in the liquid state but due to high pressure it should not be taken as mere fluid. (b) Inner Core: - the inner core extends from the depth of 5150 km to the center of the earth up to 6371 km. This is the zone of solid state where the density denotes 13.3 to 13.6. Cut to Anchor 20: So finally we have completed our today’s module-Interior of the Earth. But before I assess you all I will give a brief recapitulation of the whole content. Let’s see what we have learnt so far. Anchor pulls the super, Summary The planet Earth is made up of three main shells: the very thin, brittle crust, the mantle, and the core. The relatively thin layer of rock which envelops the interior of the Earth is called as Crust. The upper crust over continental areas is known as Sial while over oceanic areas and underlying the continental sial is the crust called Sima. The layer of mantle lies below the crust. The crust is separated from the mantle by a sudden change of density which shows up a good reflecting plane for earthquake waves. This plane is known as Mohorovicic discontinuity. At the center of the Earth lies the core, which is nearly twice as dense as the mantle because its composition is metallic (iron-nickel alloy). The Earth's core is actually made up of two distinct parts: liquid outer core and a solid inner core. 12
  13. 13. Our knowledge about the interior of the earth is based upon indirect scientific evidences i.e. grouped into three categories of artificial sources, evidences from the theories of the origin of earth and natural sources like vulcanicity and seismology. Seismology has been considered to be the only source which provides us authenticated information about the composition of the earth’s interior. Seismic waves have been categorized under primary, secondary and surface waves. These waves are refracted at the place of density changes and thus they follow a curved path inside the Earth. Different geographers viz., Suess, Daly, Jeffrey, Holmes and Van der Gracht have put forward their views regarding the composition and layering system of the Earth. Edward Suess has thrown light on the chemical composition of the earth’s interior. R.A. Daly has divided the interior of the earth in four layers on the basis of depth and density. Geographer Arthur Homes has recognized two major layers such as Crust and Substratum. These views were considered obsolete with the induction of the study of seismic waves and finally Seismology was taken as the best source to study the interior earth. Cut to ANCHOR 21 So we have explored in detail about the inside Earth. Here’s a quick fire round test for you to find out how much you have learnt. Let’s begin: keep your thinking caps on! The format of the questions will be like this —First one question will be put by the anchor and after a pause of 3-4 secs its answer will also appear on the screen.) Q1.What has been the most useful method for determining the structure of the earth's interior? Core samples Density studies Magnetic field Seismology Q2. Which layer of the earth's interior has the lowest density? Continental crust Inner core Mantle Outer core Q3. Which layer of the earth's interior has the highest density? Continental crust Inner core Mantle Outer core Q4. What percentage of the earth's volume is occupied by the mantle? 20% 50% 13
  14. 14. 65% 80% Q5. What is the lithosphere composed of? The continental and oceanic crust The crust and uppermost mantle The lower mantle and outer core The upper mantle Q6 What property distinguishes the earth's crust, mantle, and core? Composition Pressure State i.e.solid or liquid Temperature Q7. The Gutenberg discontinuity lies at the boundary of which two layers? Crust and mantle Crust and outer core Mantle and inner core Mantle and outer core Q8. The Mohorovicic discontinuity lies at the boundary of which two layers? Crust and mantle Crust and outer core Mantle and outer core Outer core and inner core Q9. The shock waves produced by an earthquake are called __?__ A. seismic waves B. sonar waves C. laser waves D. radiowaves 10. What is the approximate distance from the surface to the center of the Earth? A. 700 km B. 2900 km C. 6400 km D. 10,000 km Q10. What type of seismic wave is being recorded by the seismograph in the diagram? 14
  15. 15. A. P wave B. an S wave C. surface wave D. All of the Above Q11. Which region in the Earth consists primarily of solid iron? A. region A B. region B C. region C D. region D E. Q12. Which layer in the Earth does not transmit S-waves? A. the crust B. the mantle C. the inner core D. the outer core Q13. The crust of the earth is made mostly of A. oxygen & silicon B. iron & silicon C. iron & nickel D. copper & nickel Cut to Anchor 22: I am confident that you have all scored well. I hope you enjoyed the lesson as much as I did and are looking forward to the next class. Thank you for your attention and see you next time. 15
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