The document provides an overview of a geography lesson on the interior of the Earth. It discusses various sources of evidence for the Earth's internal structure, including theories of the planet's origin, density and pressure measurements, temperature observations, and analysis of seismic wave behavior. Seismology is identified as the primary source of information, with discussion of how P, S, and L waves change speed and behavior when passing through the core, mantle, and crust.

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. • 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. 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. 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. 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. 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. 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. 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. 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. (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. 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. 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. 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. 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. 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.
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