1. Punjab Edusat Society Production
SUBJECT : GEOGRAPHY
CLASS : BA PART I
CHAPTER : EARTH
TOPIC : INTERIOR OF THE EARTH
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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.
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ftfdnkoEhU eh s[;hI ikDd/ j' fe Xosh d/ roG ftZu eh j?< fJj ftFk G{r'b ftfrnkBh
ns/ ftfrnkBhnK bJh F{o[ s'I jh fyZu dk e/Ido pfDnk fojk j?. id''I i{b; toB/ B/ 1864
s'I @Xosh d/ roG tb :ksok# (Journey to the centre of the Earth) fbyh U[d''I Xosh
d/ roG dh gqfeqsh fej' fijh j? fJ; pko/ eJh fto'Xh f;XKs gquZbs ;B. e[M
G{ftfrnkBh ;'ud/ ;B fe Xosh pj[s f}nkdk dZphnK j'JhnK r?;K dk r'bk j? id fe eJh
j'o nfijk nB[wkB bkT[Id/ ;B fe fJ; ftu tyo'-tZyo/ gdkoEK dhnK gosK jB. j[D brgr
fJe ;dh pknd th ;kv/ e'b e'Jh f;ZXk ;p{s BjhI, fi; okjhI d; ;ehJ/ fe Xosh fe; uh}
dh pDh j'Jh j?. Xosh d/ roG pko/ ;kvh ikDekoh ngosy ftfrnkBe gqwkDK s/
nkXkfos j?. fJ;s'I gfjbK fe n;hI tZyo/-tZyo/ ;p{sK s/ ftuko eohJ/, nkU gfjbK
Xosh dh ouBk pko/ gqkgs ikDekoh s/ T[gobh B}o wkfoJ/ .
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 Anchor 3:
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
1

2. of the earth is based upon indirect scientific evidences. These sources may be
classified into three groups:
Cut to Anchor4
id'I n;hI Xosh dhnK tZyohnK gosK dh ;zxDsk pko/ ftuko efoJ/ sK fJ; dk nkXko
G{s f;XKs , s?oB dk f;XKs j?. i/ s/b, gkDh ns/ rfb;ohB ~ fJe pheo ftZu gkU sK
T[j fszB s?jK ftZu nk iKd/ jB. ;G s'I jbek sob s/b ;G s'I T[go nk ikt/rk ns/ T[;s'I
EZb/ gkDh s/ nyho ftZu rfb;ohB. fJ; soQK Xosh fizBQK gdkoEK dh pDh j'Jh
j?, fJj gdkoE th fJe d{i/ d/ T[go s?od/ jB jkbKfe fJBQK ftu'I e[M nzF m'; jB.
fszB ;dhnK gfjbK nzro/} ftfrnkBh fJ;ke fBT{NB (Isaac Newton) B/ rq?jK
ns/ r[o{st nkeoFB pb d/ nfXn?B d/ nkXko s/ fJj rDBk ehsh fe Xosh dh n";sB
;zxDsk ,fJ;dh ;sj s/ gkJhnK iKdhnK uNkBK s'I d[rDh j? ns/ fJT[I Xosh dk roG
pj[s ;zxD/ gdkoEK dk pfDnk j'fJnk j?. jkbKfe fBT{NB d/ ;w/I s'I b? e/ j[D sZe
Xosh d/ nzdob/ fjZ;/ pko/ ;kv/ frnkB ftZu ekch tkXk j'fJnk j? go fBT{NB dh
rDBk dk nzdk}k fBFu/ s"o s/ pdfbnk BjhI j?. nkU Xosh dhnK ty'-tZyohnK s?jK
dh ;zxDsk pko/ ikDhJ/.
Cut to Anchor 5
fit/I fJ; fuZso ftu n;hI t/fynk j? fe Xosh d/ e'o (Core) dh ;zxDsk ;G s'I tZX j? ns/
fJ;dk Xosh nzdob/ dpk Bkb f;ZXk ;zpzX j?. fJBQK ;bkfJvK(slides) okjhI Xosh
d/ nzdob/ dpk dh ;fEsh dk ikfJ}k bt'.
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fJ; soQK fJj nzdk}k j? fe Xosh d/ roG (e/Ido) ftZubk dpk tk:{wzvbh: dpk s'I
30-40 bZy r[DK f}nkdk j[zdk j?. Xosh d/ nzdob/ T[^u dpk ekoB jh itkbkw[yh
cNd/ jB ns/ G[ukb nkT[Id/ jB.
s[;hI ;ko/ itkbkw[yh ns/ row uFfwnK(hot springs) d// pko/ ikDd/ j'. fJj Xosh d/
nzdob/ T[^u skg d/ gOwkD jB. G{-roG ftu id'I v{zxhnK ykBK y'dhnK iKdhnK jB
sK Xosh dh ;sj s'I brksko skgwkB tZXdk iKdk j?. fiT[I Xosh d/ EZb/ iKd/ ikU
sK jo 100 whNo dh v{zxkJh s/ 2 s'I 3 doik (Celsius)skgwkB tZXdk j?. skgwkB
dk tXDk nzdo{Bh FeshnK d/ ekoD j?, o/fvUn?efNt gdkoEK dk ftxNB j'Dk,
2

3. o;kfJfDe feqnktK ns/ j'o eJh ekoDK Bkb Xosh dk nzdobk fjZ;k row ofjzdk j?.
fJ; soQK skgwkB dh do ftu fJe' fijk tkXk BjhI j[zdk .n;hI Xosh dh ;sj s'I EZb/
iKd/ jK sK skgwkB ;wkB o{g ftZu BjhI tZXdk.
.
Cut to Anchor 7
r?o e[dosh ;o'sK( fiBQK dk f}eo n;hI gfjbK jh eo u{e/ jK) s'I fJbktk Xosh dh
T[sgsh pko/ tZy'-tZyo/ f;XKs Gh Xosh d/ rop pko/ gqwkD fdzd/ jB.
Cut to Anchor 8
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
Cut to Anchor 9
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:
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3

4. 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:
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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.
Cut to Anchor 12
Xosh dh ouBk ~ ;wMD bJh itkbk w[yhnK dh e[dosh gqfefonk ftfrnkBh bJh
nfXn?B dk w[y ;o's ojh j?. e[M ftfrnkBh ftFtk; eod/ jB fe id'I row s/ sob bktk
itkbk w[yh d/ cND Bkb Xosh dh ;sj s/ c?bdk j? sK fJj ;wfMnk ik ;edk j? fe Xosh
dh ;sj d/ EZb/ fJe gos nfijh th j? i' sob o{g ftu j?. fJ; sob ;sj ~ w?rwk u?Ipo fejk
iKdk j? i' fe itkbk w[yh d/ cND s/ w?rwk (T[bpdk sob) s/ bktk eZYdh j?. fJ;
nzdk}/ nB[;ko fJj Bshik eZfYnk ik ;edk j? fe Xosh dk e[ZM fjZ;k sob j?.
d{i/ gk;/ dpk d/ tZXD Bkb uNkBK dk melting point tZX iKdk j?. fJ; soQK Xosh
nzdo pj[s f}nkdk skgwkB j'D d/ pkti{d th Xosh dk nzdo{Bh fjZ;k sob BjhI j? fJ;
dk ekoD U[gobh gosK dk Gko s/ dpkt j? . go g/gVh d/ pko pko N[ZND ekoB
nzdo{Bh uZNkBK dk melting point xZN iKdk j? fi; ekoD uZNkBK fgxb iKfdnK
jB fit/I fe n;h ikDd/ jK fe U[ZE/ b'VhIdk T[^u skgwkB gfjbK jh w"i{d j?. fJT[I
itkbk w[yh dh eko}Fhbsk Xosh d/ roG d/ nfXn?B dk :'r ;p{s BjhI g/F eo ;edh.
eh s[jk~ gsk j? fe Seismology (;hf}wkb'ih- G{ukb-ftfrnkB) dk eh noE j?<
fJj G{ukbh sozrK s/ ;[Gkt ~ ;wMD dk ftfrnkB j?. fJBQK G[ukbh sozrK ~
;hf}w'rqkc Bkwe :zso okjhI wkfgnk iKdk j?. fJj ftFtkF ehsk iKdk j? fe ;hf}wkb'ih
jh nfijk ;o's j? i' Xosh d/ roG dh ;zouBk pko/ mhe ikDekoh d/ ;edk j?. s[;hI ;ko/
4

5. G{ukb dh ouBk pko/ ikDd/ j't'r/. Xosh d/ nzdo fi; EK G[ukb F[o{ j[zdk j? T[;~
c'e; efjzd/ jB ns/ G{ukbh sozrk Xosh dh ;sj wfj;{; ehshnK ikdhnK jB. ftfrnkBe
nfXn?B s'I fJ; rb dk gsk bZfrnk j? fe id'I fJj G{ukbh sozrK Xosh d/ nzdob/ tZy-
tZy GkrK EkDhI bzxdh jB sK fJBQK sozrK d/ t/r ns/ fdFk ftu pdbkU nkT[Idk j?.
fJBQK dk behaviour (toskok) fJe wkfXnw s'I d{i/ wkfXnw ftu nkT[D s/ pdb iKdk
j?. Gkt m'; ftZu fJj j'o soQK behave eo dhnK jB ns/ sob ftu j'o soQK.
fJj G{ukbh sozrk fszB soQK dhnK jB L
w{b iK bzpdko sozrk(Primary or Longitudinal waves),
r"D sozrk(Secondary waves) ns/
bzphnK sozrk iK ;sjh sozrk (Long waves or Surface waves)
Slide t/y' ns/ jo fJe d/ r[DK dh ikBekoh bU[ -
Cut to Anchor 13
Take a look at the slides to observe the characteristics of each:
Cut to Anchor 14
fJBQK fuZsoK okjhI s[;hI t/y ;ed/ fe id'I fJj G[ukb sozrkI Xosh d/ nzdo
ubdhnK jB sK fJBQK d/ ;[Gkn ftZu eh coe nKU[Idk j?. ;bkfJvk (slide) ~ fXnkB
bk e/ ty'.
Cut to Anchor 15
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
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6. 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.
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;' fJj ;G e[M frnkB d/ ;o's ;h i' Xosh d/ roG Bkb ;zpzfXs jB. fJBQK ;p{sK ~
fXnkB ftZu oZyfdnK n;hI Xosh dh ouBk pko/ e[M nkw fBu'V eZY ;ed/ jK.
fit/I n;hI gsk ehsk j? fe Xosh dk nzdobk skg s/ dpkn, G[ukb sozrk dk t/r s/
okj, ;k~ Xosh dh nzdo{Bh ouBk d/ fGzB- fGzB G'fse r[DK, xDsk ns/ ;zxNeK
pko/ ikDekoh d/Idk j?. ;sj s/ gkJhnK iKdhnK uNkBK dh xDsk nzdobh ;sj s'I pj[s
xZN j?. o;kfJfDe pDso nB{;ko g/gVh jbehnK XksK d/ f;bhe/N s'I pDh j'Jh j?
ns/ w?INb f}nkdkso b'j/ ns/ fwFo XksK d/ f;bhe/N jB. ftfGzB G{-ftfrnkfBeK ns/
G{r'b ftfrnkBhnK fit/I fe n?vtov ;[n?; (Edward Suess), nkoHJ/H vkbh
(R.A.Daly), i?coh (Jeffrey)ns/ j'w; (Holmes) B/ o;kfJfDe ;zxDsk d/ nkXko #s/
Xosh dh nzdo{Bh ouBk pko/ nB{wkB bkJ/ jB. ;' nkU Xosh dh nzdo{Bh ouBk
d/ ;zxDe pko/ ;[n?; (Suess) d/ ftukoK s'I rb F[o{ eohJ/L
Cut to ANCHOR 17:
j[D se n;hI fJj ikfDnk fe Xosh dh ;sj s/ e'o ~ tZyohnK gosK iK fjZf;nK ftZu
tzfvnk ik ;edk j? 1940 ftZu nkoHJ/Hvkb/ B/ Xosh d/ nzdo{Bh fjZ;/ ~ uko gosK
ftZu tzfvnk. nkU fJ; G{-ftfrnkBh d/ fynkbK ~ tkuhJ/.
Cut to ANCHOR 18:
6

7. j[D n;hI j?o'bv i?coh (Harold Jeffrey) d/ ftukoK tZb Mks wkohJ/, fi;B/ G{ukbh
sozrk d/ nkXko s/ Xosh d/ nzdo{Bh fjZ;/ ftu uko gosk ~ gSkfDnk. nkU fJ;
fuZso okjhI fJ;~ ;wMD dk :sB eohJ/.
Cut to Anchor 19:
fJe j'o gf;ZX G{-ftfrnkBh nkoEo j'w} (Arthur Holmes) B/ Xosh dh pDso d/
nkXko s/ fJ; d/ nzdo{Bh fjZ;/ dhnK d' tZvhnK gosk ~ ouBk dk nkXko wzfBnk.
nkU fJBQK ~ gSkBD dk :sB eohJ/.
Cut to ANCHOR 20:
;',n;hI tZyo- tZyo// G{-ftfrnkBhnK iK ftfrnkBhnK d/ Xosh dh nzdo{Bh ;zouBk
ns/ gosk pko/ ftukoK pko/ ikDekoh bJh. fJBQK ftuko s'I fJj gqshs j[zdk j? fe
Xosh dhnK gosk dh frDsh, w'NkJh ns/ T[;d/ r[DK pko/ wsG/d jB. fJ; confusion
ekoB T[go fdZs/ ftuko oZd j' iKd/ jB. e[dosh s/ r?o e[dosh G{ukbh sozrk d/
tZy-tZy gZyK dk ftFb/FD ns/ ftfrnkBe nfXn?B B/ ftfrnkfBeK ~ Xosh d/ nzdo{Bh
fjZ;/ d/ ojZ; ~ y'bQD :'r pDkfJnk j? ns/ Bt/I ftuko fdZs/ jB. G{ukbh sozrK d/ t/r
ftu nkT[Id/ pdbkU d/ nkXko s/ n;hI Xosh d/ nzdo{Bh Gkr ~ fszB fjZf;nK ftZu tzv
;ed/ jK fiBQK d/ ty'-tZyo/ r[D jB fJj fjZ;/ jb -g/gVh, w?INb ns/ e'o. nkU fJBQK
d/ r[DK ~ y'ihJ/L
Cut to Anchor 21:
w?INb g/gVh d/ fBubh gos j?. w?INb ftZu b'jk, w?rBhFhnw s/ e?bFhnw g/gVh
s'I fes/ f}nkdk fwbdk j?. fJj f}nkdk row ns/ ;zxDh j? feT[Ife Xosh dh rfjokJh
Bkb skgwkB ns/ dpk tZX iKd/ jB. i/ s[bBk eohJ/ sK w?INb ~ T[pb/ nzv/ dh ;/dh
dh fBnKJh ;wfMnk ik ;edk j?. nkU fJ;d/ bZSDK dk nfXn?B eohJ/L
Cut to Anchor 22:
nzv/ dh }odh s'I jZN e/, Xosh dk e'o d' w[y fjZf;nK dk pfDnk j'fJnk j?. fJe 2,200
feb'whNo w'Nk sob e'o ns/ 1250 feb'whNo w'Nk m'; e'o. e'o d/ bZSDK ~ tkuD
ykso fJ; fuZso tZb t/y'.
Cut to Anchor 23:
7

8. 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.
Cut to Anchor 24:
Xosh rqfj fszB w[Zy gosk dk pfDnk j'fJnk j?. fJe gsbh g/gVh, w?INb ns/ e'o.
Xosh d/ nzdo{Bh fjZ;/ d[nkb/ gsbh uNkB ~ g/gVh efjzd/ jB. T[gobh g/gVh i' fe
wjKdhgK T[go j[zdh j?, T[;~ f;n?b(Sial) efjzd/ jB. idfe wjKdhgk dh f;n?b d/ EZb/
ns/ ;w[zdo dh sbh T[go f;w?( Sima) j[zdh j?. w?INb dh gos, g/gVh d/ EZb/
j[zdh j?. w?INb dh ;zxDsk g/gVh s'I pj[s f}nkdk j[zdh j? fi; ekoB fJj G{ukbh
sozrk bJh gfotofss ;sj pD iKdh j?. fJ; ;sj ~ w'jo'ftf;; Gzrsk(Mohorovicic
discontinuity) eoe/ ikfDnk iKdk j?.
Xosh d/ e/Ido ftu e'o j[zdk j? fi; dh xDsk w?INb s'I d[rDh j[zdh j?. feT[fe
fJ; d/ ;zxNB Xks{ (b'jk-fBeb fwFo Xks{) jB. Xosh dk e'o d' fBFfus fjZf;nK ftZu
j?. pkjobk sob (fgxfbnk) e'o ns/ nzdobk m'; e'o.
Xosh dh nzdo{Bh fjZf;nK dh ;kvh ikDekoh ngos] ftfrnkBe gqwkDk s/
nkXkfos j?. fi;~ fszB fjZf;nK ftZu tzfvnk ik ;edk j?. @r?o e[dosh ;o's, Xosh dh
T[sgsh pko/ f;XKsK ftu'I gqwkD ns/ e[dosh ;o's fi; soQK fe itkbk w[yh ns/
;hf}wkb'ih. ;hf}wkb'ih jh fJe nfijk ;o's j? i' ;k~ Xosh d/ nzdo d/ ;zxNeK dh mhe
o{g ftZu ikDekoh d/Idk j?. G{ukbh sozrk fszB torK ftZu oZyhnK rJhnK jB, w{b,
r"D ns/ ;sjh sozrk. fJj sozrK xDe pdbkU dh EK s/ ngtofss j' iKdhnK jB ns/ fJT[I
Xosh d/ nzdo N/vk o;sk ngBkT[IdhnK jB. ftfGzB G{-ftfrnkBh fit/I ;[n?;, vkbh, i?
coh ns/ j'bw} B/ Xosh dhnK gosK dh ouBk pko/ ftuko fdZs/ jB. n?vtov ;[n?;
(Edward Suess) B/ Xosh d/ nzdo dh o;kfJfDe ;zxNBk pko/ ukBDk gkfJnk j?.
nkoHJ/HvkbhH(R A Daly) B/ rfjokJh s/ xDsk d/ nkXko s/ Xosh dhnK uko gosK
wzBhnK. G{-ftfrnkBh nkoEo j'bw} (Arthur Holmes) B/ w[y d' gosk wzBhnk,
g/gVh ns/ ;p;Nq/NZw (Crust and Substratum). G{ukbh sozrk d/ n?fXn?B s'I pknd
fJBQK ftukoK ~ oZd ehsk frnk j? ns/ j[D nk]o ;hf}wkb'ih (Seismology) Xosh dh
nzdo{Bh ikDekoh bJh ;G s'I uzrk ;o's wzBh iKdh j?.
Cut to ANCHOR 25
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!
Cut to Anchor 26:
8

9. 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.
9