-
8/21/2019 NCERT- Complete Geography
1/578
CONTENTS
FOREWORD iii
UNIT I : GEOGRAPHYASADISCIPLINE 1-12
1. Geography as a Discipline 2
UNIT II : THEEARTH 13-38
2. The Origin and Evolution of the Earth 14
3. Interior of the Earth 214. Distribution of Oceans and
Continents 30
UNIT III : LANDFORMS 39-74
5. Minerals and Rocks 40
6. Geomorphic Processes 45
7. Landforms and their Evolution 58
UNIT IV : CLIMATE 75-110
8. Composition and Structure of Atmosphere 76
9. Solar Radiation, Heat Balance and Temperature 7910.
Atmospheric Circulation and Weather Systems 88
11. Water in the Atmosphere 98
12. World Climate and Climate Change 103
UNIT V : WATER(OCEANS) 111-125
13. Water (Oceans) 112
14. Movements of Ocean Water 120
UNIT VI : LIFEONTHEEARTH 126-140
15. Life on the Earth 127
16. Biodiversity and Conservation 135
GLOSSARY 141-144
http://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-1.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-1.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-1.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-1.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-1.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-1.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-1.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-1.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-1.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-1.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-2.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-3.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-4.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-5.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-6.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-7.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-8.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-9.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-10.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-11.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-12.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-13.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-14.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-15.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-16.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/Glossary.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/Glossary.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/Glossary.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/Glossary.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-16.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-15.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-14.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-13.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-12.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-11.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-10.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-9.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-8.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-7.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-6.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-5.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-4.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-3.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-2.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_1/book_publishing/CLASS%2011/Geographi-fundamenta%20and%20physical/ch-1.pdf
-
8/21/2019 NCERT- Complete Geography
2/578
GEOGRAPHYASADISCIPLINE
This unit deals with Geography as an integrating discipline; as
a science of spatial
attributes
Branches of geography; importance of physical geography
UNITI
-
8/21/2019 NCERT- Complete Geography
3/578
Y
ou have studied geography as one of thecomponents of your social
studies courseupto the secondary stage. You are
already aware of some of the phenomena ofgeographical nature in
the world and itsdifferent parts. Now, you will study Geographyas
an independent subject and learn about thephysical environment of
the earth, humanactivities and their interactive relationships.
Therefore, a pertinent question you can ask atthis stage is Why
should we studygeography? We live on the surface of the earth.Our
lives are affected by our surroundings inmany ways. We depend on
the resources tosustain ourselves in the surrounding areas.
Primitive societies subsisted on natural meansof subsistence,
i.e. edible plants and animals.With the passage of time, we
developedtechnologies and started producing our foodusing natural
resources such as land, soil and
water. We adjusted our food habits andclothing according to the
prevailing weatherconditions. There are variations in the
naturalresource base, technological development,adaptation with and
modification of physicalenvironment, social organisations and
culturaldevelopment. As a student of geography, youshould be
curious to know about all thephenomena which vary over space. You
learnabout the diverse lands and people. Youshould also be
interested in understanding thechanges which have taken place over
time.Geography equips you to appreciate diversityand investigate
into the causes responsible forcreating such variations over time
and space.
You will develop skills to understand the globeconverted into
maps and have a visual sense
of the earths surface. The understanding andthe skills obtained
in modern scientifictechniques such as GIS and computer
cartography equip you to meaningfullycontribute to the national
endeavour fordevelopment.
Now the next question which you may liketo ask is What is
geography? You know thatearth is our home. It is also the home of
manyother creatures, big and small, which live onthe earth and
sustain. The earths surface isnot uniform. It has variations in its
physicalfeatures. There are mountains, hills, valleys,plains,
plateaus, oceans, lakes, deserts and
wilderness. There are variations in its socialand cultural
features too. There are villages,cities, roads, railways, ports,
markets andmany other elements created by human beingsacross the
entire period of their culturaldevelopment.
This variation provides a clue to theunderstanding of the
relationship between thephysical environment and
social/culturalfeatures. The physical environment hasprovided the
stage, on which human societiesenacted the drama of their creative
skills withthe tools and techniques which they inventedand evolved
in the process of their cultural
development. Now, you should be able toattempt the answer of the
question posedearlier as to What is geography? In verysimple words,
it can be said that geographyis the description of the earth. The
termgeographywas first coined by Eratosthenese,a Greek scholar
(276-194 BC.). The word has
been derived from two roots from Greeklanguage geo(earth) and
graphos(description).
GEOGRAPHYASADISCIPLINE
C H A P T E R
-
8/21/2019 NCERT- Complete Geography
4/578
GEOGRAPHY AS A DISCIPLINE 3
Put together, they mean description of the earth.The earth has
always been seen as the abodeof human beings and thus, scholars
definedgeography as, the description of the earth as
the abode of human beings. You are aware ofthe fact that reality
is always multifaceted andthe earth is also multi-dimensional, that
is
why many disciplines from natural sciencessuch as geology,
pedology, oceanography,
botany, zoology and meteorology and anumber of sister
disciplines in social sciencessuch as economics, history,
sociology, politicalscience, anthropology, etc. study
differentaspects of the earths surface. Geography isdifferent from
other sciences in its subjectmatter and methodology but at the same
time,
it is closely related to other disciplines.Geography derives its
data base from all thenatural and social sciences and attempts
theirsynthesis.
We have noted that there exist variationsover the surface of the
earth in its physical as
well as cultural environment. A number ofphenomena are similar
and many are dissimilar.It was, therefore, logical to perceive
geographyas the study of areal differentiation. Thus,geography was
perceived to study all thosephenomena which vary over
space.Geographers do not study only the variationsin the phenomena
over the earths surface(space) but also study the associations
withthe other factors which cause these variations.For example,
cropping patterns differ fromregion to region but this variation in
croppingpattern, as a phenomenon, is related to
variations in soils, climates, demands in themarket, capacity of
the farmer to invest andtechnological inputs available to
her/him.
Thus, the concern of geography is to find outthe causal
relationship between any twophenomena or between more than one
phenomenon.A geographer explains the phenomena in
a frame of cause and effect relationship, as itdoes not only
help in interpretation but alsoforesees the phenomena in
future.
The geographical phenomena, both thephysical and human, are not
static but highlydynamic. They change over time as a result ofthe
interactive processes between ever
changing earth and untiring and ever-activehuman beings.
Primitive human societies weredirectly dependent on their
immediateenvironment. Geography, thus, is concerned
wi th the study of Nature and Humaninteractions as an integrated
whole. Humanis an integral part of nature and nature hasthe
imprints of human. Nature has influenceddifferent aspects of human
life. Its imprints can
be noticed on food, clothing, shelter andoccupation. Human
beings have come to terms
wi th nature through adapta tion andmodification. As you already
know, the presentsociety has passed the stage of
primitivesocieties, which were directly dependent ontheir immediate
physical environment for
sustenance. Present societies have modifiedtheir natural
environment by inventing andusing technology and thus, have
expanded thehorizon of their operation by appropriating
andutilising the resources provided by nature. Withthe gradual
development of technology, human
beings were able to loosen the shackles of theirphysical
environment. Technology helped inreducing the harshness of labour,
increasedlabour efficiency and provided leisure tohuman beings to
attend to the higher needs oflife. It also increased the scale of
productionand the mobility of labour.
The interaction between the physicalenvironment and human beings
has been verysuccinctly described by a poet in the
followingdialogue between human and nature (God).You created the
soil, I created the cup, youcreated night, I created the lamp. You
createdwilderness, hilly terrains and deserts; Icreated flower beds
and gardens. Human
beings have claimed their contribution usingnatural
resources.With the help of technology,human beings moved from the
stage ofnecessity to a stage of freedom. They have put
their imprints everywhere and created newpossibilities in
collaboration with nature. Thus,
we now find humanised nature andnaturalised human beings and
geographystudies this interactive relationship. The spacegot
organised with the help of the means oftransportation and
communication network.
The links (routes) and nodes (settlements of alltypes and
hierarchies) integrated the space and
-
8/21/2019 NCERT- Complete Geography
5/578
FUNDAMENTALS OF PHYSICAL GEOGRAPHY4
gradually, it got organised. As a social sciencediscipline,
geography studies the spatialorganisation and spatial
integration.
Geography as a discipline is concerned with
three sets of questions:(i) Some questions are related to
the
identification of the patterns of naturaland cultural features
as found over thesurface of the earth. These are thequestions about
what?
(ii) Some questions are related to thedistribution of the
natural and human/cultural features over the surface of theearth.
These are the questions aboutwhere?
Taken together, both these questions take
care of distributional and locational aspects ofthe natural and
cultural features. Thesequestions provided inventorised information
of
what features and where located. It was a verypopular approach
during the colonial period.
These two questions did not make geographya scientific
discipline till the third question wasadded. The third question is
related to theexplanation or the causal relationships
between features and the processes andphenomena. This aspect of
geography is relatedto the question, why?
Geography as a discipline is related tospace and takes note of
spatial characteristicsand attributes. It studies the patterns
ofdistribution, location and concentration ofphenomena over space
and interprets themproviding explanations for these patterns.
Ittakes note of the associations and inter-relationships between
the phenomena overspace and interprets them providingexplanations
for these patterns. It also takesnote of the associations and
inter-relationships
between the phenomena resulting from the
dynamic interaction between human beingsand their physical
environment.
GEOGRAPHYASANINTEGRATINGDISCIPLINE
Geography is a discipline of synthesis. Itattempts spatial
synthesis, and historyattempts temporal synthesis. Its approach
isholistic in nature. It recognises the fact thatthe world is a
system of interdependencies. The
present world is being perceived as a globalvillage. The
distances have been reduced bybetter means of transportation
increasingaccessibility. The audio-visual media and
information technology have enriched the database. Technology
has provided better chancesof monitoring natural phenomena as well
asthe economic and social parameters.Geography as an integrating
discipline hasinterface with numerous natural and socialsciences.
All the sciences, whether natural orsocial, have one basic
objective, ofunderstanding the reality. Geographyattempts to
comprehend the associations ofphenomena as related in sections of
reality.Figure 1.1 shows the relationship of geography
with other sciences. Every discipline, concernedwith scientific
knowledge is linked withgeography as many of their elements vary
overspace. Geography helps in understanding thereality in totality
in its spatial perspective.Geography, thus, not only takes note of
thedifferences in the phenomena from place toplace but integrates
them holistically whichmay be different at other places. A
geographeris required to have a broad understanding ofall the
related fields, to be able to logicallyintegrate them. This
integration can beunderstood with some examples.
Geographyinfluences historical events. Spatial distanceitself has
been a very potent factor to alter thecourse of history of the
world. Spatial depthprovided defence to many countries,particularly
in the last century. In traditional
warfare, countries with large size in area, gaintime at the cost
of space. The defence provided
by oceanic expanse around the countries ofthe new world has
protected them from wars
being imposed on their soil. If we look at thehistorical events
world over, each one of themcan be interpreted geographically.
In India, Himalayas have acted as greatbarriers and provided
protection but thepasses provided routes to the migrants
andinvaders from Central Asia. The sea coast hasencouraged contact
with people from East andSoutheast Asia, Europe and Africa.
Navigationtechnology helped European countries tocolonise a number
of countries of Asia and
Africa, including India as they got accessibility
-
8/21/2019 NCERT- Complete Geography
6/578
GEOGRAPHY AS A DISCIPLINE 5
through oceans. The geographical factors havemodified the course
of history in different partsof the world.
Every geographical phenomenon undergoes
change through time and can be explainedtemporally. The changes
in landforms, climate,vegetation, economic activities occupations
andcultural developments have followed a definitehistorical course.
Many geographical featuresresult from the decision making process
bydifferent institutions at a particular point oftime. It is
possible to convert time in terms ofspace and space in terms of
time. For example,it can be said that place A is 1,500 km fromplace
B or alternately, it can also be said thatplace A is two hours away
(if one travels byplane) or seventeen hours away (if one
travels
by a fast moving train). It is for this reason,time is an
integral part of geographical studiesas the fourth dimension.
Please mention otherthree dimensions?
Figure1.1 amply depicts the linkages ofgeography with different
natural and socialsciences. This linkage can be put under
twosegments.
Physical Geography and Natural Sciences
All the branches of physical geography, asshown in Figure 1.1,
have interface with natural
sciences. The traditional physical geographyis linked with
geology, meteorology, hydrologyand pedology, and thus,
geomorphology,climatology, oceanography and soil
geographyrespectively have very close link with thenatural sciences
as these derive their data fromthese sciences. Bio-Geography is
closely relatedto botany, zoology as well as ecology as human
beings are located in different locational niche.A geographer
should have some proficiency
in mathematics and art, particularly in drawingmaps. Geography
is very much linked with thestudy of astronomical locations and
deals withlatitudes and longitudes. The shape of the earthis
Geoidbut the basic tool of a geographer is amap which is two
dimensional representationof the earth. The problem of converting
geoidsinto two dimensions can be tackled byprojections constructed
graphically ormathematically. The cartographic andquantitative
techniques require sufficientproficiency in mathematics, statistics
and
econometrics. Maps are prepared throughartistic imagination.
Making sketches, mentalmaps and cartographic work
requireproficiency in arts.
Geography and Social Sciences
Each social science sketched in Figure 1.1hasinterface with one
branch of geography. Therelationships between geography and
historyhave already been outlined in detail. Everydiscipline has a
philosophy which is the raisondetrefor that discipline. Philosophy
providesroots to a discipline and in the process of itsevolution,
it also experiences distinct historicalprocesses. Thus, the history
of geographicalthought as mother branch of geography is
included universally in its curricula. All thesocial science
disciplines, viz. sociology,political science, economics and
demographystudy different aspects of social reality. The
branches of geography, viz. social, political,economic and
population and settlements areclosely linked with these disciplines
as eachone of them has spatial attributes. The coreconcern of
political science is territory, peopleand sovereignty while
political geography isalso interested in the study of the state as
aspatial unit as well as people and their political
behaviour. Economics deals with basicattributes of the economy
such as production,distribution, exchange and consumption. Eachof
these attributes also has spatial aspects andhere comes the role of
economic geography tostudy the spatial aspects of
production,distribution, exchange and consumption.Likewise,
population geography is closelylinked with the discipline of
demography.
The above discussi on shows thatgeography has strong interface
with naturaland social sciences. It follows its own
methodology of study which makes it distinctfrom others. It has
osmotic relationship withother disciplines. While all the
disciplines havetheir own individual scope, this individualitydoes
not obstruct the flow of information as incase of all cells in the
body that have individualidentity separated by membranes but the
flowof blood is not obstructed. Geographers usedata obtained from
sister disciplines and
-
8/21/2019 NCERT- Complete Geography
7/578
FUNDAMENTALS OF PHYSICAL GEOGRAPHY6
Figure1.1:Geogra
phyanditsrelationwithothersubj
ects
-
8/21/2019 NCERT- Complete Geography
8/578
GEOGRAPHY AS A DISCIPLINE 7
attempt synthesis over space. Maps are very
effective tools of geographers in which the
tabular data is converted into visual form to
bring out the spatial pattern.
BRANCHESOFGEOGRAPHY
Please study Figure 1.1 for recapitulation. It has
very clearly brought out that geography is an
interdisciplinary subject of study. The study of
every subject is done according to some
approach. The major approaches to study
geography have been (i) Systematic and
(ii) Regional. The systematic geography approach
is the same as that of general geography. This
approach was introduced by Alexander Von
Humboldt, a German geographer (1769-1859)while regional
geography approach was
developed by another German geographer and a
contemporary of Humboldt, Karl Ritter
(1779-1859).
In systematic approach (Figure 1.2), a
phenomenon is studied world over as a whole,
and then the identification of typologies or
spatial patterns is done. For example, if one is
interested in studying natural vegetation, the
study will be done at the world level as a first
step. The typologies such as equatorial rain
forests or softwood conical forests or monsoon
forests, etc. will be identified, discussed and
delimited. In the regional approach, the world
is divided into regions at different hierarchical
levels and then all the geographical phenomena
in a particular region are studied. These
regions may be natural, political or designated
region. The phenomena in a region are studied
in a holistic manner searching for unity in
diversity.
Dualism is one of the main characteristics
of geography which got introduced from thevery beginning. This
dualism depended on the
aspect emphasised in the study. Earlier scholars
laid emphasis on physical geography. But
human beings are an integral part of the earths
surface. They are part and parcel of nature. They
also have contributed through their cultural
development. Thus developed human
geography with emphasis on human activities.
BRANCHESOFGEOGRAPHY(BASEDONSYSTEMATIC APPROACH)
1. Physical Geography
(i) Geomorphology is devoted to the studyof landforms, their
evolution and relatedprocesses.
(ii) Climatologyencompasses the study ofstructure of atmosphere
and elementsof weather and climates and climatictypes and
regions.
(iii) Hydrologystudies the realm of waterover the surface of the
earth includingoceans, lakes, rivers and other water
bodies and its effect on different life
forms including human life and theiractivities.
(iv) Soil Geographyis devoted to study theprocesses of soil
formation, soil types,their fertility status, distribution
anduse.
2. Human Geography
(i) Social/Cultural Geography encom-passes the study of society
and itsspatial dynamics as well as the culturalelements contributed
by the society.
(ii) Population and Settlement Geography(Rural and Urban). It
studies populationgrowth, distribution, density, sex
ratio,migration and occupational structureetc. Settlement geography
studies thecharacteristics of rural and urbansettlements.
(iii) Economic Geographystudies economicactivities of the people
includingagriculture, industry, tourism, trade,and transport,
infrastructure andservices, etc.
(iv) Historical Geography studies thehistorical processes
through which thespace gets organised. Every region hasundergone
some historical experiences
before attaining the present day status.The geographica l fea
tures alsoexperience temporal changes and theseform the concerns of
historicalgeography.
-
8/21/2019 NCERT- Complete Geography
9/578
FUNDAMENTALS OF PHYSICAL GEOGRAPHY8
Figure 1.2 : Branches of geography based on systematic
approach
(v) Political Geography looks at the space
from the angle of political events and
studies boundaries, space relations
between neighbouring political units,
delimitation of constituencies, election
scenario and develops theoretical
frameworkto understand the politicalbehaviour of the
population.
3. Biogeography
The interface between physical geographyand human geography has
lead to thedevelopment of Biogeography whichincludes:(i) Plant
Geography which studies the
spatial pattern of natural vegetation intheir habitats.
-
8/21/2019 NCERT- Complete Geography
10/578
GEOGRAPHY AS A DISCIPLINE 9
(ii) Zoo Geography which studies thespatial patterns and
geographiccharacteristics of animals and theirhabitats.
(iii) Ecology /Ecosystem deals with thescientific study of the
habitatscharacteristic of species.
(iv) Environmental Geography concernsworld over leading to the
realisation ofenvironmental problems such as landgradation,
pollution and concerns forconservation has resulted in
theintroduction of this new branch ingeography.
BRANCHESOFGEOGRAPHYBASEDONREGIONALAPPROACH (FIGURE1.3)
1. Regional Studies/Area StudiesComprising Macro, Meso and
MicroRegional Studies
2. Regional PlanningComprising Country/Rural and Town/Urban
Planning
3. Regional Development4. Regional Analysis
There are two aspects which are commonto every discipline, these
are:(i) Philosophy
(a) Geographical Thought(b) Land and Human Interaction/
Human Ecology(ii) Methods and Techniques
(a) Cartography including ComputerCartography
(b) Quantitative Techniques/Statistical
Techniques
(c) Field Survey Methods
(d) Geo-informatics comprising
techniques such as Remote
Sensing, GIS, GPS, etc.
The above classification gives acomprehensive format of the
branches of
geography. Generally geography curricula is
taught and learnt in this format but this
format is not static. Any discipline is bound
to grow with new ideas, problems, methods
and techniques. For example, what was once
manual cartography has now been
transformed into computer cartography.
Technology has enabled scholars to handle
large quantum of data. The internet provides
extensive information. Thus, the capacity to
attempt analysis has increased tremendously.
GIS has further opened vistas of knowledge.
GPS has become a handy tool to find out exact
locations. Technologies have enhanced the
capacity of attempting synthesis with sound
theoretical understanding.
You will learn some preliminary aspects of
these techniques in your book,Practical work
in Geography Part I (NCERT, 2006).You will
continue to improve upon your skills andlearn about their
application.
PHYSICALGEOGRAPHYAND ITSIMPORTANCE
This chapter appears in the book entitledFundamentals of
Physical Geography. Thecontents of the book clearly reflect its
scope.It is therefore, appropriate to know theimportance of this
branch of geography.
Figure 1.3 : Branches of geography based on regional
approach
-
8/21/2019 NCERT- Complete Geography
11/578
FUNDAMENTALS OF PHYSICAL GEOGRAPHY10
Physical geography includes the study oflithosphere (landforms,
drainage, relief andphysiography), atmosphere (its
composition,structure, elements and controls of weather
and climate; temperature, pressure, winds,precipitation,
climatic types, etc.), hydrosphere(oceans, seas, lakes and
associated features
with water realm) and biosphere ( life formsincluding human
being and macro-organismand their sustaining mechanism, viz.
foodchain, ecological parameters and ecological
balance). Soils are formed through the processofpedogenesisand
depend upon the parentrocks, climate, biological activity and
time.
Time provides maturity to soils and helps inthe development of
soil profiles. Each element
is important for human beings. Landformsprovide the base on
which human activities arelocated. The plains are utilised for
agriculture.Plateaus provide forests and minerals.Mountains provide
pastures, forests, touristspots and are sources of rivers providing
waterto lowlands. Climate influences our housetypes, clothing and
food habits. The climatehas a profound effect on vegetation,
croppingpattern, livestock farming and someindustries, etc. Human
beings have developedtechnologies which modify climatic
elements
in a restricted space such as air conditionersand coolers.
Temperature and precipitationensure the density of forests and
quality ofgrassland. In India, monsoonal rainfall sets
theagriculture rhythm in motion. Precipitationrecharges the ground
water aquiferswhichlater provides water for agriculture anddomestic
use. We study oceans which are thestore house of resources. Besides
fish and other
sea-food, oceans are rich in mineral resources.India has
developed the technology forcollecting manganese nodules from
oceanic
bed. Soils are renewable resources, which
influence a number of economic activities suchas agriculture.
The fertility of the soil is bothnaturally determined and
culturally induced.Soils also provide the basis for the
biosphereaccommodating plants, animals and microorganisms.
The study of phys ical geography isemerging as a discipline of
evaluating andmanaging natural resources. In order toachieve this
objective, it is essential tounderstand the intricate relationship
betweenphysical environment and human beings.Physical environment
provides resources, andhuman beings utilise these resources
andensure their economic and culturaldevelopment. Accelerated pace
of resourceutilisation with the help of modern technologyhas
created ecological imbalance in the world.Hence, a better
understanding of physicalenvironment is absolutely essential
forsustainable development.
What is Geography?
Geography is concerned with the descriptionand explanation of
the areal differentiation ofthe earths surface.
Richard Hartshorne
Geography studies the differences ofphenomena usually related in
different partsof the earths surface.
Hettner
EXERCISES
1. Multiple choice questions.
(i) Which one of the following scholars coined the term
Geography?
(a) Herodotus (c) Galileo
(b) Erathosthenese (d) Aristotle
(ii) Which one of the following features can be termed as
physical feature?
(a) Port (c) Plain
(b) Road (d) Water park
-
8/21/2019 NCERT- Complete Geography
12/578
GEOGRAPHY AS A DISCIPLINE 11
(iii) Make correct pairs from the following two columns and mark
the correctoption.
1. Meteorology A. Population Geography
2. Demography B. Soil Geography
3. Sociology C. Climatology
4. Pedology D. Social Geography
(a) 1B,2C,3A,4D (c) 1D,2B,3C,4A
(b) 1A,2D,3B,4C (d) 1C,2A,3D,4B
(iv) Which one of the following questions is related to
cause-effect relationship?
(a) Why (c) What
(b) Where (d) When
(v) Which one of the following disciplines attempts temporal
synthesis?
(a) Sociology (c) Anthropology
(b) Geography (d) History
2. Answer the following questions in about 30 words.
(i) What important cultural features do you observe while going
to school?Are they similar or dissimilar? Should they be included
in the study ofgeography or not? If yes, why?
(ii) You have seen a tennis ball, a cricket ball, an orange and
a pumpkin.Which one amongst these resembles the shape of the earth?
Why haveyou chosen this particular item to describe the shape of
the earth?
(iii) Do you celebrate Van Mahotsava in your school? Why do we
plant so manytrees? How do the trees maintain ecological
balance?
(iv) You have seen elephants, deer, earthworms, trees and
grasses. Where dothey live or grow? What is the name given to this
sphere? Can you describesome of the important features of this
sphere?
(v) How much time do you take to reach your school from your
house? Hadthe school been located across the road from your house,
how much timewould you have taken to reach school? What is the
effect of the distance
between your residence and the school on the time taken in
commuting?
Can you convert time into space and vice versa?
3. Answer the following questions in about 150 words.
(i) You observe every day in your surroundings that there is
variation in
natural as well as cultural phenomena. All the trees are not of
the same
variety. All the birds and animals you see, are different. All
these different
elements are found on the earth. Can you now argue that
geography is
the study of areal differentiation?
(ii) You have already studied geography, history, civics and
economics as
parts of social studies. Attempt an integration of these
disciplineshighlighting their interface.
-
8/21/2019 NCERT- Complete Geography
13/578
FUNDAMENTALS OF PHYSICAL GEOGRAPHY12
Project Work
Select forest as a natural resource.
(i) Prepare a map of India showing the distribution of different
types of forests.
(ii) Write about the economic importance of forests for the
country.
(iii) Prepare a historical account of conservation of forests in
India with focuson Chipko movements in Rajasthan and
Uttaranchal.
-
8/21/2019 NCERT- Complete Geography
14/578
THEEARTH
This unit deals with Origin and evolution of the earth; Interior
of the earth; Wegeners
continental drift theory and plate tectonics; earthquakes
andvolcanoes
UNITII
-
8/21/2019 NCERT- Complete Geography
15/578
D
o you remember the nursery rhymeTwinkle, Twinkle little
star?
Starry nights have always attracted us sincethe childhood. You
may also have thought ofthese stars and had numerous questions
in
your mind. Questions such as how many starsare there in the sky?
How did they come intoexistence? Can one reach the end of the
sky?May be many more such questions are stillthere in your mind. In
this chapter, you willlearn how these twinkling little stars
wereformed. With that you will eventually also readthe story of
origin and evolution of the earth.
ORIGINOFTHEEARTH
Early Theories
A large number of hypotheses were put forthby different
philosophers and scientistsregarding the origin of the earth. One
of theearlier and popular arguments was by Germanphilosopher
Immanuel Kant. MathematicianLaplace revised it in 1796. It is known
asNebular Hypothesis. The hypothesis consideredthat the planets
were formed out of a cloud ofmaterial associated with a youthful
sun, which
was slowly rotating. Later in 1900, Chamberlainand Moulton
considered that a wandering starapproached the sun. As a result, a
cigar-shapedextension of material was separated from thesolar
surface. As the passing star moved away,the material separated from
the solar surfacecontinued to revolve around the sun and itslowly
condensed into planets. Sir James Jeansand later Sir Harold Jeffrey
supported this
THEORIGINANDEVOLUTIONOFTHEEARTH
C H A P T E R
argument. At a later date, the argumentsconsidered of a
companion to the sun to have
been coexisting. These arguments are called
binary theories. In 1950, Otto Schmidt inRussia and Carl
Weizascar in Germanysomewhat revised the nebular hypothesis,though
differing in details. They considered thatthe sun was surrounded by
solar nebulacontaining mostly the hydrogen and heliumalong with
what may be termed as dust. Thefriction and collision of particles
led toformation of a disk-shaped cloud and theplanets were formed
through the process ofaccretion.
Modern Theories
However, scientists in later period took up theproblems of
origin of universe rather than thatof just the earth or the
planets. The mostpopular argument regarding the origin of
theuniverse is the Big Bang Theory. It is also calledexpanding
universe hypothesis. EdwinHubble, in 1920, provided evidence that
theuniverse is expanding. As time passes, galaxiesmove further and
further apart. You canexperiment and find what does the
expandinguniverse mean. Take a balloon and mark somepoints on it to
represent the galaxies. Now, if
you start inflating the balloon, the pointsmarked on the balloon
will appear to be movingaway from each other as the balloon
expands.Similarly, the distance between the galaxies isalso found
to be increasing and thereby, theuniverse is considered to be
expanding.However, you will find that besides the increasein the
distances between the points on the
-
8/21/2019 NCERT- Complete Geography
16/578
THE ORIGIN AND EVOLUTION OF THE EARTH 15
balloon, the points themselves are expanding.This is not in
accordance with the fact.Scientists believe that though the
space
between the galaxies is increasing, observations
do not support the expansion of galaxies. So,the balloon example
is only partially correct.
Figure 2.1 : The Big Bang
The Big Bang Theory considers thefollowing stages in the
development of theuniverse.
(i) In the beginning, all matter forming the
universe existed in one place in the form
of a tiny ball (singular atom) with an
unimaginably small volume, infinite
temperature and infinite density.
(ii) At the Big Bang the tiny ball exploded
violently. This led to a huge expansion.
It is now generally accepted that the
event of big bang took place 13.7 billion
years before the present. The expansion
continues even to the present day. As it
grew, some energy was converted into
matter. There was particularly rapid
expansion within fractions of a secondafter the bang.
Thereafter, the
expansion has slowed down. Within first
three minutes from the Big Bang event,
the first atom began to form.
(iii) Within 300,000 years from the Big
Bang, temperature dropped to 4,500K
and gave rise to atomic matter. Theuniverse became
transparent.
The expansion of universe means increasein space between the
galaxies. An alternativeto this was Hoyles concept of steady state.
Itconsidered the universe to be roughly the same
at any point of time. However, with greaterevidence becoming
available about theexpanding universe, scientific community
atpresent favours argument of expandinguniverse.
The Star Formation
The distribution of matter and energy was noteven in the early
universe. These initial densitydifferences gave rise to differences
ingravitational forces and it caused the matterto get drawn
together. These formed the bases
for development of galaxies. A galaxycontainsa large number of
stars. Galaxies spread over
vast distances that are measured in thousandsof light-years. The
diameters of individualgalaxies range from 80,000-150,000 light
years. A galaxy starts to form by accumulationof hydrogen gas in
the form of a very largecloud called nebula. Eventually,
growingnebula develops localised clumps of gas. Theseclumps
continue to grow into even densergaseous bodies, giving rise to
formation ofstars. The formation of stars is believed to have
taken place some 5-6 billion years ago.
A light year is a measure of distance andnot of time. Light
travels at a speed of300,000 km/second. Considering this,the
distances the light will travel in oneyear is taken to be one light
year. Thisequals to 9.4611012 km. The meandistance between the sun
and the earthis 149,598,000 km. In terms of lightyears, it is 8.311
minutes of a year.
Formation of Planets
The following are considered to be the stages
in the development of planets :
(i) The stars are localised lumps of gas
within a nebula. The gravitational force
within the lumps leads to the formation
of a core to the gas cloud and a huge
rotating disc of gas and dust develops
around the gas core.
-
8/21/2019 NCERT- Complete Geography
17/578
FUNDAMENTALS OF PHYSICAL GEOGRAPHY16
(ii) In the next stage, the gas cloud startsgetting condensed
and the matteraround the core develops into small-rounded objects.
These small-rounded
objects by the process of cohesion developinto what is called
planetesimals.Larger bodies start forming by collision,and
gravitational attraction causes thematerial to stick together.
Planetesimalsare a large number of smaller bodies.
(iii) In the final stage, these large numberof small
planetesimals accrete to forma fewer large bodies in the form
ofplanets.
OURSOLARSYSTEM
Our Solar system consists of nine planets. Thetenth planet 2003
UB
313has also been recently
sighted. The nebula from which our Solarsystem is supposed to
have been formed,started its collapse and core formation sometime
5-5.6 billion years ago and the planets
were formed about 4.6 billion years ago. Oursolar system
consists of the sun (the star), 9planets, 63 moons, millions of
smaller bodieslike asteroidsand cometsand huge quantityof
dust-grains and gases.
Out of the nine planets, mercury, venus,
earth and mars are called as the inner planetsas they lie
between the sun and the belt ofasteroids the other five planets are
called theouterplanets. Alternatively, the first four are
calledTerrestrial,meaning earth-like as they are madeup of rock and
metals, and have relatively highdensities. The rest five are
calledJovianor GasGiant planets. Jovian means jupiter-like.
Most
of them are much larger than the terrestrialplanets and have
thick atmosphere, mostly ofhelium and hydrogen. All the planets
were formedin the same period sometime about 4.6 billion
years ago. Some data regarding our solar systemare given in the
box below.
Why are the inner planets rocky whileothers are mostly in
gaseous form?
The difference between terrestrial and jovianplanets can be
attributed to the followingconditions:
(i) The terrestrial planets were formed inthe close vicinity of
the parent star
where it was too warm for gases to
condense to solid particles. Jovianplanets were formed at quite
a distantlocation.
(ii) The solar wind was most intense nearerthe sun; so, it blew
off lots of gas anddust from the terrestrial planets. Thesolar
winds were not all that intense tocause similar removal of gases
from the
Jovian planets.(iii) The terrestrial planets are smaller and
their lower gravity could not hold theescaping gases.
The Moon
The moon is the only natural satellite of theearth. Like the
origin of the earth, there have
been attempts to explain how the moon wasformed. In 1838, Sir
George Darwin suggestedthat initially, the earth and the moon
formed asingle rapidly rotating body. The whole mass
The Solar System
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto
Distance* 0.387 0.723 1.000 1.524 5.203 9.539 19.182 30.058
39.785
Density@ 5.44 5.245 5.517 3.945 1.33 0.70 1.17 1.66 0.5-0.9
Radius# 0.383 0.949 1.000 0.533 11.19 9.460 4.11 3.88 -0.3
Satellites 0 0 1 2 16 about 18 about 17 8 1
* Distance from the sun in astronomical unit i.e. average mean
distance of the earth is 149,598,000 km = 1@ Density in gm/cm3
# Radius: Equatorial radius 6378.137 km = 1
-
8/21/2019 NCERT- Complete Geography
18/578
THE ORIGIN AND EVOLUTION OF THE EARTH 17
became a dumb-bel l- shaped body andeventually it broke. It was
also suggested thatthe material forming the moon was separatedfrom
what we have at present the depression
occupied by the Pacific Ocean.However, the present scientists do
not
accept either of the explanations. It is nowgenerally believed
that the formation of moon,as a satellite of the earth, is an
outcome of giantimpact or what is described as the big splat.
A body of the size of one to three times that ofmars collided
into the earth sometime shortlyafter the earth was formed. It
blasted a largepart of the earth into space. This portion of
blasted material then continued to orbit theearth and eventually
formed into the present
moon about 4.44 billion years ago.
EVOLUTIONOFTHEEARTH
Do you know that the planet earth initially wasa barren, rocky
and hot object with a thinatmosphere of hydrogen and helium. This
isfar from the present day picture of the earth.Hence, there must
have been some eventsprocesses, which may have caused this
changefrom rocky, barren and hot earth to a beautifulplanet with
ample amount of water andconducive atmosphere favouring the
existence
of life. In the following section, you will findout how the
period, between the 4,600 million
years and the present, led to the evolution oflife on the
surface of the planet.
The earth has a layered structure. Fromthe outermost end of the
atmosphere to thecentre of the earth, the material that exists
isnot uniform. The atmospheric matter has theleast density. From
the surface to deeperdepths, the earths interior has different
zonesand each of these contains materials withdifferent
characteristics.
How was the layered structure of the
earth developed?
Development of Lithosphere
The earth was mostly in a volatile state duringits primordial
stage. Due to gradual increasein density the temperature inside
hasincreased. As a result the material inside
started getting separated depending on theirdensities. This
allowed heavier materials (likeiron) to sink towards the centre of
the earthand the lighter ones to move towards the
surface. With passage of time it cooled furtherand solidified
and condensed into a smaller size.
This later led to the development of the outersurface in the
form of a crust. During theformation of the moon, due to the giant
impact,the earth was further heated up. It is throughthe process of
differentiation that the earthforming material got separated into
differentlayers. Starting from the surface to the centralparts, we
have layers like the crust, mantle,outer core and inner core. From
the crust to thecore, the density of the material increases. We
shall discuss in detail the properties of each ofthis layer in
the next chapter.
Evolution of Atmosphere and Hydrosphere
The present composition of earths atmosphereis chiefly
contributed by nitrogen and oxygen.
You will be dealing with the composition andstructure of the
earths atmosphere in Chapter 8.
There are three stages in the evolution ofthe present
atmosphere. The first stage ismarked by the loss of primordial
atmosphere.In the second stage, the hot interior of the earth
contributed to the evolution of the atmosphere.Finally, the
composition of the atmosphere wasmodified by the living world
through theprocess ofphotosynthesis.
The early atmosphere, with hydrogen andhelium, is supposed to
have been stripped offas a result of the solar winds. This
happenednot only in case of the earth, but also in all
theterrestrial planets, which were supposed tohave lost their
primordial atmosphere throughthe impact of solar winds.
During the cooling of the earth, gases and
water vapour were released from the interiorsolid earth. This
started the evolution of thepresent atmosphere. The early
atmospherelargely contained water vapour, nitrogen,carbon dioxide,
methane, ammonia and verylittle of free oxygen. The process through
whichthe gases were outpoured from the interior iscalled degassing.
Continuous volcaniceruptions contributed water vapour and gases
-
8/21/2019 NCERT- Complete Geography
19/578
FUNDAMENTALS OF PHYSICAL GEOGRAPHY18
to the atmosphere. As the earth cooled, the
wa ter vapour released started gett ing
condensed. The carbon dioxide in the
atmosphere got dissolved in rainwater and the
temperature further decreased causing more
condensation and more rains. The rainwater
falling onto the surface got collected in the
depressions to give rise to oceans. The earths
oceans were formed within 500 million years
from the formation of the earth. This tells us
that the oceans are as old as 4,000 millionyears. Sometime
around 3,800 million years
ago, life began to evolve. However, around2,500-3,000 million
years before the present,the process of photosynthesis got evolved.
Life
was confined to the oceans for a long time.Oceans began to have
the contribution ofoxygen through the process
ofphotosynthesis.Eventually, oceans were saturated with oxygen,and
2,000 million years ago, oxygen began toflood the atmosphere.
Eons Era Period Epoch Age/ Years Life/ Major Events
Before Present
Quaternary Holocene 0 - 10,000 Modern ManPleistocene 10,000 - 2
million Homo Sapiens
Tertiary Pliocene 2 - 5 million Early Human Ancestor
Miocene 5 - 24 million Ape: Flowering Plantsand Trees
Oligocene 24 - 37 Ma Anthropoid Ape
Eocene 37 - 58 Million Rabbits and Hare
Palaeocene 57 - 65 Million Small Mammals :
Rats Mice
Cretaceous 65 - 144 Million Extinction of Dinosaurs
Jurassic 144 - 208 Million Age of Dinosaurs
Triassic 208 - 245 Million Frogs and turtles
Permian 245 - 286 Million Reptile dominate-replaceamphibians
Carboniferous 286 - 360 Million First Reptiles:
Vertebrates: Coal beds
Devonian 360 - 408 Million Amphibians
Silurian 408 - 438 Million First trace of life on
land:Plants
Ordovician 438 - 505 Million First Fish
Cambrian 505 - 570 Million No terrestrial Life :
Marine Invertebrate
Proterozoic 570 - 2,500 Million Soft-bodied arthropods
Archean 2,500 - 3,800 Million Blue green Algae:
Unicellular bacteria
Hadean 3,800 - 4,800 Million Oceans and Continents
form Ocean and
Atmosphere are rich inCarbon dioxide
Origin of 5,000 Million Origin of the sun
Stars
Supernova 12,000 Million Origin of the universe
Big Bang 13,700 Million
Cainozoic(From 65
million yearsto the
presenttimes)
Mesozoic65 - 245Million
Mammals
Palaeozoic245 - 570
Million
Pre-
Cambrian570 Million
- 4,800Million
5,000 -13,700Million
Geological Time Scale
-
8/21/2019 NCERT- Complete Geography
20/578
THE ORIGIN AND EVOLUTION OF THE EARTH 19
Origin of Life
The last phase in the evolution of the earthrelates to the
origin and evolution of life. It is
undoubtedly clear that the initial or even theatmosphere of the
earth was not conducive forthe development of life. Modern
scientists referto the origin of life as a kind of
chemicalreaction, which first generated complex organicmolecules
and assembled them. This
assemblage was such that they could duplicatethemselves
converting inanimate matter into
living substance. The record of life that existedon this planet
in different periods is found inrocks in the form of fossils. The
microscopicstructures closely related to the present form
of blue algae have been found in geologicalformations that are
much older than these weresome 3,000 million years ago. It can
beassumed that life began to evolve sometime3,800 million years
ago. The summary ofevolution of life from unicellular bacteria to
themodern man is given in the Geological TimeScale on page 18.
EXERCISES
1. Multiple choice questions. (i) Which one of the following
figures represents the age of the earth?
(a) 4.6 million years (c) 4.6 billion years
(b) 13.7 billion years (d) 13.7 trillion years
(ii) Which one of the following has the longest duration?
(a) Eons (c) Era
(b) Period (d) Epoch
(iii) Which one of the following is not related to the formation
or modificationof the present atmosphere?
(a) Solar winds (c) Degassing
(b) Differentiation (d) Photosynthesis
(iv) Which one of the following represents the inner
planets?
(a) Planets between the sun and the earth
(b) Planets between the sun and the belt of asteroids
(c) Planets in gaseous state
(d) Planets without satellite(s)
(v) Life on the earth appeared around how many years before the
present?
(a) 13.7 billion (c) 4.6 billion
(b) 3.8 million (d) 3.8 billion
2. Answer the following questions in about 30 words.
(i) Why are the terrestrial planets rocky?
(ii) What is the basic difference in the arguments related to
the origin of theearth given by :
(a) Kant and Laplace
(b) Chamberlain and Moulton
-
8/21/2019 NCERT- Complete Geography
21/578
FUNDAMENTALS OF PHYSICAL GEOGRAPHY20
(iii) What is meant by the process of differentiation?
(iv) What was the nature of the earth surface initially?
(v) What were the gases which initially formed the earths
atmosphere?
3. Answer the following questions in about 150 words.
(i) Write an explanatory note on the Big Bang Theory.
(ii) List the stages in the evolution of the earth and explain
each stage inbrief.
Project Work
Collect information about the project Stardust (website:
www.sci.edu/public.htmlandwww.nasm.edu) along the following
lines.
(i) Which is the agency that has launched this project?
(ii) Why are scientists interested in collecting Stardust?
(iii) Where from has the Stardust been collected?
-
8/21/2019 NCERT- Complete Geography
22/578
W
hat do you imagine about the nature
of the earth? Do you imagine it to be
a solid ball like cricket ball or a
hollow ball with a thick cover of rocks i.e.lithosphere? Have
you ever seen photographs
or images of a volcanic eruption on the
television screen? Can you recollect the
emergence of hot molten lava, dust, smoke, fire
and magma flowing out of the volcanic crater?
The interior of the earth can be understood only
by indirect evidences as neither any one has nor
any one can reach the interior of the earth.
The configuration of the surface of the earth
is largely a product of the processes operating
in the interior of the earth. Exogenic as well asendogenic
processes are constantly shaping
the landscape. A proper understanding of the
physiographic character of a region remains
incomplete if the effects of endogenic processes
are ignored. Human life is largely influenced
by the physiography of the region. Therefore,
it is necessary that one gets acquainted with
the forces that influence landscape
development. To understand why the earth
shakes or how a tsunami wave is generated, it
is necessary that we know certain details of the
interior of the earth. In the previous chapter,
you have noted that the earth-forming
materials have been distributed in the form of
layers from the crust to the core. It is interesting
to know how scientists have gathered
information about these layers and what are
the characteristics of each of these layers. This
is exactly what this chapter deals with.
INTERIOROFTHEEARTH
SOURCESOFINFORMATIONABOUTTHEINTERIOR
The earths radius is 6,370 km. No one canreach the centre of the
earth and makeobservations or collect samples of the material.Under
such conditions, you may wonder howscientists tell us about the
earths interior andthe type of materials that exist at such
depths.Most of our knowledge about the interior ofthe earth is
largely based on estimates andinferences. Yet, a part of the
information isobtained through direct observations andanalysis of
materials.
Direct Sources
The most easily available solid earth material
is surface rock or the rocks we get from miningareas. Gold mines
in South Africa are as deepas 3 - 4 km. Going beyond this depth is
notpossible as it is very hot at this depth. Besidesmining,
scientists have taken up a number ofprojects to penetrate deeper
depths to explorethe conditions in the crustal portions.
Scientists
world over are working on two major projectssuch as Deep Ocean
Drilling Project andIntegrated Ocean Drilling Project. Thedeepest
drill at Kola, in Arctic Ocean, has sofar reached a depth of 12 km.
This and manydeep drilling projects have provided large
volume of information through the analysis ofmaterials collected
at different depths.
Volcanic eruption forms another source ofobtaining direct
information. As and when themolten material (magma) is thrown onto
thesurface of the earth, during volcanic eruptionit becomes
available for laboratory analysis.However, it is difficult to
ascertain the depth ofthe source of such magma.
C H A P T E R
-
8/21/2019 NCERT- Complete Geography
23/578
FUNDAMENTALS OF PHYSICAL GEOGRAPHY22
Indirect Sources
Analysis of properties of matter indirectlyprovides information
about the interior. Weknow through the mining activity
thattemperature and pressure increase with theincreasing distance
from the surface towardsthe interior in deeper depths. Moreover, it
isalso known that the density of the material alsoincreases with
depth. It is possible to find therate of change of these
characteristics. Knowingthe total thickness of the earth,
scientists haveestimated the values of temperature, pressureand the
density of materials at different depths.
The details of these characteristics withreference to each layer
of the interior arediscussed later in this chapter.
Another source of information are themeteors that at times reach
the earth. However,it may be noted that the material that
becomesavailable for analysis from meteors, is not fromthe interior
of the earth. The material and thestructure observed in the meteors
are similarto that of the earth. They are solid bodiesdeveloped out
of materials same as, or similarto, our planet. Hence, this becomes
yet anothersource of information about the interior of
theearth.
The other ind irec t sources inc lude
gravitation, magnetic field, and seismic activity.The
gravitation force (g) is not the same atdifferent latitudes on the
surface. It is greaternear the poles and less at the equator. This
is
because of the distance from the centre at theequator being
greater than that at the poles.
The gravity values also differ according to themass of material.
The uneven distribution ofmass of material within the earth
influencesthis value. The reading of the gravity at differentplaces
is influenced by many other factors.
These readings differ from the expected values.
Such a difference is called gravity anomaly.Gravity anomalies
give us information aboutthe distribution of mass of the material
in thecrust of the earth. Magnetic surveys alsoprovide information
about the distribution ofmagnetic materials in the crustal portion,
andthus, provide information about thedistribution of materials in
this part. Seismicactivity is one of the most important sources
of
information about the interior of the earth.Hence, we shall
discuss it in some detail.
Earthquake
The study of seismic waves provides a completepicture of the
layered interior. An earthquakein simple words is shaking of the
earth. It is anatural event. It is caused due to release ofenergy,
which generates waves that travel inall directions.
Why does the earth shake?
The release of energy occurs along a fault. Afault is a sharp
break in the crustal rocks.Rocks along a fault tend to move in
opposite
directions. As the overlying rock strata pressthem, the friction
locks them together. However,their tendency to move apart at some
point oftime overcomes the friction. As a result, the
blocks get deformed and eventually, they slidepast one another
abruptly. This causes arelease of energy, and the energy waves
travelin all directions. The point where the energy isreleased is
called thefocusof an earthquake,alternatively, it is called the
hypocentre. Theenergy waves travelling in different directionsreach
the surface. The point on the surface,nearest to the focus, is
called epicentre. It isthe first one to experience the waves. It is
a pointdirectly above the focus.
Earthquake Waves
All natural earthquakes take place in thelithosphere. You will
learn about differentlayers of the earth later in this chapter. It
issufficient to note here that the lithosphere refersto the portion
of depth up to 200 km from thesurface of the earth. An instrument
calledseismograph records the waves reaching the
surface. A curve of earthquake waves recordedon the seismograph
is given in Figure 3.1. Notethat the curve shows three distinct
sectionseach representing different types of wavepatterns.
Earthquake waves are basically of twotypes body waves and surface
waves. Body
waves are generated due to the release of energyat the focus and
move in all directions travellingthrough the body of the earth.
Hence, the name
-
8/21/2019 NCERT- Complete Geography
24/578
INTERIOR OF THE EARTH 23
body waves. The body waves interact with thesurface rocks and
generate new set of wavescalled surface waves. These waves move
alongthe surface. The velocity of waves changes as
they travel through materials with differentdensities. The
denser the material, the higheris the velocity. Their direction
also changes asthey reflect or refract when coming acrossmaterials
with different densities.
propagation. As a result, it creates densitydifferences in the
material leading to stretchingand squeezing of the material. Other
three
waves vibrate perpendicular to the direction of
propagation. The direction of vibrations ofS-waves is
perpendicular to the wave directionin the vertical plane. Hence,
they create troughsand crests in the material through which
theypass. Surface waves are considered to be themost damaging
waves.
Emergence of Shadow Zone
Earthquake waves get recorded in seismo-graphs located at far
off locations. However,there exist some specific areas where the
wavesare not reported. Such a zone is called the
shadow zone. The study of different eventsreveals that for each
earthquake, there existsan altogether different shadow zone. Figure
3.2(a) and (b) show the shadow zones of P andS-waves. It was
observed that seismographslocated at any distance within 105from
theepicentre, recorded the arrival of both P andS-waves. However,
the seismographs located
beyond 145from epicentre, record the arrivalof P-waves, but not
that of S-waves. Thus, azone between 105and 145from epicentre
wasidentified as the shadow zone for both the types
of waves. The entire zone beyond 105does notreceive S-waves. The
shadow zone of S-wave ismuch larger than that of the P-waves.
Theshadow zone of P-waves appears as a bandaround the earth between
105and 145awayfrom the epicentre. The shadow zone of S-wavesis not
only larger in extent but it is also a littleover 40 per cent of
the earth surface. You candraw the shadow zone for any
earthquakeprovided you know the location of the epicentre.(See the
activity box on page 28 to know how tolocate the epicentre of a
quake event).
Types of Earthquakes
(i) The most common ones are the tectonicearthquakes. These are
generated due tosliding of rocks along a fault plane.
(ii) A special class of tectonic earthquake issometimes
recognised as volcanicearthquake. However, these are confinedto
areas of active volcanoes.
Figure 3.1 : Earthquake Waves
There are two types of body waves. Theyare called P and S-waves.
P-waves move fasterand are the first to arrive at the surface.
Theseare also called primary waves. The P-wavesare similar to sound
waves. They travelthrough gaseous, liquid and solid
materials.S-waves arrive at the surface with some timelag. These
are called secondary waves. Animportant fact about S-waves is that
they can
travel only through solid materials. Thischaracteristic of the
S-waves is quiteimportant. It has helped scientists tounderstand
the structure of the interior of theearth. Reflection causes waves
to rebound
whereas refraction makes waves move indifferent directions. The
variations in thedirection of waves are inferred with the help
oftheir record on seismograph. The surface
waves are the last to report on seismograph.These waves are more
destructive. They causedisplacement of rocks, and hence, the
collapse
of structures occurs.
Propagation of Earthquake Waves
Different types of earthquake waves travel indifferent manners.
As they move or propagate,they cause vibration in the body of the
rocksthrough which they pass. P-waves vibrateparallel to the
direction of the wave. This exertspressure on the material in the
direction of the
-
8/21/2019 NCERT- Complete Geography
25/578
FUNDAMENTALS OF PHYSICAL GEOGRAPHY24
(v) The earthquakes that occur in the areas
of large reservoirs are referred to as
reservoir inducedearthquakes.
Measuring Earthquakes
The earthquake events are scaled either
according to the magnitude or intensity of the
shock. The magnitude scale is known as the
Richter scale. The magnitude relates to the
energy released during the quake. The
magnitude is expressed in absolute numbers,
0-10. The intensity scale is named after
Mercalli, an Italian seismologist. The intensity
scale takes into account the visible damage
caused by the event. The range of intensity scale
is from 1-12.
EFFECTSOFEARTHQUAKE
Earthquake is a natural hazard. The following
are the immediate hazardous effects of
earthquake:
(i) Ground Shaking
(ii) Differential ground settlement
(iii) Land and mud slides
(iv) Soil liquefaction
(v) Ground lurching
(vi) Avalanches(vii) Ground displacement
(viii) Floods from dam and levee failures
(ix) Fires
(x) Structural collapse
(xi) Falling objects
(xii) Tsunami
The first six listed above have some bearings
upon landforms, while others may be
considered the effects causing immediate
concern to the life and properties of people in
the region. The effect of tsunami would occuronly if the
epicentre of the tremor is below
oceanic waters and the magnitude is
sufficiently high. Tsunamis are waves
generated by the tremors and not an
earthquake in itself. Though the actual quake
activity lasts for a few seconds, its effects are
devastating provided the magnitude of the
quake is more than 5 on the Richter scale.
Figure 3.2 (a) and (b) : Earthquake Shadow Zones
(iii) In the areas of intense mining activity,sometimes the
roofs of undergroundmines collapse causing minor tremors.
These are called collapseearthquakes.(iv) Ground shaking may
also occur due to
the explosion of chemical or nucleardevices. Such tremors are
called explosionearthquakes.
-
8/21/2019 NCERT- Complete Geography
26/578
INTERIOR OF THE EARTH 25
Frequency of Earthquake Occurrences
The earthquake is a natural hazard. If a tremorof high magnitude
takes place, it can causeheavy damage to the life and property
of
people. However, not all the parts of the globenecessarily
experience major shocks. We shall
be discussing the distribution of earthquakesand volcanoes with
some details in the next
STRUCTUREOFTHEEARTH
The Crust
It is the outermost solid part of the earth. It is
brittle in nature. The thickness of the crustvaries under the
oceanic and continental areas.Oceanic crust is thinner as compared
to thecontinental crust. The mean thickness ofoceanic crust is 5 km
whereas that of thecontinental is around 30 km. The
continentalcrust is thicker in the areas of major mountainsystems.
It is as much as 70 km thick in theHimalayan region.
It is made up of heavier rocks havingdensity of 3 g/cm3. This
type of rock found inthe oceanic crust is basalt. The mean
densityof material in oceanic crust is 2.7 g/cm3.
The Mantle
The portion of the interior beyond the crust iscalled the
mantle. The mantle extends fromMohos discontinuity to a depth of
2,900 km.
The upper portion of the mantle is calledasthenosphere. The word
astheno means
weak. It is considered to be extending upto 400km. It is the
main source of magma that finds
chapter. Note that the quakes of highmagnitude, i.e. 8+ are
quite rare; they occuronce in 1-2 years whereas those of tiny
typesoccur almost every minute.
A view of the damaged Aman Setu at the LOCin Uri, due to an
earthquake
-
8/21/2019 NCERT- Complete Geography
27/578
FUNDAMENTALS OF PHYSICAL GEOGRAPHY26
its way to the surface during volcaniceruptions. It has a
density higher than thecrusts (3.4 g/cm3). The crust and
theuppermost part of the mantle are calledlithosphere. Its
thickness ranges from 10-200 km.
The lower mantle ex tends beyond theasthenosphere. It is in
solid state.
The Core
As indicated earlier, the earthquake waveve loci ties helped in
understanding theexistence of the core of the earth. The
core-mantle boundary is located at the depth of2,900 km. The outer
core is in liquid state whilethe inner core is in solid state. The
density ofmaterial at the mantle core boundary is around5 g/cm3and
at the centre of the earth at 6,300km, the density value is around
13g/cm3. Thecore is made up of very heavy material
mostlyconstituted by nickel and iron. It is sometimes
referred to as the nifelayer.
VOLCANOESANDVOLCANICLANDFORMS
You may have seen photographs or pictures ofvolcanoes on a
number of occasions. A volcanois a place where gases, ashes and/or
moltenrock material lava escape to the ground. A
volcano is called an active volcano if thematerials mentioned
are being released or have
been released out in the recent past. The layerbelow the solid
crust is mantle. It has higherdensity than that of the crust. The
mantlecontains a weaker zone called asthenosphere.
It is from this that the molten rock materialsfind their way to
the surface. The material inthe upper mantle portion is called
magma.Once it starts moving towards the crust or itreaches the
surface, it is referred to as lava.
The material that reaches the ground includeslava flows,
pyroclastic debris, volcanic bombs,ash and dust and gases such as
nitrogencompounds, sulphur compounds and minoramounts of chlorene,
hydrogen and argon.
Volcanoes
Volcanoes are classified on the basis of natureof eruption and
the form developed at thesurface. Major types of volcanoes are as
follows:
Shield Volcanoes
Barring the basalt flows, the shield volcanoesare the largest of
all the volcanoes on the earth.
The Hawaiian volcanoes are the most famous
Figure 3.4 : The interior of the earth
Shield Volcano
Cinder Cone
-
8/21/2019 NCERT- Complete Geography
28/578
INTERIOR OF THE EARTH 27
examples. These volcanoes are mostly madeup of basalt, a type of
lava that is very fluid
when erupted. For this reason, these volcanoesare not steep.
They become explosive if
somehow water gets into the vent; otherwise,they are
characterised by low-explosivity. Theupcoming lava moves in the
form of a fountainand throws out the cone at the top of the ventand
develops into cinder cone.
Composite Volcanoes
These vo lcanoes are characterised byeruptions of cooler and
more viscous lavasthan basalt. These volcanoes often result
inexplosive eruptions. Along with lava, largequantities of
pyroclastic material and ashes
find their way to the ground. This materialaccumulates in the
vicinity of the vent openingsleading to formation of layers, and
this makesthe mounts appear as composite volcanoes.
more than 50 m. Individual flows may extendfor hundreds of km.
The Deccan TrapsfromIndia, presently covering most of
theMaharashtra plateau, are a much larger flood
basalt province. It is believed that initially thetrap
formations covered a much larger areathan the present.
Mid-Ocean Ridge Volcanoes
These volcanoes occur in the oceanic areas.There is a system of
mid-ocean ridges morethan 70,000 km long that stretches throughall
the ocean basins. The central portion of thisridge experiences
frequent eruptions. We shall
be discussing this in detail in the next chapter.
VOLCANICLANDFORMS
Intrusive Forms
The lava that is released during volcanic
eruptions on cooling develops into igneous
rocks. The cooling may take place either on
reaching the surface or also while the lava isstill in the
crustal portion. Depending on the
location of the cooling of the lava, igneous rocks
are classified as volcanic rocks(cooling at the
surface) and plutonic rocks (cooling in the
crust). The lava that cools within the crustalportions assumes
different forms. These forms
are called intrusive forms. Some of the forms
are shown in Figure 3.5.Composite Volcano
Caldera
These are the most explosive of the earthsvolcanoes. They are
usually so explosive thatwhen they erupt they tend to collapse
onthemselves rather than building any tallstructure. The collapsed
depressions are calledcalderas. Their explosiveness indicates
that
the magma chamber supplying the lava is notonly huge but is also
in close vicinity.
Flood Basalt Provinces
These volcanoes outpour highly fluid lava thatflows for long
distances. Some parts of the
world are covered by thousands of sq. km ofthick basalt lava
flows. There can be a series offlows with some flows attaining
thickness of Figure 3.5 : Volcanic Landforms
-
8/21/2019 NCERT- Complete Geography
29/578
FUNDAMENTALS OF PHYSICAL GEOGRAPHY28
Activity : Locating an Epicentre
For this you will need
Data from 3 seismograph stations about the time of arrival of
P-waves, S-waves.
Procedure1. Find the time of arrival of P and S-waves of the
given quake for the three stations for which
you have the data.2. Compute the time lag between the arrival of
P and S-waves for each station; it is called time
lag. (Note that it is directly related to the distance of the
seismograph from the focus.)
A. Basic rule : For every second of time lag, the earthquake is
roughly 8 km away from you.
3. Using the rule quoted above, convert the time lag into
distance ( # seconds of time lag * 8)for each station.
4. On a map locate the seismograph stations.5. Draw circles,
taking the seismograph stations as the centre, with the radius
equal to the
distance you have calculated in the previous step. (Do not
forget to convert distance as perthe map scale.)
6. These circles will intersect each other in a point. This
point is the location of the epicentre.
In normal practice, the epicentres are located using computer
models. They take into accountthe structure of the earths crust.
The locations with accuracy within a few hundred metrescan be
achieved. The procedure outlined here is a much simplified version
of what is normallydone, although the principle is the same.
In the following diagram, the epicentre is located using this
procedure. It also contains atable giving necessary data. Why dont
you try for yourself?
Batholiths
A large body of magmatic material that coolsin the deeper depth
of the crust develops in theform of large domes. They appear on the
surface
only after the denudational processes removethe overlying
materials. They cover large areas,and at times, assume depth that
may be severalkm. These are granitic bodies. Batholiths arethe
cooled portion of magma chambers.
Lacoliths
These are large dome-shaped intrusive bodieswith a level base
and connected by a pipe-like
conduit from below. It resembles the surfacevolcanic domes of
composite volcano, onlythese are located at deeper depths. It can
beregarded as the localised source of lava that
finds its way to the surface. The Karnatakaplateau is spotted
with domal hills of graniterocks. Most of these, now exfoliated,
areexamples of lacoliths or batholiths.
Lapolith, Phacolith and Sills
As and when the lava moves upwards, aportion of the same may
tend to move in a
horizontal direction wherever it finds a weak
Data
Arrival time ofStation P-waves S-waves Hour Min. Sec. Hour Min.
Sec.
S1 03 23 20 03 24 45
S2 03 22 17 03 23 57
S3 03 22 00 03 23 55
Scale of the map 1cm = 40km
-
8/21/2019 NCERT- Complete Geography
30/578
INTERIOR OF THE EARTH 29
EXERCISES
1. Multiple choice questions.
(i) Which one of the following earthquake waves is more
destructive?
(a) P-waves (c) Surface waves
(b) S-waves (d) None of the above
(ii) Which one of the following is a direct source of
information about theinterior of the earth?
(a) Earthquake waves (c) Gravitational force
(b) Volcanoes (d) Earth magnetism
(iii) Which type of volcanic eruptions have caused Deccan Trap
formations?(a) Shield (c) Composite
(b) Flood (d) Caldera
(iv) Which one of the following describes the lithosphere:
(a) upper and lower mantle (c) crust and core
(b) crust and upper mantle (d) mantle and core
2. Answer the following questions in about 30 words.
(i) What are body waves?
(ii) Name the direct sources of information about the interior
of the earth.
(iii) Why do earthquake waves develop shadow zone?
(iv) Briefly explain the indirect sources of information of the
interior of theearth other than those of seismic activity.
3. Answer the following questions in about 150 words.
(i) What are the effects of propagation of earthquake waves on
the rock massthrough which they travel?
(ii) What do you understand by intrusive forms? Briefly describe
variousintrusive forms.
plane. It may get rested in different forms. In
case it develops into a saucer shape, concave
to the sky body, it is called lapolith. A wavy
mass of intrusive rocks, at times, is found at
the base of synclines or at the top of anticlinein folded
igneous country. Such wavy materialshave a definite conduit to
source beneath inthe form of magma chambers (subsequentlydeveloped
as batholiths). These are called thephacoliths.
The near horizontal bodies of theintrusive igneous rocks are
called sill orsheet, depending on the thickness of thematerial. The
thinner ones are called sheets
while the thick horizontal deposits arecalled sills.
Dykes
When the lava makes its way through cracksand the fissures
developed in the land, itsolidifies almost perpendicular to the
ground.It gets cooled in the same position to develop a
wall-like structure. Such structures are calleddykes. These are
the most commonly found
intrusive forms in the western Maharashtra area.These are
considered the feeders for the eruptions
that led to the development of the Deccan traps.
-
8/21/2019 NCERT- Complete Geography
31/578
In the previous chapter, you have studied theinterior of the
earth. You are already familiar
with the world map. You know that continents
cover 29 per cent of the surface of the earthand the remainder
is under oceanic waters.
The positions of the continents and the oceanbodies, as we see
them in the map, have notbeen the same in the past. Moreover, it is
nowa well-accepted fact that oceans andcontinents will not continue
to enjoy theirpresent positions in times to come. If this isso, the
question arises what were their positionsin the past? Why and how
do they change theirpositions? Even if it is true that the
continentsand oceans have changed and are changing
their positions, you may wonder as to howscientists know this.
How have they determinedtheir earlier positions? You will find the
answersto some of these and related questions in thischapter.
CONTINENTALDRIFT
Observe the shape of the coastline of the AtlanticOcean. You
will be surprised by the symmetryof the coastlines on either side
of the ocean. No
wonder, many scientists thought of thissimilarity and considered
the possibility of the
two Americas, Europe and Africa, to be oncejoined together. From
the known records of thehistory of science, it wasAbraham Ortelius,
aDutch map maker, who first proposed such apossibility as early as
1596.Antonio Pellegrinidrew a map showing the three continents
together.However, it was Alfred Wegenera Germanmeteorologist who
put forth a comprehensiveargument in the form of the continental
drift
DISTRIBUTIONOFOCEANSANDCONTINENTS
C H A P T E R
theory in 1912. This was regarding thedistribution of the oceans
and the continents.
According to Wegener, all the continents
formed a single continental mass, a mega oceansurrounded by the
same. The super continent
was named PANGAEA, which meant all earth.The mega-ocean was
called PANTHALASSA,meaning all water. He argued that, around
200million years ago, the super continent,Pangaea, began to split.
Pangaea first broke
into two large continental masses as Laurasiaand Gondwanaland
forming the northern andsouthern components respectively.
Subse-quently, Laurasia and Gondwanalandcontinued to break into
various smaller
continents that exist today. A variety of evidencewas offered in
support of the continental drift.Some of these are given below.
Evidence in Support of the Continental Drift
The Matching of Continents (Jig-Saw-Fit)
The shorelines of Africa and South Americafacing each other have
a remarkable and
unmistakable match. It may be noted that amap produced using a
computer programme
to find the best fit of the Atlantic margin waspresented by
Bullard in 1964. It proved to bequite perfect. The match was tried
at 1,000-fathom line instead of the present shoreline.
Rocks of Same Age Across the Oceans
The radiometric dating methods developed inthe recent period
have facilitated correlating therock formation from different
continents across
-
8/21/2019 NCERT- Complete Geography
32/578
DISTRIBUTION OF OCEANS AND CONTINENTS 31
the vast ocean. The belt of ancient rocks of2,000 million years
from Brazil coast matches
with those from western Africa. The earliestmarine deposits
along the coastline of South
America and Africa are of the Jurassic age.This suggests that
the ocean did not exist priorto that time.
Tillite
It is the sedimentary rock formed out ofdeposits of glaciers.
The Gondawana systemof sediments from India is known to have
itscounter parts in six different landmasses of theSouthern
Hemisphere. At the base the systemhas thick tillite indicating
extensive andprolonged glaciation. Counter parts of this
succession are found in Africa, Falkland Island,Madagascar,
Antarctica and Australia besidesIndia. Overall resemblance of the
Gondawanatype sediments clearly demonstrates that theselandmasses
had remarkably similar histories.
The glacial tillite provides unambiguousevidence of
palaeoclimates and also of driftingof continents.
Placer Deposits
The occurrence of rich placer deposits of goldin the Ghana coast
and the absolute absence
of source rock in the region is an amazing fact.The gold bearing
veins are in Brazil and it isobvious that the gold deposits of the
Ghanaare derived from the Brazil plateau when thetwo continents lay
side by side.
Distribution of Fossils
When identical species of plants and animalsadapted to living on
land or in fresh water arefound on either side of the marine
barriers, aproblem arises regarding accounting for
suchdistribution. The observations that Lemursoccur in India,
Madagascar and Africa led someto consider a contiguous landmass
Lemurialinking these three landmasses. Mesosaurus
was a small reptile adapted to shallow brackishwater. The
skeletons of these are found onlyin two localities : the Southern
Cape provinceof South Africa and Iraver formations of Brazil.
The two localities presently are 4,800 km apartwith an ocean in
between them.
Force for Drifting
Wegener suggested that the movementresponsible for the drifting
of the continents
was caused by pole-fleeing force and tidal force.
The polar-fleeing force relates to the rotationof the earth. You
are aware of the fact that theearth is not a perfect sphere; it has
a bulge atthe equator. This bulge is due to the rotationof the
earth. The second force that wassuggested by Wegenerthe tidal
forceis dueto the attraction of the moon and the sun thatdevelops
tides in oceanic waters. Wegener
believed that these forces would becomeeffective when applied
over many million years.However, most of scholars considered
theseforces to be totally inadequate.
Post-Drift Studies
It is interesting to note that for continental drift,most of the
evidence was collecte