PHYSICAL & WORLD GEOGRAPHY

PHYSICAL & WORLD

GEOGRAPHY

An initiative of Group

B I G L E A R N I N G S M A D E E ASY

Civil Services Examination

Physical & World Geography© Copyright, by MADE EASY Publications.

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Physical & World GeographyContents

Unit – I: The Earth

Chapter – 1

Basics of Geography.......................................21.1 Geography ...........................................................2

Geography in Relation to Other Subjects .............2

Geography and Other Disciplines ........................2

Physical Geography in Relation to Natural

and Social Sciences .............................................3

Branches of Geography .......................................3

Geography: Regional Approach ..........................4

1.2 Solar System ........................................................4

Formation .............................................................4

Structure ...............................................................5

1.3 Globe ...................................................................6

Latitudes ..............................................................7

Longitudes ...........................................................7

1.4 Time Zones ..........................................................7

Daylight Saving Time ...........................................8

Leap Second ........................................................8

International Date Line .........................................8

1.5 Maps ....................................................................9

Scale ....................................................................9

Projection .............................................................9

Generalization ......................................................9

Design ..................................................................9

Construction and Production ................................9

Types of Maps Based on Scale ............................9

Types of Maps Based on Function .....................10

1.6 Rotation and Revolution .....................................10

Rotation ..............................................................10

Revolution ..........................................................11

Chapter – 2

Geomorphology .............................................142.1 Introduction ........................................................14

2.2 Origin of Earth ....................................................14

Earlier Theories ..................................................14

Modern Theories ................................................15

2.3 Evolution of Earth ...............................................16

Evolution of Lithosphere .....................................16

Evolution of Atmosphere ....................................16

Evolution of Hydrosphere ...................................16

2.4 Basic Features of Earth ......................................16

Topography of Earth ..........................................17

2.5 Interior of Earth ...................................................17

Sources of Information .......................................17

Layered Structure of Earth’s Surface ..................18

Major Discontinuities of Earth’s Interior ..............19

2.6 Movements of Earth Crust ..................................19

Theory of Continental Drift ..................................19

Sea Floor Spreading ..........................................20

Plate Tectonics ...................................................21

Plate Boundary Interaction .................................22

2.7 Geological Movement ........................................23

Endogenetic Forces ...........................................24

2.8 Earth’s Magnetic Field ........................................25

2.9 Earthquake .........................................................25

Earthquake Waves .............................................26

Shadow Zone .....................................................26

Types .................................................................27

Measurement .....................................................27

Distribution .........................................................28

Seismic Zones of India .......................................28

Effects ................................................................29

2.10 Volcanism ...........................................................29

Classification ......................................................29

Distribution of Volcanoes in World .....................33

Volcanic Landforms ...........................................33

Unit – II: Landforms

Chapter – 3

Rocks and Minerals .......................................383.1 Introduction ........................................................38

3.2 Classification of Rocks .......................................38

3.3 Igneous Rocks ...................................................38

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Characteristics ...................................................38

Classification ......................................................39

3.4 Sedimentary Rocks ............................................40

Characteristics ...................................................41

Classification ......................................................41

3.5 Metamorphic Rocks ...........................................41

Metamorphism occurs: .......................................41

Agents ................................................................41

Classification .....................................................42

3.6 Rock Cycle .........................................................42

3.7 Minerals ..............................................................43

Chapter – 4

Landforms ......................................................444.1 Introduction ........................................................44

4.2 Weathering .........................................................44

Chemical Weathering Processes .......................44

Physical Weathering Processes .........................45

Biological Weathering ........................................45

4.3 Mass Movements ...............................................46

Slow Movements ................................................46

Rapid Movements ..............................................46

Landslide ...........................................................47

4.4 Erosion ...............................................................47

Types of Erosion .................................................47

4.5 Fluvial Landforms ...............................................48

Factors ...............................................................48

Upper Course .....................................................49

Middle Course ....................................................50

Lower Course .....................................................51

4.6 Landforms Formed by Underground Water .......53

Erosional Landforms ..........................................53

Depositional Landforms .....................................53

4.7 Glaciers ..............................................................54



4.8 Coastal Landforms .............................................55



4.9 Wind ...................................................................56



4.10 Lakes..................................................................57

Formed by Earth Movement ...............................57

Formed by Glaciation .........................................58

Formed by Volcanic Activity ...............................58

Formed by Erosion .............................................59

Formed by Deposition ........................................59

Artificial Lakes ....................................................59

Important Lakes of the World .............................59

4.11 Islands and Coral Reefs .....................................60

4.12 Coral Reefs ........................................................60

Types of Coral Reefs ..........................................60

Origin .................................................................61

Coral Bleaching ..................................................61

Coral reef in India ...............................................62

Chapter – 5

Relief Features ...............................................635.1 Introduction ........................................................63

5.2 Order of Reliefs ..................................................63

5.3 Formation of Relief Features ...............................63

Destructive Processes .......................................64

5.4 Oceanic Basin ....................................................64

Continental Margin .............................................65

Deep Ocean Basin .............................................65

Abyssal Plains ....................................................65

Oceanic Deeps or Trenches ..............................66

Mid-Oceanic Ridges ..........................................66

Rift Valleys ..........................................................66

Seamounts .........................................................67

Guyots ................................................................67

Submarine Canyons ...........................................67

Stages of Atoll Formation ...................................67

5.5 Relief Features of the Land ................................67

Provinces ...........................................................68

Shield .................................................................68

Platform ..............................................................68

Orogen ...............................................................68

Basin ..................................................................68

5.6 Mountains ...........................................................69

Major Mountain Ranges of the World .................69

Orogenesis .........................................................69

Classification of Mountains .................................70

5.7 Plateaus .............................................................72

Formation ...........................................................72

Types .................................................................72

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Unit – III: Climate

Chapter – 6

Weather and Climate .....................................766.1 Introduction ........................................................76

6.2 Weather and Climate: A Comparison .................76

6.3 Elements of Weather and Climate ......................76

Temperature .......................................................77

Humidity .............................................................77

Clouds ................................................................77

Precipitation .......................................................78

Rainfall ...............................................................78

Atmospheric Pressure ........................................78

Wind ...................................................................78

Chapter – 7

Atmosphere....................................................807.1 Introduction ........................................................80

7.2 Composition of Atmosphere ...............................81

7.3 Solar Radiation ...................................................81

Variability of Insolation .......................................82

Heating and Cooling of Atmosphere ..................82

Heat Budget .......................................................83

7.4 Water in Atmosphere ..........................................84

7.5 Temperature Inversion .......................................84

Types .................................................................85

Effects ................................................................86

7.6 Atmospheric Pressure and Global Wind ............86

Distribution of Air Pressure .................................86

Pressure Belts of Earth .......................................88

Types of Winds ...................................................89

7.7 Polar Vortex and its Impact ................................92

7.8 Ozone Layer Hole ..............................................93

7.9 Climate Change .................................................93

Causes of climate change ..................................93

Anthropogenic causes .......................................94

Control Strategy .................................................94

7.10 Urban Heat Island ..............................................94

Chapter – 8

Climatic Types of The World ........................958.1 Introduction ........................................................95

8.2 Classification ......................................................95

8.3 Types According to Koeppen ............................95

Hot Wet Equatorial Climate ................................95

Tropical Monsoon and Tropical Marine Climate .97

Savannah or Sudan Climate ...............................99

Hot Desert and Mid-latitude Desert Climate .....100

Warm Temperate Western Margin (Mediterranean) Climate ...................................101

Temperate Continental Climate ........................102

Warm Temperate Eastern Margin Climate (China Type) ....................................................103

Cool Temperate Western Margin Climate (British Type) ....................................................105

Cool Temperate Continental Climate (Siberian) 106

Cool Temperate Eastern Margin .......................107

Arctic or Polar Climate .....................................108

Chapter – 9

Precipitation .................................................1109.1 Evaporation and Condensation ........................110

9.2 Precipitation .....................................................110

Mechanism Producing Precipitation .................110

9.3 Types of Rainfall ...............................................110

Convectional Rainfall ........................................110

Frontal Rainfall .................................................110

Orographic Rainfall ..........................................111

9.4 Distribution of Rainfall ......................................111

Regional Variations in Rainfall ..........................111

Seasonal Variations in Rainfall .........................111

Factors Affecting Rainfall .................................112

9.5 Air Mass and Weather Fronts ...........................112

Air Mass ...........................................................112

Front .................................................................113

9.6 Cyclones ..........................................................114

Cyclogenesis....................................................114

Temperate Cyclones ........................................115

Tropical Cyclones ............................................115

Naming of a Cyclone ........................................117

Tropical Cyclones and Society .........................117

Recent Cyclones ..............................................117

Unit – IV: Water (Oceans)

Chapter – 10

Oceans..........................................................12010.1 Oceans .............................................................120

Reliefs of the Ocean .........................................120

10.2 Properties of the Ocean ..................................121

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10.3 Oceanic Deposits .............................................121

Classification ....................................................121

10.4 Salinity ..............................................................122

Role of Salinity ..................................................122

Some facts regarding salinity of water bodies .122

Distribution of Salinity .......................................122

10.5 Clines in Ocean water: .....................................123

Halocline ..........................................................123

Thermocline .....................................................123

Pycnocline ........................................................123

10.6 Temperature .....................................................123

Factors Affecting Temperature Distribution ......123

Distribution of Oceanic Temperature ...............124

10.7 Oceanic Movements ........................................124

Ocean Currents ................................................124

Types ...............................................................125

Currents of the Atlantic Ocean .........................125

Currents of the Pacific Ocean ..........................126

Indian Ocean Currents .....................................126

10.8 Surface Currents ..............................................127

Major Gyres ......................................................127

10.9 Deep Ocean Currents ......................................128

10.10 Effects of Ocean Currents .................................128

Weather and Climate ........................................128

Marine Life .......................................................128

Navigation ........................................................128

Marine Resources ............................................129

Chapter – 11

Tide ............................................................... 13111.1 Introduction ......................................................131

11.2 Causes for Formation of Tides .........................131

11.3 Building Block ..................................................132

11.4 Duration and Frequency of Daily Tides ............132

11.5 Stages of Tides ................................................132

Tides Based on Positions of Earth, Sun and Moon .........................................................132

Tides Based on Frequency ..............................133

Tides based on Magnitude ..............................133

11.6 Concepts Related to Tides ...............................134

Characteristics of Tides ...................................134

Inter-Tidal Zone ................................................134

Flow Tide and Ebb Tide ...................................134

Tidal Bore .........................................................134

11.7 Role of Tides ....................................................135

Navigation ........................................................135

Fishing..............................................................135

Desiltation ........................................................135

Biogeographic Significance .............................135

Climatic Significance ........................................135

Tidal Energy .....................................................135

Ports ................................................................135

Prevention from River Freezing ........................135

11.8 Tidal Energy .....................................................135

Modes of Harnessing Tidal Energy ..................135

Advantages ......................................................136

Disadvantages .................................................136

Chapter – 12

Environmental Geography..........................13712.1 Introduction ......................................................137

Concept of Environment, Ecology and Ecosystem ........................................................137

12.2 Elements of Biosphere .....................................137

Lithosphere ......................................................137

Hydrosphere ....................................................137

Atmosphere ......................................................138

12.3 Ecosystem ........................................................138

Components of Ecosystem ..............................138

Types of Ecosystems .......................................139

Ecosystem Services .........................................139

12.4 Biomes .............................................................140

12.5 Major Biomes of the World ...............................140

Tundra ..............................................................140

Taiga ................................................................141

Tropical and Temperate Rainforest ..................142

Tropical and Temperate Grassland ..................142

Mediterranean Climate .....................................142

Desert Biome....................................................143

Unit – V: World Geography

Chapter – 13

Asia ............................................................... 14713.1 Introduction ......................................................147

13.2 Physiography of Asia .......................................148

13.3 Climate .............................................................155

13.4 Economic Geography ......................................155

Main Economic Activities .................................155

Industrial Regions in Asia .................................158

UnitI

1. Basics of Geography ......................................................................2

2. Geomorphology .......................................................................... 14

The Earth

1.1 GeographyGeography as a branch of learning, is focused on understanding the relationship between man and nature. The word geography was first used by the Greek scholar Eratosthenes in the third century B.C. It is derived from the Greek geo (Earth) and graphos (description), so that geography as a discipline is focused on the description of the Earth surface as the world of man.

Geography in Relation to Other SubjectsGeography do not study only the variations in the phenomena over the Earth’s surface (space) but also study the associations with the other factors which cause these variations. For example, cropping patterns differ from region to region but this variation in cropping pattern, as a phenomenon, is related to variations in soils, climates, demands in the market, capacity of the farmer to invest and technological inputs available to her/him. Thus, the concern of geography is to find out the causal relationship between any two phenomena or between more than one phenomenon.

Geography, thus, is concerned with the study of Nature and Human interactions as an integrated whole. ‘Human’ is an integral part of ‘nature’ and ‘nature’ has the imprints of ‘human’. ‘Nature’ has influenced different aspects of human life. Its imprints can be noticed on food, clothing, shelter and occupation. Human beings have come to terms with nature through adaptation and modification.

As we know that, the present society has passed the stage of primitive societies, which were directly dependent on their immediate physical environment for sustenance. Present societies have modified their natural environment by inventing and using technology and thus, have expanded the horizon of their operation by appropriating and utilizing the resources provided by nature. With the gradual development of technology, human beings were able to loosen the shackles of their physical environment.

With the help of technology, human beings moved from the stage of necessity to a stage of freedom. They have put their imprints everywhere and created new possibilities in collaboration with nature. Thus, we now find humanized

nature and naturalized human beings and geography

studies this interactive relationship. The space got

organized with the help of the means of transportation

and communication network. The links (routes) and nodes

(settlements of all types and hierarchies) integrated the

space and gradually, it got organized. As a social science

discipline, geography studies the ‘spatial organization’

and ‘spatial integration’.

Geography as a discipline is concerned with three sets of

questions:

1. Identification of patterns of natural and cultural

features as found over the surface of the earth. These

are the questions about what?

2. Distribution of natural and cultural features over the

surface of the earth. These are questions about where?

3. Explanation or the causal relationships between

features developed and the processes and phenomena

reponsible for their formation. This is related to the

question of why?

Geography as a subject is related to space and takes

note of spatial characteristics and attributes. It studies

the patterns of distribution, location and concentration

of phenomena over space and interprets them providing

explanations for these patterns.

It also takes note of the associations and inter-relationships

between the phenomena resulting from the dynamic

interaction between human beings and their physical

environment.

Geography and Other DisciplinesGeography attempts to comprehend the associations of

phenomena as related in sections of reality. Below Figure

shows the relationship of geography with other sciences.

Every discipline, concerned with scientific knowledge

is linked with geography as many of their elements vary

over space. Geography helps in understanding the reality

in totality in its spatial perspective. Geography, thus, not

only takes note of the differences in the phenomena from

place to place but integrates them holistically which may

be different at other places.

Every geographical phenomenon undergoes change

through time and can be explained temporally. The

11Basics of Geography

changes in landforms, climate, vegetation, economic

activities occupations and cultural developments have

followed a definite historical course.

Figure: Geography and its relation with other disciplines

Physical Geography in Relation to Natural and Social SciencesPhysical geography is linked with geology, meteorology,

hydrology and pedology, and thus, geomorphology,

climatology, oceanography and soil geography

respectively have very close link with the natural sciences

as these derive their data from these sciences.

Bio-Geography is closely related to botany, zoology as

well as ecology as human beings are located in different

locational niche.

In the same way there is relation between geography

and history and every other discipline has a relation

with one another. All the social science disciplines, viz.,

sociology, political science, economics and demography

study different aspects of social reality. The branches of

geography, viz., social, political, economic and population

and settlements are closely linked with these disciplines as

each one of them has spatial attributes.

The core concern of political science is territory, people

and sovereignty while political geography is also interested

in the study of the state as a spatial unit as well as people

and their political behaviour.

Economics deals with basic attributes of the economy such

as production, distribution, exchange and consumption.

Each of these attributes also has spatial aspects and

here comes the role of economic geography to study the

spatial aspects of production, distribution, exchange and

consumption.

Likewise, population geography is closely linked with the

discipline of demography.

Branches of Geography• Physical Geography:

Figure: Branches of Geography

1. Geomorphology is the study of landforms, their evolution and related processes.

2. Climatology is the study of structure of atmosphere and elements of weather and climates and climatic types and regions.

3. Hydrology studies the realm of water over the surface of the Earth including oceans, lakes, rivers and other water bodies and its effect on different life forms including human life and their activities.

4. Soil Geography is to study the processes of soil formation, soil types, their fertility status, distribution and use.

• Human Geography:

1. Social/Cultural Geography is the study of society and its spatial dynamics as well as the cultural elements contributed by the society.

2. Population and Settlement Geography (Rural and Urban). It studies population growth, distribution, density, sex ratio, migration and occupational structure etc. Settlement geography studies the characteristics of rural and urban settlements.

3. Economic Geography studies economic activities of the people including agriculture, industry,

tourism, trade, and transport, infrastructure and

services, etc.

3Physical & World GeographyAn initiative of Group


4. Historical Geography studies the historical

processes through which the space gets organised.

Every region has undergone some historical

experiences before attaining the present-day

status. The geographical features also experience

temporal changes and these forms the concerns of

historical geography.

5. 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 framework to

understand the political behaviour of the population.

The interaction between physical geography and

human geography has lead to the development of

Biogeography which includes:

1. Plant Geography which studies the spatial pattern

of natural vegetation in their habitats.

2. Zoo Geography which studies the spatial patterns

and geographic characteristics of animals and

their habitats.

3. Ecology/Ecosystem deals with the scientific study of

the habitats characteristic of species.

4. Environmental Geography concerns world

over leading to the realisation of environmental

problems such as land gradation, pollution and

concerns for conservation has resulted in the

introduction of this new branch in geography.

Geography: Regional Approach1. Regional Studies/Area Studies: Comprising Macro,

Meso and Micro Regional Studies.

2. Regional Planning

3. Regional Development

4. Regional Analysis

There are two aspects which are common to every

discipline, these are:

1. Philosophy:

(a) Geographical Thought

(b) Land and Human Interaction/Human Ecology

2. Methods and Techniques:

(a) Cartography including Computer Cartography

(b) Quantitative Techniques/Statistical Techniques

(c) Survey Methods

(d) Geo-informatics comprising techniques such as

Remote Sensing, GIS, GPS, etc.

1.2 Solar SystemA solar system consists of a star (sun) and all of the objects

that travel around it—planets, moons, asteroids, comets

and meteoroids. The gravitational attraction between the

sun and these objects keeps them revolving around it.

Most stars host their own planets, so there are likely tens

of billions of other solar systems in the Milky Way galaxy

alone.

The solar system we call home is located in an outer

spiral arm of the vast Milky Way galaxy. It consists of the

sun (our star) and everything that orbits around it. This

includes the eight planets and their natural satellites (such

as our moon), dwarf planets and their satellites, as well

as asteroids, comets and countless particles of smaller

debris.

The solar system extends much farther than the eight

planets that orbit the sun. The solar system also includes

the Kuiper Belt that lies past Neptune’s orbit. This is a

sparsely occupied ring of icy bodies, almost all smaller

than the most popular Kuiper Belt Object, dwarf planet

Pluto.

The sun’s heliosphere doesn’t extend quite as far. The

heliosphere is the bubble created by the solar wind—a

stream of electrically charged gas blowing outward from

the sun in all directions. The boundary where the solar

wind is abruptly slowed by pressure from interstellar gases

is called the termination shock. This edge occurs between

80-100 astronomical units.

FormationOur solar system formed about 4.5 billion years ago from

a dense cloud of interstellar gas and dust. The cloud

collapsed, possibly due to the shockwave of a nearby

exploding star, called a supernova. When this dust cloud

collapsed, it formed a solar nebula—a spinning, swirling

disk of material.

At the center, gravity pulled more and more material in.

Eventually the pressure in the core was so great that

hydrogen atoms began to combine and form helium,

releasing a tremendous amount of energy. With that, our

sun was born, and it eventually amassed more than 99

percent of the available matter.

Matter farther out in the disk was also clumping together.

These clumps smashed into one another, forming larger

and larger objects. Some of them grew big enough for their

gravity to shape them into spheres, becoming planets,

dwarf planets and large moons. In other cases, planets did

4An initiative of Group


Basics of Geography

22Geomorphology

2.1 IntroductionThe word ‘Geomorphology’ has been made from integration

of three words. First is ‘geo’ which means Earth, second

is ‘morph’ which means shape or form, and the third is

‘logy’ which means scientific study in Greek. Therefore,

geomorphology is the field of science which deals with

different types of landforms on Earth’s surface. It deals

with the nature of their origin, the shapes and sizes of

landforms etc.

2.2 Origin of EarthOn a clear night, you can observe numerous stars shining

in the sky. In fact in the universe, there are millions of stars

which are not visible to the human eye. Almost all stars

are placed in their definite galaxies and frequently have

planets orbiting them. This orbiting of stars by other stars

and planets is generally termed as a ‘Star System’.

Our Earth is a part of such a system known as the Solar

System. All the planets of the solar System revolve around

the Sun which is the central star. Sun along with other

planets including Earth is part of a galaxy called as the

Milky Way.

Earlier Theories

Nebular HypothesisIt is one of the earliest hypotheses originally propounded

by German philosopher Immanuel Kant and further revised

by Laplace in 1796. This hypothesis considered that the

planets were formed out of a cloud of material associated

with a youthful sun, which was slowly rotating.

Nebula is an extremely hot cloud of gas and dust in outer

space. According to this theory, as the rotating nebula

cooled down, it started to contract in size. This resulted

in rise in the speed of rotation and the corresponding

centrifugal forces acting on outer mass of gases. When

the centrifugal force superseded the centripetal force, the

mass of gases were ejected from the nebula. This process

would continue and cause the formation of different

planets. The same process would be repeated on different

planets and would cause the formation of their satellites.

Thus the remaining part at the nucleus of the nebula

became the Sun.

The nebular hypothesis assumes that the planets were in

the initial stage, a gaseous mass, and on cooling became

in liquid condition, and because of radiation cooling they

developed a solid crust. The evolution of a solid Earth from

an initially gaseous and later liquid mass is supported by a

solid crust on the upper part of the Earth and the evidences

of a liquid molten interior as proved by volcanism.

Some of the criticisms of Nebular Hypothesis were:

1. Laplace could not explain why only nine planets were

formed and not more.

2. There appears to be every possibility that the

separation of matter from the original nebula was a

continuous phenomenon. It cannot be an intermittent

process as postulated by Laplace.

3. The fact that the satellites of Uranus and Neptune

move in the opposite direction of the motion of the

other bodies of the solar system is sufficient to show

that the solar system did not originate in the way as

assumed by Laplace.

4. Considering the masses, distances and motions of the

bodies of our solar system, it is clear that their present

total angular momentum initially found in the nebula is

not sufficient for the break up of the nebula by excess

of rotation.

Later in 1950, Otto Schmidt in Russia and Carl Weizascar

in Germany somewhat revised the ‘nebular hypothesis’ in

their own different ways. Otto Schmidt in his Interstellar

Dust Hypothesis talked about the large quantities of

gases and dust particles scattered in the universe while

Carl Weizascar emphasized on existence of cosmic dust

forming the Sun. The friction and collision of particles led

to formation of a disk-shaped cloud and the planets were

formed through the process of accretion.

Binary Star Hypothesis

In 1900, Chamberlain and Moulton considered that a

wandering star approached the sun. As a result, a cigar-

shaped extension of material was separated from the solar

surface. As the passing star moved away, the material

separated from the solar surface continued to revolve

around the sun and it slowly condensed into planets. Sir

James Jeans and later Sir Harold Jeffrey supported this

argument. At a later date, the arguments considered of

a companion to the sun to have been coexisting. These

arguments are called binary theories.

Modern Theories

Origin of the UniverseBig Bang Theory

The most popular argument regarding the origin of the

universe is the Big Bang Theory. It is also called expanding

universe hypothesis. Edwin Hubble, in 1920, provided

evidence that the universe is expanding. As time passes,

galaxies move further and further apart. The Big Bang

Theory considers the following stages in the development

of the universe:

1. 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.

2. 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.

3. Within 300,000 years from the Big Bang, temperature

dropped to 4,500 K (Kelvin) and gave rise to atomic

matter and became transparent.

The expansion of universe means increase in space

between the galaxies.

Formation of Planets

The following are considered to be the stages in the

development of planets:

1. The stars are localized 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

2. In the next stage, the gas cloud starts getting

condensed and the matter around the core develops

into small rounded objects. These small-rounded

objects by the process of cohesion develop into what

is called planetesimals. Larger bodies start forming

by collision, and gravitational attraction causes the

material to stick together. Planetesimals are a large

number of smaller bodies.

3. In the final stage, these large number of small

planetesimals accrete to form a fewer large bodies in

the form of planets

Our Solar system consists of eight planets. Out of the eight

planets, mercury, Venus, Earth and Mars are called as the

inner planets as they lie between the sun and the belt of

asteroids while the other four planets are called the outer

planets. The term inner planet should not be confused with

inferior planet, which designates those planets that are

closer to the Sun than Earth is (i.e. Mercury and Venus).

Alternatively, the first four are called Terrestrial, meaning

Earth-like as they are made up of rock and metals, and have

relatively high densities. The rest four are called Jovian or

Gas Giant planets. Jovian means Jupiter-like. Most of them

are much larger than the terrestrial planets and have thick

atmosphere, mostly of helium and hydrogen. All planets

were formed in the same period sometime about 4.6 billion

years ago. The difference between terrestrial and Jovian

planets can be attributed to the following conditions:

1. The terrestrial planets were formed in the close vicinity

of the parent star where it was too warm for gases

to condense to solid particles. Jovian planets were

formed at quite a distant location



Physical and World Geography

2. The solar wind was most intense nearer the sun; so,

it blew off lots of gas and dust from the terrestrial

planets. The solar winds were not all that intense to

cause similar removal of gases from the Jovian planet.

3. The terrestrial planets are smaller and their lower

gravity could not hold the escaping gases.

4. The Jovian planets have a ring system around them

and have large number of moons.

2.3 Evolution of EarthEarth was initially a barren, rocky and hot object with a thin atmosphere of hydrogen and helium. The Earth has a layered structure. From the outermost end of the atmosphere to the centre of the Earth, the material that exists is not uniform. The atmospheric matter has the least density. From the surface to deeper depths, the Earth’s interior has different zones and each of these contains materials with different characteristics.

Evolution of Lithosphere‘Litho’ in Greek means relating to rock. Lithosphere

denotes the surface of Earth along with its various

forms. The formation of Lithosphere is primarily due to

thermodynamic processes shortly after the creation of

Earth. The Earth was mostly in a volatile state during

its primordial stage. Due to gradual increase in density

the temperature inside has increased. As a result the

material inside started getting separated depending on

their densities. This allowed heavier materials (like iron)

to sink towards the centre of the Earth and the lighter

ones to move towards the surface. With passage of time

it cooled further and solidified and condensed into a

smaller size.

It is through the process of differentiation that the Earth

forming material got separated into different layers. Starting

from the surface to the central parts, we have layers like

the crust, mantle, outer core and inner core. From the crust

to the core, the density of the material generally increases.

Evolution of AtmosphereThere are three stages in the evolution of the present

atmosphere of Earth. The first stage is marked by the

loss of primordial atmosphere, which included primarily

Hydrogen and Helium Gases. In the second stage, the

hot interior of the Earth contributed to the evolution of the

atmosphere. Finally, the composition of the atmosphere

was modified by the living world through the process of

photosynthesis.

Evolution of HydrosphereDuring the cooling of the Earth, gases and water vapour were released from the interior solid Earth. Continuous volcanic eruptions also contributed towards addition of water vapour and gases to the atmosphere. As the Earth cooled, the water vapour released started getting 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 Earth’s oceans were formed within 500 million years from the formation of the Earth.

2.4 Basic Features of EarthSome of the Basic features of Earth are:

1. Earth is not quite a sphere. The planet’s rotation causes

it to bulge at the equator. Since the Earth is flattened at

the poles and bulges at the equator, the shape of the

Earth is compared with an oblate spheroid

2. Earth’s equatorial diameter is about 12,756 km, but from

pole to pole, the diameter is about 12,714 km, which

shows difference of only 42 km. The mean radius of Earth

is 3,959 miles (6,371 kilometers)



Geomorphology

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PHYSICAL & WORLD GEOGRAPHY