CLIMATOLOGY

ATMOSPHERE COMPOSITION AND STRUCTURE

Origin of the Atmosphere
     Initially Earth is a red hot ball like structure slowly it got cooled, as it is rotating on its own axis the centrifugal forces acted upon and made the material to segregate according to their densities, this is why the denser material like Nickel and Ferrous are their in the Core of the Earth, the less dense material like Aluminium is located at the periphery and the intermediate material like Magnesium is located in the intermediate level between these two, apart from these minerals there are certain very less density minerals like Hydrogen, Helium, Nitrogen, etc., because of their less dense nature they are thrown out of the earth, this is the process of De-gassing.  These gases have enveloped the earth and are held to the earth due to the gravity.
Composition of Atmosphere
Gravity of the Earth plays a major role in the distribution of gases according to their densities.  The following picture reveals that the density is more near the surface of the earth and reduces with the altitude

  It is said that 97 percent of the atmospheric mass is upto the height of 25 kms.  The major gases like Nitrogen and Oxygen accounts for 99 percent of the gases and all other gases like Argon, Carbon dioxide, Neon, Helium, Hydrogen, Krypton, Xenon accounts just one percent.
Structure of the Atmosphere
The Earth's atmosphere is a layered structure, basing on temperature and pressure these layers can be divided into two, one Homosphere and other Heterosphere.  Homosphere consists of three layers namely, Troposphere, Stratosphere and Mesosphere.  The Heterosphere consists of two layers, namely Ionosphere and Exosohere.
Troposphere:
Tropos means Turbulence, since all the turbulence of the atmosphere is restricted in this layer alone.
This layer consists 99 percent of water vapour.
This layer consists 75 percent of Atmospheric mass.
Temperature decreases with height in this layer this phenomenon is called Normal Lapse Rate, for every 165 meters of assent 1 degree temperature will reduce, or for every one kilometer of assent 6.5 degrees of temperature will get reduces.  

Continental Drift theory

CHAPTER-V

CONTINENTAL DRIFT AND PLATE TECTONICS

The possibility of drifting of continents was first suggested by the French scholar Antonio Snider in 1858, but was opposed.  In 1910 F.B.Taylor of America invoked the hypothesis of horizontal displacement of continents, with a view of explaining the distribution of mountain ranges, but Taylor received a scant attention.  German professor Alfred Wegener was the first to put forward this idea in the form of a theory in 1912,its English translation was made in 1924 since then it has attracted much attention and publicity, and a huge literature has grown around this theory.

     According to the Wegener, all the continental mass which he called ‘Pangaea’ was united.  This super continent was surrounded by a mega ocean called ‘Panthalassa’, meaning all water.  He argued that, around 200 million years ago, the super continent Pangaea began to split.  First it broke into two large continents called Laurasia and Gondwana forming the northern and southern components respectively.  These two blocks were separated by a long shallow inland sea called “Tethys”.  The super continent Pangaea started breaking and the present shape and relative position is the result of fragmentation of Pangaea by rifting and the drifting apart of the broken parts.  According to this theory the continents are made of lighter SIAL and are floating on the denser SIMA.  The drifting of Pangaea was made possible chiefly due to differential gravitational forces.  The continents drifted in two directions – one towards Equator and other towards West.  On account of equatorial drift Africa and Eurasia were pushed closer together and the Tethys marine deposits located in between the two raised up in the form of mighty fold mountains extending from the Pyrenees and the Alps, and the Atlas mountain of N.Africa to the extensive Himalayan ranges of Asia.  On account of this equator ward drift Peninsular India and Africa separated from Antarctica and Australia, and as a result of their further drift in the course of time a portion of panthalasa got converted into Indian ocean.  The reason for the equatorial movement was the gravitational attraction exerted by the earth’s equatorial buldge.  The other movement of the continents was towards the west, the main reason for this drift as given by Wegener was the tidal force of the moon and the sun on the continents.  North America and the South America got separated from Europe and Africa respectively and the Atlantic ocean came into existence.

Evidence in favour of the Drift theory

Jig-saw Fit evidence:  He was struck by the geographical similarity between the opposing coasts of the Atlantic Ocean.  The outlines of the coast on two sides of the Atlantic are such that they can be easily joined together and one appears to be a detached portion of the other.  The eastern coast of South America can be fitted into the western coast of Africa. Similarly the eastern coast of North America can be fitted against the western coast of the Europe.

Geological structure:  There is remarkable similarity in the geological structure of the lands located on the two coasts of the Atlantic Ocean.  One, the Appalachian mountains of the North America which come right upto the coast and then continue their trend across the North Atlantic Ocean in the fold mountains of South West Ireland, Wales and Central Europe.

Paleo-climatic evidence:  The distribution of the Permo-carboniferous glaciations presents a powerful proof of the fact that at one time these landmasses were assembled together, since the evidences of these glaciations are found in Brazil, Falkland, South Africa, Peninsular India as well as in Australia. It is difficult to explain the distribution of glacial on land and water.  In the opinion of Wegener, all these land masses were united together to form one super mass of land.

Paleontological evidences:  Fossil remains of land animals and plants and of fresh water species in distant lands provide good evidence as they are now separated by oceans.  These species could migrate freely across united continents but not across as intervening ocean.

Polar wandering:  Paleomagnetic studies have shown that there has been periodic change in the position of magnetic pole that it recorded in the rocks by way of permanent magnetism.  It shows the changing position of the earth’s poles in geological time scale.  This is known as polar wandering.  This clearly demonstrates that the continents have frequently moved and changed direction of their motion from time to time. 

Weathering, Mass wasting and Erosion

CHAPTER – IV

WEATHERING, MASS WASTING AND EROSION

Weathering is the disintegration and decomposition of rock in place.  It is a general term applied for a group of processes which act at or near the earth’s surface and reduce solid rock masses by physical disintegration or by chemical decomposition.  It is a process of the breakdown of rocks.

This disintegrated rock debris are called as regolith are subjected to gravity and tend to fall or slip down the slopes especially when aided by the lubricating action of water, though water is not the transporting agent in this case.  This process of gravitational transfer of mass of rock debris down slopes is called Mass wasting.

Erosion is essentially concerned with various ways in which the mobile agencies acquire and remove rock debris.  The principal erosional agents are running water, ground water, wind, glaciers, waves and currents.  Each of the agents does erosion in distinctive processes and gives rise to distinctive landforms.  Basically there are five common aspects

i.                     The acquisition of rock fragments

ii.                   Wearing away the surface through impact of rock materials in transit

iii.                  Breaking down the rock particles by mutual wear while in transit

iv.                 Transportation of the acquired rock debris by moving medium

v.                   Ultimately its deposition somewhere either in transit or at the end.

Factors controlling the weathering:

Broadly speaking four factors influence the rate of weathering – rock structure, climate, topography, and vegetation.

Types of Weathering:

Weathering is of two types – Physical or mechanical and Chemical weathering.  In the physical weathering the rocks are disintegrated by temperature changes, frost action and organism.  While in chemical weathering the rock minerals are decomposed, dissolved and loosened by water, oxygen and carbon dioxide of the atmosphere and soil water and by organisms and the products of their decay.  The physical, chemical and biological agents co-operate with one another actively and both mechanical breaking up or disintegration and chemical decomposition of rocks proceed simultaneously in nature.

The physical or mechanical weathering takes place in four ways. 

i.                     Frost action and crystal growth

ii.                   Thermal expansion and contraction by temperature changes

iii.                  Organic activity

iv.                 Expansion by unloading.

Physical weathering:

Frost action and crystal growth:  This type is found in cold climatic areas.  When water fills the pores, cracks and crevices in rocks and then freezes it expands in volume and exerts a bursting pressure thereby the rocks are ruptured, fragmented and wedged apart.  It is the most effective weathering process in the areas where there is repeated freezing and thawing takes place.

                Closely related to the formation of ice crystals in rocks is the disintegration of rocks by the growth of salt crystals.  The salt crystals form in dry climates as a result of capillary action of water containing salts.  During the long dry period as the water rises to the surface and evaporates, tiny crystal of salt are left behind in the porous outer zone of the sandstone.  The force generated by these crystals lead to grain-by-grain breaking if the sandstone which disintegrates into sand.

Thermal expansion and contraction by temperature changes:  when the rock surfaces are exposed to marked diurnal changes of temperature as in the hot deserts, the alternate heating and cooling results in alternate expansion and contraction which exerts a powerful disruptive force on the rocks.  In the hot dry regions the difference between the day and night temperatures often exceeds 30 degrees centigrade.  The intense heat of the day causes the thin surface layer of the rock to expand and to pull it away from the cooler layer within.  This process of peeling of flakes and curved shells of rock just as in onion is called Exfoliation.

Organic activity:  This type referrers to the action of plants and animals.  As the plant roots grow, they wedge the rocks apart and cause the widening of joints and other fractures.  Organic activity is however, is of great importance in chemical than in physical weathering. Dead organisms produce acids as they decay and thus promote chemical weathering.  Earthworms, ants, termites and other burrowing animals move material to or near the surface where they are more readily subjected to chemical weathering processes.

Expansion by unloading:  unloading occurs when large igneous bodies are exposed through the erosional removal of overlying rock the resultant reduction in pressure.  Igneous and metamorphic rocks formed at great depths are in a compressed state because of the continuing pressure of the overlying rock.  On being exposed to the surface they expand slightly in volume.  Expansion or dilation accompanying the unloading causes thick shells of rock to break free from the parent mass below.  The process which produces thin onion like layers or concentric large scale fractures is called Exfoliation.

Chemical weathering:

In general, chemical weathering is probably more important than physical weathering, this is particularly in the warm and humid climates of the equatorial, tropical, sub-tropical zones, where heat and moisture are abundant.  Water is the main agent of chemical weathering.  Although water in a pure form is almost inactive, but when mixed with oxygen or carbon dioxide it becomes an active chemical agent.  Oxygen, carbon dioxide as well as watervapour are present in the atmosphere in abundant near the earth’s surface. Under this influence the rocks decompose, decay and break into smaller particle size and new secondary minerals are formed.  The chief chemical weathering processes are

i.                     Solution

ii.                   Oxidation

iii.                  Hydration and hydrolysis

iv.                 Carbonation

Solution:  it is a simple process in which the rock salt, gypsum and other minerals get dissolved in the water.  Limestone is not soluble in pure water but gets easily dissolved in rain water which contains carbon dioxide.  In fact atmospheric carbon dioxide is dissolved in all surface waters of the land, including rain water, soil water and river water.

Oxidation:  The presence of the dissolved oxygen in water in contact with mineral surfaces leads to oxidation.  Since some dissolved oxygen is always present in rainwater, surface water as well as sub-surface water oxidation is a universal phenomenon.  The effects of oxidation are most apparent in rocks containing Iron.  Iron rusts or oxidizes under the influence of moisture, as the dissolved oxygen changes the ferrous iron in mineral compounds to the more oxidized ferric state.  When iron combines with oxygen, the original mineral structure is destroyed and the mineral components are free to participate in other chemical reactions.

Hydration and Hydrolysis:  The process of hydration involves the absorption of water.  Most rock- forming minerals absorb rain water.  This not only increases their volume but also produces chemical changes resulting in the formation of new minerals which are relatively softer and more voluminous.  By the process of hydration a hydrite is converted to gypsum and haematite to limonite.  Both these reactions are however reversible upon application of heat, which indicates that there has been no fundamental chemical change.  In hydrolysis, on the other hand, there is a chemical change, and both the mineral and water molecules decompose and react to form new compounds. The significant result of hydration and hydrolysis is that the new minerals formed are more easily attacked by the chemical and physical weathering processes.  The hydrolysis of exposed granite surfaces results in grain-by-grain break-up of the rock, creating many interesting boulder and pinnacle forms by rounding of angular joint blocks.

Carbonation:  Carbonation and hydrolysis are closely linked.  Rain dissolves some carbon dioxide as it falls through the atmosphere, and additional amounts released by decaying organic matter are acquired as the water percolates through the soil.  Carbonic acid particularly attacks minerals which contain iron, calcium, magnesium, sodium or potassium.  These elements are soluble in carbonic acid and the minerals and the rocks containing them start decaying under its influence.  

volcanoes

Volcanoes: The volcanic phenomenon is a majestic natural phenomenon which we can neither prevent nor regulate.  But the ejection is not alike in all the cases.  On the basis of frequency of eruption, there are active, dormant and extinct volcanoes.  The volcanoes which erupt frequently as compared to other are active, best example is Mt. Stramboli.  The dormant or sleeping volcanoes are one which eruption has occurred in the past and every possible chance of eruption is there in the future, the best example is Mt. Vesuvius.  On the other hand Extinct is one where once the eruption had occurred and the possibility of eruption again is ruled out, example is Mt. Kilimanjaro.  Many a time a volcano thought to be extinct may suddenly become active. It happened in case of Vesuvius and Krakatao.

Volcanic types:  Volcanic eruptions are divided into two principal cases based on the modes of eruption

i.                     Central eruption

ii.                   Fissure eruption

CENTRAL ERUPTION:  Eruption is confined to a pipe-like vent and after the eruption, cone and crater structure is developed.  Example is Mt. Cotapoxi of Ecuador. In the central eruption the nature and intensity of the eruption show great variation according to the pressure of gases and viscosity of the lava.  When the lava is acidic meaning more silica content, therefore more viscous, the eruption is explosive.  On the contrary, when the lava is basic meaning, less content of silica, the eruption is peaceful and absence of explosion.

     Volcanoes of the central eruption may be sub divided into five types based on the nature and intensity

i.                     Hawaiian type

ii.                   Strambolian type

iii.                  Vulcanian type

iv.                 Vesuvian type

v.                   Pelean type

Hawaiian type : This type shows less explosion and eruption is peaceful.  Lava is thin basaltic variety.  Pit like crater or lateral cracks develops as lava rivers.  When the wind is strong the lava pieces are stretched into long shiny threads known as ‘Pele’s hair’ in the Hawaiian islands.  Ex. Hawaiian islands, Columbia plateau and Iceland.

Strambolian type : The basaltic lava is not quite as thin as in the Hawaiian type, the gases come either continuously or interruptedly with moderate explosive action.  The explosion is relatively mild, liquid lava fragmental materials are also ejected.  No cloud of black smoke can be seen either in Hawaiian or strambolian type.  This type is majorly found in the stramboli island in the Mediterranean sea.  The lava fountain activity of stramboli, reflected at night as a red glow on the down side of a towering steam plume has caused the volcano to be known as “ light house of the Mediterranean”.

Vulcanian type :  This type has been named after the volcano located in the Lipri islands, north of Sicily in the Mediterranean sea.  Vulcanian activity is explosive.  In this lava is so thick and viscous that it is unable to remain in liquid condition after coming in contact with air and solidifies and seals the mouth of the crater in between two eruptions.  This blocks the passage of the gases from inside, and after sometime when the gases have collected in adequate quantities and their pressure is intense, they force through the solidified vent with explosion.  Masses of black clouds filled with ash and dust rise to great heights and give the appearance of huge cauliflower from a distance.

Vesuvian type : In this type there is a violent explosion due to the intensity of the gases and the lava comes out with great force.  Lava comes out from the lateral cracks, the gases keep on accumulating in the main vent.  When the pressure has eased a little bit on the top on account of the ejection of lava from the lateral cracks, then under the influence of intense gases the lava comes out rapidly with a explosion.  The gases forming cauliflower like clouds.  The clouds rise to great heights and look very shining and bright, causing downpour of ash.

Pelean type : This type of Volcanic eruption is Violently explosively and the lava is highly viscous.  At the time of eruption the dense lava solidifies and closes the mouth of the crater and a dome is formed there.  After sometime, the powerful gases trapped inside either break through this obstacle or come out along the hill slope, and then exceedingly dense mass of hot, highly gas charged lava mixed with fragmental materials and ash flows down the slope like a avalanche.  These have been called “Nuees ardentes”.  This nuees ardentes is extremely dense but highly mobile on account of gases and moves rapidly down the hill slope almost without friction.  It is the most terrifying form of explosive volcanic activity.  It is however, soundless, as in spite of the fact that it has the velocity of winds in a hurricane.

FISSURE ERUPTION:  Lava of basic composition is less viscous and hence less explosive than central eruption.  There is a voluminous lava flow which spreads out over large areas like a thin sheet because of its low viscosity, covering the pre-existing topography.  Such outflows of basaltic lava builds large lava domes, shield volcanoes also lava plains and plateaus.  Basalt emerges from numerous fissures rather than a single pipe like vent, forming a huge plateau or the plain covering larger areas. Examples for this type are Deccan plateau of India, Columbia plateau of USA.

EARTH'S MOVEMENTS

CHAPTER – III

THE EARTH MOVEMENTS

In the beginning there were neither mountains nor oceans, plains or plateaus as familiar to us today.  The powerful internal forces operating from within the crust are called earth movements, both slow and sudden.  They gave birth to all the physical relief features on the earth.  These forces are of two types one, Endogenic and other Exogenic forces these two forces acted continuously and created all the features of today. 

Endogenic forces:  The forces which are acting from inside the earth are called Endogenic forces, which are of two types (i) Diastrophic and (ii) catastrophic movements 

Diastrophic movements:  These are slow forces which act unnoticeably but create most massive structures.  These forces act continuously and witnessed in the upliftment of plateaus or subsidence of crust.  These are of again two types (i) Epierogenic forces and (ii) orogeny forces.                                                          Epierogenic forces are otherwise called as Radial forces as they act along the radius of the earth, resulting in submergence and emergence of the crust.  The continental shelf in the oceans is a result of submergence of the continent and the emergence of the land from the oceans results in the plateau formation eg Siberian plateau.  India is a classical example for the emergence and submergence, the west coast of India from south of Kathiawar up to Malabar is a submergence coast.  The features like Dwaraka and Mahabaleshwaram proves the submergence.  On the other hand the east coast from Malabar till sundarbans represents the emergence, features like backwaters of Kerala, lagoons best represents the emergence.                                                                                                                                                           Orogeny forces, means the mountain building forces.  These forces act tangentially to the earth surface so called as tangential forces.  These are horizontal forces and are of two types compression forces and tensional forces.  Compression forces results in creating Fold Mountains, when two forces are operating toward a centre compression can result forming fold mountains and block mountains example the formation of Alps, Himalayas.  Tensional forces are the forces which are acting away from the centre they result in Faulting & Rifting. Rhine valley in Germany and Vosges mountains are the best examples.

Catastrophic forces:  Unlike the Diastrophic movements these Catastrophic movements are sudden the best examples are Volcanism and Earthquakes.

Earth's Crust

CHAPTER – II

THE EARTH’S CRUST

The outer part of the earth what we see is the Lithosphere.  The word lith means Rock.  Rocks are made of individual substances which are called minerals.  Each mineral usually contains two or more simple substances called elements.  The major element in the earth’s crust is the Silicates.  Quartz, for example has two elements silica and oxygen, united together form a compound known as carbonate of lime. 

Classification of the Rocks

On the basis of the mode of formation rocks are usually classified into three major types.

1.       Igneous rocks

2.       Sedimentary rocks

3.       Metamorphic rocks

Igneous rocks: All rock material at one time are hot, liquid and a sticky thing called Magma.  This rock forming material generally moves towards the surface from 60 – 100 km depths when steam pushes it up through cracks.  It hardens below or upon reaching the earth’s surface.  The hardened rock particle is called Igneous rocks.  Ignis in Latin means Fire.  Igneous rocks are the parent rocks of all other rocks and are known as primary rocks.  Broadly  these are divided into two 1. Extrusive and 2. Intrusive.  Extrusive rocks is the name given to the magma erupting and solidifying of lava on reaching the surface of the earth, the lave cools down rapidly on coming out of the earth’s hot interior, the mineral crystals change their structure and are very small, making them looked fine grained.  These rocks have glassy appearance.  The best example for such a rock is Basalt.  These are extensively found in the northwest of peninsular India called as Deccan Traps.  This material is used for building roads and yields a fertile black soil locally called Regur.  The intrusive rock is formed by solidification of magma at moderate depths beneath the earth’s surface.  The cooling is slow because of great heat at depths and crystals formed are large, best examples are Granite and Dolerite. 

Characteristics:

1.       They are massive having no layers

2.       They are hard and compact

3.       They are free from fossils

4.       They are dark as Basalt or light coloured as Granite depending on silica content

5.       They are crystalline rocks

6.       These rocks are of great economic value, they are associated with the minerals like gold, copper, nickel, zinc, chromite, manganese and rare metals like diamond and platinum.

The intrusive igneous rocks include two types, Plutonic and Hyper bassal.  The rocks solidified at greater depths are called Plutonic igneous rocks and the rocks solidified at intermediate depths are called hyper bassal rocks, these include, batholiths, dykes, sills, laccoliths.  Batholiths are the largest intrusive igneous rock bodies.  They may be 50 km across and hundred kilometers in length.  The batholiths covering smaller areas are called Stocks, having somewhat rounded form and same characteristics.  Laccoliths are huge masses of rocks in roughly mushroom shape or a loaf of bread.  Dykes are near vertical formations from a few meters to kilometers in length.  Sills are the thin sheets of magma in horizontal shape parallel to the layers of existing rocks.

Sedimentary rocks

These rocks occupy three fourth of earth’s crust.  These rocks are formed from sediment accumulation over a long period, usually under low lying areas, meaning, any rock on earth’s surface is exposed to weather changes and to the agents of erosion.  It thus gets broken into fragments, further reduced into small particles called sediments.  These are derived from igneous, metamorphic or even from older sedimentary rocks.  All the sediments are carried by running water, wind or ice.  These are left buried layer by layer at favourable sites, mostly settling down along silent water of a stream or a lake.  The sediments get sorted by the transporting agents like running water, wind, waves; the larger and the heavier particles being deposited first after moving for a relatively short distance.  The smaller and finer particles are carried far away.  But most of the material transported by moving ice are not sorted out and are all dropped together when the ice melts.  As sedimentation is favoured by water, most of the sedimentary rocks have been formed under water.  The Loess is one such example of fine sand carried by wind and deposited as wind borne sedimentary rocks as in northwestern China.  The organic matter derived from plants and animal remains is also the raw material for the formation of the sedimentary rocks in course of time.  Well known examples of sedimentary rocks of organic are coal and limestone.  Another category of sedimentary rocks is the direct precipitation of mineral from their solutions in water.   The rock salt, gypsum, and saltpeter are examples of such chemically formed sedimentary rocks.

Characteristics:  

1.       These rocks are stratified rocks

2.       They have fossils embedded into their layers   

3.       They may be hard like Limestone and soft like lime sandstone

4.       They are the sources of rich aquifers

5.       Most of the rocks have ripple marks left by the water.

Metamorphic rocks:

All rocks undergo changes, when the original character of the rocks- their colour, hardness, texture and mineral composition is partly or wholly changed, it gives rise to metamorphic rocks, under favourable  conditions of heat and pressure.  Metamorphic means change of form in Greeck language.  The process of metamorphism takes place at depths under the pressure of overlying rocks or as a result of contact with a hot igneous material.  The formation of metamorphic rock under the stress of pressure is called Dynamic metamorphism.  In this case the Granite is converted into Gnesis, Clay and Shale into Schist at great depths.  The change of form or re-crystallisation of minerals under the influence of high temperatures is known as Thermal or Contact metamorphism.  In areas of mountain building or volcanism, molten matter is injected into the existing layers of rocks near the surface.  Such a contact with heat turns the rocks into Metamorphic rock.  Here, Sandstone is changed into Quartize; clay and shale into Slate, Coal to graphite and limestone into Marble.

Charateristics:

1.       These rocks are of great hardness

2.       They have closely banded structures and interlocking of crystals

3.       They contains precious stones and minerals like Rubies, Gems & Sapphires.

ROCK CYCLE

All rock materials originating from beneath the earth’s surface form igneous rocks.  As soon as igneous rock is exposed to weather on the surface of earth, it is eroded by various agents.  The material changes into sedimentary rocks at some place and at some point of time. Either of the two rocks are likely to change into metamorphic rocks in course of time.  A change into sedimentary rock takes place at the earth’s surface and conversion into a metamorphic rock takes place within the crust of the earth.  The sedimentary rocks may again be buried so deep that they melt forming igneous rocks.  The change of one rock into another type under different conditions is known as rock cycle.  The matter of earth’s crust is not lost and the process changing one form to another becomes cyclic.

The sources of energy powering this cycle are two.  one, the heat inside the earth which is capable of melting the existing rock.  It may also bring about the changes within the remaining rock.  Second, is the solar energy responsible for breaking and decomposing the rocks on earth’s surface for converting them into sedimentary rocks.  Deep burial and strong compression during volcanism activity may also change the sedimentary into metamorphic or igneous rock.  The metamorphic rock can also furnish sediments to produce a sedimentary rock.  All known materials in the form of minerals and rocks are defined as mineral matter.  Throughout hundreds of millions of years, the rock cycle has been re-cycling the mineral matter of the earth’s crust.

GEOMORPHOLOGY

INTERIOR OF THE EARTH

Man with his technological up gradation had send the rovers like “Curiosity” to the other planets and even the instruments like “Voyeger-1 and voyager-2” to the areas beyond Neptune (area recently named as Magnetic Highway).  Exploring the earth beneath our feet is a more difficult task than mapping the moon.  The deepest drill on this earth till date is near the kola peninsular of just 12 kms deep.  Direct observation of the earth’s interior is not possible because of the tremendous heat energy inside the earth but there are certain indirect sources through which we can able to know what is there inside the earth.  The sources which provide the knowledge about the inside of the earth can be grouped into two.

1. Natural sources

2. Artificial sources

Natural sources like Volcanism, Seismology and evidence from meteorites, where as the artificial sources like Temperature, Densityof its different shells & the pressure inside the earth.  It is these sources which provide enough knowledge about the interior of the earth. By using seismograph a graphic recording of the earthquake waves or vibrations is made.  An earthquake occurs when ever a rock breaks inside the earth, this will release energy in the form of waves called seismic waves, Seismic waves are vibrations in Earth caused by the rupture and sudden movement of rock, they will travel all over the globe just like ripples in the well.  The seismic waves are of two types

1.       The Body waves

2.       The Surface waves.

  The body waves are those waves which travel through the earth’s interior and are of two types, Primary waves denoted by the letter P and the Secondary wave denoted by the letter S.  The surface waves are those waves which travel along the surface of the earth for long period waves and are denoted with the letter L, these are of two types, one Rayleigh waves denoted by R and the Love waves denoted by Q.

Primary waves: also called Longitudinal waves or compression waves which are analogous to the sound waves wherein particles move both to and fro in the line of the propagation of the wave.  These waves travel faster through solids, though, these also travels through liquids and gaseous but their speed is slowed down.

Secondary waves:   also called as transverse waves which are analogous to the light waves.  These can travel only through solid media couldn’t travel through liquid or gaseous media.

Surface waves:  also called Long period waves or simply L waves. These affect the surface of the earth and die out at smaller depths.  Though their speed is less than P and S waves but these are most violent and destructive.

There is a change in the course and velocity of the waves on crossing the boundaries of different zones inside the earth.  If the ground through which the wave travels is solid, they behave in one way.  If it is liquid, the waves behave in a different way.  Their velocity in both the cases differs for example the velocity of the P and S waves increases with depth but up to 2900kms.  Afterwards, S wave passing across the direction of their movement do not pass and the P waves travelling in the direction of their movement generally pass at a reduced velocity.  The long L waves do not pass and do not go deeper in the earth.  The S waves cannot pass through a liquid and are transmitted only through a rigid solid body.  The velocity of the P waves passing through inner core again increases as compared to their passage through the outer core.  This data briefly point out that the inner core of the earth is solid iron core and the outer core has probably the properties of a liquid.  It may be concluded that as a whole behaves like a solid even when the parts of its interior are reported to be in a plastic or semi- liquid state.  The rock samples from various depths have also provided the evidence of the density of the materials. 

    The Meteorites belonging to our solar system are another source of our information for a better understanding of the earth’s structure.  The meteors outer layered burnt during their fall to the earth, as the stony material of the meteorites are similar to those found on the earth’s surface, these are scarcely recognized.  But the composition of the heavier materials confirms the similar composition of inner core of the earth. 

Temperature and Pressure:  The evidence of the volcanic eruptions and the hot springs indicate that high temperatures prevail in the interior of the earth.  A progressive rise in the temperature with the increasing depth is recorded in mines and deep wells all over the world, the average rate of the increase being 1 degree for every 32 meters of descent.  Normally, at this rate of increase in temperature, the rocks at great depths should be in a liquid state.  At one time, on the basis of this view, it was accepted that thin solid crust of the earth was perhaps resting on a molten core.  But the behavior of the earthquake waves as hinted above has led us to revise our views.  The rate of increase in temperature is now considered to be variable and there is no uniform increase from the surface to the centre of the earth.  The rate of increase in the overlying pressure makes the melting point higher but only to a certain degree.  In upper 100kms, the increase is estimated at 12 degrees per km.  it is 2 degree centigrade per km in the next 300km and 1 degree per km below it.  By this calculation the temperature is actually 2000 degree centigrade at the core of the earth.  The heat or rise in temperature is the result of internal forces, automatic disintegration of radioactive substances, chemical reaction and other sources keeping the earth’s interior hot.  It indicates the liquid or perhaps the gaseous conditions prevailing at the greater depths.  But at the same time there is a tremendous increase in the pressure of overlying layers on earth’s interior.  Thus, even under extremely high temperature towards the central part of the earth, the liquid nature of its core has acquired the properties of a solid and is probably in a plastic state.  The earth is rigid and behaves mostly as a solid down to a depth of 2900 km because of such pressure conditions.  Wherever even a slight release of pressure occurs, the underlying matter escapes to the surface and becomes molten because of high temperatures prevailing there.  While solid material melts inside the earth, the liquid also takes up the properties of a solid as alluded above.

DENSITY: The velocity and the path followed by earthquake waves, temperature and pressure conditions inside the earth tell us of varying physical properties, density and composition prevailing there.  The structure of earth’s interior is therefore layered.  The arrangement of layers is comparable to onion with its shells, one inside another.  The inside of the earth has a shallow crust as thin as an eggshell which can be compared with the size of a ball.  Below the surface capped by the sedimentary material, upper layer of the crust is mainly composed of crystalline igneous and metamorphic rocks, acid in nature.  The lower layer of the crust has basaltic and ultra basic rocks.  The layer of heavier or inner silicate is not found beneath oceans.  The oceans are mostly under laid by a thick greenish and tremendously hot layer.  The continents are composed of silicates termed as SIMA or silica and Aluminium.  The oceans have heavier silicates named SIMA or silica and Magnesium.  The continents of lighter material are floating in a sea of heavier and denser material.  The central core has the heaviest mineral materials of highest density.  It is composed of NIFE or Nickel and Ferrous.  A zone of mixed heavy metals and silicates separates the core from the other layers.

Based on the chemical composition of the earth’s interior, different scientists have given different views about the interior of the earth.

1.       Edward Suess has identified three zones of different matter below the outer thin sedimentary layer.

SIAL : It is located just below the outer sedimentary cover.  It composed of Granite.  This layer is dominated by Silica and Aluminium – SIAL.  The average density is 2.9 whereas thickness ranges between 50 – 300 kms.  Continents have been formed by sialic layer.

SIMA : It is located just below the sialic layer.  This layer composed of basalt and is the source of Magma and Lava during the volcanic eruptions.  Silica and Magnesium are the dominating materials in this layer.  Average density of this layer is 2.9 to 4.7 whereas the thickness varies from 1000km to 2000km.

NIFE :  It is located just below the SIMA layer.  This layer is composed of Nickel and Ferrium.  It is thus apparent that this layer made of heavy metals which are responsible for very high density.  The diameter of this zone is 6880 km.  The presence of the Iron (ferrium) indicates the magnetic property of the earth’s interior.  This property also indicates the rigidity if the earth.

2.       Van Der Gracht has identified 4 layer system of the composition of the earth.

Outer sialic crust : This layer varies in thickness, under the continents it is 60 km and under the oceans it is 20km esp Atlantic ocean, completely absent under the Pacific ocean. Density of this layer is between 2.75 to 2.9

Inner silicate mantle : it extends between 16km to 1140 km and has the density of 3.1 to 4.75.

Zone of mixed metals and silicates : the thickness of this layer from 1140km to 2900km where as the density of this layer varies between 4.75 to 5.0

Metallic nucleus : This layer thickness is from 2900km to 6371km and density is 11.0.

It appears that there are different opinions about the number, thickness and density of the layers.  In order to avoid the confusion a commonly accepted view has been brought by majority of the scientists.

     The scientific study and the analysis of various aspects of seismic waves – mainly its velocity and path of the waves, also the earthquakes have enabled the scientists to unravel the mystery of the earth’s interior.  Three zones of varying properties have been identified in the earth e.g. crust, mantle and the core.

CRUST:  The very first layer of the earth is the Crust, it extends up to a depth of 50 km on an average.  It is divided into two the Oceanic crust and the Continental crust, the oceanic crust is denser as it is made up of basalt rock which is denser than the granitic rock, with which the continental crust is made of.  The thickness of the crust is more under the continents the thickness is less under the oceans.  This crust based upon the depth is again divided into two, outer and lower crust.  The average density of the outer and lower crust is 2.8 and 3.0 respectively.  This difference in the density is because of the Pressure of superincumbent load.  The formation of the minerals of the upper crust was accomplished at relatively lower pressure than the minerals of the lower crust.

MANTLE: It is the second layer just below the crust, it extends up to a depth of 2900 km inside the earth.  This mantle is divided initially into two zones based on the changes in the velocity of seismic waves and density, the upper mantle and the lower mantle.  The upper mantle starts from 50 km and extends up to 1000km and the lower mantle from 1000km to 2900km but now the mantle is divided in to three based on the information received from the discovery of International Union of Geodesy and Geophysics.  (i) first zone extending from the crust to 200km depth. (ii) Second zone extends from 200km to 700km and  (iii) third zone extends from 700km to 2900km depth.  The velocity of the seismic waves relatively slows down in the upper most zone of the mantle for a depth of 100 to 200 km.  This zone is called the zone of low velocity, i.e the rocks here are in the semi molten or Gel like form, this layer is also called as Asthenosphere.   There is a sudden increase in the velocity of the seismic waves at the base of the lower crust and the upper mantle this trend of seismic waves denotes discontinuity.  This discontinuity was discovered by Mohorovicic in 1909 and thus it is called as Moho discontinuity. 

CORE:  The core, the deepest and the most inaccessible zone of the earth, extends from the lower boundary of the mantle at the depth of 2900km to the centre of the earth.  The mantle  - core boundary is determined by the “Weichert – Gutenberg Discontinuity” at the depth of 2900km there is a pronounced change in the density of the core from 5.5 to 10.0, this sudden change in the density is indicated by sudden increase in the velocity of P waves along the mantle core boundary i.e the Gutenberg discontinuity.  The density further increases from 10.0 to 13.0 with the increasing depth of the core.  Thus it appears that the density of the core is twice the density of the mantle.  The core is further divided into two zones the outer and the inner core, the dividing line being at the depth of 5150km.  S, waves disappears in this outer core indicating it as molten state.  The next layer is the inner core which extends from 5150km to 6371km i.e the centre of the earth.  The density of this layer is 13.0 where the P waves travel at greater velocity than that of the outer core indicating this layer as  a solid zone.  It is believed that the core is composed of Iron and Nickel and so it the most density part in the interior of the earth.

catastrophic theories

CATASTROPHIC THEORIES

Planetesimal Hypothesis :  Mr. Chamberlin along with an astronomer Moulton postulated this theory in 1905.  According to Chamberlin, our sun is a proto-star which was formed of solid particles and was cold and circular in shape.  There was another star, termed as intruding star which was destined to pass very close to the proto-sun.  when the intruding star came very close to the proto-sun infinite number of small particles were detached from the outer surface of the proto-sun due to the massive gravitational pull exerted by the giant intruding star.  Chamberlin called these detached small particles as planetesimals.  Initially, the detached particles were just like dust particles.  These particles are not of uniform size, the large particles attracted the smaller planetesimals thus numerous particles were added to the larger planetesimal called nuclei, around this nuclei remaining dust particles started accumulated to form other remaining planets.  With the passage of time, the remaining proto-sun changed into present day sun.  The satellites of the planets were created due to the repetition of the same processes and mechanism.

Tidal Hypothesis : Sir James Jeans, a British scientist propounded this theory in 1919 along with other scientist by name Harold Jeffery.  According to them initially the sun is a giant incandescent gaseous mass of matter, besides the sun, there was another star termed as intruding star.  There was a great impact of the tidal force of the intruding star on the surface of the primitive sun.  The intruding star was continuously moving along such a path that it was coming nearer to the primitive sun, its gravitational force went on increasing and became maximum, with the result a giant Cigar shaped tide of matter ejected from the primitive sun, thousands of kilometers in length was created.  This ejected cigar shaped matter Jeans called this as filament, which was thicker in the centre and thinner and sharper at the ends.  This shape is because, when the intruding star was at distant place, it could exert less pull and when it comes near to the primitive sun the force of attraction increased to maximum.  Therefore the shape of matter ejected is in the shape of a cigar.  The formed cigar or the filament later on cooled to get contract and broke into smaller pieces and each piece condensed to form one planet.

 Binary star Hypothesis: This theory is based on the dualistic concept in 1937 postulated by Mr. Russell.  According to him there were two stars neat the primitive sun, in the beginning the companion star was revolving around the primitive sun.  Later on one giant star, the third star approached the companion star but the direction of revolution of the approaching star was opposite to that of the companion star.  Thus, large amount of the matter from the companion star was attracted towards the giant approaching star because of the gravitational pull.  This ejected matter started revolving in the direction of the giant approaching star and thus opposite to the direction of the revolution of companion star.  Later on planets were formed from the ejected matter.  In the beginning the planets might have been nearer to each other and thus matter might have ejected out from these planets due to the mutual attraction and thus satellites might have been formed from the matter.

Super Novae Hypothesis: Propounded by Mr. Hoyle in 1946, this theory is based on the principles of Nuclear physics.  According to Hoyle initially there were two stars one primitive star and the two companion star.  This companion star later on became supernova due to the nuclear reaction.  It may be pointed out that every star will be emitting the energy in the form of light, heat, etc., is generated by the process known as Nuclear fusion, where in atoms of lighter elements combine under intense heat and pressure to form atoms of heavier elements, releasing a vast amount of energy.  The stars generally contain Hydrogen this slowly combine with each other to form Helium which is a heavier atom than hydrogen.  In this process vast amount of energy is also released. This same reaction was also going on in Hoyle’s primitive sun and companion sun but the rate of nuclear fusion was many times greater in the companion star. With the passage of time all the hydrogen of the companion star was consumed and got collapsed by exploding violently this Hoyle called as Supernova.  This explosion resulted in spread of enormous gaseous matter and mass of dust which started revolving around the primitive sun.  Thus the matter and dust became building material for the formation of future planets.

Non catastrophic theories

Non - Catastrophic theories

Gaseous Hypothesis :  Immanuel kant, the German philosopher, presented this hypothesis in 1755.  His theory is based on the Newton’s laws of gravitation and rotatory motion.  According to Kant, there was a primeval, slowly rotating cloud of gas, (now called nebula) and matter comprised of very cold, solid and motionless particles.  He further assumed that these particles began to collide against each other under their mutual gravitational attraction.  This collision generated random motion in the primordial matter along with the frictional force which generated heat energy as a result the primordial matter got heated up and started up rotating.  The rise in temperature also changed the state of matter from solid to gaseous, thereby the rotating matter started to move as a nebula.  With continuous rise in temperature and rate of rotatory motion the nebula started expanding in size. 

     According to Immanuel kant as the heat increased, the size of nebula increased and as the size of nebula increased, the angular velocity or rotatory speed further increased.  Due to continues increase in the size of nebula the speed of rotation become so fast that the centrifugal force exceeded the centripetal force.  The nebula started spinning so rapidly that an irregular ring was separated from the middle part of the nebula and was ultimately thrown off due to centrifugal force, by repetition of the same process eight concentric ring were separated from the nebula.  The residual central mass remained as the sun.  The irregularity of the rings caused the development of the cores for the formation of the corresponding planets. In other words, all the matters of the each ring were aggregated at a point to form and ultimately grew as planets in due course of time.

 Nebular Hypothesis : This was propounded by the French mathematician Laplace in 1796.  This hypothesis is just the modification of the kant’s hypothesis.  According to Laplace, there was a huge and hot gaseous nebula in the space and from the very beginning this huge and hot nebula was rotating on its axis, therefore because of the rotation the nebula continuously cooling due to loss of heat from its outer surface through the process of radiation and thus it was continuously reducing in size due to the contraction on cooling.  As the size of the nebula continued to reduce in size, the velocity of the rotatory motion continued to increase.  Thus nebula started spinning at very fast and consequently the centrifugal force became so great that it exceeded the centripetal force, when this stage was reached the material at the periphery  that is the outer layer cooled and contracted so it couldn’t rotate with the same velocity of that of nuclei and was separated from the remaining part of the nebula.  This separated ring of material started moving around the nebula.  This original ring further divided into eight rings and each ring moved away from each other.  All the materials of each ring condensed at a point in the form of hot gaseous agglomeration.  Each such agglomeration was later cooled and condensed to form planet.

INTRODUCTION

The word Universe is derived from French word “Univers”, which means “All turned into one”.  The Universe is everything that we can perceive.  In 1927, the Belgian priest Georges Lemaitre proposed that the Universe began with the explosion of a Primeval atom, which he called this as “BIG BANG THEORY”, his proposal came after observing the Red shift in distant nebulas.  The Red shift, in simple means, the displacement of spectrum lines towards the red end of the visible light.  Years later, Edwin Hubble found experimental evidence to help justify Lemaitre’s theory.  He found that distant galaxies in every direction are going away from us with speeds proportional to their distance.  Finally, the big bang theory received its strongest confirmation when Radiation was discovered in 1964 by Arno Penzias and Robert Wilson, who later won the Nobel prize for this discovery. 

    The Universe is the vast and infinite space having millions of galaxies.  It is estimated that the age of our universe is between 15 and 20 billion years old.  The three most common elements in the universe are: 1. Hydrogen 2. Helium and 3. Oxygen.  However, Hydrogen comprises around 90 percent of all matter in the universe.  About 70 percent of the universe has dark energy and 25 percent consists of dark matter.  It is only 5 percent of the universe is visible to us. 

The Origin of the Earth

Our solar system is a small part of the system of stars collectively called Milky way.  It consists of more that thousands million of stars.  Like other stars, the Sun with its solar system is revolving around the centre of the Milky way, there are several theories which explain the formation of the solar system, in which earth is a part.  These theories can be broadly classified under two groups called Catastrophic and Non catastrophic theories. 

The catastrophic theories like

Planetesimal Hypothesis of Chamberlin

Binary star Hypothesis of Russell and Littleton

Super Novae Hypothesis of Hoyle

Tidal Hypothesis of James Jeans

     The Non-catastrophic Hypothesis like
 Gaseous Hypothesis of Immanuel Kant
 Nebular Hypothesis of Laplace.

content

CONTENTS

PART – I

INTRODUCTION

GEOMORPHOLOGY

• 1.       Interior of the Earth
• 2.       The Earth’s crust
• 3.       Vulcanism and Earthquake
• 4.       Weathering and mass movement
• 5.       Continental drift & Plate tectonics
• 6.       Landforms

 CLIMATOLOGY

• 1.       Atmosphere composition and structure
• 2.       Insolation and Heat budget
• 3.       Temperature Humidity and Precipitation
• 4.       Air pressure and Winds
• 5.       Air masses, Fronts and Cyclones
• 6.       World climate

OCEANOGRAPHY

• 1.       Relief of Ocean basins
• 2.       Salinity
• 3.       Ocean deposits
• 4.       Ocean currents
• 5.       Ocean tides and waves
• 6.       Coral reefs and Atolls
• 7.       Marine resources

BIO GEOGRAPHY

• 1.       Biosphere : an Eco system
• 2.       Soils of the world
• 3.       Biomes of the world

ENVIRONMENT GEOGRAPHY

• 1.       Man and Environment symbiosis
• 2.       Global warming
• 3.       Climate change and recent conventions
• 4.       The Cryosphere
• 5.       Bio-diversity & Hotspots, Biosphere reserve and wildlife           conservation
• 6.       Environmental Impact Assessment – EIA
• 7.       Disaster management

PART – II

INDIAN GEOGRAPHY

PHYSICAL GEOGRAPHY OF INDIA

• 1.       Origin of peninsular India
• 2.       The Himalaya
• 3.       The Great Northern Plains

DRAINAGE

• 1.       The Drainage pattern
• 2.       Indian river systems – Himalayan & Peninsular
• 3.       Interlinking of the rivers

CLIMATE

• 1.       Introduction to Indian climate
• 2.       Monsoons
• 3.       Jet streams and Tibetan plateau
• 4.       El-Nino, La-Nina and ENSO
• 5.       Seasons in India
• 6.       Rainfall in India and its variability
• 7.       Climatic regions of India
• 8.       Drought and Floods

NATURAL VEGETATION

• 1.       Distribution of the natural vegetation
• 2.       Classification of forests
• 3.       Endemic species
• 4.       Social forestry and conservation
• 5.       Wildlife and conservation
• 6.       Mangroves

SOILS

• 1.       Characteristics of the Indian soils
• 2.       Classification of soils
• 3.       Problems and conservation

ECONOMIC GEOGRAPHY

RESOURCES

• 1.       Mineral resources
• 2.       Energy resources

AGRICULTURE

• 1.       Land reforms
• 2.       Characteristics of Indian agriculture
• 3.       Green revolution
• 4.       Problems in Indian agriculture
• 5.       Cropping patterns
• 6.       Agro climatic regions of India

INDUSTRIES

• 1.       Industrial development in India
• 2.       Industrial clusters, Industrial policy and Globalization
• 3.       Iron and steel industry
• 4.       Textile industry
• 5.       Fertilizer industry
• 6.       Pharmaceutical industry
• 7.       Special economic zones

TRANSPORT & TRADE

• 1.       Land , water and air transport
• 2.       Trade policy, Balance of Trade

SOCIAL GEOGRAPHY

CULTURAL SETTINGS

• 1.       Races in India
• 2.       Demographic features
• 3.       Literacy
• 4.       Age composition
• 5.       Sex ratio
• 6.       Migration
• 7.       Human development index
• 8.       Urbanization