Geographical Set Up: India takes its standard time from the meridian of 82 30 E, which is 5 ½ hours ahead of Greenwich Mean time ( 0 longitude).Pakistan time is 5 hours ahead of GMT and Bangladesh time is 6 hours ahead of GMT.
Significance of Location: Barring the plateau of Baluchistan (which form part of Pakistan), the two great ranges of Sulaiman and Kirthar cut it off from the west. Along the north, the great mountain wall formed by the Hindukush, Karakoram and the Himalayas, which is difficult to cross, cuts it off from the rest of the continent. Similarly, the southward of-shoots of the Eastern Himalayas separate it from Russia. The tropical monsoon climate of India, which ensures a fair supply of moisture and forms the basis of farming in India, is also a result of its location in the southern part of Asia. Since the opening of Suez Canal (1867) India’s distance from Europe has been reduced by 7,000km. It thus bridges the space between the highly industrialized nation of the west and the semi-arid, and south-western Asia and the most fertile and populated regions in the south-east and far-east countries.
PHYSIOGRAPHIC UNITS OF INDIA
| S.NO | UNITS | AREA KM (Sq) (appro) | % OF TOTAL AREA |
| 01 | Northern mountains | 578,000 | 17.9 |
| 02 | Great Plains | 550,000 | 17.1 |
| 03 | Thar Desert | 175,000 | 5.4 |
| 04 | Central Highlands | 336,000 | 10.4 |
| 05 | Peninsular Plateaus | 1,241,000 | 38.5 |
| 06 | Coastal Plains | 335,000 | 10.4 |
| 07 | Islands | 8,300 | 0.3 |
The Trans Himalayas or Tibetan Himalayas: The largest glaciers are Hispar and Batura (over 57 km long) of Hunza Valley and Biafo and Baltaro (60 km long) of Shigar Valley. The Siachen of Nubra Valley is the longest with a length of over 72 km.The Purvachal or the Eastern Hills: In the east after crossing the Cihang gorge the Himalayas bend towards south forming a series of hills running through Arunachal Pradesh, Nagaland, Manipur, Mizoram, Tripura and eastern Assam and form the boundary between India and Burma. Brahmaputra rivers divide Himalayas into three sections: the main Himalayas, the northwest Himalayas and the southeast Himalayas. The main Himalayas running from the Pamir Plateau in the northwest to Arunachal Pradesh in the southeast are the youngest mountains in the world. The highest peak of the word, the Mount Everst(8,884m, named after Sir George Everst). There are about 140 peaks in the Himalayas whose elevation is more than the Mount Blanc (4,810m),the highest peak of the Alps. The three mountain ranges: the Himadri in the north(the greater Himalayas)the Himachal in the middle(the lesser Himalayas) and the Siwalik(the Outer Himalayas),facing thr palins of India. The Himadri is of grat elevations (6,000m) which remains covered with everlasting snows. The Siwalik have some flat-floored structural valleys knowns as duns. Dehradun is well-known. Between the Himadri and the Himachal are some broad synclincal valleys. We also classify them as Punjab Himalayas, Kumayun, Assam Nepal and Northern.
Significance of Himalayas: (i) Physical Barriers (ii) Birthplace of Rivers (iii) Influence on climate (iv) Flora and Fauna (v) Mineral Resources (vi) Economic Resources (vii) Tourist
II The Great Northern Plains:
Lies between the great Himalayas in the North and the plateau of Peninsular India in the south. Nearly 2400 km long around 250-320 km broad, the most extensive plan indeed. It is said that this region was once a vast depression, filled with silt – brought down by the three Himalayas River, namely the Indus, the Ganga and the Brahmaputra and their numerous tributaries. It contains some of the richest soils. The bhangar refers to the upland formed by deposition of older alluvium in the river beds and the Khadar are lowlands formed by deposition of detritus of new alluvium in the river beds.
Bhabar and Terai: Includes those regions where the Himalayas and other hilly regions join the plains. Coarse sand and pebbles are deposited. Bhabar lands are narrower in the east and extensive in the western and north-western hilly. Water converts large areas along the river into swamps known as Terai.
The Western or Rajasthan Plains: are known as Marusthali of Thar and the adjoining Bagar areas to the west of Aravalli. Luni whose water is sweet in the upper reaches and saltish by the time is reaches the sea. The several salt lakes in the region such as the Sambhar, Degana, Kuchaman and Didwana; from which table salt is obtained. In most of the region shifting sand dunes occur.
The Punjab-Haryana Plain: These plains owe their formation to the Sutlej, the Beas and the Ravi rivers. Many low lying flood plains (called bets) are found here. The Bari Doab between Ravi and Beas rivers, the Bist Doab between the Beas and Sutlej and the Malwa plain are relatively more fertile plain.
The Ganga Plain: The Ganga-Yamuna Doab comprising the Rohilkhand and the Avadh Plain is the tile area that is drained by the tributaries of Ganga.
The North Bengal Plains: the Plains extending from the foot of Eastern Himalayas to the northern limb of Bengal basin cover an area of 23,000km2.
Brahmaputra Plains: This is a low level plain, rarely more than 80km broad, surround by High Mountain on all sides except on the west.
Significance of the Great Plains: Riverine region, Fertile soil, favorable climate, flat surface, constructions of roads, extensive system of irrigation.
The Peninsular Plateau: oldest structure of the Indian subcontinent whose slow and steady movement towards north and north-east has been responsible for creation of the Himalayas and the Northern Plains in place of the Tethys sea of geological time. It is marked of from the Indo-Gangetic plain by the mountain and hill ranges such as the Vindhyas, the satpura, and Mahadeo, Maikal, and Sarguja ranges with the average height is usually divided into two major subdivisions with the Narmada valley as the line of demarcation. The region north of the Narmada valley is known as the Central Highlands and in south of the Narmada valley lies the Deccan Plateau.
III The Central Highlands:
Old Aravalli Mountain on the west and the Vindhyas on the south. This region slopes northward to the Ganga plains. The western part of the Central highlands is known as the Malwa Plateau. The Central part has a number of small plateaus like those of Rewa, Baghelkhand and Bundlekhand. The eastern part of the Central Highlands comprises the Chotanagpur plateau.
The Deccan Plateau: The Deccan Plateau extends from the vindhyas to the southern tip of the Peninsula. This triangle plateau is at its widest in the north. The Vindhya Range and its eastern extension namely Mahadev hills Kaimuir Hills and Maikal Range from its northern edge. Western Ghats are known by different regional names such as the Sahyadris in Maharastra and Karnataka, the niligris in Tamil Nadu and Annamalai and the Cardamon hill along the Kerala and Tamil nadu border. The elevation of the ghats increases towards the south. The highest peak, Anaimudi (2,695 m) is in Kerala. The most important gap in the Western Ghats is the Palghat gap which links Tamil Nadu with Kerala. The Bhorghat and the Thalghat are other gaps lying in Maharastra state.
Eastern Ghats: These hills rise steeply from the Coromandel coastal plain. The Eastern Ghats are well developed in the region between the Godavari and Mahanadi rivers. The Eastern Ghats and Western Ghats converge in the Nilgiri hills. Dodda Betta (2,637 m) is the highest peak in the Nilgiri hills.
Significance of Peninsular Plateau: (i) Geological richness (ii) Sources of Irrigation and hydroelectricity (iii) Agricultural Resources (iv) Forest Resources (v) Rich Fauna
(vi) Cultural Influences.
IV THE COASTAL PLAINS AND ISLANDS
The Coastal plains: The Peninsular plateau is bounded by coastal plains on the east and west. There is wide difference between the eastern and western coastal plain. The west coast is narrower but wet. East coast much wider but relatively dry. A number of river deltas occur on the east coast. The deltas of east coast from the ‘granary’ of the five southern states- Andhra Pradesh, Tamil Nadu, Karnataka, Kerala and Pondicherry. The western coastal strips which have a large number of lagoons and back waters on other hand are noted for spices, areca nuts, coconuts palms etc.
Western coastal Plain: These lies between the Western Ghats and the Arabian seas and stretch from Kutch in the north to Kanyakumari in the south. The Gujarat plain is a broad and flat plain. The Kutch Peninsula, Gulf of Kutch, and the Gulf of Cambay. The Kathiawar Peninsula, also known as Saurashtra which lies to the south of Kutch, is also a plain level area except for some hills rising into Mount Girnar. Sun-divided regionally into the Konkan coast in Maharastra Canara coast in Karnataka and Malabar Coast in Kerala.
Eastern Coastal Plain: The eastern coastal low lands extend from the mouth of the Ganga to Kanyakumari. The northern half is called Northern Circars or Kalinga coast, while the southern half is known as the Coromandal coast. The border part is the Carnatic region, which is about 480 km wide. They are not suitable for harbours as their mouths being full of sit.
Significance of Coastal plains: (i) Harbours (ii) Specialized crops (iii) Fisheries and Navigation (iv) Economic Influence (v) Historical Importance
V ISLANDS
1.Bay of Bengal Islands: The Andaman & Nicobar group of islands are separated by 10 Degree channel. These islands have been formed by extension of tertiary mountain chain of Arakan Yoma. The Andaman group of island is divided into 3 major groups’ viz., North Andaman, Middle Andaman and south Andaman, collectively called Great Andamans. Little Andaman is separated from Great Andamans by Duncan passage. The Nicobar group of islands of which Great Nicobar is largest and southern most one. Saddle peak situated in Andaman Islands is the highest peak of Andaman & Nicobar group.
The Dhuliar peak is the highest peak of Nicobar group of islands.More habitable and different origin thanofArabian sea islands. Barran island is dormant volcano and Narcondam island is extinct volcano.
2) Lakshwadeep islands: Coral- More Muslim population and have fringing reefs. They are 25 small island groups. The island’s north is known as Amindivi and spot is Cannonore island. Extreme south is Minicoy islands which is largest.
CLIMATE REGIONS
1. Tropical Rainy climate Region: This region has consistently even temperature, which stays above 18 C even in December, April, and May are the hottest months, the temperature varying from 18 C to 27 C. July and August are the coolest months, which copious rainfall. The average rainfall exceeds 250cm, which encourages wet evergreen forests. The western coastal strip, Western Ghats, south of Bombay, Meghalaya, western Nagaland and Tripura come in this climatic region.
2. Tropical Savanna Region: The chief feature of this climate is the long dry period. Temperature even in winter stay above 18 C, and in summer may even go up to 46 c. Rainfall, except in the southeastern parts, is in summer and averages about 100cm. In the south eastern parts, the retreating monsoons bring sufficient rains. A major part of the southern peninsula, except the arid tract lying east of the Western Ghats, northeastern Gujarat, south Bihar, major parts of Madhya Pradesh, Orissa, northern Andhra Pradesh, eastern Maharastra, and eastern TamilNadu coast come under this region.
3. Tropical Steppe Region: The average temperature is over 27 C, the lowest temperature being about 23 C April and May are the hottest months, when temperature may rise over 30 C. Average rainfall being less than 75cm, the region comprises a part of the famine zone of the country. The southwest monsoons bring rain to this region. The region comprises the rain shadow areas lying east of the Western Ghats and covers Karnataka, interior TamilNadu, western Andhra Pradesh and central Maharastra,
4. Sub-Tropical Steppe Region: The average temperature rises over 27 C and as high 48 C is recorded during summer. Rainfall from the southwest monsoon averages between 50 to 75 cm. It often fails, leading to widespread drought conditions. This region comprises tracts stretching and encompassing western Rajasthan and northern Gujarat.
5. Tropical Desert Region: The summer Temperature rises over 48 C, while in winter it goes down to 1 C. May and June are the hottest months. Average rainfall is 12.5 cm and very unreliable. Excessive evaporation during summer and intense cold during winter hinder crop production except through river irrigation. Western Rajasthan and parts of Kutch, which are purely sandy plains, come in this region.
6. Humid Sub-Tropical Region: Summer temperatures are 46 C to 48 C. Average rainfall, mostly from summer monsoons, is about 62.5 cm, which increases to over 250cm in the east. Winters are virtually dry. This region is spread over the foothills of the Himalayas, eastern Rajasthan, plains of U.P, Bihar, northern Bengal, part of Assam and Arunachal Pradesh.
7. Mountain Region: Average temperature in June is 15 C to 17 C, in winter it goes below 8 C. On the northern slopes of the Himalayas, the rainfall is scanty, about 8-10 cm, but the western slopes enjoy a heavy rainfall of over 250 cm. The entire Himalayan belt comprising both the trans-Himalayas and the main Himalayas come under this region.
THE PENINSULAR PLATEAU
The Peninsula plateau is roughly triangular in shape with base coinciding with southern edge of the great edge of the Great Plains. It covers a total area of 160,000km 2. (About half of total land area of the country)
The Plateaus of Peninsular India
1. The Marwara Upland: It lies east of Aravali range made up of stand stone, shales and limestone of Vindhayan period. The upland is drained by Banas River originating in Aravali range.
2. The Central Highland: Also called the Madhya Bharat Pathar, lying in the east of Marwara upland and drained by Chambal and its tributaries.
3. The Bundelkhand Upland: To south of Yamuna river between Madhya Bharat Pathar and the Vindhyan scarap lands consists of granites and gneiss.
4. Malwa Plateau: Bonded by Aravali range in the west and Bundlekhand in east and Vindhayas in south. It is an extensive lava plateau in M.P. with black soil drained by a number of north flowing rivers like Betwa, Parbati, Kali Sindh, Chambal and Mahi.
5. Baghelkhand: East of Makal range and bounded by Son River on the north.
6. Chhotanagpur Plateau: It covers mostly Jharkhand adjoining eastern Madhya Pradesh and Purulia of West Bengal. This Plateau is composed mainly of Gondwana rocks with patches of granites ad gneisses and Deccan lavas. The highest general elevation is in the Midwest portion known as patlands (high level laterite plateau e.g. Netarhat). The Plateau is drained by numerous rives in a radial pattern such as Damodar, Subarnrekha, North Koel, South Koel and Barakar river.
7. Meghalaya Plateau: This Plateau has been separated from main block of the peninsular plateau by a gap called Ganu-Raj Mahal gap. From east to west the plateau comprises Gana, Khasi and Jaintia hills and Mikir hills. Shilong is the highest point of the plateau.
8. The Deccan Plateau: This is the largest unit covering an area of 5 lakh sq.km. It comprises Maharastra Plateau, Karnataka plateau and the Telengana plateau (Andhra Pradesh). The general slope is form west to east. Indicated by flow of major rivers like Mahanadi, Godwari, Krishna and Cauveri.
9. The Chhattisgarh Plain: It is the only plain worth the name in the vast stretch of plateau drained by upper course of Mahanadi. This saucer shaped depression lies between Makal range and Orissa hills.
HILL RANGE OF THE PENINSULA 1. Aravali Range: Aravalis are the world’s oldest fold mountain running in north east to southwest direction from Delhi to Palampur in Gujarat. Gurushikhar is the highest peak situated in Mount Abu. Barr, Piplighat, Dewair and Desuri passes allow movements by roads and railways.
2. Vindhyan Range: It raises as an escarpment flauting the northern edge of the Naramada, Son-trough. The Vindhyas are continued eastward as the Bharner and Kaimur hills. This range acts a s a water divided between Ganga system and river system of South India. The Makal range forms a connecting link between Vindhyan and Satpuras.
3. Satpura Range: It is a series of seven (Sat) mountains running in east-west direction south of vindhyas and in between the Narmada and Tapi. Commencing from Rajpipla hills in the west through the Mahadeo hills it extends to Makal range in the east. Dhupgarh near Panchmarhi on Mahadeo hills is highest peak of Satpuras.
4. Western Ghats (Sahyadris): The western Ghat run in north-south direction from Tapi valley to north of Kanyakumari. Along the Arabian sea-coast for about 1600 Km. these are Block Mountains due to the down warping of the land to the Arabian Sea. Sahyadris form the real water divide of the peninsula. All the important rivers rise from these hills and flow eastward. The Sayadris up to 16 north latitude are mainly composed of basalt. In this portion Kalsubai is the highest peak. South of Goa Sahyadris are composed of granites and Gneisses. In the Nilgiri hills, Eastern Ghats join the Sahyadris to form a mountain knot whose highest point is Doddabetta (2637 m). South of it is Palghat gap connecting Tamil Nadu with Kerala. South of Palghat there is mountain knot comprising Annamalai hills in north. Patni hills in the north-east and the Cardamon hills in the south. Anaimudi (2695 m ) situated in the Annamalai hills is the highest peak of Sahyadri. Kodaikanal hill station is located on the Patni hills. There are 3 important passes in the Sahyadris:
(a) Thalghat (b) Bhorghat (c) Palghat
5. Eastern Ghat: It is a chain of highly broken and detached hills starting from Mahanadi in Orissa to Vaigai in Tamil Nadu. These are part of the very old fold mountains. It is only in the northern part between Mahanadi and Godavari that Eastern Ghats exhibit true mountain character comprising Maliya and Maduguala konda ranges, South of Godawari the broken hill ranges are Nallamalai, Palkonda, and Javadi, Shavroy and Biligiri Rangan hills. Mahendragiri is the tallest peak of eastern Ghat.
SOILS
1. COMPOSITION OF SOIL: Soil is the loose material which forms the upper layer of the mantel rock, i.e., the layer of loose fragments which covers most of the earth’s land area. It has definite and constant composition. It contains both decayed plants and animals substances. The four main constituents of soils are;
(i) Silica: The chief constituent of sand
(ii) Clay: is a mixture of silicates and contains several minerals such as iron, potassium, calcium, sodium and aluminum. Particles of clay absorb water and swell.
(iii) Chalk: (calcium carbonate) provides calcium, the most important element for the growth of plants.
(iv) Humus: is not a mineral, it is an organic matter. It is formed by decomposed plant remains, animal manure and dead animals and is the most important element in the fertility of the soil. It helps retain moisture in the soil and helps the plant in absorbing materials from the soil for building its body. A soil looks dark on account of the presence of humus.
2. TOP SOIL AND SUB SOIL: Two layers namely top soil and sub soil. Top soil(the upper layer) is of greater importance. Good top soil means good crops. It varies considerably in depth and also in character and ability to grow crops. It is only a few meters deep. Million of bacteria, insects and worms live in it. Top soils develop very slowly. It may take years to form top soil suitable for plants, but it can be washed away in a few years if proper precautions are not taken. Sub soils consist of the parent material from which soil is formed. It also contains plant food and moisture but it is not a s productive as top soil. It has to be converted into soil and it may take years to convert sub soil into soil. Below the sub soil generally there is solid rock.
3. FORMATION OF SOIL: The natural processes involved in the formation of soil are
(i) Weathering: process of disintegration of rocks into soil.
(ii) Deposition: process of progressive lying down of rock particles carried by rivers, ice, marine, currents wind or tides.
(iii) Biochemical processes
Soil formation depends upon the following factors;
*Nature of the parent rock, * Climate, * Natural Vegetation, * Topography, * Time
4. GENERAL CHARACTERISTICS OF DIFFERENT SOILS
a) Sandy Soil (light soil): It contains more than 60% sand and les than 10% clay. It is easy to cultivate and is favoured for fruits and vegetables.
b) Clayey Soil: It has high proportion of clay. It becomes sticky when mixed with water. A soil very rich in clay is called ‘heavy’,
c) Loam: is rich soil and consist of a mixture of sand and clay. All loamy soils are good for farming and general gardening.
5. MAJOR SOIL TYPES
The Indian Council of Agricultural Research (ICAR) classifies the soils of India into eight categories.
6. ALLUVIAL SOIL: This is the most important and widespread group of soils. It covers about 15 lakh sq.km of the land area in Great Plains from Punjab to Assam and also in the valleys of the Narmada and Tapi, Mahanadi, Godavari, Krishna and Cauvery. These soils have been brought down and deposited by three great Himalayan rivers Sutlej, Ganga and Brahmaputra. These soils consist of varying proportions of san, silt and clay. Khadar is the newer alluvium which is sandy, light coloured and occurs near river beds where deposition takes place regularly and bhangar or older alluvium. Alluvial soils as a whole are very fertile and therefore the best agricultural soils of the country. The regions of these of these soils constitute the’ wheat and rice bowls’ of India.
7. BLACK SOIL: As the name indicates these soils are black in Colour and since they are ideal for growing cotton, they are also called cotton soil. These soils, covering an area of 5.46 lakh sq.km, are most typical of the Deccan trap (Basalt). The black Colour of regur is variously attributed to the presence of titaniferrous magnetite, compounds of iron and aluminum-Unsuitable for heavy irrigation. Ideally suited to dry farming. Suitable for cotton, cereals, oilseeds like linseed, castor and safflower, many kinds of vegetables and citrus fruits.
8. RED SOIL: These soil occupy about 5-18 lakh sq.km over the peninsula reaching up to Rajmahal Hills in the east, Jhansi in the north and Kutch in the West. In North western peninsula is covered by the black soils and the remaining south-eastern half is covered by red soils- Entire black soil in the eastern part of Peninsula comprising of Chhotanagpur plateau, Orissa, east Madhya Pradesh, Telengana, the Niligris, Tamilnadu plateau and Karnataka. The soil have reddish colour due to iron compounds. It is suitable for rice, ragi, tobacco and vegetables.
9. LATERITE SOILS: These soils occupying an area of 1.26 lakh sq.km- Found capping the flat uplands, and are spread in western coastal region receiving very heavy rainfall – Poor in nitrogen, phosphoric acid, potash, lime – suitable for rice, ragi, tapioca and cashewnuts.
10. FOREST AND MOUNTAIN SOIL: These soils occupy about 2.85 lakh sq.km in the hilly regions of the country – described as soils in the making – found in the Himalayas and the other ranges in the north and high hill summits in the Sahyadris, Eastern Ghats and Peninsula – poor in potash, phosphorous – Temperate fruits, maize, wheat and barley are grown in Jammu and Kashmir and Himachal Pradesh where soils are mostly podzols which are acidic in re-action.
11. ARID AND DESERT SOILS: Northwestern parts of the country and occupy about 1.42 sq. km area in Rajasthan, south Haryana, north Punjab and Rann of Kutch. Thar Desert alone occupies an area of 1.06 sq. km. It contains high percentage of soluble salts and a low to very low organic matter.
12. SALINE AND ALKALINE SOILS: These soils occupy about 170 lakh sq. km of arid and semi-arid areas of Rajasthan, Punjab, Haryana, Uttar Pradesh, Bihar and whole of Maharastra. Textually they are sandy to loamy sand. Saline soils contain free sodium. Crops grown on these soils include rice, wheat, cotton, sugarcane and tobacco.
13. PEATY AND MARSHY SOILS: These soils cover an area of about 150 sq. km in the Kottayam and Allepey districts of Kerala. They are suitable for paddy cultivation.
14. SOIL FERTILITY: The factor responsible for deficiency of Indian soils are: (i) loss of nutrients, largely brought about through the removal of harvested crops, (ii) leaching which occurs under heavy monsoonal rains, causes loss of nutrients, sandy soils are more subject to leaching than the heavier ones and bare soils are more than those covered by plants. Indian soils are mainly deficient in nitrogen, phosphorus and potash. These can be supplied to the soils by application of organic manures and fertilizers.
15. SOIL EROSION: Soil erosion is the removal of soil particles by natural agencies such as water and wind and also as a result of human and animal interference.
16. TYPES OF SOIL EROSION: Two types of soil erosion:
(i) Water Erosion: The important types of this erosion are sheet, rill and gully. In sheet erosion thin layer of soil is removed by the water during heavy rains. If the erosion continues unchecked, numerous finger-shaped grooves may develop all over the area as a result of the silt-landen run-off. This is called rill erosion. The rills may deepen and enlarge into gullies.
(ii) Wind Erosion: Wind erosion is mainly confined to arid and semi-arid areas devoid of vegetation. Wind, particularly during sand-storms, lifts and carries away soil particles leaving behind a depression devoid of top fertile soil. Rajasthan and the adjoining areas of Haryana, Uttar Pradesh and Gujarat show this type of soil erosion.
17. CONSEQUENCES OF SOIL EROSION: (i) heavy floods in rivers, (ii) lowering down of sub soil water level, (iii) reduction of soil fertility, (iv) silting of streams and water courses, (v) disappearance and downfall of civilizations.
18 a) SOIL CONVERSATION: Soil conservation is an effort made by man to prevent soil erosion to retain the fertility of soil. It may not be possible to stop soil erosion entirely.
b) Measures for Soil Conservation: (i) Planting cover crops, (ii) Adoption of correct farming techniques, (iii) Terracing the practice of cutting steps in hillside, to create level land for cultivation, (iv) Construction of check dams, (v) Creation of wind break, (vi) Controlling of grazing of pastures, (vii) Suspending cultivation for one season and more so as to help the soil recover its fertility.
THE EARTH’S CRUST
The earth is made up of several concentric layers. The outer layer of the earth’s crust is called lithosphere, which comprises two distinct parts. The upper parts consist of granitic rocks and form the continents. Its main mineral constituents are silica and alumina knows as Sial. It has an average density of 2.7. The lower part is a continuous zone of densers, basaltic rocks forming the ocean’s floors. Comprising mainly silica, iron and magnesium known as Sima and has an average density of 3.0. The Sial and the Sima together form the earth’s crust which varies in thickness 4.8 to 6.4 km, beneath the oceans and about 48 km under some o continents. Beneath the lithosphere is the mantle known as the mesosphere about 2880 kms thick. Composed mainly very dense rock rich in Olivine. The interior layer is the core known as baryshpere about 2456 km in radius is made up mainly iron (Fe) and nickel (ni) known as nife. The temperature of core is as high as 2000 C and subject to extremely high pressure. The crust forms only 0.5% of the volume of the earth, 83% consist of the mantle and 16% makes the core that of the earth. The mean radius of the earth is 6400 km. the average rate of increase temp 1 C for every 32 meters of descent. But in upper 100 kms, the increase is estimated at 12 C/kms. It is 2 C/Km in next 300 kms and 1 C/kms below it.
| Name of the layer | Chemical Composition | Volume (Earth) | Mars (Earth) | Density | Physical Properties |
| CRUST (A) (i) Outer-part of lithosphere (ii) Inner part of Lithosphere | Sial | 1% of the earth | 10% | 2.75 to 2.90 | Solid |
| MANTLE (B) (i) Outer part of mantle (ii) Inner part of mantel | Silica with Sima Wholly Sima | 83% | 68% | 3.10 to 4.75 4.75 to 5.00 | Partly molten Close to melting point |
| CORE (C) (i) Outer part of Core (ii) Inner part of Core | NiFe | 16% | 32% | 5.1 to 13 | Plastic state Solid and rigid because of tremendous overlying pressure. |
Composition of Earth’s Crust
1) oxygen: 46.6% 2) Silicon- 27.27% 3) Aluminium: 8.13% 4) Iron- 5% 5) Calcium-3.63%
6) Sodium- 2.83% 7)Pottasium- 2.59% 8) Magnesium- 2.09% 9)Others- 1,41%
CLASSIFICATION OF ROCKS ACCORDING TO ORIGIN
1. IGNEOUS ROCKS: Igneous rocks are formed by the cooling and solidification of molten rock (magna) from beneath the earth’s crust. They one normally crystalline in structure. They do not occur in layers and not contain fossils. Some rocks can form a high percentage of silica are said to be acid. E.g., Granite. Other rocks such as Basalt contain a high percentage of iron or Aluminium or magnesium oxides are called basic rocks. There are two main groups:
(i) Volcanic Rocks: These are mole nocks poured out of volcanoes as lavas. They solidify rapidly on the earth’s surface and the crystals are small. E.g. basalt.
(ii) Plutonic Rocks: These are igneous rocks solidified deep in the earth’s crust and they reach the surface only by being exposed by erosion. E.g., granite, diorite and gabbros etc.,
2. SEDIMENTARY ROCKS: Sedimentary rocks are formed from sediment accumulated over long periods, usually under water and deposited usually in layers by water, wind or moving ice. They are non-crystalline and often contain fossils of animals, plants and other micro-organisms. There are three main groups;
(i) Mechanically-formed: (a) Wind-deposited e.g loess, (b) River-deposited e.g., clays, gravels, and alluviums, (c) Glaciers-deposited e.g., morains, sands and gravels and boulder clay, (d) Sea-deposited.
(ii) Organically formed: (a) From animals e.g., chalk and coral, (b) From plants e.g., Peat, lignite, coal.
(iii) Chemically formed: e.g., rock slat, borax, gypsum, nitrates, potash and certain limestone.
3. METAMORPHIC ROCKS: All those rocks whose structure and appearance have been changed by great heat or great pressure or both. Any rock can be changed into a metamorphic rock. In theses manner (a) State (from clay), (b) Marble (from limestone), (c) Quartzite (from sandstone), (d) Graphite (from coal), (e) Gneiss (from granite), (f) Schist (from shale).
STRUCTURE OF ATMOSPHERE
According to Petterssen, the atmosphere is divided into the following five layers:
1. TROPOSPHERE: The lowermost layer of the atmosphere is known as Troposphere and is the most important layer because almost all of the weather phenomena is occurred in this layer. E.g., Fog, cloud. Thunder, lightning, etc., occurs in this layer. It extends roughly to a height of eight kilometers near the poles and about 18 kilometers at the Equator. The thickness of the troposphere at the equator is the greater heights by strong conventional currents. Temperature decreases with increasing height at the rate of 6.5 C per 1000m. This rate of decrease of temperature is called normal lapse rate. This layer contains dust particles and over 90% of the earth’s water vapour. The upper limit of the tropopause is called troposphere which is about 1.5km. Thick. Temperature ceases to fall with the air temperature at the troposphere is about-80 C over the equator and about -45 covers the poles. The word troposphere literally means zone or region of mixing whereas the word tropopause means where the mixing stops.
2. STRATOSPHERE: The Stratosphere begins at the tropopause which forms its lower boundary. The lower stratosphere is isothermal in character, i.e, the temperature in the lower part of this layer does not change with altitude. The stratosphere extends up to a height of 50 km. Afterwards it gradually increases up to a height of 50 km because of the presence of ozone layer which absorbs the Sun’s Ultra-Violet Rays. Clouds are almost absent and there is very little dust or water Vapours. The air movement is almost horizontal. The upper boundary of the stratosphere is called Statopause. Above this level there is a steep rise in temperature.
3. MESOSPHERE: Over the stratopause there exists the third layer known as mesosphere. It extends up to a height of 80 kms. Temperature decreases with height again and reaches up to – 100 C at the height of 80 kms.
4. IONOSPHERE: Ionosphere is located between 80 km to 400 kms. It is electrically charged layer. Radio waves transmitted from the earth are reflected back to the earth by this layer. Temperature again starts increasing with height because of radiation from the sun. The ionosphere consists of the following ionized layers:
D – Layer: 60 -99 km
E – Layer: 90 – 130 km
Sporadic Layer: 110 km
E2 Layer: 150 km
F1 Layer, F2 Layer: 130 -1890 km
G Layer: 400 km and above.
5. EXOSPHERE: The outermost layer of the earth’s atmosphere is known as the exosphere which lies between 400 and 1000kms. The atmosphere in this region is so rarefied that it resembles a nebula-hydrogen and helium gases predominates in this outermost region. The temperature becomes 5568 C at its outer limit but this temperature is entirely different from the air temperature of the earth’s surface.
LATITUDE, LONGITUDE AND TIME
1. INTRODUCTION: The earth is nearly a sphere and it has no edges. It presents some difficulties in positioning its surface features. To over come this problem, a network of imaginary lines is drawn on a globe or a map to help us locate places. The spinning of the earth on its axis provides – the North Pole and South Pole. They form the basis for the geographical grid. The grid consists of two sets of lines – horizontal and vertical. The horizontal lines, running eat-west, are circular and parallel to each other. The line drawn midway between the North Pole and the South Pole is called the equator. It is the largest circle and hence, is called a great circle. All other parallels get smaller in size in proportion to their distances form the equator towards the Poles. These imaginary lines running east-west are commonly known as parallels of latitude. The vertical lines, running north-south are halves of the great circle and join the two Poles. They are called meridians of longitude. The latitudes and longitudes are commonly referred to as coordinates because they provide systematic network of lines upon which position of various surface features of the earth can be represented.
2. LATITUDES: The latitude of a place on the earth’s surface its distance north to south of the equator measured along the meridian of that places as an angle from the centre of the earth. Lines joining places with the same latitudes are called parallels. The value of equator is 0 and the latitude of the poles are 90 N and 90 S. If the parallels of latitude are drawn at an interval of one degree, ther will be 90 parallels in the northern and southern hemisphere each. The total number of parallels thus drawn including the equator, the letter N or S is written along with the value of latitude. If the earth were a perfect sphere – 23 ½ N –Tropic Cancer, 23 ½ S – Tropic of Capricorn, 60 ½ N – Artic, 60 ½ S – Antarctic, 1 of latitude (a one- degree arc of a meridian) would be a constant value i.e., 111 km – a degree of latitude changes slightly in length from the equator it is 110.6 km, at the poles it is 111.7 km. Latitude of a place may be determined with the help of the altitude of the sun or the Polar Star.
3. LONGITUDE: Unlike the parallels of latitude, which are full circles, the meridians of longitude are semi-circles touching the poles. Meridians intersect the equator at right angles. The meridian of longitude passing through the Greenwich observatory (near London) has been adopted as the Prime Meridian by an international agreement and has been given the value of 0 degree. The numerical value of a longitude varies form 0 degree to 180 degree East or West – be 360 degree meridians.
4. LONGITUDE AND TIME: While rotating on its axis, the earth completes one circle (360 degree) in approximately 24 hours time. In other words, it move 15 degree longitudes per hour. As such the sun appears to be traversing 15 degree of longitude from east to west every hour or 1 degree of longitude in every 4 minutes. Thus, when it is 12 noon at Greenwich (Prime meridian), the time at 30 degree east of Greenwich will be 30*4= 120 minutes or 2 hours ahead of Greenwich time. In order to maintain uniformity of time as far as possible within the territorial limits of a country us taken as the standard meridian and its local time is taken as the standard time for the whole country. The standard meridian is selected in a manner that it is divisible by 15 degree or 7 degree 30’ so that the difference between its standard time and the Greenwich Mean Time may be expressed as multiples of an hour or half an hour. The Standard meridian of India is 82degree30’ E and the standard time is 5 ½ hours a head of Greenwich Mean Time
