General Awareness Geography |Questions & Answers | Notes
One of the theories suggests that it is an outcome of a star formation. About 4,600 million years ago, a giant cloud of gas and dust in space, having a swirling motion, gradually contracted under its own gravity. As the gas cloud or nebula shrank in size, it spinned faster to conserve its angular momentum. The rapid rotation prevented it from total collapse into one object and a large number of smaller units were formed. The core of nebula rotating slowly became new star-the Sun.
Surface Features of the Earth
• Major surface features of the earth are continents and ocean basins.
• Less than l/3rd of the whole surface of the earth is landmass, the rest is covered by water.
• The continents and ocean basins are irregularly arranged on the earth.
• The northern hemisphere has more land than the southern hemisphere.
• For several million years, large parts of continents were covered with thick masses of ice. This period on the earth is called Ice age.
• It is believed that nearly 150 million years ago, there was a single continent on earth called Pangaea. This super-continent broke into several pieces, which began to drift apart.
Realms of the Earth
1. Lithosphere (land masses)
2. Atmosphere (air envelope)
3. Hydrosphere (water bodies)
4. Biosphere (life forms)
Layers of the Earth :
(According to Volume):
1. Crust. It forms only 0.5 per cent of the volume of the earth
2. Mantle. It forms 16 percent of the volume of the ‘ earth
3. Core : It forms 83 percent of the volume of the earth
Earth being a spherical body, it has its centre at 6,400 km viz., mean radius of the earth.
Some Numerical Facts About the Earth
|Land||Greatest known height (in meters)||Oceans and Seas||Greatestknowndepth|
|Mount Everest||8863||Mariana Trench||11035|
|Average height||840||Average depth||3808|
|Size and shape (in km)||Area (in millions sq. km.)|
|Equatorial semi-axis, a||6378.2||Land (29.22 per cent)||149|
|Polar semi-axis, b||6356.8||Ice sheets and glaciers||15.6|
|Mean radius||6371.0||Oceans and seas (70.78 per cent)||361|
|Equatorial circumference||40076||Land plus continental shelf||177.4|
|Poiar (meridian) circumference||! ‘40009 ? :||Oceans and seas minus continental shelf||332.6|
|Ellipticity, (a-b)/a ,||1/298 –||Total area of the Earth||510.0|
On the basis of the mode of formation, rocks are usually classified into three major types :
1. Igneous Rocks
At one time, all parent rock material was liquid, hot and a sticky thing called magma. It hardens below or upon reaching the earth’s surface. When it hardens, it forms igneous rock.
Igneous rocks are parents of all other rocks and are also called primary rocks.
2. Sedimentary Rocks
They are formed by deposition and consolidation of mineral and organic material from precipation of minerals from solution.
3. Metamorphic Rocks
When 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.
About 120 million years ago, the landmass called Gondwana land started breaking because of the earth movements, volcanic eruptions and sea floods all working together.
It is the earth movements which bring about these vast changes.
The concentration of great internal forces within the earth raise local areas upwards or cause them sinking downwards.
There are three major landforms :
An uplifted portion of the earth’s surface is called hill or mountain.
Classification of mountains
Mountains are classified on the basis of their origin or mode of formation as follows :
(i) Structural mountains (Tectonic)
(ii) Fold mountains
(iii) Block mountains e.g. Vosges in France
(iv Volcanic mountains
e.g. Mt. Fuji Yama in Japan
(v) Residual or Dissected mountains e.g. Nilgiri, Parasnath, Girnar
A plateau is an elevated area generally in contrast to
the nearby areas. It has a large area on its top unlike a mountain and has an extensively even or undulating surface. The great Deccan Plateau with its slope towards east is a tilted plateau in our country.
A relatively flat and a low-lying land surface with least difference between its highest and lowest points is called plain.
A plain may be as low as 30 metres to the east of Mississippi river near the Appalachian range and as high as 1,500 metres above sea level to the west of the river.
The volcanic phenomenon is a majestic natural phenomenon.
Classification of volcanoes
On the basis of frequency of eruption, volcanoes are classified as:
1. Active volcano
These erupt fairly frequently as compared to others
2. Dormant or sleeping volcano
In these eruption has not occurred recently.
e.g. one in Barren Island to the east of Andamans in India
3. Extinct or Ancient volcano
These have recorded no eruption in historic times are called extinct.
• Any sudden disturbance below the earth’s surface, may produce vibrations or shakings at the crust. When rocks break, the particles next to the break are set in motion. It is the movement of one rock mass against another that causes vibrations. Some of these vibrations reach the surface and are called earthquakes. The place of origin of an earthquake inside the earth is called its focus.
• The point on the earth’s surface vertically above the focus is called epicentre.
• Soil is a mixture of many solid, liquid and gaseous substances.
• It forms the topmost layer of earth’s crust.
• It has both non-living and the living matter like
mineral particles, decaying plant remains and insects living together with countless bacteria on its organic matter. .
• Soil holds water. This moisture is taken in by the roots of plants.
• There is air in the open spaces within the soil containing more of carbon dioxide and also oxygen and nitrogen.
• Soil is final product of the interactions between weathering of underlying rock, climate, plants and activities of millions of insects earthworms.
Rain-water or snow-melt that neither runs off along the surface nor evaporates but sinks into the ground is called underground water.
The level below which the rocks are completely saturated with water is called water table.
Wells are man-made holes dug into the earth’s surface in order to get underground water for irrigation or for human consumption.
A special type of well in which water rises automatically under the pressure of a column of water to the ground surface, either through a natural or man-made hole, is called artesian well.
Springs are places where a flow of water rises to the surface through natural rock opening under hydraulic pressure from the depth.
A spring or a chain of them are common at the junctions of permeable and impermeable rocks.
Hot springs and Geysers
The ground water comes in contact with the heated or superheated steam inside the earth and emerges at the surface as a hot spring.
Geyser is a hot spring in which water is forced up by steam pressure at intervals.
The atmosphere extends to thousands of kilometers, but it has no clear upper limit and it gradually merges with the outer space.
The atmosphere is a mixture of many discrete gases, in which varying quantities of tiny solid particles are suspended.
Pure dry air constitutes mainly of (by volume) Nitrogen – 78 % Oxygen – 21%
Remaining one per cent is accounted for by gases like argon (0.93 per cent) carbon dioxide (0.03 per cent) hydrogen, helium and ozone.
• Water vapour absorbs parts of the insolation from the sun and thus reduces its amount reaching the earth’s surface.
• It also preserves the earth’s radiated heat. It thus, acts like a blanket allowing the earth neither to become too cold nor too hot.
• The movements of the atmosphere are sufficient to keep a large quantity of tiny solid particles suspended with in it.
• Carbon dioxide constitutes only 0.03 per cent of the volume of the air. Even so it is very important meteorologically because it is transparent to the incoming solar radiation but opaque to outgoing terrestrial radiation.
• Ozone is other important component of the atmosphere. It acts as a filter and absorbs ultra¬violet radiation from the sun. It is concentrated mainly between 10 to 50 kilometres above the earth’s surface.
Atmosphere can broadly be divided into four layers :
It is the lowest layer of the atmosphere.
It extends roughly to a height of kilometres near the poles and about 18 kilometres at the equator.
Above 20 km it gradually increases upto a height of 50 kilometres because of the presence of ozone layer which absorbs sun’s ultra-violet rays.
It extends upto a height of 80 kilometres.
Temperature decreases with height again and reaches upto – 100°C at the height of 80 kilometres.
In its lower part, there is an electrically charged layer called ionosphere
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.
Here atmospheric gases are very thin.
This part is extremely rarefied and gradually merges with the outer space.
Types of Winds
(1) Planetary winds
• Winds which blow throughout the year from one latitude to the other in response to the latitudinal differences in air pressure, are called prevailing winds or planetary winds.
(2) Periodic winds
o The winds changing their direction periodically with change in season are called periodic winds.
• Monsoons are the best example of large scale modification of the planetary wind system.
(3) Local winds
Local winds develop as a result of local differences in temperature and pressure.
Humidity is the general term which describes invisible amount of water-vapour present in the air.
It is the process by which water is transformed from liquid to gaseous form.
Rate of evaporation
It depends on
ii) moisture content or degree of dryness of air
(iii) movement of air
• It is the process of change of state from gaseous to liquid or solid state.
• Condensation depends on
i) amount of cooling
ii) relative humidity of the air
When the moisture is deposited in the form of water droplets on cooler surface of solid objects such as stones, grass blades and plant leaves, it is called dew.
When condensation takes place at a dew point which is at or below freezing point (0°C), excess moisture is deposited in the form of minute ice crystals instead of droplets of water. It is called white frost.
It is defined as a cloud with its base at or very near the ground.
In this type of fog, visibility is more than 1 kilometre but less than 2 kilometres.
It is a mass of minute droplets of water or tiny crystals of ice formed by condensation of the water-vapour in free air at considerable elevations.
• Condensation of water-vapour in air in the form of water droplets and ice and their falling on the ground is called precipitation.
• The precipitation in the form of drops of water is called rainfall.
• When temperature is less than 0°C, precipitation takes place in the form of fine flakes of snow and is called snow-fall.
• Sleet is frozen raindrops and re-frozen melted snow water. It may be a mixture of snow and rain or merely partially melted snow.
• Precipitation in the form of hard rounded pellets is called hail.
• It is largest of all the water bodies.
• Together with its associated seas, it covers about one-third of the earth’s surface and exceeds total land area of the world in size.
• It is the deepest of all oceans.
• The major portion of the basin has an average depth of about 7,300 metres.
• This vast ocean is dotted with more than 20,000 islands.
• It is roughly half the size of the Pacific Ocean and covers about one-sixth of the earth’s total area.
• It resembles the letter S in shape.
• It has numerous marginal seas on both sides, especially in its northern part.
• It’s most striking feature is the presence of mid-Atlantic Ridge. It extends from the north to the south paralleling the S shape of the ocean itself.
• It is smaller than the Atlantic Ocean.
• It average depth is 4,000 metres which is comparatively lesser than that of other oceans.
• The floor has fewer irregularities in comparison to the other two oceans. Linear deeps are almost absent. The only exception is the Sunda Trench, which lies south of the island of Java and runs parallel to it.
• Temperature and salinity of the ocean water, determine movements of large masses of water.
• Temperature decreases according to the increasing depth of the ocean.
• Generally, temperature in ocean waters varies from below -5°C to over 33°C.
Movement of Water
Facts responsible for movement of water are follows.
• Sea water contains a number of dissolved salts which result in the property of salinity.
• The salinity is expressed as the number of grams of dissolved salts in 1,000 grams of sea water.
• Average salinity of the’ sea water is about 35 per thousand or 35%; which means that in one kilogram of sea water there are 35 grams of dissolved salts.
• Waves are oscillatory movements in water, manifested by an alternate rise and fall of the sea surface.
• Top part of a wave is called its crest and lower part between two waves is called trough.
3. Ocean currents
It is general movement of a mass of water in a fairly defined direction over great distances.
• Sea-water rises regularly twice a day at constant intervals. This is periodic phenomenon of alternate rise and fall in the level of the seas is called tides.
• These are produced as a gravitational interaction of the earth, moon and the sun.
• It refers to that part of the earth in which all life forms exist.
• Organisms or life forms in the biosphere vary in size from minute bacteria to large whales or huge trees.
All organisms may broadly be grouped under two categories :
(i) Plant kingdom (ii) Animal kingdom
Human beings are one of the species of the biosphere called Homo sapiens.
Study of the interactions between organisms and their environment is called ecology.
All life forms are made of primarily three most abundant elements
Other elements such as nitrogen, iron, sulfur, phosphorus and manganese are required only in small quantities. These elements are also called nutrients.
Transfer of energy in the ecosystem takes place in a series of steps or levels, called food chain.
First level in the food chain are plants called producers. They use light energy to convert carbon dioxide and water to produce carbohydrates and eventually to other biochemical molecules required to support life. This process of energy conversion is called photosynthesis.
Second level of the foqd chain are primary consumer. These are plant eating animals (herbivores) such as insects, mice and goat.
Third level are the secondary consumers, who feed on the primary consumers (carnivores) such as owl and lion.
Some of the species are called omnivores because they are both herbivores and carnivores. Human beings come under this category.
Decomposers (microscopic organisms and bacteria) feed on the detritus or decaying organic matter derived from all levels. They help in recycling mineral nutrients into ecosystem and thus food chain is completed.
• India is often described as a sub-continent and is a part of the Asian continent.
• It sprawls between snowy heights of the Himalaya and shores of the Indian Ocean.
• The country gets an abundance of sunshine from the tropical sun and moisture from the splashing monsoon rains.
• India is situated in the Northern Hemisphere.
• The Tropic of Cancer passes approximately through the middle region of the country.
• The northern-most fringe of India consists of a mountain system which radiates from the Pamirs, roof of the world, in the heart of Asia.
• The hot and humid Kanyakumari constitutes the southern-most tip where the Indian peninsula, getting narrower and narrower, loses itself into the ocean.
• Distance from northern-most to the southern-most points in the mainland of India is about 3,200 kilometres.
• East to west, India is approximately 3,000 kilometres long.
• Across the eastern borders of India and the Bay of Bengal lie Myanmar (Burma). Malaysia, Indonesia, Thailand, Cambodia (Kampuchea), Laos and Vietnam.
• Across the western borders of India lie Pakistan, Iran, Iraq and the Arab countries.
At the macro level India may be divided into three
1. Himalayan Mountain Chain
It consists of a series of parallel mountain ranges with bold relief and are characterised by highly rugged topography.
Himalayan mountain chain, all along its longitudinal axis, is arranged into three main series of a parallel ranges :
(i) Great Himalayas
(ii) Lesser Himalayas
Others as inner, middle and the outer Himalayas.
2. Plain of India
It occupies the space between Plateau and the northern mountains.
Evolution of the plain is attributed to a process of gradual filling of an initial rift valley stretched in front of the northern mountains and formed as a consequence of a fracture in the crust.
3. Peninsular Plateau
It is a block of old crystal rocks lifted above the level of sea in which these rocks were deposited in the Pre-Cambrian times and never submerged again.
• Indian islands in the Bay of Bengal consist of the Andaman and the Nicobar groups.
• There are as many as 200 islands in the Andaman group alone, extending for 350 kilometres.
• There are 19 islands in the Nicobar group. Some of the islands have a length of 60 to 100 km, forming a cluster south of the Andaman group.
• Arabian Sea Islands consist of Lakshadweep group They are formed on a coral deposit off the Kerala coast. The southermost of the these islands lies just to the north of the Maldives.
On the basis of origin, the river systems of India can be classified into two categories:
1. Himalayan rivers
• These have large basins, their catchment areas extending over hundreds of thousands of square kilometres.
• The Indus drains over an area of approximately 250,000 sqkm within the Himalayan region alone.
• Himalayan rivers is perennial.
• Himalayan rivers which have evolved through a long and chequered history, consist of the three principal systems :
|Basic area of Himalayan rivers.|
2. Peninsular rivers
• These flow through shallow valleys which are more or less completely graded in most cases.
• A large number of them are seasonal as their flow is mainly dependent on rainfall.
• Many of the Peninsular rivers have, straight and generally linear courses.
East flowing peninsular rivers
West flowing peninsular rivers
World’s Biggest Countries (in order of population)
|Name||Population (in Millions)||Continent|
World’s Smallest Countries (in order of population)
World’s Biggest Countries (in order of area)