Part-1 Flashcards

Question

Body Waves

Answer 1

* Earthquake waves are of two types — body waves and surface waves. **P- Waves** 1. P-waves are also known as the Primary waves. They are the first waves to arrive at the surface. 2. The characteristics of P-waves are like sound waves. They travel through all three mediums- solid, liquid and gas. 3. These waves have a tendency to vibrate parallel to the direction of wave propagation. This causes density differences in the material through which they travel. 4. These waves are responsible for elongating and squeezing of material. **S- Waves** 1. S- Waves arrive after some time after the happening of Earthquake and they are called secondary waves. 2. A significant characteristic of these S-waves is that they travel only through a solid medium. 3. The direction of vibration of these S – wave is perpendicular to the direction of wave propagation, thereby creating crests and troughs in the material of their transmission.

Answer 2

1. The shadow zone is the zone of the earth from angular distances of 104 to 140 degrees from a given earthquake that does not receive any direct P waves. 2. The shadow zone results from P waves being refracted by the liquid core and S waves being stopped completely by the liquid core. 3. A zone between 105° and 145° from the epicentre was recognised as the shadow zone for both the waves types. 4. The entire zone beyond 105° does not receive S-waves. 5. The shadow zone of S-wave is larger than that of the P-waves. 6. The shadow zone of P-waves appears as a band around the earth between 105° and 145° away from the epicentre.

Answer 3

The following are the immediate hazardous effects of Earthquake: * Shaking of ground * Disparity in ground settlement * Natural disasters like Tsunami, land slide, mud slides and avalanches * Soil liquefaction * Ground lurching and displacement * Floods and fires * Infrastructure collapse.

Answer 4

All earthquakes are different in their intensity and magnitude. The instrument for measurement of the vibrations is known as Seismograph. **Magnitude scale** * Richter scale is used to measure the Magnitude of the earthquake * The energy released during a quake is expressed in absolute numbers of 0-10. **Intensity scale** * The mercalli scale is used to measure the intensity of an earthquake * It measures the visible damage caused due to the quake. * It is expressed in the range of 1-12.

Answer 5

1. A volcano is a vent or fissure in Earth’s crust through which lava, ash, rocks, and gases erupt. 2. An active volcano is a volcano that has erupted in the recent past. 3. The mantle contains a weaker zone known as asthenosphere. 4. Magma is the material present in the asthenosphere. 5. Material that flows to or reaches the ground comprises lava flows, volcanic bombs, pyroclastic debris, dust, ash and gases. The gases maybe sulphur compounds, nitrogen compounds, and trace amounts of argon, hydrogen and chlorine.

Answer 6

Volcanoes are classified on the basis of nature of eruption and the form developed at the surface. 1. Shield Volcanoes 2. Composite Volcanoes 3. Caldera 4. Flood Basalt Provinces 5. Mid-Ocean Ridge Volcanoes

Answer 7

1. The Shield volcanoes are the largest of all the volcanoes on the earth, which are not steep. 2. These volcanoes are mostly made up of basalt. 3. They become explosive if in some way water gets into the vent, otherwise, they are characterized by low-explosivity. 4. The lava that is moving upwards does so in a fountain-form and emanates the cone at the vent’s top and then develops into cinder cone. 5. Eg: Hawaiian shield volcanoes

Answer 8

1. Composite Volcanoes are characterized by outbreaks of cooler and more viscous lavas than basalt. 2. They are constructed from numerous explosive eruptions. 3. Large quantities of pyroclastic material and ashes find their way to the ground along with lava. 4. This material gathers near the vent openings resulting in the creation of layers. 5. Mayon Volcano in the Philippines, Mount Fuji in Japan, and Mount Rainier in Washington are the major composite volcanoes in the world. 6. The major composite volcano chains are Pacific Rim which known as the “Rim of Fire”.

Answer 9

1. Calderas are known as the most explosive volcanoes of Earth. 2. They are generally explosive in nature. 3. When they erupt, they incline to collapse on themselves rather than constructing any structure. 4. The collapsed depressions are known as calderas.

Answer 10

1. Flood Basalt Province volcanoes discharge highly fluid lava that flows for long distances. 2. Many parts of the world are covered by thick basalt lava flows.

Answer 11

1. These volcanoes are found in the oceanic areas. 2. There exists a system of mid-ocean ridges stretching for over 70000 km all through the ocean basins. 3. The central region of this ridge gets frequent eruptions.

Answer 12

Volcanic eruptions result in the formation of landforms as given below: 1. Intrusive Forms 2. Batholiths 3. Lopolith 4. Phacolith 5. Sills 6. Dykes

Answer 13

1. The lava that is discharged during volcanic eruptions on cooling develops into igneous rocks. 2. The cooling may take place either on arriving on the surface or also while the lava is still in the crustal portion. 3. According to the location of the cooling of the lava, igneous rocks are categorized as plutonic rocks and volcanic rocks. 4. The lava that cools inside the crustal portions takes diverse forms. These forms are called intrusive forms. Some of the forms are shown in Figure given below

Answer 14

1. Batholiths are the cooled portion of magma chambers. 2. It is a large body of magmatic material that cools in the deeper depth of the crust moulds in the form of large domes. 3. They appear on the surface only after the denudation processes eliminate the overlying materials. 4. These are granitic bodies.

Answer 15

1. These are large dome-shaped intrusive bodies with a level base and linked by a pipe-like channel from below. 2. It bears a similarity to the surface volcanic domes of the composite volcano, only these are located at deeper depths. 3. It can be considered as the localized source of lava 4. The Karnataka plateau is patterned with dome hills of granite rocks.

Answer 16

1. When the lava moves upwards, a part of the same tends to move in a horizontal direction wherever it finds a weak plane. 2. It can get rested in various forms. If it develops into a saucer shape, concave to the sky body, it is called lopolith.

Answer 17

1. It is a wavy mass of intrusive rocks found at the base of synclines or at the top ofthe anticline in the folded igneous country. 2. These wavy materials have a definite outlet to source beneath in the form of magma cavities.

Answer 18

1. The near horizontal bodies of the intrusive igneous rocks are called sill 2. The thick horizontal deposits are called sills whereas the thinner ones are called sheets.

Answer 19

1. Dykes are the most commonly found intrusive forms in the western Maharashtra area. 2. When the lava makes its channel through cracks and the fissures, it solidifies almost perpendicular to the ground. 3. This gets cooled in the same position to grow a wall-like structure. Such structures are known as dykes. 4. These are regarded as the feeders for the eruptions that led to the development of the Deccan traps.

Answer 20

1. Nitrogen-is the most plentiful gas in the air. 2. Plants need nitrogen for their survival. 3. Oxygen- is the second most abundant gas in the air. 4. Humans and animals take oxygen from the air as they inhale. 5. Carbon dioxide- is another most important gas. 6. Green plants use carbon dioxide to make their food and release oxygen. 7. Argon

Answer 21

Our atmosphere is divided into five layers starting from the earth’s surface. 1. Troposphere-the most important layer of the atmosphere. Its average height is 13 km. The air we inhale exists here. Most weather phenomena like rainfall, hailstorm, etc. occur in this layer. 2. Stratosphere- just above the troposphere lies the stratosphere. It extends up to a height of 50 km. Being free from associated weather phenomenon, this layer is most ideal for flying aeroplanes. Contains ozone. 3. Mesosphere-: This is the next & third layer of the atmosphere. It lies above the stratosphere. It extends up to the height of 80 km. 4. Thermosphere -In thermosphere temperature rises very rapidly with increasing height. Ionosphere is a part of this sphere. It extends between80-400 km. This layer helps in radio communications. 5. Exosphere-The last & upper most layer of the atmosphere is known as exosphere.

Answer 22

1. Weather is day to day condition of the atmosphere. 2. The average weather condition of a place for a longer period of time represents the climate of a place. 3. Temperature-The degree of hotness and coldness of the air (body) is known as temperature. 4. Air Pressure-is defined as the pressure exerted by the weight of air on the earth’s surface. 5. Wind-The movement of air from high pressure area to low pressure areas is called wind. 6. Winds can be broadly divided into three types * **Permanent winds** – The trade winds, easterlies and westerlies are the permanent winds. They blow throughout the year constantly in a particular direction. * **Seasonal winds** – These winds change their direction in different seasons- example monsoon winds in India. * **Local winds** – These winds blow only during a certain period of the day or year in a small area. For example, land breeze and sea breeze. – Ex-hot and dry local wind of northern plains of India is called loo.

Answer 23

1. **Lithospheric Plates**: The lithosphere broken into a number of plates is known as the Lithospheric plates. 2. These plates move around very slowly – just a few millimetres each year. 3. This is because of the movement of the molten magma inside the earth. 4. The movement of these plates causes changes on the surface of the earth. 5. The earth movements are divided based on the forces that cause them on the basis of the forces which cause them * **Endogenic forces**: The forces which act in the interior of the earth. * Endogenic forces sometimes produce abrupt movements due to which earthquakes and volcanoes occur and cause mass destruction over the surface of the earth and at the other times produce slow movements. * **Exogenic forces**: The exogenic forces work on the surface of the earth. 1. **Volcano**: It is an opening or a vent in the earth’s crust through which molten material erupts. 2. **Earthquakes**: Lithospheric plates move, the surface of the earth vibrates. The vibrations can travel all round the earth. These vibrations are called earthquakes. 3. **Focus**: The place in the crust where the movement starts is called the focus. 4. **Epicentre**: The place on the surface above the focus is called the epicentre.

Answer 24

1. The landscape is being continuously worn away by two processes, * **Weathering**: the breaking up of the rocks on the earth’s surface is called weathering * **Erosion**: the wearing away of the landscape by different agents like water, wind and ice is called erosion 1. **Work of a River:** When the river tumbles at steep angle over very hard rocks or down a steep valley side it forms a waterfall. 2. **Work of Sea Waves:** The coastal ladnforms are formed due to the erosion and deposition of the sea waves. 3. **Work of Ice:** Glaciers are “rivers” of ice which too erode the landscape by bulldozing soil and stones to expose the solid rock below. 4. **Work of wind:** An active agent of erosion and deposition in the deserts is wind. In deserts you can see rocks in the shape of a mushroom, commonly called mushroom rocks.

Answer 25

1. The earth is made up of several concentric layers with one inside another. 2. Crust- 3. The uppermost layer over the earth’s surface. 4. It is the thinnest of all the layers. 5. It is about 35 km. on the continental masses and only 5 km. on the ocean floors. 6. The main mineral constituents of the continental mass are silica and alumina. It is thus called si-al (si-silica and al-alumina) 7. The oceanic crust mainly consists of silica and magnesium; it is therefore called sima (si-silica and ma-magnesium) 8. Mantle- 9. Just beneath the crust is the mantle which extends up to a depth of 2900 km. 10. Core- 11. The innermost layer is the core with a radius of about 3500 km. 12. It is mainly made up of nickel and iron and is called nife (ni – nickel and fe – ferrous i.e. iron). 13. The central core has very high temperature and pressure.

Answer 26

1. The earth’s crust is made up of various types of rocks. 2. Rock- Any natural mass of mineral matter that makes up the earth’s crust. 3. There are three major types of rocks- 4. Igneous rocks-when the molten magma cools; it solidifies to become igneous rock. 5. Sedimentary rocks- igneous rocks are broken down into small particles that are transported and deposited to form sedimentary rocks. 6. Metamorphic rocks- When the igneous and sedimentary rocks are subjected to heat and pressure they change into metamorphic rocks. 7. Rocks are made up of different minerals. 8. Minerals- are naturally occurring substances which have certain physical properties and definite chemical composition. 9. Minerals are very important to humankind. Some are used as fuels. For example, coal, natural gas and petroleum. They are also used in industries – iron, aluminium, gold, uranium, etc, in medicine, in fertilisers, etc.

Answer 27

1. The place, people, things and nature that surround any living organism is called environment. 2. It is a combination of natural and human-made phenomena. 3. The natural environment refers to both biotic and abiotic conditions existing on the earth. * **Biotic**- The world of living organisms. E.g. plants and animals. * **Abiotic**- The world of non-living elements. E.g. land.

Answer 28

1. Lithosphere 2. Hydrosphere 3. Atmosphere 4. Biosphere

Answer 29

1. It is the solid crust or the hard top layer of the earth. It is made up of rocks and minerals and covered by a thin layer of soil. 2. Lithosphere is the domain that provides us forests, grasslands for grazing, land for agriculture and human settlements. It is also a source of mineral wealth.

Answer 30

1. The domain of water is referred to as hydrosphere 2. It comprises various sources of water and different types of water bodies like rivers, lakes, seas, oceans, etc.

Answer 31

1. It is the thin layer of air that surrounds the earth. 2. The gravitational force of the earth holds the atmosphere around it. 3. It protects us from the harmful rays and scorching heat of the sun. 4. It consists of a number of gases, dust and water vapour. The changes in the atmosphere produce changes in the weather and climate.

Answer 32

1. Plant and animal kingdom together make biosphere. 2. It is a narrow zone of the earth where land, water and air interact with each other to support life.

Answer 33

* All plants, animals and human beings depend on their immediate surroundings. This relation between the living organisms, as well as the relation between the organisms and their surroundings, forms an ecosystem.

Answer 34

India is a country of massive geographical area. **It is bound by-** * The lofty Himalayas in the North; * The Arabian Sea in the West; * The Bay of Bengal in the East; and * The Indian Ocean in the South India has an area of about 3, 28 million sq. km. * The north-south extent from Kashmir to Kanyakumari measures about 3,200 km. * The east-west extent from Arunachal Pradesh to Kucchi measures about 2,900 km.

Answer 35

India is located in the Northern Hemisphere **The Tropic of Cancer** (23°30′ N) passes almost halfway through the country. **Latitude and Longitude** of India **Latitude**: 8°4′ N and 37°6′ N, from south to north. **Longitudes**: 68°7′ E and 97°25′ E, from west to east.

Answer 36

1. There are seven countries that share land boundaries with India. 2. Sri Lanka is separated from India by the Palk Strait.

Answer 37

India is a vast country. For administrative purposes, the country is divided into 29 states and 7 Union Territories. Telangana became the 29th state of India on 2 June 2014.

Answer 38

1. **The Himalayan mountains-** They are divided into three main parallel ranges. The northernmost is the Great Himalaya or Himadri. The world’s highest peaks are located in this range. Middle Himalaya or Himachal lies to the south of Himadri. The Shiwalik is the southernmost range. 2. **Northern Indian plains-** They lie to the south of the Himalayas. They are generally level and flat. 3. **Great Indian desert-** They lie In the western part of India. It is a dry, hot and sandy stretch of land. It has very little vegetation. 4. **Peninsular plateau-** It lies to the south of northern plains. It is triangular in shape. The relief is highly uneven. This is a region with numerous hill ranges and valleys. 5. **The Vindhyas and the Satpuras** are the important ranges. The rivers Narmada and Tapi flow through these ranges. These are west-flowing rivers that drain into the Arabian Sea. In the west, the Western Ghats or Sahyadris border the plateau and the Eastern Ghats provide the eastern boundary. 6. **Coastal plains –** They lie to the West of the Western Ghats and the East of Eastern Ghats. Western coastal plains are very narrow. The eastern Coastal plains are much broader. 7. **Islands -**Two groups of islands also form part of India. Lakshadweep Islands are located in the Arabian Sea. These are coral islands located off the coast of Kerala. The Andaman and the Nicobar Islands lie to the southeast of the Indian mainland in the Bay of Bengal.

Answer 39

It is about the day to day changes in the atmosphere. It includes changes in temperature, rainfall and sunshine etc.

Answer 40

1. It is about the average weather condition, which have been measured over many years. 2. The climate of a place is affected by its, * Location * Altitude * Distance from the sea * Relief **The major seasons recognized in India:** 1. Cold Weather Season (Winter) – (December to February) The sun rays do not fall directly in the region. As a result the temperatures are quite low in northern India. 2. Hot Weather Season (Summer)- (March to May) In the hot weather season sun rays more or less directly fall in this region. Temperature becomes very high. 3. Southwest Monsoon Season (Rainy)- (June to September) This season is marked by the onset and advance of monsoon. The winds blow from Arabian Sea and Bay of Bengal towards the land. They carry moisture with them. When these winds strike the mountain barriers, rainfall occurs. 4. Season of Retreating Monsoon (Autumn)- (October and November) Winds move back from the mainland to the Bay of Bengal. This is the season of the retreating monsoons. The southern parts of India, particularly Tamil Nadu and Andhra Pradesh receive rainfall in this season.

Answer 41

The grasses, shrubs and trees, which grow on their own without interference or help from human beings are called natural vegetation. 1. Tropical Rain Forest 2. Tropical Deciduous Forests 3. Thorny Bushes 4. Mountain Vegetation 5. Mangrove Forests

Answer 42

1. The tiger is our national animal. It is found in various parts of the country. Gir forest in Gujarat is the home of Asiatic lions. Elephants and one-horned rhinoceroses roam in the forests of Assam. Elephants are also found in Kerala and Karnataka. Camels and wild asses are found in the Great Indian desert and the Rann of Kuchchh respectively. Wild goats, snow leopards, bears, etc. are found in the Himalayan region. Besides these, many other animals are found in our country such as monkey, wolf, jackal, nilgai, cheetah, etc. 2. India is equally rich in bird life. The peacock is our national bird. Other common birds are parrots, pigeons, mynah, geese, bulbul, and ducks. 3. There are several hundreds of species of snakes found in India. Cobras and kraits are important among them. 4. In order to protect them many national parks, sanctuaries and biosphere reserves have been set up. The Government has also started Project Tiger and Project Elephant to protect these animals.

Answer 43

The surface of the earth is uneven, some parts may be rugged and some flat. The earth has an immeasurable variety of landforms. These landforms are a result of two processes and they are: 1. Internal process- The Internal Process leads to the upliftment and sinking of the earth’s surface. 2. External process- It is the continuous wearing down and rebuilding of the land surface and includes two processes namely: * Erosion– It is the wearing away of the earth’s surface. * Deposition– It is the rebuilding of a lowered surface (occurred due to erosion). The erosion and deposition processes are carried out by running water, ice and wind. Landforms can be grouped based on the elevation and slope and they are: 1. Mountains 2. Plateaus 3. Plains

Answer 44

1. Any natural elevation of the earth surface is called a **Mountain**. 2. **Range**- Mountains arranged in a line. 3. **Glaciers** – Glaciers are permanently frozen rivers of ice in mountains. There are three types of mountains and they are: 1. Fold Mountains * They are rugged relief and high conical peaks. * g. Himalayan Mountains and the Alps (Young fold mountains) * The Aravali range in India (oldest fold mountain system in the world) * The Appalachians in North America and the Ural mountains in Russia (very old fold mountains) 1. Block Mountains * Created when large mass of land are broken and displaced vertically. * The Rhine valley and the Vosges mountain in Europe 1. Volcanic Mountains * Formed due to volcanic activity. * Mt. Kilimanjaro in Africa and Mt. Fujiyama in Japan. **How the Mountains are useful?** * Mountains are very useful in various ways. * They are storehouse of water and many rivers have their basis in the glaciers in the mountain. * Reservoirs are made and water is harnessed for the use of people. * Water from the mountains is also used for irrigation and generation of hydro-electricity. * Mountains have a rich variety of flora and fauna. * The forests provide fuel, fodder, shelter and other products like gum, raisins, etc. * Mountains also provide a tranquil site for tourists.

Answer 45

* A plateau is an elevated flat land. * It is a flat-topped table land standing above the surrounding area. * e.g. The Deccan plateau in India is one of the oldest plateaus. * The Western plateau of Australia, the East African Plateau in Kenya (The Tanzania and Uganda), the Tibet plateau (the highest plateau in the world) etc. **How the Plateaus are useful?** * Plateaus are very useful as they are rich in mineral deposits. * E.g. African plateau is famous for gold and diamond mining * Chhotanagpur plateau in India is a huge reserves of iron, coal and manganese

Answer 46

1. Plains are large stretches of flat land. 2. Generally, not more than 200 metres above mean sea level. 3. Generally, plains are very fertile; hence these plains are very thickly-populated regions of the world. * E.g. largest plains made by the rivers are found in Asia and North America * Large plains in Asia are formed by the Ganga and the Brahmaputra in India and the Yangtze in China. **How the Plains are useful?** 1. Plains are the most useful areas for human habitation. 2. Building houses, construction of transport network, as well as for cultivation is easy. 3. In India, the Indo-Gangetic plains are the most densely populated regions.

Answer 47

The earth’s surface is a complex zone in which the three major components of the environment meet, overlap and interact. The Four Domains of the Earth 1. **Lithosphere**: The solid portion of the earth 2. **Atmosphere**: The gaseous layers that surround the earth 3. **Hydrosphere**: Water covers a very big area of the earth’s surface and this area is called the Hydrosphere 4. **Biosphere**: It is the narrow zone where land, water and air together are found.

Answer 48

* The solid portion of the earth is called the Lithosphere. * It comprises the rocks of the earth’s crust and the thin layers of soil that contain nutrient elements which sustain organisms. **There are two main divisions of the earth’s surface:** 1. Continents- the large landmasses. 2. Ocean basins- the huge water bodies. *_Mt. Everest is the highest mountain peak measuring 8,848 metres above the sea level. The greatest depth of 11,022 metres is recorded at Mariana Trench in the Pacific Ocean._*

Answer 49

There are seven major continents and these are separated by large water bodies. 1. Asia 2. Europe 3. Africa 4. North America 5. South America 6. Australia 7. Antarctica

Answer 50

1. Asia is the largest continent covering one-third of the total land area of the earth. 2. The continent lies in the Eastern Hemisphere. 3. The Tropic of Cancer passes through Asia. 4. The Ural mountains on the west separates from Europe.

Answer 51

1. Europe is much smaller than Asia lying to the west of Asia. 2. The Arctic Circle passes through it. 3. Its three sides are bound by water bodies.

Answer 52

1. Africa is the second largest continent after Asia. 2. A large part of Africa lies in the Northern Hemisphere. 3. Africa is the only continent through which the Tropic of Cancer, the Equator and the Tropic of Capricorn pass. ***The Sahara Desert, the world’s largest hot desert, is located in Africa. The continent is bound on all sides by oceans and seas. The world’s longest river the Nile, flows through this continent.***

Answer 53

1. North America is the third largest continent of the world. 2. The continent lies completely in the Northern and Western Hemisphere. 3. The Isthmus of Panama a narrow strip links North America and South America. 4. This continent is surrounded by three oceans and they are the Atlantic Ocean, the Pacific Ocean, and the Arctic Ocean.

Answer 54

1. South America lies mostly in the Southern Hemisphere. 2. It is surrounded by two oceans; the Pacific Ocean on the west and the Atlantic Ocean on the east and north. ## Footnote ***The world’s longest mountain range, The Andes and the world’s largest river, the Amazon are in South America.***

Answer 55

1. Australia is the smallest continent that lies entirely in the Southern Hemisphere. 2. It is surrounded on all sides by the oceans and seas. 3. It is called an island continent.

Answer 56

* Antarctica is a huge continent and lies completely in the Southern Hemisphere. * The South Pole lies in the South Polar Region almost at the centre of this continent and is permanently covered with thick ice sheets. ## Footnote ***Various countries have their research stations here. India also has its research stations here, namely Maitri and Dakshin Gangotri.***

Answer 57

1. The earth is called the blue planet. 2. More than 71 per cent of the earth is covered with water and 29 per cent is with land. Hydrosphere consists of water in all its forms. 3. More than 97% of the Earth’s water is found in the oceans and is too salty for human use. 4. Hydrosphere consists of water in all its forms like running water in oceans and rivers and in lakes, ice in glaciers, underground water and the water vapour in atmosphere. 5. 97% of the Earth’s water is found in the oceans and is too salty, the rest of the water is in the form of icesheets and glaciers or under the ground and a very 6. small percentage is available as fresh water for human use

Answer 58

* The three chief movements of ocean waters are the waves, the tides and the ocean currents. * Oceans are the major part of hydrosphere and they are all interconnected. * The five major oceans in order of their size are 1. **The Pacific Ocean**: It is almost circular in shape. Asia, Australia, North and South Americas surround it. 2. **The Atlantic Ocean**: It is the second largest Ocean in the world. It is ‘S’ shaped. It is flanked by the North and South Americas on the western side, and Europe and Africa on the eastern side. 3. **The Indian Ocean**: It is the only ocean named after a country, that is, India. The shape of ocean is almost triangular. In the north, it is bound by Asia, in the west by Africa and in the east by Australia. 4. **The Southern Ocean**: It surrounds the continent of Antarctica 5. **The Arctic Ocean**: It is located within the Arctic Circle and surrounds the North Pole. The Berring strait a narrow stretch of shallow water connects it with the Pacific Ocean.

Answer 59

The earth is surrounded by a layer of gas called the atmosphere. * The atmosphere extends up to a height of about 1,600 kilometres. * The atmosphere is divided into five layers based on composition, temperature and other properties and they are: 1. the troposphere 2. the stratosphere 3. the mesosphere 4. the thermosphere 5. the exosphere * A bout 99 per cent of clean and dry air in the atmosphere is composed mainly of nitrogen and oxygen. Nitrogen 78 per cent, oxygen 21 per cent and other gases like carbondioxide, argon and others comprise 1 per cent by volume.

Answer 60

1. The biosphere is the narrow zone of contact between the land, water and air. 2. It is the zone where life exists that makes this planet unique. 3. The organisms in the biosphere are commonly divided into: * the plant kingdom * the animal kingdom 1. The three domains of the earth interact with each other and affect each other in some way or the other.

Answer 61

**Rotation** * Rotation is the movement of the earth on its axis **Revolution** * Revolution is the movement of the earth around the sun in a fixed path or orbit **Orbital Plane** * Orbital plane is the plane formed by the orbit. **The axis of the earth** * The axis of the earth is an imaginary line that makes an angle of 66½° with its orbital plane.

Answer 62

1. The circle of illumination is the circle that divides the day from night on the globe. 2. It takes 365¼ days (one year) for earth to revolve around the sun. 3. Six hours saved every year are added to make one day (24 hours) over a span of four years. This surplus day is added to the month of February. Thus every fourth year we have leap year with 366 days. 4. Earth goes around the sun in an elliptical orbit. Note that throughout its orbit, the earth is inclined in the same direction.

Answer 63

1. A year is usually divided into summer, winter, spring and autumn seasons. 2. Seasons change due to the change in the position of the earth around the sun. 3. Summer Solstice: The longest day and the shortest night. It occurs on 21st June in northern hemisphere ## Footnote ***On 21st June, the Northern Hemisphere is tilted towards the sun. The rays of the sun fall directly on the Tropic of Cancer. Therefore, these areas experience more heat. The areas near the poles receive less heat as the rays of the sun are slanting. The North Pole is inclined towards the sun and the places beyond the Arctic Circle experience continuous daylight for about 6 months.***

Answer 64

The nights are longer than the days. It occurs On 22nd December. ## Footnote ***( On 22nd December, the Tropic of Capricorn receives direct rays of the sun as the South Pole tilts towards it. As the sun’s rays fall vertically at the Tropic of Capricorn (23½° S), a larger portion of the Southern Hemisphere gets light)***

Answer 65

The whole earth experiences equal days and equal nights. It occurs on 21st March and September 23rd. ## Footnote ***(On 21st March and September 23rd, direct rays of the sun fall on the equator. At this position, neither of the poles is tilted towards the sun)***

Answer 66

Map is a representation or a drawing of the earth’s surface or a part of it on a flat surface according to a scale.

Answer 67

1. **Physical or Relief Maps** * Maps showing natural features of the earth such as mountains, plateaus, plains, rivers, oceans etc. are known as physical or relief maps. 1. **Political Maps** * Maps showing cities, towns, villages, states, and different countries of the world with their boundaries are called political maps. 1. **Thematic Maps** * Maps that focus on specific information like road maps, rainfall maps, distribution of forests, industries etc. are called thematic maps. 1. **Sketch** * It is a drawing mainly based on memory and spot observation and not to scale 1. **Plan** * It is a drawing of a small area on a large scale. * A large-scale map gives a lot of information.

Answer 68

1. **Distance** * Maps are drawings, which reduce the entire world or a part of it to fit on a sheet of paper. A scale is being used to do this accurately. A scale is a ratio between the actual distance on the ground and the distance shown on the map 1. **Direction** * There are 4 cardinal points namely-North, South, East, West. * Other four intermediate directions are north-east (NE), southeast(SE), south-west (SW) and north-west (NW) * It is possible to locate any place more accurately with the help of these intermediate directions. 1. **Symbols** * Different features such as buildings, roads, bridges, trees, railway lines or a well. So, they are shown by using certain letters, shades, colours, pictures and lines on the maps. These symbols give a lot of information in a limited space. * With the use of these symbols, maps can be drawn easily and are simple to read.

Answer 69

1. **Equator** * Equator is an imaginary line running on the globe that divides it into two equal parts. * Northern half of the earth is known as the Northern Hemisphere and Southern half is known as the Southern Hemisphere. 1. **Parallels of latitudes** * Parallels of latitudes are parallel circles from the equator up to the poles. * They are measured in degrees. The equator represents the zero degrees latitude. Its distance from the equator to either of the poles is one-fourth of a circle round the earth, it will measure ¼th of 360 degrees, i.e. 90°. Thus, 90 degrees north latitude marks the North Pole and 90 degrees south latitude marks the South Pole. 1. **Important Parallels of Latitudes** * Tropic of Cancer (23½° N) in the Northern Hemisphere * Tropic of Capricorn (23½° S) in the Southern Hemisphere * Arctic Circle at 66½° north of the equator * Antarctic Circle at 66½° south of the equator

Answer 70

1. **Torrid Zone** * The mid-day sun is exactly overhead at least once a year on all latitudes in between the Tropic of Cancer and the Tropic of Capricorn. It therefore, receives the maximum heat. 1. **Temperate Zones** * The mid-day sun never shines overhead on any latitude beyond the Tropic of Cancer and the Tropic of Capricorn. The angle of the sun’s rays goes on decreasing towards the poles. and the Tropic of Capricorn and the Antarctic Circle in the Southern Hemisphere, They have moderate temperatures 1. **Frigid Zones** * Areas lying between the Arctic Circle and the North Pole in the Northern Hemisphere and the Antarctic Circle and the South Pole in the Southern Hemisphere, are very cold. It is because here the sun does not rise much above the horizon.

Answer 71

1. **Prime Meridian** * The meridian which passed through Greenwich, where the British Royal Observatory is located. This meridian is considered as the Prime Meridian. * Its value is 0° longitude and from it we count 180° eastward as well as 180° westward. The Prime Meridian and 180° meridian divide the earth into two equal halves, the Eastern Hemisphere and the Western Hemisphere 1. **Longitude and Time** * The best means of measuring time is by the movement of the earth, the moon and the planets. The sun regularly rises and sets every day. * When the Prime Meridian of Greenwich has the sun at the highest point in the sky, all the places along this meridian will have mid-day or noon. * As the earth rotates from west to east, those places east of Greenwich will be ahead of Greenwich time and those to the west will be behind it. * It can be calculated this way- The earth rotates 360° in about 24 hours, which means 15° an hour or 1° in four minutes. Thus, when it is 12 noon at Greenwich, the time at 15° east of Greenwich will be 15 × 4 = 60 minutes, i.e., 1 hour ahead of Greenwich time, But at 15° west of Greenwich, the time will be behind Greenwich time by one hour

Answer 72

1. The local time of places which are on different meridians are bound to differ. 2. In India, for instance, there will be a difference of about 1 hour and 45 minutes in the local times of Dwarka in Gujarat and Dibrugarh in Assam. 3. In India, the longitude of 82½° E (82° 30’E) is treated as the standard meridian. The local time at this meridian is taken as the standard time for the whole country. It is known as the Indian Standard Time (IST).

Answer 73

1. Celestial bodies are objects like Sun, moon, stars and others that shine in the night sky. 2. Some celestial bodies are very big and are made up of gases and heat. They have their own heat and light which is emitted in large amounts. These celestial bodies are called stars and our Sun is a star. 3. The sun, the moon and all those shining objects in the night sky are called celestial bodies.

Answer 74

1. Different groups of stars form various patterns and they are called constellations. Saptarshi is an example of constellations. 2. In ancient times, with the help of stars directions were determined during night time. The North Star indicates the north direction (Pole Star) and it remains in the same position in the sky. 3. Celestial bodies that do not have their own heat and light and lit by the light of the stars are called planets.

Answer 75

The solar system is made up of the Sun, eight planets, satellites and other celestial bodies.

Answer 76

1. The sun is in the centre of the solar system. 2. It is huge and made up of extremely hot gases. 3. It provides the pulling force that binds the solar system.

Answer 77

* There are eight planets in our solar system. * In order of their distance from the sun, they are: 1. Mercury 2. Venus 3. Earth 4. Mars 5. Jupiter 6. Saturn 7. Uranus and 8. Neptune

Answer 78

1. These planets are very close to the sun. 2. They are made up of rocks. 3. Inner Planets are: * **MERCURY**- One orbit around sun – 88 days, One spin on axis – 59 days. * **VENUS** – One orbit around sun – 255 days. One spin on axis – 243 days * **EARTH** – One orbit around sun – 365 days. One spin on axis – 1 day Number of moons – 1 * **MARS** – One orbit around sun – 687 days One spin on axis – 1 day, number of moons – 02

Answer 79

* Very-very far from the sun and are huge planets made up of gases and liquids 1. **JUPITER** – One orbit around sun – 11 years, 11 months about 12 years. One spin on axis – 9 hours, 56 minutes, number of moons – 16 2. **SATURN** – One orbit around sun – 29 years, 5 months. One spin on axis – 10 hours 40 minutes, number of moons – about 18. 3. **URANUS** – One orbit around sun – 84 years. One spin around axis – 17 hours 14 minutes, number of moons – about 17. 4. **NEPTUNE** – One orbit around sun – 164 years. One spin on axis-16 hours 7 minutes, number of moons – 8

Answer 80

1. Asteroids are numerous tiny bodies which also move around the Sun apart from the stars, planets and satellites. 2. They are found between the orbits of Mars and Jupiter.

Answer 81

* Meteoroids are small pieces of rocks which move around the sun.