CBSE Class 11

Detailed, Step-by-Step NCERT Solutions for Class 11 Geography Chapter 7 Landforms and their Evolution Questions and Answers were solved by Expert Teachers as per NCERT (CBSE) Book guidelines covering each topic in chapter to ensure complete preparation.

Landforms and their Evolution NCERT Solutions for Class 11 Geography Chapter 7

Landforms and their Evolution Questions and Answers Class 11 Geography Chapter 7

Question 1.
Multiple choice questions :
(i) In which of the following stages of landform develop¬ment, downward putting is dominated?
(a) Youth stage
(b) Late mature stage
(c) Early mature stage
(d) Old stage
Answer:
(a) Youthstage.

(ii) A deep valley characterised by steep step-like side slopes is known as
(a) U-shaped valley
(b) Gorge
(c) Blind valley
(d) Canyon
Answer:
(d) Canyon.

(iii) In which one of the following regions the chemical weathering process is more dominant than the mechanical process?
(a) Humid region
(b) Limestone region
(c) Arid region
(d) Glacier region
Answer:
(b) Limestone region.

(v) Which one of the following sentences best defines the term ‘Lapies’?
(a) A small to medium sized shallow depression.
(b) A landform whose opening is more or less circular at the top and funnel shaped towards bottom.
(c) A landform forms due to dripping water from surface.
(d) An irregular surface with sharp pinnacles, grooves and ridges.
Answer:
(d) an irregular surface with sharp pinnacles, grooves and ridges.

(v) A deep, long and wide trough or basin with very steep concave high walls at its head as well as in sides is known as
(a) cirque
(b) glacial valley
(c) lateral moraine
(d) esker
Answer:
(a) cirque.

Question 2.
Answer the following questions in about 30 words each :

(i) What do incised meanders in rocks and meanders in plains of alluviam indicate?
Answer:
Meandering courses over flood plains and delta plains are found where stream gradients are very gentle. But very deep and wide meanders can also be found cut in hard rocks. Such meanders are called incised meanders. Meander loops develop over original gentle surfaces in the initial stages of development of streams.

(ii) Explain the evolution of valleys sinks or uvaias.
Answer:
A sinkhole is an opening more or less circular at the top and funnel-shaped towards bottom with sizes vary ing in areas. When sink-holes and dolines join together because of slumping of materials along their margins or due to roof collapse of caves, long, narrow to wide trenches called valley sinks or uvaias form.

(iii) Underground flow of water is more common than surface run-off in limestone areas. Why?
Answer:
Surface runoff gradually diminishes and is diverted to underground passages developing subterranean drainage. If there is enough water, surface drainage too will develop. Surface runoff and infiltration into the ground starts the solution process along the fractures, faults, bedding planes and other zones of weakness. Subterranean drainage begins to develop.”Solution on the surface and through the ground results in shallow holes and sinkholes.

(iv) Glacial valleys show up many linear depositional forms. Give their locations and names.
Answer:
The linear depositional formed by the glacier are called moraines. These are terminal moraines, lateral moraines and ground moraines. A deep valley characterised by steep step-like side slopes is known as :

• U-shaped valley.
• Gorge.
• Blind valley.
• Canyon.

(v) How does wind perform its task in desert areas? Is it the only agent responsible for the erosional features in deserts?
Answer:
Wind is one of the two dominant agents in hot deserts. The desert floors get heated up too much and too quickly because of being dry and barren. The heated floors heat up the air and results in upward movements in the hot lighter air with turbulence, whirlwinds, updrafts and downdrafts.

Winds move along the desert floors with great speed. There are storm winds which are very destructive. Winds cause deflation, abrasion and impact. Wind action creates a number of t – interesting erosional and depositional features in the deserts.

Question 3.
Answer the following questions in about 150 words each :
(i) “Running water is by far the most dominating geomorphic agent in shaping the earth’s surface in humid as well as in arid climates.” Explain.
Answer:
Running water is considered the most important geomorphic agent in bringing about the degradation of land surface. There are two components of running water:
(1) overland flow on general land surface as a sheet, and
(2) linear flow as streams and rivers in the valleys. Most of the erosional landforms made by running water are associated with vigorous and youthful rivers flowing over steep gradients. With time, stream channels over steep gradients turn gentler due to continued erosion. The greater is the deposition, downward cutting becomes less dominant and lateral erosion of banks increases and, as a consequence, the hills and the valleys are reduced to plains.

Overland flow causes sheet erosion. Depending upon theirregularities of the land surface, rills, gullies, valleys are formed. In arid regions, rain is scarce. It comes down torrentially in a short period of time. These regions owe their formation to mass wasting and running water as sheet floods. Stream channels are broad, smooth and indefinite and flow for a brief time after rains.

Landscape evolution is primarily concerned with the formation and extension of pediments. Such rocky floors form as a result of erosion of mountainfront through a combination of lateral erosion by streams and sheet flooding through the extension of pediments. These low featureless plains are called pediplains.

(ii) Limestones behave differently in humid and arid climates. Why? What is the dominent and almost exclusive geomorphic process in limestone areas and what are its results?
Answer:
The result of the work of ground water cannot be seen in all types of rock. But in rocks like limestones or dolomites, rich in calcium carbonate, the surface water as well as ground water through the chemical process of solution and precipitation develop varieties of landforms. These two processes of solution and precipitation are active in limestones or dolomites occuring either exclusively or interbedded with other rocks.

Any limestone region showing typical landforms produced by the action of ground water through the process of solution and precipitation is called karst topography. Limestone is calcium carbonate which is slightly soluble in pure water. Due to erosional activity, shallow holes, small to large sinkholes, dolines, cavities and tunnels and trenches form on the surface of limestones.

If there is enough water (humid climate), surface drainage too will develop, and mass wasting also plays a role in the degradation of limestone rocks. Surface runoff and infiltration into ground starts the solution process along the fractures, faults, bedding planes and other zones of weakness. Solution on the surface and through the ground results in the formation of swallow holes and sinkholes.

Cavities and tunnels develop underground. Sinkholes and dolines not only increase in their number but also in their diameter. They enlarge and merge creating long and wide trenches. The trenches widen and suffer headward erosion through mass wasting. Gradually, most of the surface of the limestone is eaten away by these pits and trenches leaving it extremely irregular and forming grooves and fluted lapies. The lapie field may turn into somewhat smooth limestone pavements.

In areas of arid climate, where the alternating beds of rocks (shales, sandstones, quartzites) with limestones or dolomites, are dense, massive and occuring as thick beds, cave formation is prominent. It is along ; these bedding planes that limestone dissolves and long and narrow to wide gaps called caves result. Caves normally have an opening through which cave stream discharges out, called tunnels.

Many beautiful depositional forms develop within the limestone caves,.known as depositional landforms. Stalagmites rise up from the floor of the caves. These are formed due to dripping water from the surface, of the stalactite, immediately below it. Stalagmites may take the shape of a column, disc, crater like depression. The stalagmites and stalactites fuse to give rise to columns and pillars of different diameters with smooth or fluted surface.

(iii) How do glaciers accomplish the work of reducing high mountains into low hills and plains?
Answer:
Masses of ice moving as sheets over the land are called glaciers. The movement of glaciers isfslow. Glaciers move because of the force of gravity. Erosion by glaciers is tremendous because of the friction caused by the sheer weight of the ice. The material plucked from the land by glaciers gets dragged along the floor or sides of the valleys and cause great damage through abrasion and plucking. Glaciers can cause significant damage and can reduce high mountains into low hills and plains.

The accumulated ice, while moving down the mountaintops, cuts and scoops amphitheatre-like basins called cirques. Ice masses move down the cirques and join together to move along a valley. If three or more radiating glaciers cut headward until their cirques meet, high, sharp-pointed and steep-sided peaks called horns form. As glaciers continue to move, debris gets removed, divides get lowered and eventually, the slope is reduced to such an extent that glaciers will stop moving, leaving only a mass of low hills and vast outwash plains along with other depositional features.

Erosional landforms
Cirque : Cirques are the most common landform in glacialiated mountains. They are found at the heads of glacial valleys.

Horns and serrated ridges : Homs form through headward erosion of the cirque-walls. The divides between cirque side walls or head walls get narrow because of progressive erosion and turn into serrated or saw-toothed ridges.

Glacial valleys/troughs : Glaciated valleys are trough like and U-shaped with broad floors and over steepened sides. Very deep glacial troughs filled with sea water and making up shorelines are called fiords.

Ice-scoured plains: Striations, grooves and polished surfaces, rock basins and rounded rock knobs are found on ice-scoured plains with patches of glacial drift deposits.

Depositional landforms – Large quantity of eroded material accompanies a glacier. Strip of dirt and rock that flows with the ice and is deposited along the side of valley is known as lateral moraine.

When the lateral moraine of two glaciers merge, they form a single medieval moraine in the middle. Plucking of bedrocks by the over-riding glacier beds to this formation of glacial trough a channel at the valley glacier. The glacial trough is filled up by water and gives rise to trough lake.

The glacial troughs formed near the sea get filled in by the sea water giving rise to fiords. At the head of each trough, a semi¬circular basin is formed called cirque. Below the snow lines, the glacier melts and materials carried by it are deposited. Eskers, drumlins, out- wash plain and many other features are noticeable in the area.

Detailed, Step-by-Step NCERT Solutions for Class 11 Geography Chapter 6 Geomorphic Processes Questions and Answers were solved by Expert Teachers as per NCERT (CBSE) Book guidelines covering each topic in chapter to ensure complete preparation.

Geomorphic Processes NCERT Solutions for Class 11 Geography Chapter 6

Geomorphic Processes Questions and Answers Class 11 Geography Chapter 6

Question 1.
Multiple choice questions :

(i) Which one of the following processes is a gradational process?
(a) Deposition
(b) Diastrophism
(c) Volcanism
(d) Erosion
Answer:
(d) Erosion.

(ii) Which one of the following materials is affected by hydration process?
(a) Granite
(b) Clay
(c) Quartz
(d) Salts
Answer:
(d) Salts.

(iii) Debris avalanche can be included in the category of:
(а) Landslide
(b) Slow flow mass movements
(c) Rapid flow mass movements
(d) Subsidence
Answer:
(c) Rapid flow mass movements.

Question 2.
Answer the following questions in about 30 words :
(i) It is weathering that is responsible for bio-diversity on earth. How?
Answer:
Weathering is an important exogenetic geomorphic process. It is the mechanical disintegration and chemical decomposition of rocks through the actions of various elements of weather and climate. Weathering processes are conditioned by many complex geological, climatic, topographic and vegetative factors.

Biological weathering is contribution to or removal of minerals and ions from the weathering environment. Burrowing and wedging by organisms help in exposing the new surfaces to chemical attack and assist in the penetration of moisture and air. Decaying plant and animal matter helps in the production of humic matter.

(ii) What are mass movements thsU are real rapid and *” perceptible? List.
Answer:
Mass movements involve the transfer of mass of rock debris down the slopes under the direct influence of gravity. The mass movements may range from slow to rapid, affecting shallow to deep column of materials and include creep, flow, slide and fall.

(iii) What are the various mobile and mighty exogenic geomorphic agents and what is the prime job they perform?
Answer:
Water, ice, wind, etc. are capable of acquiring and transporting earth materials. They are known as exogenetic geomorphic agents. When these natural agents become mobile due to gradients, they remove the materials and transport them over the, slopes. An agent is a mobile medium (like running water, moving ice masses, wind, etc.) which removes, transports and deposits earth materials. Running water, ground water, glaciers, wind waves and currents, etc. can be called geomorphic agents.

(iv) Is weathering essential as a pre-requisite in the formation of soils? Why?
Answer:
When rocks undergo weathering, some materials are removed through chemical or physical leaching by ground water and thereby the concentration of- remaining materials increases. Without such a weathering taking place, the concentration of the same valuable material may not be sufficient and economically viable to exploit, process and refine. Thus, weathering is essential.

Question 3.
Answer the following questions in about 150 words each :
(i) “Our earth is a playfield for two opposing groups of geomorphic processes.” Discuss.
Answer:
The endogenic and exogenic forces causing physical stresses and chemical actions on earth materials and bringing about changes in the configuration of the surface of the earth are known as geomorphic processes.

Diastrophism and volcanism are endogenetic geomorphic processes. Weathering, mass wasting, erosion and deposition are exogenetie processes.

The earth’s surface is being continuously subjected to the external forces originating within the earth’s atmosphere and the internal forces from within the earth, an it is ever-changing. The action of exogenetie ; forces result in wearing down (degradation) of relief/elevations and filling up (aggradation) of basins/depressions on the earth’s surface.

The endogenetic forces continuously elevate or build up parts of the earth’s surface and ‘hence’ the exogenetie processes fail to even out l the relief variations of the surface of the earth. The building up and wearing down of the earth’s surface by endogenetic and exogenetie forces respectively is going on from the time the earth’s crust was 1 developed and enveloped by the atmosphere. Hence, our earth is a playfield of two opposing forces.

(ii) Exogenic gemorphic processes derive their ultimate energy from sun’s heat. Explain.
Answer:
Exogenic geomorphic processes vary from region to region. Temperature and precipitation are the two important climatic elements S that control various processes. All the exogenetie processes are covered under a general term  denudation, which means to strip off or to uncover. Weathering, mass wasting/movements, erosion and  transportation are the type of denudation processes.

Climatic factors being equal, the intensity of action of exogenetie geomorphic processes depends upon the type and structure of rocks.The density, type and distribution of vegetation, which largely depends upon precipitation and temperature, exert an indirect influence – on exogenetie geomorphic processes. Within different climatic regions, there may be local variations of the effects of different climatic elements due to altitudinal differences. For all exogenetie processes, the energy/ heat is received from the sun. Hence, sun is the ultimate source of energy.

(iii) Are physical and chemical weathering processes independent of each other? ]f not, why? Explain with examples.
Answer:
Chemical weathering processes: The weathering processes, viz, hydration reduction, oxidation, carbonation, solution act on the rocks to decompose, dissolve or reduce them to a fine clastic state through chemical reactions. Water and air. along with heat, must be present to speed up all chemical reactions.

Physical weathering : Physical weathering depends on some applied forces:

• Gravitational forces,
• Expansion forces due to temperature changes,
• Water pressures controlled by wetting and drying cycles.

Physical weathering and chemical weathering are not independent, Both are dependent on each other. The hydration and dehydration both physically and chemically affect the weathering processes. Under certain moisture and temperature conditions, calcium sulphate takes in water and turns to gypsum causing a volume change in material. During this process, both physical and chemical weathering occurs. All weathering processes take place physically as well as chemically. Hence, both processes are dependent on each other.

(iv) How do you distinguish between the process of soil formation and soil forming factors? Wliat is the role of climate and biological activity as two important control factors in the formation of soils?
Answer:
Several processes like eluviation, illuviation, cheluviation, and leaching are involved in soil formation. Soil forming factors: All soil forming processes involve weathering. There are several other factors that influence the end product of weathering. Five of them are primary factors. They are responsible for the development of various types of soils. These factors are: parent material, climate, biota, topography and time.

Role of climatic factor: Climate affects soil formation in the following ways:

• Seasonal distribution of temperature.
• Amount of rainfall.
• The quality of water seeping into rock materials.
• Type and effectiveness of weathering.of parent-rock material.
• Different types of micro-organisms present in the soil.
• Climate affects the vegetation which helps in the soil formation.

Microflora or bacterial activity is quite a significant controlling factor in soil formation: With undecomposed organic matter, because of low bacterial activity, layers of peat develop in sub-arctic and tundra climates. Bacteria and other soil organisms take gaseous nitrogen from the air and convert it into a chemical form that can be used by plants. This process is known as nitrogen fixation.

Earthworms are important in humid regions. They change the texture and chemistry of the soil as it passes through their digestive systems. Large quantities of soil are L brought up to the surface by ants and termites from the lower horizons.Burrowing animals like rodents disturb and rearrange the soil. In this way, biological activities play an important role in soil formation.

Detailed, Step-by-Step NCERT Solutions for Class 11 Geography Chapter 5 Minerals and Rocks Questions and Answers were solved by Expert Teachers as per NCERT (CBSE) Book guidelines covering each topic in chapter to ensure complete preparation.

Minerals and Rocks NCERT Solutions for Class 11 Geography Chapter 5

Minerals and Rocks Questions and Answers Class 11 Geography Chapter 5

Question 1.
Multiple choice questions.
(i) Which one of the following are the two main constituents of granite?
(a) Iron and Nickel
(b) Iron and Silver
(c) Silica and Aluminium
(d) Iron oxide and Potassium
Answer:
(c) Silica and Aluminium.

(ii) Which one of the following is the salient feature of metamorphic rocks?
(a) Changeable
(b) Quite
(c) Crystalline
(d) Foliation
Answer:
(a) Changeable.

(iii) Which one of the following is not a single element mineral?
(a) Gold
(b) Silver
(c) Mica
(d) Graphite
Answer:
(c) Mica.

(iv) Which one of the following is the hardest mineral?
(a)Topaz
(b) Diamond
(c) Quartz
(d) Feldspar
Answer:
(b) Diamond.

(v) Which one of the following is not a sedimentary rock?
(a) Tillite
(b) Borax
(c) Breccia
(d) Marble
Answer:
(a) Tillite.

Question 2.
Answer the following questions in about 30 words each :

(i) What do you mean by rocks? Name the three major classes of rocks.
Answer:
A rock is an aggregate of one or more minerals. It may be soft or hard and in varied colours.
Three classes of rocks are :

• Igneous rocks
• Sedimentary rocks, and
• Metamorphic rocks.

(ii) What is an igneous rock? Describe the method of formation and characteristics of igneous rock.
Answer:
The solid form of the magma is known as igneous rocks. These rocks are formed from lava hurled out of a volcano or from the cooling of the magma below the crust.
Characteristics:

• These are massive and found in bulks.
• These rocks have different types of crystals.
• These rocks are formed due to the cooling of magma.

(iii) What is meant by sedimentary rock? Describe the mode of formation of sedimentary rock?
Answer:
The rocks which are formed by the accumulation of sediments are known as sedimentary rocks. These are formed by sediments brought by the erosion and weathering of other rock types. When deposited in sea, they are compressed and hardened to form layers of rocks. Sandstone is made from grains of sand which have been naturally cemented here.

(iv) What relationship explained by rock cycle between the major type of rock?
Answer:
Rock cycle is a continuous process through which old rocks are transformed into new ones. Igneous rocks are primary rocks and other are rocks formed from these. They can be changed into metamorphic rocks. The fragments derived out of igneous and metamorphic rocks form into sedimentary rocks.

The sedimentary rocks can turn into fragments and the fragments can form sedimentary rocks. The crustal rocks once formed may be carried down into the mantle through subduction process and melt down due to the increase in temperature in the interior and turn into molten magma, the original source of igneous rocks.

Question 3.
Answer the following questions in about 150 words each :
(i) Define the term ‘mineral’ and name the major classes of minerals with their physical characteristics.
Answer:
A mineral is an inorganic element or compound having definite chemical composition and definite atomic structure. All the commonly occuring minerals are classified into six major mineral groups that are known as major rock forming minerals.

Physical characteristics :
(1) External crystal structure : They have six types of crystal structure – cubes, octahedrons, hexagonal prisms, etc.

(2) Cleavage : They undergo cleavage in one or more direction and, at any angle to each other.

(3) Fracture : The crystal will break in an irregular manner, not
along the plane of cleavage. ‘

(4) Lusture : Each mineral has a distinctive lusture like metallic, silky, glossy, etc.

(5) Colour: Some minerals have characteristic colour determined by their molecular structure – malachite, azurite, chalcopyrite, etc. Some minerals are coloured by impurities, such as quartz.

(6) Streak: The colour of the ground powder of any mineral may be the same as the mineral or may differ.

(7)

• Transparency : When light rays pass through the objects, they can be seen plainly.
• Translucent: Light rays pass through but will get diffused, so that object cannot be seen clearly.
• Opaque : Light rays will not pass at all.

(8) Structure: Minerals have particular arrangement of individual crystals : fine, medium or coarse grained.

(9) Hardness: The degree to which a mineral surface resist being scratched is known as hardness.

(10) Specific gravity : It is the ratio between the weight of a given object and the weight of an equal volume of water.

(ii) Describe the nature and mode of origin of the chief types of rocks at the earth’s crust. How will you distinguish them?
Answer:
A rock is an aggregate of one or more minerals. There is a close relationship between rocks and landforms. The rocks are grouped under three types of categories :

• Igneous rocks
• Sedimentary’ rocks
• Metamorphic rocks.

Igneous rocks: They form out of magma and lava from the interior of the earth. These are known as primary rocks. They are classified on the basis of texture (structure).

Sedimentary Rocks : These rocks are formed by deposition of fragments of rocks by exogenous processes. Fragments are transported in by various exogenous agencies and deposited through compaction/or cementation. This process is called lithification. Depending upon their mode of formation they are classified into three major groups :

• Mechanically formed
• Organically formed, and
• Chemically formed.

Metamorphic Rocks : These rocks are formed under the action of x pressure, volume and temperature (PVT). Metamorphism is a process ’ by which already consolidated rocks undergo recrystallization and reorganization of materials within original rocks. They are classified into two major groups – foliated and non-foliated rocks.

(iii) What are metamorphic rocks? Describe the types of matamorphic rock and how they are formed.
Answer:
The solid form of the magma is known as igneous rocks. These rocks are formed from lava hurled out of a volcano or from the cooling of the magma below the crust.
Characteristics:

• These are massive and found in bulks.
• These rocks have different types of crystals.
• These rocks are formed due to the cooling of magma.

Detailed, Step-by-Step NCERT Solutions for Class 11 Geography Chapter 11 Distribution of Oceans and Continents Questions and Answers were solved by Expert Teachers as per NCERT (CBSE) Book guidelines covering each topic in chapter to ensure complete preparation.

Distribution of Oceans and Continents NCERT Solutions for Class 11 Geography Chapter 4

Distribution of Oceans and Continents Questions and Answers Class 11 Geography Chapter 4

Question 1.
Multiple choice questions :

(i) Who amongst the following was the first to consider the possibility of Europe, Africa and America having been located side by side?
(a) Alfred Wegner
(b) Abraham Ortelius
(c) Antonia Pellegrini
(d) Edmond Hess
Answer:
(b) Abraham Ortelius.

(ii) Polar fleeing force relates to ………..
(a) Revolution of the earth
(b) Gravitation
(c) Rotation of the earth
(d) Tides
Answer:
(c) Rotation of the earth.

(iii) Which one of the following is not a minor plate?
(a) Nazca
(b) Arabia
(c) Philippines
(d) Antarctica
Answer:
(d) Antarctica.

(iv) Which one of the following facts was not considered by those while discussing the concept of sea floor spreading?
(a) Volcanic activity along the mid-oceanic ridges
(b) Stripes of normal and reverse magnetic fiel observed in rocks of ocean floor
(c) Distribution of fossils in different continents
(d) Age of rocks from the ocean floor.
Answer:
(c) distribution of fossils in different continents.

(v) Which one of the following is the type of plate boundary of the Indian plate along the Himalayan mountains?
(a) Ocean-continent convergence
(b) Divergent boundary
(c) Transform boundary
(d) Continent-continent convergence
Answer:
(d) Continent-continent convergence.

Question 2.
Answer the following questions in about 30 words each :
(i) What were the forces suggested by Wegner for the movement of the continents?
Answer:
(1) Pole fleeing force and
(2) Tidal force.

These were the two forces suggested by Wegner for the movement of the continents. He believed that these forces would become effective when applied over many million years.

(ii) How are the convectional currents in the mantle initiated and maintained?
Answer:
These currents are generated due to radioactive elements causing thermal differences in the mantle portion. The currents move in radial direction and develop in cell patterns.

(iii) What is the major difference between the transform boundary and the convergent or divergent boundaries of the plates?

(iv) What was the location of Indian landmass during the formation of Deccan Traps?
Answer:
(a) India was in the southern hemisphere when the volcanie activity began and was drifting northward during the span of this activity.

(b) Deccan Trap flows having an altitude of around 600 m (2000 ft.) and above were found to be magnetized normally.

Question 3.
Answer the following questions in about 150 words each :

(i) What are the evidences in support of continental drift theory?
Answer:
There were a number of evidences offered in support of the continental drift. Some of them are given below :
(1) The matching of continents : The shorelines of Africa and S. America facing each other have a remarkable and unmistakable match. The match was tried at 1000 fathom line instead of the present shoreline. However, with slight modification, a reasonably good and acceptable map of the continents was demonstrated.

(2) Rocks of same age across the oceans: The radiometric dating methods developed in recent period have facilitated correlating the rock formation from different continents across the vast ocean. The earliest marine deposits along the coastline of either S. America or Africa are of Jurassic age. This suggests that the ocean did not exist prior to that time.

(3) Tillite: Tillite are the sedimentary rocks formed out of deposits of glaciers. The Gondawana system of sediments is known to have its counterpart in six different landmasses of southern hemisphere. At the base, the system has thick tillite indicating extensive and prolonged glaciation. Overall resemblance of the Gondawana type sediments clearly demonstrate that these landmasses had remarkably similar histories. The glacial tillites provide unambiguous evidence of palaeoclimates and also of drifting of continents.

(ii) Bring about the basic difference between the drift theory I and plate tectonics.
Answer:
The basic concept regarding continental drift was that all the
continents formed a single continental mass – a protocontinent. This covered about all the present continents and was surrounded by an ocean. This was named PANGAEA. It was argued that around 200 million years ago, the super continent pangaea began to split apart. Pangaea first broke into two large continental landmasses, Laurasia in the Northern Hemisphere and Gondawana in the Southern Hemisphere. A number of evidences were offered in support of the continental drift.

Plate tectonic : According to plate tectonic theory, the earth’s lithosphere is divided into six major and some minor plates. At present, Antarctica and the surrounding ocean, Americas with western Atlantic floor, Pacific floor, India to Australia and New Zealand, Africa with eastern Atlantic floor, Eurasia and adjacent ocean are the major plates.

Cocos plate, Nazca plate, Arabian plate, Philippine plate, Caroline plate and Fuji plate are minor plates. These plates are moving over the globe throughout the history of the earth. The plate boundaries are the most active areas along which there is always some kind of tectonic activity going on.

(iii) What were the major post drift discoveries that rej uvenated the interest of scientists in the study of distribution of oceans and continents?
Answer:
The positions of the continents and the ocean bodies have not been the same in the past. The oceans and continents will not continue to enjoy their present position in times to come. If this is so, then the question arises what were their positions in the past? Why and how do they change their positions? How do the scientists know this?
Observe the shape of the coastline of Atlantic ocean.

There is symmetry between the coastlines on either side of the ocean. Many scientists thought of this similarity and considered the possibility of the two Americas, Europe and Africa to be once joined. From the known records of the history of science, it was Abraham Ortelius, a Dutch map maker, who first proposed such a possibility as early as 1596.

Antonio Pellegrini drew a map showing the three continents together. Wegner’s theory was based on the remarkable fit of the south American and African continents and the occurrences of unusual geologic structures and of plant and animal fossils found on the matching coastlines of two continents widely separated by the Atlantic ocean. The presence of identical fossil species along the coastal parts of Africa and South America was convincing evidence of the fact that two continents lay side by side in the past.

Detailed, Step-by-Step NCERT Solutions for Class 11 Geography Chapter 3 Interior of the Earth Questions and Answers were solved by Expert Teachers as per NCERT (CBSE) Book guidelines covering each topic in chapter to ensure complete preparation.

Interior of the Earth NCERT Solutions for Class 11 Geography Chapter 3

Interior of the Earth Questions and Answers Class 11 Geography Chapter 3

Question 1.
Multiple choice questions :
(i) Which one of the following earthquake waves is more destructive?
(a) P-waves
(b) S-waves
(c) surface waves
(d) None of the above
Answer:
(c) surface waves.

(ii) Which one of the following is a direct source of information about the interior of the earth?
(a) Earthquakes waves
(b) Volcanoes
(c) Gravitational force
(d) Earth magnetism
Answer:
(b) Volcanoes.

(iii) Which type of volcanic eruptions have caused Deccan Trap formations?
(a) Shield
(b) Composite
(c) Flood
(d) Caldera
Answer:
(b) Flood.

(iv) Which one of the following describes the lithosphere :
(a) upper and lower mantle
(b) crust and core
(c) crust and upper mantle
(d) mantle and core
Answer:
(c) crust and upper mantle.

Question 2.
Answer the following questions in about 30 words each :

(i) What are body waves?
Answer:
The waves generated due to the release of energy at the focus are called body waves. They radiate and move in all directions from ” the point of hypocenter and travel through the body of the earth.

(ii) Name the direct sources of information about the interior of the earth,
Answer:

• Mining ar|as
• Deep Ocean Drilling Project
• Integrated Ocean Drilling Project
• Volcanic eruptions

(iii) Why do the earthquake waves develop shadow zone?
Answer:
The earthquake waves get recorded world over, but it is found that earthquakes are not recorded in some specific zones. Such a zone is called ‘shadow zone.’

(iv) Briefly explain the indirect sources of information of the interior of the earth other than the seismic activity.
Answer:
Analysis of properties of matter indirectly provides the information about the interior. Through the mining activities, we know the temperature and pressure increases with the increase in distance from the surface to the depth. Gravitation, magnetic field and seismic activity are the other indirect sources of information,

Question 3.
Answer the following questions in about 150 words each :

(i) What are the effects of propagation of earthquake waves on the rock mass through which they travel?
Answer:
There are three types of waves. The velocity of waves changes K as they travel through materials with different densities.
There are two types of Body waves ‘P’ and ‘S’ waves. ‘P’ waves move faster and are the first to arrive at the surface. They travel through gaseous, liquid and solid materials. ‘S’waves move slowly and arrive at the surface with some time lag. They can travel only through solid materials. It has helped scientists to understand the structure of the t interior of the earth.

Both ‘P’ and ‘S’ waves reflect and refract as they encounter different a materials along their path. Reflection causes waves to rebound and move in different directions. The surface waves are the last to report. These waves are the most destructive. They cause displacement of rocks and, hence, the collapse of structures.

(ii) What do you understand by intrusive form? Briefly describe various intrusive forms.
Answer:
The lava released during volcanic eruptions on cooling develops into igneous rocks. Depending on the location of the cooling of the lava, igneous rocks are classified as volcanic rocks and plutonic rocks. The lava that cools within the crustal portion assumes different forms.

These forms are called intrusive forms.

Different Intrusive forms are :

Batholiths : A large body of magmatic material that cools in the deeper depth of the crust develops in the form of large domes. These are the cooled portion of magma chambers.

Lacoiiths : These are large dome-shaped intrusive bodies with a level base and connected by a pipe-like conduit from below. Karnataka plateau is spotted with domal hills of granite-rocks.

Lapolith, Phacolith and Sills : When the lava moves upwards, a portion of the same may tend to move in a horizontal direction and develop into a saucer shape, concave to the sky body, it is called lapolith. A wavy mass of intrusive rocks, having a definite conduit to source are called phacoliths. The near horizontal bodies of the intrusive igneous rocks are called sills or sheets.

Dykes : When the lava makes its way through cracks and the fissures developed in the land, it gets cooled to develop a wall-like structure, called dykes.

Detailed, Step-by-Step NCERT Solutions for Class 11 Geography Chapter 2 The Origin and Evolution of the Earth Questions and Answers were solved by Expert Teachers as per NCERT (CBSE) Book guidelines covering each topic in chapter to ensure complete preparation.

The Origin and Evolution of the Earth NCERT Solutions for Class 11 Geography Chapter 2

The Origin and Evolution of the Earth Questions and Answers Class 11 Geography Chapter 2

Multiple Choice Questions
Question 1.
(i) Which one of the following figures represents the age of the earth?
(a) 4.6 million years
(b) 13.7 billion years
(c) 4.6 billion years
(d) 13.7 trillion years
Answer:
(c) 4.6 billion years.

(ii) Which one of the following has longest duration?
(a) Eons
(b) Period
(c) Era
(d) Epoch
Answer:
(b) Period.

(iii) Which one of the following is not related to the formation or modification of the present atmosphere?
(a) Solar winds
(b) Differentiation
(c) Degassing
(d) Photosynthesis
Answer:
(a) Solar winds.

(iv) Which one of the following represents the inner planets?
(a) Planets between the sun and the earth
(b) Planets between the sun and the belt of asteroids
(c) Planets in gaseous state
(d) Planets without satellite(s)
Answer:
(b) Planets between the sun and the belt of asteroids

(v) Life on earth appeared around how many years before the present?
(a) 13.7. billion
(b) 4.6 billion
(c) 3.8 ihillion
(d) 3.8 billion
Answer:
(d) 3.8 billion.

Question 2.
Answer the following questions in about 30 words each :
(i) Why are the terrestrial planets rocky?
Answer:
Mercury, Venus, Earth and Mars are known as terrestrial planets,They are rocky because they are made up of rocks and metals and have relatively high densities.

(ii) What is the basic difference in the arguments related to the origin of the earth given by
(a) Kant and Laplace, and
(b) Chamberlain and Moulton?
Answer:
(a) Kant and Laplace gave Nebular Hypothesis. The planets were formed out of a cloud of material associated with a youthful sun, which was slowly rotating.

(b) Chamberlain and Moulton – A wandering star approached the sun. As a result, a cigar shaped tongue of material was separated from the solar surface. As the passing star moved away, the material separated from the solar surface continued to revolve around the sun and it slowly condensed into planets.

(iii) What is meant by the process of differentiation?
Answer:
After the formation of earth, due to immense heat the earth became partially molten. The lighter and denser materials on melting mixed and got separated depending on their densities. This allowed the separation of heavier and lighter materials called differentiation. During the formation of moon, due to the giant impact, the earth was further heated up leading to the next phase of differentiation. .Through the process of differentiation, earth got separated into different layers.

(iv) What was the nature of the earth’s surface initially?
Answer:
The earth has a layered structure. From the outermost end of the atmosphere to the centre of the earth, the material that exists is not uniform. The atmospheric matter has the least density. From the surface to deeper depths, the earth’s interior has different zones and each of these contains materials with different characteristics.

(v) What were the gases which initially formed the earth’s atmosphere?
Answer:
The planet earth initially was a barren, rocky and hot object with a thin atmosphere of hydrogen and helium. This is far from the present day picture of the earth.

Question 3.
Answer the following questions in about 150 words.
(i) Write an explanatory note on the ‘Big Bang Theory’.
Answer:
In the present world, the most popular argument regarding the origin of the universe is the ‘Big Bang Theory’. This is also called “expanding universe”. The Big Bang theory considers the following stages in the development of the universe :

(ii) In the beginning all matter forming the universe existed in one place in the form of a ‘tiny ball’ with a small volume, infinite temperature and infinite density.

(ii) At the Big Bang the ‘tiny ball’ exploded violently. This led to a huge expansion. The expansion continues even to present day. As it grew, some energy was converted into matter. There was particularly very rapid expansion within fractions of a second after the bang. Thereafter, expansion has slowed down. Within first three minutes from the Big Bang event, first 1 atom began to form.

(iii) Within 300,000 years from the Big Bang, temperature dropped to 4500°K and gave rise to atomic matter. The universe becametransparent.The expansion of universe means increase in space between the galaxies.

(ii) List the stages in the evolution of the earth and explain each ‘ stage in brief,
Answer:
Evolution of the Earth (Development of layered structure):
Initially earth was a barren, rocky and hot object with a thin atmosphere of hydrogen and helium. There must have been some events processes, which may have changed the earth from a rocky, barren and hot place to a beautiful planet. The earth has a layered structure. The material existing on the earth, from centre to the end of atmosphere, is not uniform. Earth’s interior has different zones and each of them contains materials with different characteristics.

Development of layered structure :

• Many planetesimals moved together to form planets.
• The mass forming the earth, collect through gravitation, and had impact on the existing materials. The impact generated lots of heat which caused melting of the materials. This occurred after the formation of the earth.
• Due to this heat, the earth became partially molten and the heavier and denser materials got separated. This allowed heavier materials to sink towards the centre and lighter towards the surface. This process is called differentiation.
• During the formation of Moon, due to the giant impact, the earth was further heated up and got separated into different layers. Starting from the surface to the eentral parts, we have layers like crust, mantle, outer core and inner core.