3. Interior of the Earth

  NCERT Questions:

 Multiple choice questions:

  (i) Which one of the following earthquake waves is most destructive?

a) P waves

b) S wave

c) Surface waves

d) None of the above

Ans. c) Surface waves

(ii) Which one of the following is a direct source of information about the interior of the Earth?

a) Earthquake waves

b) Volcanoes

c) Gravitational force

d) Earth magnetism

Ans.b) Volcanoes

Which type of volcanic eruption has caused Deccan Trap formations?

a) Shield

b) Flood

c) Composite

d) Caldera

Ans.b) Flood

(iv) Which one of the following describes the lithosphere?

a) Upper and lower mental

b) Crust and upper mantle

c) Crust and core

d) Mantle and Core

Ans.b) Crust and upper mantle

2. Answer the following questions in about 30 words.

(i) What are body waves?

Ans.

a) Body waves are generated due to the release of energy at the focus and move in all directions travelling through the body of the earth.

b) There are two types of body waves:

c) They are called:

i) P waves (Primary waves)

ii) S waves (Secondary waves)

d) P waves move faster and are the first to arrive at the surface. The P waves are similar to sound waves.

e) S waves arrive at the surface with some time lag. An important fact about S waves is that they can travel only through solid materials.

(ii) Name the direct source of information about the interior of the Earth.

Ans.

a) The most easily available solid earth material is surface rock or rocks we get from mining areas. Eg. Gold mines in South Africa are as deep as 3 to 4 kilometres.

b) Scientists world over are working on two major projects such as deep ocean drilling project and integrated ocean drilling project.

c) The deepest drill at Kola, in Arctic Ocean has so far reached a depth of 12 kilometres.

d) Volcanic eruption forms another source of obtaining direct information.

(iii) Why do earthquake waves develop shadow zone?

Ans.

a) The P and S waves at the time of earthquake represent a curved path.

b) This shows that the density increases inside the Earth.

c) P and S waves are recorded near the focus of the earthquake, beyond the depth of 2900 kilometres. S waves disappear and the P waves travel with reduced velocity.

d) Hence, the zone that does not show the P and S waves is called shadow zone.

(iv) Briefly explain the indirect sources of information of the interior of the earth other than those of seismic activity.

Ans.

a) Analysis of properties of matter indirectly provides information about the interior.

b) Through the mining activity, we know that temperature and pressure increases with the increasing distance from the surface towards the interior in deeper depths.

c) The density of the material also increases with depth.

d) Knowing the total thickness of the Earth, scientists have estimated the values of temperature, pressure and density of materials at different depths.

e) Another source of information is the meteors that at times reach the Earth as they are similar to that of the Earth.

f) The other indirect sources include gravitation, magnetic field and seismic activity.

g) The gravitational force (g) gravity anomaly is not the same at different latitudes on the surface.

3. Answer the following questions in about 150 words:

(i) What are the effects of propagation of earthquake waves on the rock mass through which they travel?

a) As the waves move or propagate, they cause vibration in the body of the rocks through which they pass.

b) P waves vibrate parallel to the direction of the wave.

c) This exerts pressure on the material in the direction of the propagation.

d) As a result, it creates density differences in the material, leading to stretching and squeezing of the material.

e) Other three waves vibrate perpendicular to the direction of propagation.

f) The direction of vibrations of S waves is perpendicular to the wave direction in the vertical plane.

g) Hence they create troughs and crest in the material through which they pass.

(ii)  What do you understand by intrusive forms? Briefly describe various intrusive forms.

The lava that cools within the crystal portions assumes different intrusive forms:

 Batholiths

a) A large body of magmatic material that cools in the deeper depth of the crust develops in the form of large domes.

b) They appear on the surface only after the denudation processes remove the overlying materials.

c) Batholiths are the cooled portion of magma chambers.

 Laccoliths

a) These are large dome shaped intrusive bodies with a level base and connected by a pipe like conduit from below.

b) It resembles the surface volcanic domes of composite volcano, only these are located at deeper depths.

c) It can be regarded as the localised source of lava that finds its way to the surface.

d) The Karnataka plateau is spotted with Dome shaped hills of granite rocks.

e) Most of these, now exfoliated are examples of laccoliths or batholiths.

Lapolith, Phacolith and Sills

a) As and when the lava moves upwards, a portion of the same may tend to move in a horizontal direction wherever it finds a weak place.

b) It may get rested in different forms.

c) In case it develops into a saucer shape, concave to the sky body it is called lapoliths.

d) A wavy mass of intrusive rocks at times it is found at the base of synclines or at the top of anticlines in folded igneous country.

e) Such wavy materials have a definite conduit of source beneath in the form of magma chambers. (Subsequently developed as batholiths).

f) These are called phacoliths.

g) The near horizontal bodies of the intrusive igneous rocks are called sill or sheet depending on the thickness of the material.

h) The thinner ones are called sheets, while the thick horizontal deposits are called sills.

i) When the lava makes its way through cracks and the fissures developed in the land solidifies an almost perpendicular to the ground.

j) It gets cooled in the same position to develop a wall like structure.

k) Such structures are called dykes.

l) These are the commonly found intrusive forms in the western Maharashtra region. These are considered the feeders for the eruptions that led to the development of the Deccan Traps.

Questions bank:

 Multiple choice questions:

1. The gravitational force is lesser near the equator and greater near the:

a) Tropic of cancer

b) Tropic of Capricorn

c) Poles

d) Prime Meridian

Ans. c) Poles

The poles are closer to the centre due to the equatorial bulge, and thus have a stronger gravitational field.

2. A celestial body, which is the source of information about the interior of the earth is:

a) Sun

b) Moon

c) Stars

d) Meteors

Ans. d) Meteors

Meteors are the source of information about the interior of the earth as they were formed at the time other planets and earth was formed.

3. The vibration direction parallel to the wave direction in the vertical plane is present in:

a) P waves

b) S waves

c) Surface waves

d) Love waves

Ans. a) P waves

P wave is always longitudinal. Thus, the particles in the solid have vibrations along or parallel to the travel direction of the wave energy.

4. The intensity scale is named after an Italian Seismologist:

a) Bellini

b) Emilio

c) Mercalli

d) Giorgio

Ans. c) Mercalli

A scale of intensity based on observed effects and ranging from I (detectable only with the instruments) to XII (causing almost total destruction), is named after Giuseppe Mercalli.

5. A zone where seismic waves are not reported is known as:

a) Blank zone

b) Zero zone

c) Empty zone

d) Shadow zone

Ans. d) Shadow zone

It is the area of the earth from angular distance of 105˚ – 145˚, from a given earthquake that does not receive any direct P waves and bent by liquid core will create the shadow zone. S waves when stopped entirely by the liquid core will create a shadow zone from 105˚ – 105˚.

6. An earthquake generated due to the sliding of the rocks along a fault plane is known as:

a) Collapse earthquake

b) Explosion earthquake

c) Volcanic earthquake

d) Tectonic earthquake

Ans. a) Collapse earthquake

Once the transformation of convergent plates gets locked, the relative motion is continued between the plates, which lead to increasing stress. The stress rises and continues until it breaks through the asperity; suddenly allowing the sliding over the locked portion of the fault, releasing the stored energy.

7. The Hawaiian volcanoes are:

a) Composite cones

b) Shield cones

c) Caldera

d) Cinder cone

Ans. b) Shield Volcanoes

Barring the basalt flows, the shield volcanoes are the largest of all the volcanoes on the earth. The Hawaiian volcanoes are the most famous examples. These volcanoes are mostly made up of basalt, a type of lava that is very fluid when erupted. For these reasons these volcanoes are not very steep. They become explosive somehow water gets into vent; otherwise they are characterised by low explosivity.

8. Which is not a type of volcano?

a) Shield volcano

b) Composite volcano

c) Ridge

d) Caldera

Ans.  c) Ridge

Ridge is not a volcano. Volcanoes are classified on the basis of nature of eruption and the forms developed at the surface.

9. The core mantle boundary is located at the depth of:

a) 2660 Km

b) 2900 Km

c) 2700 Km

d) 2500 Km

Ans. b) 2900 Km

The core mantle boundary is at 2900 Km. the density of mantle increases with depth from mantle to core.

10. What is the thickness of the earth’s crust in the Himalayan region?

a) 75Km

b) 60Km

c) 70Km

d) 65Km

Ans. c) 70 Km

The thickness of the earth’s crust in the Himalayan region is about 70 Km.

11. Which waves are last to be recorded on the seismograph?

a) Body waves

b) Surface waves

c) P waves

d) S waves

Ans. b) Surface waves

Surface waves are last recorded on the seismograph. These are the most destructive than the body waves.

12. Dykes are:

a) Wall like structure

b) Horizontal sills

c) Cliff like structure

d) Collapsed depression

Ans. a) Wall like structure

When the lava makes its way through cracks and the fissure develop in the land, it solidifies almost perpendicular to the ground. It gets cooled in the same position to develop a wall like structure. Such structures are called dykes.

13. The depth of Kola drill is:

a) 262 Km

b) 262 Km

c) 262 Km

d) 262 Km

Ans. c) 12.262 Km

The deepest hole ever created by humankind lies beneath the tower enclosing Kola drill is 12.262 Kms (7.5 Miles) into the earth.

14. What is the radius of the earth?

a) 5,370 Km

b) 5,530 Km

c) 6,370 Km

d) 6, 270 Km

Ans. c) 6,370 Km

The earth’s radius is 6,370 Km. No one can reach centre of the earth and make observations or collect samples of the material from here.

15. The processes which are producing the surface of the earth are a result of _________

a) Endogenic forces

b) Exogenic forces

c) Both a and b

d) None

Ans. c) Both (a) and (b)

The configuration of the surface of the earth is largely a product of the processes operating in the interior of the earth. Exogenic as well as endogenic processes are constantly shaping the landscape.

16. The interior of the earth can only be understood by:

a) Direct methods

b) Indirect methods

c) Both the direct and indirect methods

d) None

Ans. c) Both direct and indirect methods

Interior of the earth can only be understood by direct and indirect methods.

17. From Moho’s discontinuity, mantle extends up to a depth of:

a) 900 Km

b) 1, 900 Km

c) 2, 900 Km

d) 4, 900 Km

Ans. c) 2,900 Km

The mantle extends from Moho’s discontinuity to a depth of 2, 900 Km. the upper portion of the mantle is called asthenosphere.

18. To know the interior of the earth the deepest drilling has been done so far at Kola. Kola is at:

a) Atlantic ocean

b) Pacific ocean

c) Arctic ocean

d) Antarctic ocean

Ans. c) Arctic Ocean

The deepest drill at Kola, in Arctic Ocean, has so far reached a depth of 12.262 Km. This and many deep drilling projects have provided large volume of information through the analysis of materials collected at different depths.

19. Plutonic rocks are formed due to:

a) Cooling of lava during explosion

b) Cooling of lava at the surface

c) Cooling of lava in the crust

d) Cooling of lava

Ans. c) Cooling of lava in the crust

Depending on the location of the cooling of lava, igneous rocks are classified as volcanic rocks (cooling at surface) and plutonic rocks (cooling in the crust).

20. ___________ is a type of volcanic rock:

a) Batholith

b) Sand stone

c) Limestone

d) Shale

Ans. a) Batholith

Batholith is a type of volcanic rock whereas others are sedimentary rocks.

21. Magma refers to the:

a) Rocks

b) Material in upper mantle

c) Material in upper core

d) Material in the crust

Ans. b) Material in upper mantle

Magma in upper mantle is a molten rock that is found beneath the surface of the earth. Beside molten rock magma may also contain suspended crystals and gas bubbles. Magma often collects in a magma chamber inside a volcano.

22. Volcanoes are:

a) Indirect source of information about earth’s interior

b) Direct source of information about the interior of the earth

c) Not a source of information about the interior of the earth

d) Good source of ascertain earth’s temperature

Ans. b) Direct source of information about the interior of the Earth

Volcanic eruption forms a source of obtaining direct information. As and when the molten material, magma is thrown onto the surface of the earth, during volcanic eruption it becomes available for the laboratory analysis.

23. Earthquake waves are recorded on the:

a) Seismograph

b) Barograph

c) Pantograph

d) Ergo graph

Ans. a) Seismograph

A seismograph is a device that scientists use to measure earthquakes. The goal of a seismograph is to accurately record the ground motion during a quake.

24. The density of a material at the mantle core boundary is:

a) 3 g/cm³

b) 5 g/cm³

c) 8 g/cm³

d) 15 g/cm³

Ans. b) 5 g/cm³

The density of a material at the mantle core boundary is 5 g/cm³ and at the centre of the earth at 6, 300 Km, the density value is around 15 g/cm³.

25. At the different latitudes, the gravitational force (g) is:

a) Same

b) Not known

c) Not the same

d) Not present

Ans. c) Not the same

The gravitational force (gravity anomaly) is not the same at different latitudes at the surface. It is greater near the poles and less at the equator. This is because of the distance from the centre at the equator being greater than the poles.

26. Waves that can travel only through solids are:

a) S waves

b) P waves

c) Surface waves

d) L waves

Ans. a) S waves

P waves can travel through gaseous, liquid and solid materials. S waves arrive at the surface with some time lag. These are called secondary waves. An important fact about s waves is that they can travel only through solid materials.

27. Which one of the following is not a volcanic rock?

a) Batholith

b) Laccolith

c) Phacolith

d) Tacolith

Ans. d) Tacolith

Laccolith, Batholith, Lapoliths, Phacolith etc. are the intrusive volcanic landforms:

28. Intrusive volcanic rocks are those which are formed:

a) When cooling occurs at the surface

b) When cooling occurs within the crust

c) By all the volcanic rocks

d) None

Ans. b) When cooling occurs within the crust

When cooling occurs within the crust the intrusive volcanic rocks are formed. The lava that is released during volcanic eruptions cooling develops into igneous rocks. The lava that cools within the crustal portions assumes different forms. These forms are called intrusive forms.

29. The trap is a large:

a) Flood plain

b) Flood basalt province

c) Lava plain

d) Shield volcano

Ans. b) Flood basalt province

The Deccan Traps from India, presently covering most of the Maharashtra plateau are a much larger flood basalt province. It is believed that initially the trap formations covered a much larger area than the present.

30. The near horizontal layers of the intrusive igneous rocks are called ______________

a) Bills

b) Sills

c) Tills

d) Rills

Ans. b) Sills

The near horizontal bodies of the intrusive igneous rocks are called sill or sheet, depending on the thickness of the material. The thinner ones are called sheets the thick horizontal deposits are called sills.

31. Magma refers to:

a) Rocks

b) Material in upper mantle

c) Material in upper core

d) Material in crust

Ans. b) Material in upper mantle

The material in upper mantle is called magma.

32. What is Nife?

a) Core

b) Mantle

c) Inner core

d) Crust

Ans. a) Core

The core is made up of very heavy material mostly constituted by nickel and iron. It is sometimes referred to as the nife (ni+fe=nickel and ferrous) layer.

33. The mean thickness of the ocean crust is:

a) 4 Km

b) 5 Km

c) 6 Km

d) 7 Km

Ans. b) 5 Km

The thickness of the crust varies under the oceanic and continental areas. Oceanic crust is thinner as compared to the continental crust. The mean thickness of oceanic crust is approximately 5 Km whereas that of continental is around 30 Km.

34. The upper mantle is also called:

a) Biosphere

b) Asthenosphere

c) Hemisphere

d) Troposphere

Ans. b) Asthenosphere

The portion of the interior beyond the crust is called the mantle. The mantle extends from Moho’s discontinuity to a depth of 2, 900 Km. the upper portion of the mantle is called asthenosphere.

35. Which of the following is not an indirect source of information about the interior of the earth?

a) Gravitation

b) Magnetic field

c) Seismic activity

d) Deep drilling

Ans. d) Deep drilling

The deepest drill at Kola, in Arctic Ocean, has so far reached a depth of 12.262 Km. this and many deep drilling projects have provided large volume of direct information through the analysis of materials collected at different depths.

36. Which one of the following describes the lithosphere?

a) Upper and lower mantle

b) Crust and upper mantle

c) Crust and core

d) Mantle and core

Ans. b) The crust and upper mantle

The lithosphere refers to the portion of depth up to 200 Km from the surface of the earth.

37. Which type of volcanic eruptions has caused Deccan trap formations?

a) Shield

b) Flood basalt

c) Composite

d) Caldera

Ans. b) Flood basalt

The Deccan Traps are a large igneous province and one of the largest volcanic features on earth. They consists of multiple layers of solidified flood basalt that together are more than, 2,000 metre thick and cover an area of 500,000 Km².

38. Which source provides direct information about the interior of the earth?

a) Earthquake waves

b) Volcanoes

c) Gravitational force

d) Earth magnetism

Ans. b) Volcanoes

Volcanic eruptions form a source of direct information. As and when the molten material magma is thrown onto the surface of the earth, during volcanic eruption it becomes available for analysis.

39. The upper mantle is in the ________.

a) Solid state

b) Molten state

c) Semi solid state

d) Gaseous state

Ans. c) Semi solid state

The material in upper mantle portion is called magma, it is in semi-solid state. Once it starts moving towards the crust or it reaches the surface, it is referred to as lava.

Very short answer type questions:

1. Name the three layers of the earth?

Ans. The Three layers are the crust, mantle and core.

2. What are two main materials found in the core?

Ans. The two main materials found in the core are Nickel and Iron (nife).

3. Outline seismograph.

Ans. A seismograph is the device that scientists use to measure earthquakes.

4. What are the two types of body waves?

Ans. The two types of body waves are P – waves and S – waves. As they move or propagate, they cause vibration in the body of the rocks through which they pass.

5. What is asthenosphere?

Ans. The upper mantle from the crust to the depth of about 650 Km is the asthenosphere. The word astheno means weak.

6. What is the temperature of the core?

Ans. The temperature of the core is about 5200˚C.

7. What are the two types of earthquake waves?

Ans. The two types of earthquake waves are surface waves and body waves. The Love and Rayleigh waves are the subtype of surface waves and P-waves and S-waves are the subtype of body waves.

8. Name the source of heat inside the earth.

Ans. The source of heat inside the earth is residual heat and decay of radioactive elements. The radioactive element decay is a natural process.

9. What is the radius of the earth’s core?

Ans. The radius of the earth’s core is 3,486 Km.

The core is made up of two layers, the inner core and outer core. Seismic evidence tells us that the inner core is solid while the outer core is liquid. The inner core has a radius of 1,216 Km and the total radius of the core is 3,486 Km.

Short answer type questions:

1. Name the two types of forces responsible for changing the face of the earth.

Ans. The two types of forces responsible for shaping the landscape are:

a) Endogenic forces

b) Exogenic forces

2. Differentiate between the crust and mantle.

3. Why does an earthquake occur?

Ans. An earth quake occurs due to the release of energy along the fault. Rocks along the fault tend to move in opposite directions. As the overlying strata press them, friction locks them together. However their tendencies to move apart at some point of the blocks get deformed and eventually, they slide past one another abruptly. This causes the release of energy and the origin of earthquake waves.

4. Define surface waves. Mention different types of surface waves.

Ans. Waves that move along the upper crust of the earth are known as surface waves. They are of two types:

a) Rayleigh waves: These waves travel as ripples with motions that are similar to those of waves on the surface of water.

b) Love waves: These waves are named after the physicist A E H Love. Motion in Love waves is entirely horizontal, at right angles and to the direction of the wave motion.

5. How do earthquake waves behave when subjected to the rocks of the earth mantle?

Ans. The P – waves make abrupt drop in velocity at the mantle core border; whereas S – waves terminate at the mantle core boundary. Though earth’s mantle is 2900 Km deep the speed of earthquake waves is so high that only very tight and dense rock will satisfy the condition.

6. Name the direct source of information about the interior of the earth?

Ans. The direct sources of information about the interior of the earth are:

a) Earth material got from mining

b) Material got from volcanic eruption

7. How are earthquake events scaled?

Ans. Earthquake events are scaled either according to the magnitude or the intensity of the shock.

a) The magnitude relates to the energy released during the quake. It is scaled with the help of Richter scale. The magnitude is expressed in absolute numbers 0-10.

b) The intensity relates to the visible damage caused by the earthquake. It is scaled by Mercalli scale. The range of intensity scale is from 1 – 12.

8. Write a short note on propagation of earthquake waves and their effects on the rocks they pass through.

Ans. Earthquake waves propagate in different manner. Propagation of these waves causes vibration in rocks they pass through.

P – Waves vibrate to the direction of the wave. This exerts pressure on the material in the direction of propagation. These waves create density differences in the material, leading to stretching and squeezing of the material.

S – Waves vibrate perpendicular to the wave direction in vertical plane. Hence, they create troughs and crest in the material.

Surface waves also vibrate perpendicular to the direction of propagation.

9. What do you mean by shadow zone?

Ans. Beyond the depth of 2,900 Km, S – waves disappear and P – waves travel with reduced velocity. On reaching the core, S – waves disappear. This area is known as shadow zone. A shadow zone of 105˚ to 105˚ but P – waves are refracted as a result no wave is marked or a shadow is created. Generally it is found at an angular distance of 105˚ to 145˚ from a given earthquake that does not receive any direct P waves. Its presence shows that the earth’s core is composed of heavy materials, like nickel and iron whose density is 11 to 13g/cm³.

10. What are the intrusive landforms formed by volcanoes?

The major intrusive landforms formed by volcanoes are:

a) Batholiths: These are cooled sections of the magma chamber and large granitic domes.

b) Lacoliths: these are large dome shaped intrusive bodies with a levelled base and connected by a pipe from below.

c) Lapoliths: these are formed when lava cools and develops a saucer shaped concave in the middle part.

d) Phacolith: a wavy mass of intrusive rocks found at the base of synclines or at the top of anticlines.

e) Sills: the horizontal bodies between rock layers.

f) Dykes: when lava is solidified between the cracks and fissures in the form of a line, it is called dykes. It solidifies almost perpendicular to the ground.

11. Why do earthquake waves develop shadow zones?

Ans. There are some specific areas where the waves are not reported. Such zone is called the ‘shadow zone’. The earthquake waves develop shadow zone because the P and S waves follow a curved path in the interior of the earth which proves that density increases inside the earth. P and S waves are recorded along the surface, near the focus of the earthquake. Beyond the depth of 2,900 Km, S waves disappear and P waves travel with reduced velocity. The zone between 105˚ and 145˚ from epicentre is identified as the shadow zone for P waves and 105˚ to 105˚ is the shadow zone of S waves. The shadow zone of S – waves is much larger than that of the P – waves.

12. What is gravity anomaly?

Ans. The gravitational force is not the same at different latitudes on the surface, which is caused by the uneven distribution of the mass material within the earth. It is greater near the poles and lesser at the equator. The reading of gravity at different places is influenced by many other factors. This reading differs from the expected value. Such a difference is called the gravity anomaly.

13. Describe the earth’s mantle.

Ans. The portion of the interior beyond the crust is called the mantle. The mantle extends from Moho’s discontinuity to a depth of 2, 900 Km. The upper portion of the mantle is called asthenosphere. It is considered to be extending up to 400 Km. the lower mantle extends to Guttenberg discontinuity 2, 900 Km. it is in solid state.

14. Briefly describe the various types of volcanoes on the basis of the form developed at the surface.

Ans. The major types of volcanoes are as follows:

a) Shield volcanoes: These are mostly made up of shield basalt lava. Therefore, they are not steep. They become explosive if somehow water gets into the vent. The upcoming lava moves in the form of a fountain.

b) Composite volcano: these volcanoes are characterised by the eruption of cooler and viscous lava. They often result in explosive eruptions. Pyroclastic materials accumulate near vent openings, leading to the formation of layers.

c) Caldera: These are the most explosive volcanoes. Usually, when they erupt, they tend to collapse themselves. The collapsed depressions are called calderas.

d) Flood Basalt Provinces: these volcanoes outpour highly fluid lava that flows for long distances. There can be a series of flows, with some of them attaining the thickness of 50 meters individual flows can extend hundreds of kilometres.

e) Mid-ocean Ridge Volcanoes: These volcanoes occur in oceanic areas.