A abampere (aA) The unit of electric current in the CGSeniu system, defined as that current that, if flowing through two parallel conductors of negligible cross section and infinite length, placed 1 cm apart in vacuo, would produce on each conductor a force of 1 dyne per centimeter of length. 1 abampere = 1 abcoulomb/s = r statampere (where c = speed of light in cm/s) = 10 ampere. aberration Imperfect image formation due to geometric imperfections in the optical elements of a system ablation 1 . The wasting of glacier ice by any process (calving, melting, evaporation, etc.). 2. The shedding of molten material from the outer sur- face of a meteorite or tektite during its flight through the atmosphere. absolute age The age of a natural substance, of a fossil or living organism, or of an artifact, obtained by means of an absolute dating method. See absolute dating method. absolute density Density in kg/m' or, more commonly, in g/cm\ both at STP. Cf. density, relative density abso
The Earth class 11 geography MCQ & SAQ
Earth class 11 geography NCERT SOLUTIOn:
(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
► (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
► (b) Volcanoes
(iii) Which type of volcanic eruptions have caused Deccan Trap formations?
(a) Shield
(b) Flood
(c) Composite
(d) Caldera
► (b) Flood
(iv) 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
► (b) crust and upper mantle
2. Answer the following questions in about 30 words.
(i) What are body waves?
Answer
Body waves are those earthquake waves, which are generated due to release of energy at the focus and move in all directions traveling through the body of the earth.
(ii) Name the direct sources of information about the interior of the earth.
Answer
Rocks obtained from mining areas and materials obtained from volcanic eruptions are the direct sources of information about the interior of the earth.
(iii) Why do earthquake waves develop in the shadow zone?
Answer
A seismic shadow zone is an area of the Earth's surface where seismographs cannot detect an earthquake after its seismic waves have passed through the Earth. It was observed that seismographs located at any distance within 105° from the epicenter, recorded the arrival of both P and S-waves. However, a zone between 105° and 145° from the epicenter was identified as the shadow zone for both the types of waves.
(iv) Briefly explain the indirect sources of information of the interior of the earth other than those of seismic activity.
Answer
The indirect sources of information of the interior of the earth are:
• Temperature, Pressure and Density: These increase with the increasing distance from the surface towards the interior in deeper depths.
The rate of change of Temperature, pressure and density are known. Knowing the total thickness of the earth, scientists have estimated the values of temperature, pressure and the density of materials at different depths.
• Meteors: These are not from the interior of the earth but the material and the structure observed in the meteors are similar to that of the earth. This makes them another source of information about the interior of the earth.
• Gravitation force: It is greater near the poles and less at the equator. The gravity values also differ according to the mass of the material. The uneven distribution of mass of material within the earth influences this value.
• Magnetic Field: Magnetic surveys also provide information about the distribution of magnetic materials in the crustal portion, and thus, provide information about the distribution of materials in this part.
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?
Answer
The earthquake waves cause vibration in the body of the rocks through which they pass. P-waves vibrate parallel to the direction of the wave. This exerts pressure on the material in the direction of propagation. As a result, it creates density differences in the material leading to stretching and squeezing of the material. Other three waves vibrate perpendicular to the direction of propagation. The direction of vibrations of S-waves is perpendicular to the wave direction in the vertical plane. Hence, they create troughs and crests in the material through which they pass. Surface waves are considered to be the most damaging waves.
(ii) What do you understand by intrusive forms? Briefly describe various intrusive forms.
Answer
The lava that is released during volcanic eruptions on cooling develops into igneous rocks. These forms are called intrusive forms.
Various 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 portions of magma chambers.
• Laccoliths: These are large dome-shaped intrusive bodies with a level base and connected by a pipe-like conduit from below. It resembles the surface volcanic domes of composite volcanoes, only these are located at deeper depths.
• Laccolith: 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 plane. It may get rested in different forms. In case it develops into a saucer shape, concave to the sky body, it is called laccolith.
• Phacolith: A wavy mass of intrusive rocks located near the top of an anticline or the bottom of a syncline.
• 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 while the thick horizontal deposits are
called sills.
• Dykes: When the lava makes its way through cracks and the fissures developed 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.
The Earth class 11 geography MCQ
Question : The average density of the earth is-
a) 2.3 gm/cm3
b) 5.5 gm/cm3
c) 17.2 gm/cm3
d) 6.5 gm/cm3
Answer : B
Question : Which material reaches the ground during volcanic eruptions?
(a) gasses
(b) sulfur compounds
(c) nitrogen compounds
(d) all of them
Answer : D
Question : The outer core of the Earth is made up of
(a) nickel-iron alloy
(b) platinum
(c) copper
(d) iron
Answer : A
Question : On the basis of the satellite data the average density of the core of the earth is-
(a) 13 g cm3
(b) 12 g cm3
(c) 11 g cm3
(d) 10 g cm3
Answer : C
Question : The currents that are formed in the mantle of the Earth are classified as
(a) convection currents
(b) continental currents
(c) oceanic currents
(d) drift currents
Answer : A
Question : The thickness of the outer core of the Earth is about
(a) 2,250 km
(b) 1,250 km
(c) 1,500 km
(d) 1,870 km
Answer : B
Question : The magnitude is expressed in absolute number
(a) 0 to 10
(b) 1 to 12
(c) 0 to 12
(d) 1 to 10
Answer : A
Question : The upper portion of mantle is known as
(a) Asthenosphere
(b) Crust
(c) Lithosphere
(d) Fossil Sphere
Answer : A
Question : Lithosphere is mostly composed of-
(a) Amphibolite
(b) Granite
(c) Basalt
(d) Peridotite
Answer : B
Question : What is the radius of earth?
(a) 6370 km
(b) 6360 km
(c) 6380 km
(d) 636 km
Answer : A
Question : Volcanoes are
(a) indirect source of information about the 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 to ascertain earth’s temperature.
Answer : B
Question : The process of transformation of rocks from one form to the other is called _____
(a) Rock metamorphosis
(b) Rock cycle
Rock change
Transfer of rocks
Answer : B
Question : The asthenosphere is-
(a) Totally motel
(b) Partially molten
(c) Totally solid
(d) Partially solid
Answer : B
Question : On the basis of velocity, seismic waves are divided into_______sets of waves-
(a) six
(b) five
(c) four
(d) three
Answer : D
Question : The range of thickness of crust is
(a) 5 to 60 km
(b) 10 to 50 km
(c) 15 to 40 km
(d) 8 to 38 km
Answer : A
Question : The minimum thickness of crust under the oceans is
(a) 8 km
(b) 2 km
(c) 5 km
(d) 10 km
Answer : C
Question : The intensity of an earthquake is measured in
(a) Richter Scale
(b) Mercalli scale
(c) Measuring scale
(d) Seismograph
Answer : B
Question : Which wave moves faster to arrive at the surface?
(a) ‘P’
(b) ‘S’
(c) ‘P’ and ‘S’
(d) none of these
Answer : A
Question : The common mineral in the continental masses and the oceanic crust is _____
(a) Silicon
(b) Magnesium
(c) Aluminum
(d) Iron
Answer : A
Question : Which one of the following describes the lithosphere?
(a) Upper and middle mantle
(b) Crust and upper mantle
(c) Crust and core
(d) Mantle and core
Answer : B
Question : Fossils are the remains of dead _______
(a) Plants
(b) Animals
(c) Both a and b
(d) None of the above
Answer : C
Question : What is the thickness of the crust?
(a) 10 km to 200 km
(b) 5 km to 30 km
(c) 30 km to 400 km
(d) 100 km to 200 km
Answer : A
Question : Which one of the following describe the lithosphere?
(a) Upper and middle mantle
(b) Crust and upper mantle
(c) Crust and core
(d) Mantle and core
Answer : B
Question : The theory which states that the plates of earth are continuously moving is classified as
(a) The Trench Drift Theory
(b) The Sphere Drift Theory
The Continental Drift Theory
The Oceanic Drift Theory
Answer : C
Question : What is the density of the rocks between the adjoining mantle and core?
(a) 3-4 gm. per sq. cm
(b) 5 gm. per sq. cm
(c) 4-5 gm. per sq. cm
(d) 6 gm. per sq. cm
Answer : B
Question : Magma refers to ____
(a) Rocks
(b) Material in upper mantle
(c) Material in upper core
(d) Material in the crust
Answer : B
Question : 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
Question : 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
Answer : B
Question : Which type of volcanic eruptions have caused Deccan Trap formations?
(a) Shield
(b) Flood
(c) Composite
(d) Caldera
Answer : D
Question : 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
Answer : B
Question : Which one of the following is a direct source of information about the interior of the earth?
(а) Earthquake waves
(b) Volcanoes
(c) Gravitational force
(d) Earth magnetism.
Answer : A
1. Which one of the following is a direct source of the information about the interior of the Earth?
(a) Earthquake waves
(b) Volcanoes
(c) Gravitational force
(d) Earth magnetism
► (a) Earthquake waves
2. Which is not a type of volcano?
(a) Shield volcano
(b) Composite volcano
(c) Ridge volcano
(d) Caldera
► (c) Ridge volcano
3. Which one of the following describe the lithosphere?
(a) Upper and middle mantle
(b) Crust and upper mantle
(c) Crust and core
(d) Mantle and core
► (b) Crust and upper mantle
4. The magnitude of earthquake is measured in
(a) Richter Scale
(b) Mercalli scale
(c) Measuring scale
(d) Seismograph
► (a) Richter Scale
5. Which one of the following describe the lithosphere?
(a) Upper and middle mantle
(b) Crust and upper mantle
(c) Crust and core
(d) Mantle and core
► (b) Crust and upper mantle
6. What is the thickness of the earth’s crust in the Himalayan region?
(a) 75 kms
(b) 60 kms
(c) 70 kms
(d) 65 kms
► (c) 70 kms
7. The intensity of earthquake is measured in
(a) Richter Scale
(b) Mercalli scale
(c) Measuring scale
(d) Seismograph
► (b) Mercalli scale
8. The upper portion of mantle is known as
(a) Asthenosphere
(b) Crust
(c) Lithosphere
(d) Fossil Sphere
► (a) Asthenosphere
9. The interior of the earth can only be understood by ______________
(a) Direct methods
(b) Indirect methods
(c) Both the indirect and direct methods
(d) None of the Above
► (c) Both the indirect and direct methods
10. What is the density of the rocks between the adjoining mantle and core?
(a) 3-4 gm. per sq. cm
(b) 5 gm. per sq. cm
(c) 4-5 gm. per sq. cm
(d) 6 gm. per sq. cm
► (b) 5 gm. per sq. cm
11. What is the approximate depth of the mantle?
(a) 2400 km
(b) 2900 km
(c) 3200 km
(d) 3500 km
► (b) 2900 km
12. The Deccan trap is a large
(a) flood plain.
(b) flood basalt province.
(c) lava plain.
(d) shield volcano.
► (b) flood basalt province.
13. What is the thickness of the crust?
(a) 10 km to 200 km
(b) 5 km to 30 km
(c) 30 km to 400 km
(d) 100 km to 200 km
► (a) 10 km to 200 km
14. 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) L-waves.
► (a) P-waves.
15. What is the mean thickness of oceanic crust?
(a) 5 km
(b) 30 km
(c) 10 km
(d) 70 km
► (a) 5 km
16. 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 to ascertain earth's temperature.
► (b) direct source of information about the interior of the earth.
17. Magma refers to ____
(a) Rocks
(b) Material in upper mantle
(c) Material in upper core
(d) Material in the crust
► (b) Material in upper mantle
18. Earthquake waves are recorded on the
(a) Seismograph.
(b) Barograph.
(c) Pantograph.
(d) Ergograph.
► (a) Seismograph.
The Earth class 11 geography SAQ
What is a protostar?
Protostar means original star. It is believed that the gaseous cloud exploded to form a supernova. The explosion caused shock waves that caused the denser portion of the cloud to collapse under their own gravity. The dense core grew larger and hotter and its gravity attracted more material. In this process, the hot core developed into a protostar. ‘ Finally, it became the infant sun.
Explain Heterogeneous Accretion Hypothesis.
According to Heterogeneous Accretion Hypothesis, the composition of the material from which the earth accreted changed r with time giving rise to the layered structure of the earth. According to this model, the earth formed ‘ inside out’ with an oxidized and volatile-rich nucleus and more metal-rich and depolarised outer rings.
Differentiate between supernova and protostar.
What do you mean by plate tectonics?
Plate tectonics is a theory. According to it, the crust and mantle (lithosphere) are divided into plates and blocks. Different tectonic movements take place along their edges. These plates drift due to convection currents. Continents also drift along with these plates, known as tectonic plates.
The moon was born along with the earth. How?
Regarding the birth of the moon, there are many hypotheses. Radiometric dating of the rocks from the moon shows that it was born along with the earth. It either came out of the sun in a gaseous form but was too small to be attracted by the earth, or it flew out of the earth due to a huge meteorite falling on the earth.
Why are inner planets heavier than the outer ones?
Initially, the nebula was revolving in the form of a flat disc. Due to high temperature, the heavy materials of the flat disc condensed in the inner part of the disc. These include iron and aluminum. Thus, inner planets Mercury, Venus, Earth and Mars were formed.
What is the Collision hypothesis?
This hypothesis was proposed by Sir James Jeans and Sir Harold Jeffreys, a mathematician in England. According to this hypothesis, gaseous material was pulled away from the pre-existing sun by the gravitational force of a passing star.
Name the three layers of the earth’s interior.
The Earth’s crust (lithosphere)
The intermediate layer (mantle)
The inner core (metallic core)
Why does the inner core of the earth behave like a solid?
The inner core of the earth should have been molten owing to high temperature in such a great depth, but it is not molten; it behaves like a solid because of the great pressure of the outer shells.
What do you understand by a light-year?
A light-year is a measure of distance and not of time. Light travels at a speed of 300,000 km/second. The distance that the light travels in one year is taken to be one light year. This is equal to 9.461 xlO12 km. The mean distance between the sun and the earth is Y‘ 149,598,000 km. In terms of light-years, it is 8,3 31 minutes.
How was the solid crust formed?
The solid crust was formed by the cooling and condensation of the gaseous material on the surface of the earth.
What do you understand by the birth of the solar system?
The entire solar system forms a very small part of the galaxy that consists of many stars. Our galaxy is called the Milky Way. The gaseous cloud exploded to form a supernova. The explosion caused shock waves that caused the denser portion to collapse under its own gravity. In the process, the hot core developed into a protostar. Finally, the protostar became the infant sun.
What are the outer and inner planets?
The four planets Mercury, Venus, Earth and Mars are called inner planets. They lie between the sun and the belt of asteroids.
The five planets Jupiter, Saturn, Uranus, Neptune and Pluto are called outer planets. These are also known as Jovian or Gas Giant planets.
Write a note on Heterogeneous Accretion Hypothesis.
This hypothesis explains the layered structure of the earth. According to this theory, the earth is formed by the accretion of different types of materials. The materials changed with time. The earth formed from inside out due to the change of materials. It had an oxidized and hot nucleus and more metal-rich rings.
Q. 1. Name a philosopher who believed that the earth was at the center of the universe.
Ans. Aristotle—a Greek Philosopher.
Q. 2. What was meant by Geo-centric Theory ?
Ans. It meant that the moon, sun, planets and stars orbited around earth.
Q. 3. What is a Helio-centric Solar System ?
Ans. The sun is the center of the solar system. All the planets, stars moved around the sun.
Q. 4. Name an Indian Scientist who believed in the Helio-Centric System.
Ans. Aryabhatta.
Q. 5. How many planets are there in the Solar System ?
Ans. Eight.
Q. 6. Name the inner planets.
Ans. Mercury, Venus, Earth and Mars.
Q. 7. Name the outer planets.
Ans. Jupiter, Saturn, Uranus and Neptune.
Q. 8. Name the unique planet where life exists.
Ans. Earth.
Q. 9. Who forwarded the Nebula Hypothesis ?
Ans. German Philosopher Immanuel Kant and Laplace.
Q. 10. Who Forwarded the Collision Hypothesis ?
Ans. Sir James Jeans and Harold Jeffreys.
Q. 11. What was the shape of the tongue of matter ejected from the sun ?
Ans. Cigar shaped.
Q. 12. What do you mean by Supernova ?
Ans. A star million times brighter than the sun.
Q. 13. Which scientist of Russia modified the Nebular Hypothesis in 1950.
Ans. Otto Schmidt.
Q. 14. Which is the Hypothesis of Jeans and Jeffreys ?
Ans. Binary Hypothesis.
Q. 15. Which is the most popular theory regarding the origin of the Universe.
Ans. Big Bang Theory.
Q. 16. How much distance is traveled by light in a light year ?
Ans. 9.461 × 1012 km.
Q. 17. What do you mean by a ‘light year’ ?
Ans. A light year is a measure of distance and not of time. Light travels at a speed of 300,000 km/second. Considering this, the distance the light will travel in one year is taken to be one light year. This equals 9.461 × 1012 km. The mean distance between the Sun and the Earth is 149,598,000 km. In terms of light years it is 8.311 minutes.
Q. 18. What is the Solar System ? When was it formed ?
Ans. Our Solar System. Our Solar system consists of eight planets. The nebula from which our Solar system is supposed to have been formed started its collapse and core formation sometimes 5 to 5.6 billion years ago and the planets were formed by about 4.6 to 4.56 billion years ago. Our Solar system consists of the Sun, 8 planets, 173 moons, millions of smaller bodies like asteroids and comets and huge quantities of dust grains and gasses.
Q. 19. How did oceans originate ?
Ans. Carbon dioxide in the atmosphere dissolved in rainwater and the temperature further decreased causing more condensation and more rain. The rainwater falling on to the surface got collected in the depressions to give rise to oceans. The earth’s oceans were formed within 500 million years from the formation of the earth. This tells us that the oceans are as old as 400 million years.
Q. 20. Describe the different stages in the evolution of the present day atmosphere.
Ans. There are three stages in the evolution of the present atmosphere. The first stage is marked by the loss of the primordial atmosphere. In the second stage the hot interior of the earth contributed to the evolution of the atmosphere. Finally, the composition of the atmosphere was modified by the living world through the process of photosynthesis.
Q. 21. (i) What is a Nebula ?
Ans. Nebula is a slowly rotating cloud of Gases. It contains hot gaseous matter of dust-gas clouds.
(ii) What are planetesimals ?
Ans. Due to the collision of the sun and the passing star, a filament of gaseous material was pulled away from the pre-existing sun. This filament (tongue-shaped) was broken into small chunks which went flying as cold bodies. These are called planetesimals.
(iii) Who first proposed Nebular Hypothesis ?
Ans. The Nebular Hypothesis was first proposed by German Philosopher Immanuel Kant in 1755.
(iv) What is a Protostar ?
Ans. The Nebula of hot gaseous clouds exploded to form a Supernova. Its denser portions collapsed under their own gravity. The dense core became larger and hotter. It is called Protostar. It finally became the infant sun.
Q. 22. Describe the modification proposed in Nebular Hypothesis by Otto Schmidt.
Ans. In 1950 Otto Schmidt in Russia and Carl Weizascar in Germany somewhat revised the ‘nebular hypothesis’, though differing in details. They considered that the Sun was surrounded by solar nebula containing mostly the hydrogen and helium alongwith what may be termed dust. The friction and collision of particles led to formation of a disc-shaped cloud and the planets were formed through the process of accretion.
Q. 23. Describe the process of Star Formation.
Ans. The Star Formation. The distribution of matter and energy was not even in the early Universe. These initial density differences gave rise to differences in gravitational forces and it caused the matter to get drawn together. These formed the basis for the development of galaxies. The galaxies contain a large number of
stars. They spread over vast distances, to be measured in thousands of light-years. These range in size with diameters ranging from 80,000 to 150,000 light years.
A galaxy starts to form by accumulation of hydrogen gas in a very large cloud called a nebula. Eventually the growing nebula develops localized clumps of gas, which continue to grow into even denser gaseous bodies giving rise to formation of stars. The formation of stars is believed to have taken place some time 5 to 6 billion years ago.
Q. 24. Compare the inner planets and outer planets.
Ans. Of the eight planets Mercury, Venus, Earth and Mars are called inner planets as they lie between the Sun and the belt of asteroids called the asteroid belt. The other four planets, lining up after the asteroid belt are Jupiter, Saturn, Uranus and Neptune are called outer planets. Alternatively the first four are called ‘Terrestrial’, meaning Earth-like, as they are made up of rock and metals and have relatively high densities. The other four are called Jovian or Gas Giant planets. Jovian means Jupiter like. Most of them are much larger than the terrestrial planets and have a thick atmosphere mostly of helium and hydrogen. All the planets were formed in the same period, some time about 4.6 billion years ago.
Q. 25. Describe a comparative analysis of planets as regards distance from the sun, density, radius and satellites.
Ans
Q. 1. Upto which depth, man’s knowledge of the structure of earth, is limited ?
Ans. Upto a depth of 12 km.
Q. 2. Name the three layers of the earth.
Ans. Crust, mantle and core.
Q. 3. What is the density and thickness of Crust ?
Ans. 2.7 to 50 kms.
Q. 4. What does the word SIAL stand for ?
Ans. The crust consists of silica and aluminum (SIAL).
Q. 5. What does the word SIMA stand for ?
Ans. SIMA is the layer below the sial (Silica + Aluminium = SIMA).
Q. 6. What does the word NIFE stand for ?
Ans. The center core of the earth (Nickel + Ferrous = NIFE).
Q. 7. What is the density of NIFE ?
Ans. 17 and 2500 km.
Q. 8. From which Greek word, the term volcano has been derived ?
Ans. From the Greek word ‘Vulcan’ meaning God of the Underground.
Q. 9. What name is given to the molten matter within the earth ?
Ans. Magma.
Q. 10. What name is given to magma, when it appears on the surface of the earth ?
Ans. Lava.
Q. 11. Name the main parts of a volcano.
Ans. (i) Vent or opening
(ii) Volcanic pipe
(iii) Crater.
Q. 12. Name two types of volcanic eruptions.
Ans. (i) Central eruption
(ii) Fissure eruption.
Q. 13. Name an active volcano in India.
Ans. Barren island near Andaman islands.
Q. 14. Name the largest active volcano in the world.
Ans. Mauna Loa (Hawaii islands).
Q. 15. Which volcano is known as the ‘lighthouse of the Mediterranean ?’
Ans. Stromboli.
Q. 16. Which type of volcanoes are called ‘sleeping volcanoes ?’
Ans. Dormant volcanoes.
Q. 17. Name the three belts where volcanoes are found.
Ans. (i) Circum Pacific belt
(ii) Mid-world mountain belt
(iii) African rift valley.
Q. 18. Name the three types of earthquake waves.
Ans. There are three types of earthquake waves :
(i) Longitudinal waves or Primary or P-waves.
(ii) Transverse or Secondary or S-waves. (iii) Surface or Long R-waves.
Q. 19. What do you understand by the term ‘Discontinuity’ ?
Ans. The boundary separating the different layers of the earth is called Discontinuity. This demarcates the different layers of the earth having different densities.
Q. 20. Define the terms Sial and Sima.
Ans. Sial : It is the uppermost layer of the earth.
It consists of Silica and Aluminium. (Sial = Silica + Aluminium). Its average depth is 60 kms. It has an average density of 2.75.
Sima : The layer below the Sial is called Sima. It consists of Silica and Magnesium (Sima = Silica + Magnesium). Its average depth is 2800 kms. It has a density of 4.75.
Q. 21. Define the term Nife.
Ans. Nife : The core of the earth is called ‘Nife’. It consists of Nickel and Ferrous. It has an average depth of 3500 kms. It has a density of 13.
Q. 22. Name the direct and indirect sources of information regarding the interior of the earth ?
Ans. Direct Sources : (i) Mines (ii) Wells (iii) Bores Indirect sources : (i) Temp. (ii) Pressure (iii) Density (iv) Earthquake waves (v) Meteorites (vi) Gravity.
Q. 23. How are earthquakes measured ?
Ans. Measuring earthquakes. The earthquake events are scaled either according to the magnitude or intensity of the shock. The magnitude scale is known as the Richter scale. The magnitude relates to the energy released during the quake while the intensity scale takes into account the visible damage caused by the event. The magnitude is expressed in absolute numbers 0 to 10. The intensity scale is named after Mercalli, an Italian seismologist. The range of intensity scale is from 1 to 12. The intensity relates to the actual damage caused by the quake. On the Richter scale, earthquakes with high intensity are rare.
Q. 24. Write a short note on ‘Barysphere’.
Ans. Barysphere. The central core of the earth is called the Barysphere. It has a depth of 4980 km to 6400 kms. It has a density of 17. It consists of heavy minerals and is called core. The core is metallic in nature.
Q. 25. Describe the location and importance of ‘Shadow Zone’.
Ans. Due to reflection and refraction suffered by earthquake waves, some areas do not experience any waves. Such areas are called ‘Shadow Zones’. From the epicenter, S-waves are deflected at an angle of 103° to 143° only. P-waves travel down to the boundary at the Core. These waves suffer reflection and refraction and emerge on the surface as P.K.P. waves. Thus two shadow zones on either side of the core are formed. These suggest the presence of the liquid core. These zones are free from earthquake waves. Only surface waves pass through it.
Q. 26. What do you mean by Mohorovicic Discontinuity ?
Ans. The abrupt changes in the velocity of seismic waves suggest that the crust is distinguished from the mantle. The surface of sudden increase in wave velocity which separates the crust above from the mantle below is called Mohorovicic discontinuity or M discontinuity. The P waves near the surface travel at about 6 km per second and increase to 7 km per second to the base of the crust. This is named after the Yugoslav seismologist Mohorovicic who first recognised the discontinuity in 1909.
Q. 27. How is it that our knowledge is based on indirect observations about the structure of earth’s interior ?
Ans. High temperatures are found in the interior of the earth. So direct observation is not possible as man cannot go deep down. Direct observation is limited only to a depth of 3 kms. Deepest mines go up to a depth of 3 kilometers. Due to an increase in temperature with depth, we reach a very high temperature (2000°C) in the interior. Mines, wells and boreholes provide limited knowledge. The depth of the deepest borehole (6 kilometers) is quite insignificant as compared to the radius of the earth (6,400 kms). So, we have to depend upon indirect sources of evidence like earthquakes, waves, volcanic eruptions and meteorites.
Q. 28. How do we know that the core of earth is liquid ?
Ans. Three types of earthquake waves have different types of path and velocity. Both P and S Waves are reflected and refracted while passing through a different layer. S-waves cannot travel through liquid and have never been observed in the core. Hence, the core is considered liquid. The rigidity of the material of the core is zero, which is also a characteristic of a liquid core.
Q. 29. What is a Seismogram ?
Ans. Seismograph is an instrument which records earthquake waves. Study of Seismographic records is called a Seismogram.
Q. 30. Name two types of surface waves.
Ans. Surface waves are those earthquake waves which move freely along the upper crust of the earth.
These produce disastrous effects of earthquakes. These are of two types : (a) Rayleigh Waves or R-waves. These are named after the English Physicist, Lord Rayleigh. These are similar to water waves traveling across the surface of a still pond when a pebble is tossed into water. Figure 2 shows Rayleigh waves.
(b) Love waves or L-waves. The second type of surface waves is the love wave. These are named after the Physicist A.E.H. Love. These move in a horizontal plane. These move at right angles to the direction of wave motion. Figure 3 shows Love Waves.
The Earth class 11 geography long question
Write short notes on :
1. Collision Hypothesis
2. Homogeneous Accretion Hypothesis
3. Origin of the Moon
1. Collision Hypothesis – Sir James Jeans and Sir Harold Jeffreys gave this hypothesis. According to this hypothesis, gaseous material was pulled away from the pre-existing sun by the gravitational force of a passing star. By collision and gravitational attraction, the larger planetesimals swept up the smaller pieces and thus formed the planets.
2. Homogeneous Accretion Hypothesis – This hypothesis maintains that the earth accreted from an intimate mixture of silicate particles and metal particles. The material was assumed to have been formed in the solar nebula by a complex series of chemical and physical processes, which had occurred prior to the accretion of planets. According to a hypothesis, accretion of the earth occurred over a sufficiently long period (10—10s years) so that its gravitational potential energy was efficiently radiated away and it formed in an initially ‘cool’ and unmelted condition.
3. Origin of the moon – Radiometric dating of the rocks from the moon shows that it was born along with the earth. Apparently, there are two possibilities. It either came out of the sun in a gaseous form but was too small to be attracted by the earth, or it flew out of the earth due to a huge meteorite falling on the earth. The area where the meteorite fell, a huge hollow was created, which is now filled up by an ocean and the landmass plunged to outer space to create the moon.
Discuss the various hypotheses for the evolution of the planets.
There are two hypotheses :
Nebula hypothesis
Collision hypothesis
1. Nebula hypothesis – In 1755, German philosopher Immanuel Kant, hypothesized that a slowly rotating cloud of gas, called Nebula, in some unspecified manner, condensed into a number of discrete and globular bodies. The great French mathematician Laplace also proposed, more or less, the same theory in 1796.
According to Kant and Laplace, the original mass of gas-cooled and began to contract. The rotational speed increased as a consequence of the law of conservation of angular momentum. Then, successive rings of gaseous material were spun off from the central mass by centrifugal force. In the final stage, the rings condensed into planets.
2. Collision hypothesis – Sir James Jeans and Sir Harold Jeffreys gave this hypothesis. According to this hypothesis, gaseous material was pulled away from the pre-existing sun by the gravitational force of a passing star. By collision and gravitational attraction, the larger planetesimals swept up the smaller pieces and thus formed the planets.
Describe the evolution of the Solar system,
The entire solar system consists of the sun, the nine planets and their various satellites. The sun is a large brilliant star in the center of the solar system. It is thought to be about 5 billion years old. The pressure and temperature at the center of the Nebula (cloud of gas) that produced the solar system became so great that it triggered a nuclear reaction. Some of the hydrogen in the cloud fused into helium, releasing a great amount of energy.
The gaseous cloud exploded to form a supernova. The explosion caused shock waves that pushed the denser portion of the cloud to collapse under its own gravity. The dense core grew larger and hotter as its gravity attracted more material. In the process, the hot core developed into a protostar that finally became the sun.
Describe the origin of life and die cause for its origin,
Modern scientists refer to the origin of life as a kind of chemical reaction, which first generated complex organic molecules and then assembled them. This assemblage was such that they could duplicate themselves by converting inanimate matter into living substance. The record of life that existed on this planet in different periods is found in rocks in the form of fossils. The microscopic structures closely related to the present form of blue algae have been found in geological formations that are much older than some 3000 million years. It can be assumed that simpler forms precede these. Scientists believe that life began to evolve sometime 3800 million years ago.
The last phase in the evolution of the earth relates to the origin and evolution of life. The initial or even the early atmosphere of the earth was not conducive for the development of life.
Describe in short the evolution of atmosphere and hydrosphere (oceans).
There are three stages in the evolution of the present atmosphere. The first stage is the loss of the primordial atmosphere. In the second stage, the hot interior of the earth contributed to the evolution of the atmosphere. The third stage in the composition of the atmosphere was modified by the living world through the process of photosynthesis.
The early atmosphere, with hydrogen and helium, has been stripped off as a result of the solar winds. All the terrestrial planets are supposed to have lost their primordial atmosphere through the impact of solar winds. During the differentiation and cooling of the earth, gasses and water vapor were released from the interior solid earth. This started the evolution of the present atmosphere. The early atmosphere largely contained water vapor, nitrogen, carbon dioxide, methane, ammonia and very little of free oxygen.
The process through which the gasses were outpoured from the interior is called degassing. Continuous volcanic eruptions contributed water vapor and gasses to the atmosphere. As the earth cooled, the water vapor released started getting condensed. The carbon dioxide in the atmosphere dissolved in rainwater and the temperature further decreased causing more condensation and more rain. The rainwater falling on the surface got collected in the depressions to give rise to oceans. The earth’s oceans were formed within 500 million years from the formation of the earth. Oceans began to have the contribution of oxygen through the process of photosynthesis.
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