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NCERT Class 11 Geography Chapter 2 The Origin and Evolution of The Earth
Also, you can read the NCERT book online in these sections Solutions by Expert Teachers as per Central Board of Secondary Education (CBSE) Book guidelines. CBSE Class 11 Geography Solutions are part of All Subject Solutions. Here we have given NCERT Class 11 Geography Part I: Fundamentals of Physical Geography, Part II: Indian: Physical Environment, Part III: Practical Work in Geography. NCERT Class 11 Geography Chapter 2 The Origin and Evolution of The Earth Notes, NCERT Class 11 Geography Textbook Solutions for All Chapters, You can practice these here.
The Origin and Evolution of The Earth
Chapter: 2
GEOGRAPY [ PART – I ]
SHORT ANSWER TYPE QUESTIONS
Q.1. What is Nebula?
Ans. Nebula is the name given to the hot and slowly rotating clouds.
Q.2. What are planetesimals?
Ans. Planetesimals are just like dust particles which came into being by breaking of tonnes of matter out of the sun caused by a passing star.
Q.3. Why do planets differ in size and temperature?
Ans. The planets differ in size and temperature due to their varying distances from the sun.
Q.4. Name our galaxy.
Ans. Milky Way, Akash Ganga.
Q.5. What is a protostar?
Ans. Protostar is the name given to that core of denser gas which finally became the infant sun.
Q.6. Who first propose the Nebular hypothesis?
Ans. The German philosopher Immanuel Kant.
Q.7. When was the earth formed?
Ans. The earth came into existence about 4600 million years ago.
Q.8. What is the meaning of angular momentum ?
Ans. The product of the moment of inertia and the angular velocity of a rotating body is called its angular momentum.
Q.9. How was the solid crust of the earth formed?
Ans. The cooling and condensation of the gaseous material of the surface of the earth led to the formation its solid crust.
Q.10. How was the atmosphere formed?
Ans. The higher gaseous material started floating over the crust over the earth forming atmosphere.
Q.11. How does the planet earth appears from the space?
Ans. It appears blue from the space.
Q.12. What are the inner planets?
Ans. Mercury, Venus, Earth and Mars are called as inner planets as they lie between the sun and the belt of asteroids.
Q.13. Which are the Gas Giant planets?
Ans. Jupiter, Saturn, Uranus, Neptune and Pluto are called Gas Giant planets.
Q.14. What is degassing?
Ans. The process through which the gases were outpoured from the interior is called degassing.
Q.15. What is solar system?
Ans. The sun, its nine planets and their satellites form a complete family known as solar system.
Q.16. What is the centrifugal force?
Ans. A force which pulls a mass away from the centre of a rotating body is called the centrifugal force.
Q.17. What is the Milky Way?
Ans. The galaxy to which our solar system belongs is popularly known as the Milky Way or Akash Ganga.
SHORT ANSWER TYPE QUESTIONS
Q.1. Write any three features of outer planets.
Ans. Features of outer planets:
(i) The outer planets are Jupiter, Saturn, Uranus, Neptune and Pluto.
(ii) They lie away from the asteroid belt.
(iii) These are gasious planety as they are made of gases.
(iv) They are called Jovian planets.
(v) They are relatively larger in size. Their higher gravity holds up the gases.
Q.2. Why are the terrestrial planets rocky?
Ans. The terrestrial planets are rocky because they are earth-like and are made up of rocks and earth-live materials and have relatively high densities.
Q.3. What was the nature of the earth’s surface initially?
Ans. The nature of the earth’s surface initially was a torrid, rocky and hot, having a thin atmosphere of hydrogen and helium.
Q.4. What were the gases which initially formed the earth’s atmosphere?
Ans. Hydrogen and helium.
Q.5. Distinguish between inner planets and outer planets.
Ans.
| Inner planets | Outer planets |
| 1. The inner planets are Mercury, Venus, Earth and Mars. | 1. The outer planets are Jupiter, Saturn, Uranus, Neptune and Pluto. |
| 2. They are lying between the sun and the belt of asteroids. | 2. They lie away from the asteroid belt. |
| 3. These are solids like earth. | 3. These are gaseous planets as they are made up of gases. |
| 4. These are called terrestrial planets. | 4. They are called Jovian planets. |
| 5. They are relatively smaller and their lower gravity could not hold the escaping gases. | 5. They are relatively larger in size. Their higher gravity holds up the gases. |
Q.6. What is the basic difference in the arguments related to the origin of the earth given by:
(a) Kant and Laplace.
(b) Chamberlain and Moulton?
Ans. The Nebular Hypothesis, as proposed by Immanuel Kant and later revised by Laplace in 1796 considered that the planets were formed out of a cloud of material associated with a youthful sun, which was slowly rotating while, in 1900, Chamberlain and Moulton considered that a wandering star approached the sun. As a result, a cigar-shaped material separated from the solar surface. As the passing star moved away, the material separated from the sun, continued to revolve around the sun and it slowly condensed into planets.
Q.7. What is meant by process of differentiation?
Ans. Planetesimal material moved together to form the planets. The collection of the mass forming the earth also believed to have followed the same sequence. As the material was following collected through gravitation the bodies getting collected had impact on the existing materials. These impacts generated lots of heat. The process continued and the heat generated caused melting of the materials. This occurred during and soon after the formation of the earth. The mix of lighter and denser material on melting started getting separated depending on their demities. This allowed the heavier material like iron to sink towards the centre of the earth and the lighter ones to move towards the surface. This process of separation of lighter and denser material is called differentiation.
Q.8. Describe the collision Hypothesis proposed by Sir James Jeans and Sir Harold Jeffereys.
Ans. This theory belongs to two stars theories, According to this theory planets are bi-parental in origin. It is also known as Tidal Hypothesis.
Outline of the Hypothesis:
(i) The sun was originally a very hot gasious mass in the space.
(ii) Another star several times bigger than the sun came close to the sun and caused tidal disruptions.
(iii) Due to gravitational pull of the approaching to star gaseous matter was pulled away from the pre-existing sun. The ejected matter called Filament was cigar shaped.
(iv) This Filament was broken into small chunks called planetesimals.
(v) By collision and gravitational attraction the larger planetesinal collected the small bricks and condensed into planets.
Merits: It is most accepted Hypothesis. The present arrangement of planets confirm the idea. The number of satellites also proves the theory.
Demerits: This theory fails to explain the location of Mars. The temperatures of sun is too high for formation of planets.
LONG ANSWER TYPE QUESTIONS
Q.1. Write an explanatory note on the ‘Big Bang Theory’.
Ans. The ‘Big Bang Theory’ is the most popular argument regarding the origin of universe. It is also called expanding universe hypothesis. It considers the following stages in the development of the universe:
Stage I: Initially all the matter existing today is concentrated in one place in the form of a “tiny ball” (singular atom or primordial matter) with unimaginable small volume, infinite temperature and infinite density.
Stage II: At the time of the big bang about 13.7 billion years before, this ‘tiny ball’ explodes violently. This leads to its expansion continuing up to the present time. As the size increases, some energy gets converted into matter. A rapid expansion starts within the fractions of a second after the bang which later slows down. The first atom starts to be formed within the first three minutes of the Big Bang event.
Stage III: Within 3,00,000 years from the Big Bang, temperature drops to 4,500 K and gives rise to atomic matter. The universe becomes transparent.
Q.2. Describe the evolution of Atmosphere and Hydrosphere.
Ans. There are three stages of the formation of the atmosphere:
(i) In the first stage: The early atmosphere consist of hydrogen and helium loss of primordial atmosphere due to solar winds.
(ii) Second stage: Gases were released from the earth’s interior such as water vapor and other gases. There were water vapor nitrogen carbon dioxide methane ammonia and little free oxygen. The process of out pouring the gases from the interior of the earth is called degassing volcanic eruptions contributed the water vapour and gases of the co-disolved in the rain water and converted into acid rain. Rain water collected into the dipressions called oceans. The oceans were formed 4000 m year. The life began to evolve about 3.8 B year. The photo synthesis evolved about 2500 to 3000 m year. Oceans began to contribute oxygen to the atmosphere.
(iii) The third stage: Living organisms changed the composition of the atmosphere due to photo synthesis.
Q.3. List the stages in the evolution of the earth and explain each stage in brief.
Ans. Following are considered to the stages in the development of planet
(i) Formation of disc: The stars are there localised lumps of gas with in a nebula. The gravitational force with in the dumps leads to the formation of a core to the gas cloud and the huge rotating disc of gas and dust develops around the gas core.
(ii) Formation of planetesimals: In the next stage gas clouds starts getting condensed and the matter around the core develops into small rounded objects. These small rounded objects by process of cohession develop into what is called as planetesimals.
(iii) Cohesion: Larger bodies start forming by collision and cause the material to stick together by gravitational attraction. These are large number of small bodies.
(iv) Formation of planets: In the final stages these large number of planetesimals accurate to form a fewer large bodies in uniform of planets.
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