Class 11 Geography Chapter 2 The Origin and Evolution of the Earth NCERT Exercise Solution (English Medium)
NCERT – Exercise Question
Que 1 Choose the correct answer from the four options given below:-
(i) Which 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
ANS. (c) 4.6 billion years
(ii) Which one of the following is not related to the formation or modification of the present atmosphere?
(a) Solar winds
ANS. (c) 4.6 billion years
(ii) 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
ANS. (a) Solar winds
(iii) Life on the earth appeared around how many years before the present?
(a) 13.7 billion
ANS. (a) Solar winds
(iii) Life on the earth appeared around how many years before the present?
(a) 13.7 billion
(b) 3.8 million
(c) 4.6 billion
(c) 4.6 billion
(d) 3.8 billion
ANS. (d) 3.8 billion
Que 2 Answer the following questions in about 30 words: -
(i) What do you mean by the process of differentiation?
ANS. In the process of differentiation, the heavier substances settle towards the center and the lighter ones towards the outer surface. For example, at the time of the origin of the earth, heavy materials like iron and nickel were established towards the center and silica and aluminum towards the earth's crust.
(ii) What was the nature of the Earth initially?
ANS. In the early period, that is, about 460 million years ago, when the Earth was born, the Earth was in a hot and liquid state. It was completely deserted, gradually the earth cooled and its upper part became solid in the lithosphere.
(iii) What were the gases which initially formed the earth's atmosphere?
ANS. In the early stages, the atmosphere was sparse, composed of hydrogen and helium. In the beginning, water vapor, nitrogen, carbon dioxide (CO2), methane (CH4) and ammonia etc. were in high quantity in the atmosphere. There was very little free oxygen.
Que 3 Answer the following questions in about 150 words: -
(i) Write an explanatory note on the ‘Big Bang Theory’.
ANS. The Big Bang theory was presented by Edwin Hubble in 1920. According to this theory, the universe is continuously expanding. This theory is also called the expanded universe hypothesis. This Big Bang event happened 13.7 billion years ago.
ANS. (d) 3.8 billion
Que 2 Answer the following questions in about 30 words: -
(i) What do you mean by the process of differentiation?
ANS. In the process of differentiation, the heavier substances settle towards the center and the lighter ones towards the outer surface. For example, at the time of the origin of the earth, heavy materials like iron and nickel were established towards the center and silica and aluminum towards the earth's crust.
(ii) What was the nature of the Earth initially?
ANS. In the early period, that is, about 460 million years ago, when the Earth was born, the Earth was in a hot and liquid state. It was completely deserted, gradually the earth cooled and its upper part became solid in the lithosphere.
(iii) What were the gases which initially formed the earth's atmosphere?
ANS. In the early stages, the atmosphere was sparse, composed of hydrogen and helium. In the beginning, water vapor, nitrogen, carbon dioxide (CO2), methane (CH4) and ammonia etc. were in high quantity in the atmosphere. There was very little free oxygen.
Que 3 Answer the following questions in about 150 words: -
(i) Write an explanatory note on the ‘Big Bang Theory’.
ANS. The Big Bang theory was presented by Edwin Hubble in 1920. According to this theory, the universe is continuously expanding. This theory is also called the expanded universe hypothesis. This Big Bang event happened 13.7 billion years ago.
According to this, the galaxies, stars and planets in the universe are constantly moving away from each other and their size is increasing. For example, when the balloon is inflated, the marks on it also get bigger and the distance between them increases.
 |
| Edwin Hubble |
(ii) List the stages in the evolution of the earth and explain each stage in brief.
ANS. The planet earth initially 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 caused the change from rocky, barren and hot earth to a beautiful planet with ample amount of water and conducive atmosphere favouring the existence of life, between the 4,600 million years and the present, led to the evolution of life on the surface of the planet.
(a) Evolution of Lithosphere
The earth was mostly in a volatile state during its primordial stage. Due to gradual increase in density the temperature inside has increased. As a result the material inside started getting separated depending on their densities. This allowed heavier materials (like iron) to sink towards the centre of the earth and the lighter ones to move towards the surface. With passage of time it cooled further and solidified and condensed into a smaller size. This later led to the development of the outer surface in the form of a crust.
(b) Evolution of Atmosphere and Hydrosphere
The early atmosphere, with hydrogen and helium, is supposed to have been stripped off as a result of the solar winds. During the cooling of the earth, gases and water vapour were released from the interior solid earth. This started the evolution of the present atmosphere. The early atmosphere largely contained water vapour, nitrogen, carbon dioxide, methane, ammonia and very little of free oxygen. The process through which the gases were outpoured from the interior is called degassing. Continuous volcanic eruptions contributed water vapour and gases to the atmosphere. As the earth cooled, the water vapour released started getting condensed. The carbon dioxide in the atmosphere got dissolved in rainwater and the temperature further decreased causing more condensation and more rains. The rainwater falling onto 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 4,000 million years. Sometime around 3,800 million years ago, life began to evolve. However, around 2,500-3,000 million years before the present, the process of photosynthesis got evolved. Life was confined to the oceans for a long time. Oceans began to have the contribution of oxygen through the process of photosynthesis. Eventually, oceans were saturated with oxygen, and 2,000 million years ago, oxygen began to flood the atmosphere.
(c) Origin of Life
The last phase in the evolution of the earth relates to the origin and evolution of life. It is undoubtedly clear that initially the earth or even the atmosphere of the earth was not conducive for the development of life. Modern scientists refer to the origin of life as a kind of chemical reaction, which first generated complex organic molecules and assembled them. This assemblage was such that they could duplicate themselves converting inanimate matter into living substance. The microscopic structures closely related to the present form of blue algae have been found in geological formations much older than some 3,000 million years. It can be assumed that life began to evolve sometime 3,800 million years ago.
ANS. The planet earth initially 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 caused the change from rocky, barren and hot earth to a beautiful planet with ample amount of water and conducive atmosphere favouring the existence of life, between the 4,600 million years and the present, led to the evolution of life on the surface of the planet.
(a) Evolution of Lithosphere
The earth was mostly in a volatile state during its primordial stage. Due to gradual increase in density the temperature inside has increased. As a result the material inside started getting separated depending on their densities. This allowed heavier materials (like iron) to sink towards the centre of the earth and the lighter ones to move towards the surface. With passage of time it cooled further and solidified and condensed into a smaller size. This later led to the development of the outer surface in the form of a crust.
(b) Evolution of Atmosphere and Hydrosphere
The early atmosphere, with hydrogen and helium, is supposed to have been stripped off as a result of the solar winds. During the cooling of the earth, gases and water vapour were released from the interior solid earth. This started the evolution of the present atmosphere. The early atmosphere largely contained water vapour, nitrogen, carbon dioxide, methane, ammonia and very little of free oxygen. The process through which the gases were outpoured from the interior is called degassing. Continuous volcanic eruptions contributed water vapour and gases to the atmosphere. As the earth cooled, the water vapour released started getting condensed. The carbon dioxide in the atmosphere got dissolved in rainwater and the temperature further decreased causing more condensation and more rains. The rainwater falling onto 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 4,000 million years. Sometime around 3,800 million years ago, life began to evolve. However, around 2,500-3,000 million years before the present, the process of photosynthesis got evolved. Life was confined to the oceans for a long time. Oceans began to have the contribution of oxygen through the process of photosynthesis. Eventually, oceans were saturated with oxygen, and 2,000 million years ago, oxygen began to flood the atmosphere.
(c) Origin of Life
The last phase in the evolution of the earth relates to the origin and evolution of life. It is undoubtedly clear that initially the earth or even the atmosphere of the earth was not conducive for the development of life. Modern scientists refer to the origin of life as a kind of chemical reaction, which first generated complex organic molecules and assembled them. This assemblage was such that they could duplicate themselves converting inanimate matter into living substance. The microscopic structures closely related to the present form of blue algae have been found in geological formations much older than some 3,000 million years. It can be assumed that life began to evolve sometime 3,800 million years ago.
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