CHAPTER 2:The Origin and Evolution of the Earth NCERT SOLUTION CLASS 11TH Geography| EDUGROWN NOTES

Short Answer Type Questions :

Q1. Why are the terrestrial planets rocky?

Answer

The terrestrial planets are rocky because:

• The terrestrial planets were formed in the close vicinity of the parent star where it was too warm for gases to condense to solid particles. Jovian planets were formed at quite a distant location.

• The solar wind was most intense nearer the sun; so, it blew off lots of gas and dust from the terrestrial planets. The solar winds were not all that intense to cause similar removal of gases from the Jovian planets.

• The terrestrial planets are smaller and their lower gravity could not hold the escaping gases.

Q2. 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

Answer

The Nebular Hypothesis, 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.

Q3. What is meant by the process of differentiation? 
Answer
The process by which earth forming material got separated into different layers is called differentiation. Starting from the surface to the central parts, we have layers like the crust, mantle, outer core and inner core. From the crust to the core, the density of the material increases.

Q4. What was the nature of the earth surface initially? 
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.

Q5.What were the gases which initially formed the earth’s atmosphere?
Answer

Hydrogen and helium were the gases which intially formed the earth’s atmosphere. 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. 

Q6. Write an explanatory note on the ‘Big Bang Theory’.
Answer
The ‘Big Bang Theory’ also known as expanding universe hypothesis. Edwin Hubble, in 1920, provided evidence that the universe is expanding. The distance between the galaxies is also found to be increasing and thereby, the universe is considered to be expanding.

Various stages in the development of the universe according to Big Bang Theory are:
• In the beginning, all matter forming the universe existed in one place in the form of a “tiny ball” (singular atom) with an unimaginably small volume, infinite temperature and infinite density.

At the Big Bang the “tiny ball” exploded violently. This led to a huge expansion. It is now generally accepted that the event of big bang took place 13.7 billion years before the present. The expansion
continues even to the present day. As it grew, some energy was converted into matter. There was particularly rapid expansion within fractions of a second after the bang. Thereafter, the expansion has slowed down. Within first three minutes from the Big Bang event, the first atom began to form.

• Within 300,000 years from the Big Bang, temperature dropped to 4,500K (Kelvin) and gave rise to atomic matter. The universe became transparent.

Q7. List the stages in the evolution of the earth and explain each stage in brief.
Answer
Stage I: The earth was mostly in a volatile state during its primordial stage. Due to gradual increasein 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 which led to the formation of the crust.

• During the formation of the moon, due to the giant impact, the earth was further heated up. It is through the process of differentiation that the earth forming material got separated into different
layers. Starting from the surface to the central parts, the crust, mantle, outer core and inner core formed.

Stage II: 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 which 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.

• 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.
• Life was confined to the oceans for a long time. Oceans began to have the contribution of oxygen through the process of photosynthesis.

Stage III: The last phase in the evolution of the earth relates to the origin and evolution of life.
• 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.

Long Answer Type Questions:

Q1.Explain how did life evolve on the earth?
Answer:
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 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 the blue algae have been found in geological formations m uch older than some 3,000 million years. It can be assumed that life began to evolve sometime 3,800 million years ago.

Q2.Explain different phases of evolution of planets.
Answer:
Evolution of planets can be understood in three stages:

1. Formation of Disc; The stars are localised lumps of gas within a nebula. The gravitational force within the lumps leads to the formation of a core to the gas cloud and a huge rotating disc of gas and dust develops around the gas core.

2. Formation of Planetesimals: In the next stage, the gas cloud starts and getting condensed and the matter around the core develops into small rounded objects. These small rounded objects by the process of collision develop into what is called planetesimals. Larger bodies start forming by collision and gravitational attraction causes the materials to stick together. Planetesimals are a large number of smaller bodies.

3. Formation of Planets: In the final stage, these large number of small planetesimals accrete to form fewer large bodies in the form of planets.

Q3.Explain the earliest theory associated with the origin of the earth.
Answer:
A large number of hypotheses were put forth by different philosophers and scientists regarding the origin of the earth. One of the earlier and popular arguments was by German philosopher Immanuel Kant. Mathematician Laplace revised it in 1796. It is known as Nebular Hypothesis. According to this theory there was a hot and rotating gas cloud called Nebula in the space. From Nebula there was a gradual loss of heat due to its rotation which resulted in cooling of its outer surface. This gradual cooling caused contraction in size of Nebula, but its speed increased due to angular momentum. The outer layer was separated from the remaining part of Nebula.

The centre of Nebula became ‘Sun’ and the planets were formed of the smaller units. The lighter material gases and the heavier dust particle gave the fact of inner and outer planets. In 1950, Otto Schmidt in Russia and Carl Weizasear 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 along with what may be termed as dust. The friction and collision of particles led to formation of a disk-shaped cloud and the planets were formed through the process of accretion.

Q4.Explain the modern theory associated with evolution of the earth.
Answer:
In modern theory the evolution of the earth is associated with Big Bang Theory. It was put forth by Edwin Hubble in 1920. In the beginning, all matter forming the universe existed in one place in the form of a ‘tiny ball” \yith an unimaginably- small volume infinite temperature and infinite density. At the Big Bang “tiny ball” exploded violently. This led to a huge” expansion. it is now generally? accepted that the event of big. bang took place 13.7 billion years before the present. The expansion continues even to the present day. As it grew, some energy’ was converted into matter. There was particularly rapid expansion within fractions of a second’ after the bang. Thereafter, the expansion has slowed down. Within first Big Bang event, the first atom began to form.

Within 300,000 years from the Big Bang, temperature dropped to 4,500k and gave rise to atomic matter. The universe became transparent. The expansion of universe means increase in space between the galaxies. An alternative to this was Hoyle’s concept of steady state. It considered the universe to be roughly the same at any point of time. However, with greater evidence becoming available about the expanding universe, scientific community at present favours argument of expanding universe.

Q5.Explain the collision and accretion I hypothesis associated with the evolution of the earth.
Answer:
Collision hypothesis and accretion hypothesis are described below in short.
1.  Collision Hypothesis: It was given by Sir James and Harold Jeffrey.

• According to this theory, a large nebula ’wandering in the space came very close to smaller nebula (Sun) and its huge upsurge of matter on the surface of smaller nebula. The matter was detected from the smaller nebula and on cooling condensed into planets.

2. Accretion Hypothesis: It was given by? Schmidt and Carl Weizascar.

• According to them, solar system started out as a cloud of gas and dust drifting in a space called nebula. This gaseous cloud
  exploded violently to form supernova. The exploitation left the vast spinning cloud and gases and thus to collapse under its own gravity and develop as denser core.
• The denser core became larger and hotter and began to burge. Later it developed into protostar which finally evolved as ‘infant Sun.
•  Away from its central surface, particles of dust began to clump together and converted into first smaller fragments of rocks and then becoming larger bodies which were called planetesimals which collided with one another to form rocky inner planets like Mercury, Venus, Earth and Mars and the remaining were outer planets.