Fundamentals of Physical Geography

Chapter 2: The Origin and the Evolution of the Earth

Q1. Write a short note on Nebular Hypothesis.
Q2. Discuss about the 'Big bang theory' with diagram.
Q3. Differentiate between terrestrial and jovian planet.
Q4. Discuss about the process of the formation of atmosphere.
Q5. What do you mean by 'degassing'?
Q6. Why terrestrial planets are rocky and juvian planets are gaseous?
Q7. What is the role of the process photosynthesis in the formation of atmosphere?

Q.1. Name different hypothesis associated with the formation of the Earth. 
Or
Explain the earliest theories associated with the origin of the Earth.
Ans:
Important hypothesis associated with the formation of the Earth are: -
 Nebular Hypothesis: -
1) 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.
2) From Nebula there was a gradual loss of heat due to its rotation which resulted in cooling of its outer surface.
3) 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.
4) The center 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.
Q.2. Write an explanatory note on the ‘Big Bang Theory’.
Or
Explain the modern theory associated with evolution of the Earth.
Ans: 
The Big Bang Theory, also called as expanding universe hypothesis is given by Edwin Hubble in 1920 when he provided the evidence that the universe is expanding. The theory tells that galaxies are moving away from each other as the time passes. The universe appears to be growing larger.
 The Big Bang Theory: -
1) In the beginning, all matter forming the universe existed in one place in the form of a ‘tiny ball” with an unimaginable small volume, infinite temperature and infinite density.
2) At the Big Bang “tiny ball” exploded violently. This led to a huge expansion.
3) It is 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.
4) 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.
5) Within 300,000 years from the Big Bang, temperature dropped to 4,500k and gave rise to atomic matter. The universe became transparent.
Q.3. What are the differences between Terrestrial Planets and Jovian Planets?
Ans: 
i) Terrestrial Planets
ii) Jovian Planets
1.
Definition
i) Terrestrial planets are made of solid surfaces.
ii) Jovian planets are made of gaseous surfaces.
2.
Area
i) They are found between belt of asteroids and the Sun.
ii) They are found after the belt of asteroids.
3.
Sub-Names
i) They are also called inner planets.
ii) They are called outer planets.
4.
Size
i) They are smaller in size and their lower gravity could not hold the escaping gases.
ii) They are bigger in size and they have more gravity that could hold the escaping gases.
5.
Density
i) They have high density.
ii) They have low density.
6.
Temperature
i) They are warm as they are closer to the Sun.
ii) They are cold as they are far away to the Sun.
7.
Examples
i) Mercury, Venus, Earth and Mars are called Inner Planets.
ii) Jupiter, Saturn, Uranus, Neptune and Pluto are called Outer Planets.
Q.4. Who gave their opinions about the formation of the moon? What did they opine?
Or
What is the opinion of present day scientists about the origin of moon?
Ans: 
 Fission Theory: -
1) In 1838, Sir George Darwin, the son of Charles Darwin, suggested that initially the Earth might have been spinning so fast that part of our planet spun off into space but was hold by Earth's gravity.
2) Fission theorists supposed that the material separated from the Earth was formed as moon and the place became the Pacific Ocean.
3) But when moon rocks analyzed this theory was rejected because the moon rock compositions differed from those in the Pacific Ocean.
4) In short, the Pacific Ocean is too young to be the source of the moon.
 Capture Theory: -
1) Capture theory suggests that the Moon was a wandering body (like an asteroid) that formed elsewhere in the solar system.
2) It was captured by Earth's gravity as it passed nearby.
3) It proposes that the Moon formed during a collision between the Earth and another small planet, about the size of Mars.
4) The chemical components of both the Earth and the moon suggest they formed at around the same time.
 Co-accretion Theory: -
1) It is also known as the Condensation Theory, this hypothesis offers that the moon and the Earth formed together while orbiting a black hole.
2) However, this theory does not neglect an explanation of why the moon orbits the Earth, nor does it explain the difference in densities between the moon and Earth.
 Giant Impact Theory: -
1) The present theory is the “Giant Impact Theory” or “Big Splat Theory”. A large size body of Mars-sized called "Theia" collided with the Earth and that portion was separated from the Earth. (in Greek mythology, Theia was the mother of the moon Goddess)
2) When ‘Theia’ hit Earth, a portion of the planet came off and became hardened into the moon about 4.44 billion years ago.
3) This theory does a better job than others of explaining the similarities in chemical compositions of the Earth and the Moon; however it doesn't explain why the moon and the Earth are chemically similar.
4) The theory does not tell about the size of Theia, at what angle it hit the Earth and precisely what it was made of, the giant impact hypothesis will have to remain just that a hypothesis.
Q.5. How’ was the layered structure of the Earth developed?
Or
Explain the origin and evolution of Lithosphere of the Earth.
Ans:
 Stage 1: - Origin of the Earth
In the first stage the formation of plant symbols started and Earth was originated after ‘the Big Bang’.
 Stage 2: - Evolution of Lithosphere
The planet Earth initially was a barren, rocky arid hot object with a thin atmosphere of ‘Hydrogen and Helium’. It is said that in initial stage the Earth was in liquid form. But, there must have been some events- processes, which may have caused this change from rocky, barren and hot Earth to a beautiful planet with large amount of water and conductive atmosphere favoring the existence of life.
1) The Earth was mostly in a volatile state during its primordial (ancient) stage.
2) Due to gradual increase in density the temperature inside has increased. As a result the material inside started getting separated depending on their densities.
3) This allowed heavier materials (like iron and nickel) to sink towards the center of the Earth and the lighter ones to move towards the surface.
4) 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. It is through the process of differentiation that the Earth forming material got separated into different layers.
Q.6. What are different stages of development of Atmosphere on Earth?
Ans:
1) In the first stage the primordial (ancient) atmosphere which contained the thin layer of hydrogen and helium gas was stripped (removed) off by solar energy winds.
2) In the second stage during the cooling the interior of the Earth contributed to the evolution of the atmosphere as many gases and water vapour were released by the
process of degassing (outgassing). This started the evolution of present atmosphere. The early atmosphere mainly contained water vapour, nitrogen, carbon dioxide, methane, ammonia and a small proportion of free oxygen.
3) In the third stage the composition of atmosphere was modified by the living world by the process of photosynthesis.
Q.7. Explain the origin and evolution of Hydrosphere of the Earth.
Ans:
1) Continue volcanic eruptions contributed water vapours and gases to the early atmosphere. As the Earth cooled, the water vapour released started getting condensed.
2) The carbon dioxide in the atmosphere got dissolved in rainwater and the temperature further decreased causing more condensation and more rains.
3) The rainwater falling onto the surface got collected in the depressions to give rise to oceans and the Earth’s oceans were formed within 500 million years from the formation of the Earth.
4) Oceans began to have the contribution of oxygen through the process of photosynthesis.
5) Eventually, oceans were saturated with oxygen, and 2,000 million years ago, oxygen began to flood the atmosphere.
Q.8. Explain how did life evolve on the Earth?
Ans:
1) The origin of life is a kind of chemical reaction, which first generated complex organic molecules and then assembled them.
2) Due to this assemblage they could duplicate themselves converting inanimate matter into living substance.
3) The record of life that existed on this planet in different periods is found in rocks in the form of fossils.
4) The microscopic structures closely related to the present form of the blue algae have been found in geological formations much older than some 3,000 million years.
5) It can be assumed that life began to evolve sometime 3,800 million years ago.