2. The Origin and Evolution of the Earth

 NCERT Questions:

1. Multiple choice questions:

(i) Which one of the following figures represent 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. b) 13.7 billion years

 (ii) Which one of the following has the longest duration?

a) Eons

b) Era

c) Period

d) Epoch

Ans. a) Eons

(iii) 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. b) Differentiation

(iv) Which one of the following represents the inner planets?

a) Planets between the sun and the Earth

b) Planets between the Sun and the belt of asteroids

c) Planets in gaseous state

d) Planets without satellite(s)

Ans. b) Planets between the Sun and the belt of asteroids

 (v) Life on the earth appeared around how many years before the present?

a) 13.7 billion

b) 3.8 million

c) 4.6 billion

d) 4.6 million

Ans. b) 3.8 million

2. Answer the following questions in about 30 words

(i) Why are the terrestrial planets rocky?

Ans.

a) The planets that fall under the title terrestrial planets are Mercury, Venus, Earth and Mars.

b) They are similar to Earth in composition.

c) And these planets are also nearer to the sun.

d) Due to extreme heat from the Sun, evaporated lightweight elements like hydrogen and helium, from these terrestrial planets, leaving behind rocky and metallic elements.

 (ii) What is the basic difference in the arguments related to the origin of the earth given by?

a) Kant and Laplace

b) Chamberlain and Molten

Ans.

a) Kant and Laplace

German philosopher Immanuel Kant was well known for his argument on nebular hypothesis. Then in 1796, mathematician Laplace revised it. According to them, the planets were formed out of a cloud of materials associated with the youthful Sun, which was slowly rotating. This cloud was known as Nebula.

b) Chamberlain and Mountain

In 1900, Thomas Crowder Chamberlain and Forest Ray Molten proposed the Planetesimal hypothesis.

a) They consider that the wandering star approached the Sun.

b) As a result, a cigar shaped extension of material was separated from the solar surface.

c) As the passing star moved away, the material separated from the solar surface continued to revolve around the sun, and it slowly condensed into planets.

Sir James Jeans and later Sir Herald Jeffrey supported this argument. At a later date, the arguments considered of a companion to the sun have been coexisting. These arguments are called binary theories.

(iii) What is meant by processing of the differentiation?

Ans. It is a process in which the materials that formed the layers of the Earth, which are crust, upper mantle and lower mantle, outer core and inner core. These layers got separated based on their material densities.

(iv) What was the nature of the Earth surface initially?

Ans. The planet Earth initially was a barren, rocky and hot object with thin atmosphere of hydrogen and helium.

(v) What were the gases which initially formed the Earth’s atmosphere?

Ans. The gases which initially form the Earth’s atmosphere are:

Hydrogen and Helium

3. Answer the following questions in about 150 words:

(i) Write an explanatory note on The Big Bang theory.

Ans. The other name for Big Bang Theory is the Expanding Universe hypothesis.

a) It is referred as the modern theory when it comes to the origin of the Earth.

b) This theory explains about the beginning of the universe.

c) In 1920. Edwin Hubble after whom the famous Hubble Space Telescope is named. He provided evidence that the universe is expanding and as the time passes, galaxies move further and further apart. But other scientists believed that there is no evidence that supports the galaxies themselves is expanding.

(ii) List the stages in the evolution of the Earth and explain each stage in brief.

 Ans.

Evolution of the Earth

a) The planet Earth initially was a baron, rocky and hot object with a thin atmosphere of hydrogen and helium.

b) The Earth has a layered structure.

c) From the outermost end of the atmosphere to the centre of the Earth, the materials that exist are not uniform.

d) The atmospheric matter has the least density.

Evolution of lithosphere

a) The earth was mostly in a volatile state during its primordial stage.

b) Due to gradual increase in density, the temperature inside has increased.

c) As a result, the material inside started getting separated depending on their densities.

d) This allowed heavier materials like iron to sink towards the centre of the earth and the lighter ones to move towards the surface.

e) With passage of time it cooled further and solidified and condensed into a smaller size.

f) This letter led to the development of the outer surface in the form of a crust.

Evolution of atmosphere

a) The present composition of the Earth’s atmosphere is chiefly contributed by nitrogen and oxygen. The three stages in the evolution of the present atmosphere are:

i) The first stage is marked by the laws of primordial atmosphere.

ii) In the second stage, the hot interior of the earth contributed to the evolution of the atmosphere.

iii) Finally, the composition of the atmosphere was modified by the living world through the process of photosynthesis.

b) The early atmosphere with hydrogen and helium is supposed to have been stripped off as a result of the solar winds.

c) This happened not only in the case of the Earth, but also in all the terrestrial planets which were supposed to have lost their primordial atmosphere through the impact of solar winds.

d) 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.

e) The early atmosphere largely contained water vapour, nitrogen, carbon dioxide, methane, ammonia and very little of free oxygen.

f) The process through which the gases were out poured from the interior is called degassing.

g) Continuous volcanic eruptions contributed water vapour and gas to the atmosphere.

h) As the earth cooled, the water vapour was released and started getting condensed.

i) The carbon dioxide in the atmosphere got dissolved in rain water and the temperature further decreased, causing more condensation and more rains.

j) The rain water falling on to the surface got collected in the depressions to give rise to the oceans.

k) The Earth oceans were formed within 500 million years from the formation of the Earth. This tells that the oceans are as old as 4000 million years sometime around 3,800 million years ago, this began to evolve.

l) However, 2,500 to 3,000 million years before the present, the process of photosynthesis got involved. Life was confined to the oceans for a long time.

m) Oceans began to have the contribution of oxygen through the process of photosynthesis. Eventually, oceans were saturated with oxygen, and 2000 million years ago, oxygen began to flood the atmosphere.

Question Bank:

 Multiple choice questions:

1. The Big Bang theory is also known as:

a) Expanding universe hypothesis

b) Nebular theory

c) Classical theory of the origin of the earth

d) Binary star theory

Ans. a) Expanding universe hypothesis

Edwin Hubble, in 1920, provided evidence that the universe is expanding. As time passes, galaxies move further and further apart. The most popular argument about the origin of the universe is Big Bang Theory. It is also known as Expanding Universe Hypothesis.

2. John Michell in 1783 propounded the theory of:

a) Binary star theory

b) Big Bang

c) Inter Staller dust hypothesis

d) Black hole

Ans. d) Black hole

The idea of a body so massive that even light could not escape was first put forward by John Michell in a letter written to Henry Cavendish in 1783 of the Royal Society. Journalist Ann Ewing in her article ‘Black Hole’ in Space first used this term in 18^th January 1964.

3. When did the Big Bang take place?

a) 7 million years

b) 7 billion years

c) 4 billion years

d) 6 million years

Ans. b) 13.7 billion years before

It is now generally accepted that the event of Big Bang took place 13.7 billion years before the present.

4. Expansion of universe means:

a) Increase in the number of stars

b) Increase in space between the galaxies

c) Discovery of new celestial bodies

d) Increase in the speed of rotation of planets

Ans. b) Increase in space between the galaxies

The distance between the galaxies is found to be increasing and there by the universe is considered expanding.

5. From the crust of the earth towards the core the density of the material:

a) Decreases

b) Increases

c) Remains the same

d) Keeps changing

Ans. b) Increases;

Due to gradual increase in the density the temperature inside has increased. As a result, the material inside started getting separated depending on their densities. This allowed heavier material (like iron) to sink towards the center of the earth and the lighter ones to move towards the surface.

6. The process of differentiation means:

a) Separation of material into different layers

b) Separation of earth’s surface into different layers

c) Differences that exist the earth’s hydrosphere

d) Separation of planets

Ans. a) Separation of material into different layers;

It is through the process of differentiation that the earth’s material got separated into different layers. Starting from the surface to the central parts, the layers like the crust, mantle, outer core and inner core. From the crust to the core, the density of the material increases.

7. The formation of stars is believed to have taken place between:

a) 5-6 billion years ago

b) 4-6 billion years ago

c) 3-5 billion years ago

d) 6-8 billion years ago

Ans. a) 5-6 billion years ago;

A galaxy started to form by accumulation of hydrogen gas in the form of a very large cloud called nebula. Eventually, growing nebula developed localised clumps of gas. These clumps continued to grow into even denser gaseous bodies, giving rise to formation of stars. The formation of stars is believed to have taken place some 5-6 billion years ago.

8. The Sun is about:

a) 6 million Km from Earth

b) 6 million Km from Earth

c) 6 million Km from Earth

d) 6 million Km from Earth

Ans. b) 149.6 million Km from Earth

The average distance from the Sun to the earth is 149.6 million Km (149, 598, 000 Km) (or 92.58 million miles) the minimum distance from the Sun to the Earth is 146 million Km (or 91 million miles), and the maximum distance from the Sun to the Earth is 152 million Km (or 94.5 million miles)

9. The light year is a measurement of:

a) Distance

b) Time

c) Energy

d) Speed

Ans. a) Distance

A light year is a unit of distance. It is the distance that light can travel in one year. Light moves at a velocity of about 300,000 Km/second. So in a year, it can travel about 10 trillion Km. more precisely, one light year is equal to 9,500,000,000,000 Km.

10. The primordial atmosphere is lost by the:

a) Planetary winds

b) Solar winds

c) Living world

d) Degassing

Ans. b) Solar winds

The early atmosphere, with hydrogen and helium is supposed to have been stripped off as a result of the solar winds. This happened for all the terrestrial planets, which were supposed to have lost their primordial atmosphere through the impact of solar winds.

11. The material forming the moon was separated from:

a) Arctic Ocean

b) Atlantic Ocean

c) Indian Ocean

d) Pacific Ocean

Ans. d) Pacific Ocean

In 1838, Sir George Darwin suggested that initially, the earth and the moon formed a single rapidly rotating body. The whole mass became the dumb bell shaped body and eventually broke. It was also suggested that the material forming the moon was separated from what we have at present, the depression occupied by the Pacific Ocean.

12. Our Solar system consists of the Sun (the Star), 8 planets and –

a) 63 satellites

b) 53 satellites

c) 43 satellites

d) 16 satellites

Ans. a) 63 satellites

Our solar system consists of the sun (the star), 8 planets, 63 satellites, millions of smaller bodies like asteroids and comets and huge quantity of dust-grains and gases.

13. The terrestrial planets were formed in the close vicinity of the:

a) Asteroids

b) Parent star

c) Escaping gases

d) Outer planets

Ans. b) Parent Star;

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.

14. The inner planets are the planets:

a) Between the Sun and Earth

b) Between the Sun and the belt of asteroids

c) In gaseous state

d) Without satellites

Ans. b) Between the Sun and the belt of asteroids

Out of the eight planets Mercury, Venus, Earth, Mars are called the inner planets or terrestrial planets as they lie between the Sun and the belt of asteroids the other four planets Jupiter, Saturn, Uranus and Neptune are called the outer or Jovian planets.

15. Which of the following is not a Jovian planet?

a) Venus

b) Neptune

c) Uranus

d) Saturn

Ans. a) Venus

Venus is a terrestrial planet. It is not a Jovian planet.

16. The composition of the atmosphere was modified by the process of:

a) Evaporation

b) Photosynthesis

c) Solidification

d) Precipitation

Ans. b) Photosynthesis

There are three stages in the evolution of the present atmosphere. The first stage is marked by the primordial atmosphere. In the next stage the hot interior of the earth contributed to the evolution of the atmosphere. And in the final stage the composition of the atmosphere was modified by the living world through the process of photosynthesis.

17. The first life on the Earth was:

a) Soft bodied arthropods

b) Unicellular

c) Blue green algae

d) Marine invertebrate

Ans. b) Unicellular

The first life on the earth was the unicellular or an organism made of single cell.

18. The major event of tertiary period does not include:

a) Modern man and Homo sapiens

b) Anthropoid ape, small mammals, etc.

c) Flowering plants and trees

d) Early Human ancestors

Ans. b) Modern man and Homo sapiens

The major event of tertiary period does not include Modern man and Homo sapiens

19. The vast distance between the galaxies is measured in:

a) Kilometres

b) Years

c) Light years

d) None

Ans. c) Light Years

For most space objects, we use ‘Light Years’ to describe their distance. One light year is equal to 9.461 x 10¹⁵. A light year is the distance light travels in one Earth year.

20. The Interstellar Dust Hypothesis is about:

a) Large quantities of gases

b) Large quantities of fire and dust

c) Large quantities of gases and dust

d) Small quantities of gases and dust

Ans. c) Large quantities of gases and dust

The Interstellar Dust Hypothesis is about large quantities of gases and dust. The concept was given by Otto Schmidt a Russian Scientist.

21. Big Bang hypothesis was first suggested by:

a) George Lemaitre

b) Edwin Hubble

c) Schmidt

d) Wegner

Ans. a) George Lemaitre

George Lemaitre first said that the universe began from a single primordial atom. The idea subsequently received major boosts by Edwin Hubble’s observation. This became the Big Bang theory in 1920. The theory was first postulated by Edwin Hubble.

22. First life on the earth was originated in:

a) Water

b) Air

c) Plain land

d) Mountains

Ans. a) Water

First life on the earth was originated in oceans (water). Ocean began to have the contribution of oxygen through the process of photosynthesis.

23. The accumulation of hydrogen gas in the form of a very large cloud gave birth to:

a) Planets

b) Meteors

c) Sun

d) Galaxies

Ans. d) Galaxies

A galaxy starts to form by the accumulation of hydrogen gas in the form of a very large cloud called nebula.

24. According to Laplace, when the nebula became cool, it’s speed of rotation:

a) Decreased

b) Increased

c) Remained constant

d) First decreased and then increased

Ans. b) Increase

The increase in the speed of rotation resulted in the increase in centrifugal force.

25. From the Big Bang event, the first atom began to form within:

a) 3 minutes

b) 13 minutes

c) 3 hours

d) 3 days

Ans. a) 3 minutes

At the Big Bang the tiny ball exploded violently. This led to a huge expansion. It is now generally accepted that the event of the 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 a bang. Thereafter, the expansion was slowed down. Within first three minutes from the Big Bang event, first atom began to form.

26. The first lives on the Earth were:

a) Soft bodied arthropods

b) Unicellular

c) Blue green algae

d) Marine invertebrate

Ans. b) Unicellular

The microscopic structures closely related to the present form of the blue algae have been found in geological formations that are much older than some 3,000 million years ago. It can be assumed that life began to evolve sometime 3,800 million years ago.

27. Initially Earth’s surface was in:

a) Molten state

b) Solid state

c) Gaseous state

d) Semi molten state

Ans. c) Gaseous state

The planet earth initially was a barren, rocky and hot object with a thin atmosphere of hydrogen and helium (Gaseous state).

28. ______ is the wrong statement (Terrestrial planets):

a) They are formed at quiet a distant location

b) They have low gravitational pull

c) They could not hold the escaping gas

d) They are made up of rock metal and have relatively high densities.

Ans. a) They are formed at quiet a distant location;

The terrestrial planets were formed in the close vicinity of the parent star.

29. Water vapour and gases in the atmosphere were contributed by:

a) Magnetism

b) Seismic activities

c) Volcanism

d) Tectonic activity

Ans. c) Volcanism

Continuous volcanic eruptions contributed water vapour and gases to the atmosphere. As the earth cooled, the water vapour released and started getting condensed. The carbon dioxide in the atmosphere got dissolved in rainwater and the temperature further decreased.

30. The Earth’s primordial atmosphere (gases) is believed to have been eliminated by:

a) Planetary winds

b) Solar winds

c) Living worlds

d) Degassing

Ans. b) Solar winds

Earth’s primordial atmosphere was probably similar to the gas cloud that created the sun and planets. It consisted of hydrogen and helium, along with methane, ammonia, and water. The first stage is marked by the loss of the primordial atmosphere. The early atmosphere, with hydrogen and helium, is supposed to have been stripped off as a result of the solar winds.

31. Initially the Earth’s atmosphere consisted of:

a) Nitrogen and oxygen

b) Carbon and neon

c) Hydrogen and helium

d) Hydrogen and nitrogen

Ans. c) Hydrogen and helium

The planet earth initially was a barren rocky and hot object with a thin atmosphere of hydrogen and helium, but the present composition of earth’s atmosphere is chiefly contributed by nitrogen and oxygen.

32. Fossils are:

a) Remains of plants and animals in the rocks

b) The old rocks

c) The old books related to the origin of the earth

d) Remains of dust particles in atmosphere

Ans. a) Remains of plants and animals in the rocks

Fossils are preserved remains or traces of animals, plants and other organisms from the remote past. Fossils vary in size from microscope, such as single bacterial cells, only one micro meter in diameter, to gigantic, such as dinosaurs and trees many meters long and weighing many tons.

33. The vast distance between the galaxies is measured by:

a) Kilometres

b) Years

c) Light years

d) Miles

Ans. c) Light years

A light year is the unit of distance. It is the distance that light can travel in one year. Light moves at a velocity of about 3,000,000 Kilometres each second. So in one year it can travel about 10 trillion Km. More precisely, one light year is equal to 9,500,000,000,000 Km.

34. Modern man was born in:

a) Pliocene period (2 – 5 million years)

b) Holocene period (0 – 10,000 years)

c) Oligocene (24 – 37 million years)

d) Eocene period (37 – 55 million years)

Ans. a) Pliocene period 2.6 million years ago

35. Expanding universe hypothesis is also known as:

a) Binary Star Theory

b) Big Bang Theory

c) Expanded Universe Theory

d) Nebular Hypothesis

Ans. b) Big Bang Theory

The most popular argument regarding the origin of the universe is the Big Bang Theory. It is also called Expanding Universe Hypothesis. Edwin Hubble, in 1920, provided evidence that the universe is expanding.

36. Big Bang theory was postulated by:

a) Hoyle

b) Edwin Hubble

c) Schmidt

d) Immanuel Kant

Ans. b) Edwin Hubble

The most popular argument regarding the origin of the universe is the Big Bang Theory. It is also called Expanding Universe Hypothesis. As time passed, galaxies move further and further apart.

According to the Big Bang theory, the expansion of the observable universe began with the explosion of a single particle at a definite point of time. George Lemaitre, (1894 – 1966) Belgian Cosmologist, Catholic priest, is considered as father of the Big Bang theory.

37. Degassing refers to:

a) Shortage of gases

b) Absence of gases from the atmosphere

c) The process through which the gases were outpoured from the atmosphere

d) The process through which the gases were out poured from the interior of the earth

Ans. d) The process through which the gases were out poured from the interior of the earth is called degassing.

38. The terrestrial planets are rocky because:

a) They are formed away from the parent star

b) They are formed at quite a distant location

c) Formed of the rotating nebula

d) They are made up of rocks and material, and have relatively high densities

Ans. d) They are made up of rocks and material, and have relatively high densities.

The terrestrial planets are rocky because they are made up of rocks and material, and have relatively high densities. The terrestrial planets were formed in the close vicinity of the parent stars.

39. The life on the earth appeared around:

a) 7 billion years ago

b) 8 million years ago

c) 6 billion years ago

d) 8 billion years ago

Ans. b) 3.8 million years ago

The life on the earth appeared around 3.8 million years ago. The earth has a layered structure but it is not uniform everywhere.

40. Which one of the following is not related to the formation or modification of the present atmosphere?

a) Solarwinds

b) Degassing

c) Differentiation

d) Photosynthesis

Ans. c) Differentiation;

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

41. Which one of the following has the longest duration?

a) Supereon

b) Era

c) Period

d) Epoch

Ans. a) Supereon;

The largest defined unit of time is the Supereon, composed of eons. Eons are divided into eras, which are further subdivided into periods, epochs and ages. The terms eonothem, erathem, system, series and stages are used to refer to the layers of rocks that correspond to these periods of geologic time in earth’s history.

42. Which one of the following represent the age of the earth?

a) 6 billion years

b) 6 billion years

c) 7 billion years

d) 7 trillion years

Ans. b) 4.6 billion years

The age of the earth is 4.6 billion years. This age is based on evidence from radiometric age dating of meteorite material and is consistent with the radiometric ages of the oldest known terrestrial and lunar samples.

43. Modern man was born in:

a) Pliocene period (2 – 5 million years)

b) Holocene period (10,000 years)

c) Oligocene period ( 24 – 37 million years)

d) Eocene period (37 – 55 million years)

Ans. b) Holocene period (0 -10,000 years)

Modern man was born in Holocene period (0 -10,000 years).

44. The period of 570 million – 4800 million years is known as __________

a) Precambrian

b) Palaeozoic

c) Mesozoic

d) Cainozoic

Ans. a) Precambrian

Time period extends from 4.7 billion years ago to the beginning of the Cambrian Period, 542 million years ago. It represents more than 80 % of the total geologic record.

45. Fossils are:

a) Remains of plants and animals of the rocks

b) The old rocks

c) The old records related to the origin of the earth

d) The dust particles

Ans. a) Remains of plants and animals of the rocks

Fossils are remains of plants and animals of the rocks.

46. Initially the Earth’s surface was:

a) Molten state

b) Solid state

c) Barren, rocky and hot

d) Semi liquid state

Ans. c) Barren, rocky and hot

The planet Earth was initially a barren, rocky and hot object with a thin layer of atmosphere of hydrogen and helium.

47. The processes of differentiation means:

a) Separation of materials into different layers

b) Difference that exist on the surface of the earth

c) Separation of earth’s surface and its atmosphere

d) Differences between the densities

Ans. a) Separation of materials into different layers

The process of differentiation means that the earth forming material got separated into different layers. Starting from the surface to the central parts, we have layers like crust, mantle, outer core and inner core.

48. The hot rotating gaseous Nebula hypothesis was first proposed by:

a) Immanuel Kant

b) James Jeans

c) Laplace

d) Emanuel Swedenborg

Ans. d) Emanuel Swedenborg

There is evidence that the Nebular hypothesis was first proposed in 1734 by Emanuel Swedenborg and developed by Immanuel Kant (German Philosopher) in 1755. This was again revised by Laplace (Mathematician) in 1796.

49. Tertian period belongs to:

a) Pleistocene epoch

b) Miocene epoch

c) Eocene epoch

d) Holocene epoch

Ans. b) Miocene epoch

Tertian period belongs to Miocene epoch. It ranges from 5 – 24 million years and includes apes, flowering plants, trees etc.

50. Distance of the nearest star Alpha Centauri from the earth is:

a) 29 light years

b) 29 light years

c) 29 light years

d) 11 light years

Ans. b) 4.29 light years

Alpha Centauri is the brightest star and in the southern constellation. Alpha Centauri is also the closest star to the solar system, being only 1.34 parsecs, or 4.29 light years (23.5 trillion miles or 37.8 trillion Km) away from our Sun.

51. The oceans were formed about:

a) 5,000 million years ago

b) 4,000 million years ago

c) 3,000 million years ago

d) 2,000 million years ago

Ans. b) 4,000 million years ago

The rain water falling onto the surface got collected into the depressions to give rise to the oceans. 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.

52. A ring moved away from the Nebula when:
53. a) The centrifugal force exceeded the gravitational force
54. b) The gravitational force exceeded the centrifugal force
55. c) Both the forces were equal
56. d) The centrifugal force preceded the gravitational force

Ans. a) The centrifugal force exceeded the gravitational force

A ring moved away from the Nebula when the centrifugal force exceeded the gravitational force.

53. The reported ring broke into many smaller rings and these rings on cooling became:

a) Sun

b) Planets

c) Stars

d) Comets

Ans. b) Planets

The reported ring broke into many smaller rings and these rings on cooling became planets and satellites.

54. The Planetesimal hypothesis was put forwarded by:

a) Sir James Jeans

b) Chamberlain and Moulten

c) Immanuel Kant

d) H. Jeffreys

Ans. b) Chamberlain and Moulten

The Chamberlin – Moulton Planetesimal hypothesis was proposed in 1950 by geologist Thomas Chrowder Chamberlin and astronomer Forest Ray Moulton describe the formation of the solar System. It was replacement for the Laplacian version of the nebular hypothesis that had prevailed since 19^th century.

Very short answer type questions:

1. What is the range of diameters of individual galaxies?

Ans. The diameters of individual galaxies range from 80,000 to 15,000 light years.

2. What is Nebula?

Ans. Nebula is the name given to the hoot and slowly rotating dust cloud.

3. What is Planetesimal?

Ans. Planetesimal are just like dust particles that came into being by breaking of tonnes of matter out of the Sun caused by a passing star.

4. Why do planets differ in size and temperature?

Ans. The planets differ in size and temperature due to their varying distance from the sun.

5. What is a Pro-star?

Ans. A pro-star is contracting mass of gas which represents an early stage in the formation of star, before nucleon-synthesis begun. It was the core of dense gas, which finally becomes the infant star.

6. Who first proposed the Nebular hypothesis?

Ans. The German philosopher Immanuel Kant proposed the Nebular hypothesis for the first time. It was modified by Pierre Laplace in 1796.

7. When was the Earth formed?

Ans. The Earth was formed about 4.6 billion years ago out of a mixture of dust and gas around the young sun. It grew larger after countless collisions between dust particles, asteroids and other growing planets, including one last giant impact that threw enough rock, gas and dust into space to form the moon.

8. 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 of the earth’s crust.

9. How was atmosphere formed?

Ans. The higher gaseous material floating over the Earth’s crust formed the atmosphere.

10. Which are the gas giant planets?

Ans. Jupiter, Saturn, Uranus and Neptune are called gas giant planets.

11. What is degassing?

Ans. The processes through which the gasses are outpoured from the interior of solid earth are known as degassing.

12. Name the most popular theory regarding the origin of the universe.

Ans. The most popular argument regarding the origin of the universe is the Big Bang Theory. It is also called Expanding Universe Hypothesis.

13. Why are terrestrial planets rocky?

Ans. The terrestrial planets are rocky because they are made up of rocks and metals and have higher densities.

Short answer type questions:

1. Explain the Nebular Hypothesis by Otto Schmidt and Carl Weizascar.

Ans. Otto Schmidt and Carl Weizascar revised the Nebular Hypothesis in 1950. They considered:-

1. a) The Sun was surrounded by solar nebula containing mostly hydrogen and helium, along with dust.
2. b) The friction and collision of particles led to the formation of disk shaped cloud and planets were formed through the process of accretion.

2. What is Binary theory?

Ans. Chamberlain and Moulton considered that the wandering star approached the sun. As a result, a cigar shaped extension of material was separated from the solar matter surface. As the passing star moved away, the material separated from the solar surface and continued to revolve around the sun and slowly condensed into planets. Sir James Jeans and later Sir Harold Jeffrey supported this argument. These arguments are called binary theories.

3. Describe the three stages in the formation of atmosphere.

Ans.

1. a) The first stage is marked by the loss of primordial atmosphere.
2. b) In the second stage, the hot interior of the earth contributed to the evolution of the earth.
3. c) Finally, the composition of the atmosphere was modified by the living world through the process of photosynthesis.

4. Distinguish between inner planets and outer planets.

Ans.

5. Grade the stages considered in the development of planets?

Ans. The following stages are considered in the development of planets:-

a) Stars are localized lumps of gas within a nebula. The gravitational force within the lumps leads to the formation of a core to the gaseous cloud and a huge rotating disc of gas and dust develops around the gas core.

b) In the next stage, the gas cloud condenses and the matter around the core develops into small rounded objects that further, by the process of cohesion, develop into Planetesimal. Thereafter, the larger bodies start forming by collision, gravitational attraction causes the material to stick together.

c) In the final stage, these large numbers of small Planetesimal fuse to form fewer large bodies in the form of planets.