NCERT Solutions for Class 11 Geography Chapter 2: The Origin and Evolution of the Earth (NCERT 2026–27)

These Class 11 Geography Chapter 2 solutions cover The Origin and Evolution of the Earth from Fundamentals of Physical Geography, the NCERT textbook for the 2026–27 session. The chapter belongs to Unit II, The Earth, and explains the early hypotheses about the origin of the earth, the modern Big Bang Theory of the origin of the universe, the formation of stars and planets, and how the barren, rocky early earth evolved its lithosphere, atmosphere, hydrosphere and finally life. Below you get step-by-step answers to all NCERT Exercises, clear notes on key terms, extra practice, MCQs, Assertion–Reason and FAQs.

Class: 11 Subject: Geography Book: Fundamentals of Physical Geography Unit: II – The Earth Chapter: 2 Session: 2026–27
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Class 11 Geography Chapter 2 – Overview

Chapter 2, The Origin and Evolution of the Earth, traces the story of the earth from the birth of the universe to the appearance of life. Early hypotheses such as the Nebular Hypothesis of Kant (revised by Laplace in 1796, and later by Schmidt and Weizsacker) tried to explain how planets formed from a cloud of material around a young sun. The modern explanation for the origin of the universe is the Big Bang Theory (expanding universe hypothesis), supported by Edwin Hubble’s 1920 evidence that galaxies are moving apart. The chapter then describes how stars formed from nebulae and how planets grew through cores, planetesimals and accretion. Finally it explains the evolution of the earth — differentiation that produced the layered lithosphere, degassing and condensation that built the atmosphere and oceans (hydrosphere), and the origin of life around 3,800 million years ago through photosynthesis and chemical evolution.

Key Concepts & Terms

Nebular Hypothesis: an early hypothesis (Immanuel Kant; revised by Laplace in 1796) that planets formed out of a cloud of material associated with a youthful, slowly rotating sun. Schmidt and Weizsacker later revised it, holding that the sun was surrounded by a solar nebula of hydrogen, helium and dust whose friction and collision formed a disk and then the planets.

Big Bang Theory: the most popular argument for the origin of the universe, also called the expanding universe hypothesis. All matter once existed as a “tiny ball” (singular atom) of infinite density which exploded about 13.7 billion years ago, expanding ever since; Edwin Hubble (1920) showed the universe is expanding.

Expanding universe: the increase in space between galaxies as time passes, so galaxies move further apart — demonstrated using the inflating-balloon model.

Light year: a measure of distance (not time) — the distance light travels in one year at 300,000 km/second, equal to about 9.461 × 1012 km.

Nebula: a very large cloud of hydrogen gas; its localised, denser clumps grow into stars.

Planetesimals: small, rounded bodies that form by cohesion from matter around a gas core; they collide and accrete to form a few large bodies — the planets.

Accretion: the process by which a large number of small planetesimals stick together under gravity to form fewer, larger bodies (planets).

Differentiation: the process by which the earth’s heated material separated by density — heavier materials (like iron) sank to the centre and lighter ones rose to the surface — producing the layers crust, mantle, outer core and inner core.

Degassing: the process through which gases and water vapour were outpoured from the interior of the solid earth, beginning the evolution of the present atmosphere.

Photosynthesis: the process (evolved around 2,500–3,000 million years ago) by which living organisms added oxygen to the oceans and later flooded the atmosphere with oxygen.

Other key terms: steady state concept (Hoyle’s alternative, holding the universe to be roughly the same at any time), primordial atmosphere (the early hydrogen–helium atmosphere stripped off by solar winds), and fossils (records of past life preserved in rocks).

NCERT “Exercises” — Full Solutions

All questions below are reproduced verbatim from the NCERT textbook’s end-of-chapter Exercises. Answers are original, written in exam-ready style.

1. Multiple choice questions.

(i) Which one of the following figures represents the age of the earth? (a) 4.6 million years    (c) 4.6 billion years (b) 13.7 billion years    (d) 13.7 trillion years

ANSWER (c) 4.6 billion years. The earth is about 4,600 million (4.6 billion) years old. Option (b), 13.7 billion years, is the age of the universe (the time since the Big Bang), not of the earth.

(ii) Which one of the following is not related to the formation or modification of the present atmosphere? (a) Solar winds    (c) Degassing (b) Differentiation    (d) Photosynthesis

ANSWER (b) Differentiation. Solar winds stripped off the primordial atmosphere, degassing released gases from the interior, and photosynthesis modified the atmosphere by adding oxygen — all are linked to the atmosphere. Differentiation is the separation of the earth’s interior into layers by density and relates to the lithosphere, not the atmosphere.

(iii) Life on the earth appeared around how many years before the present? (a) 13.7 billion    (c) 4.6 billion (b) 3.8 million    (d) 3.8 billion

ANSWER (d) 3.8 billion. Life is believed to have begun to evolve around 3,800 million (3.8 billion) years ago, as suggested by microscopic structures resembling blue algae found in geological formations.

2. Answer the following questions in about 30 words.

(i) What is meant by the process of differentiation?

ANSWER Differentiation is the process by which the earth’s heated material separated according to density — heavier materials like iron sank towards the centre and lighter ones rose to the surface — forming the layers: crust, mantle, outer core and inner core.

(ii) What was the nature of the earth surface initially?

ANSWER Initially the earth was a barren, rocky and hot object with a thin atmosphere of hydrogen and helium. It was in a volatile state during its primordial stage, far from today’s planet with water and a life-supporting atmosphere.

(iii) What were the gases which initially formed the earth’s atmosphere?

ANSWER The early atmosphere largely contained water vapour, nitrogen, carbon dioxide, methane and ammonia, with very little free oxygen. The first, primordial atmosphere of hydrogen and helium had already been stripped away by solar winds.

3. Answer the following questions in about 150 words.

(i) Write an explanatory note on the ‘Big Bang Theory’.

ANSWER The Big Bang Theory, also called the expanding universe hypothesis, is the most widely accepted explanation for the origin of the universe. In 1920, Edwin Hubble provided evidence that the universe is expanding, with galaxies steadily moving apart. The theory proposes the following stages: (i) In the beginning, all matter forming the universe existed in one place as a “tiny ball” (singular atom) with an unimaginably small volume, infinite temperature and infinite density. (ii) About 13.7 billion years ago this tiny ball exploded violently, causing a huge expansion; within fractions of a second the expansion was extremely rapid, then slowed, and within the first three minutes the first atoms began to form. (iii) Within about 300,000 years the temperature dropped to around 4,500 K, atomic matter formed and the universe became transparent. The expansion continues even today, meaning the space between galaxies keeps increasing. Hoyle’s steady state concept was an alternative, but the expanding-universe view is now favoured.

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

ANSWER The earth evolved from a barren, hot, rocky body into a life-supporting planet through the following stages: 1. Evolution of the lithosphere: The early earth was volatile and hot. Rising density and temperature caused the material to separate by density (differentiation) — heavier matter like iron sank to form the core and lighter matter rose to form the crust, giving the layered structure (crust, mantle, outer core, inner core). 2. Evolution of the atmosphere: The primordial hydrogen–helium atmosphere was stripped off by solar winds. Then, through degassing, the cooling interior released water vapour, nitrogen, carbon dioxide, methane and ammonia, building a second atmosphere. 3. Evolution of the hydrosphere: As the earth cooled, water vapour condensed and rained down; the rainwater collected in depressions to form oceans, which are about 4,000 million years old. 4. Origin of life: Around 3,800 million years ago, chemical reactions formed complex organic molecules that could self-replicate; photosynthesis later flooded the oceans and atmosphere with oxygen, completing the modern atmosphere.

Project Work

Collect information about the project “Stardust” (website: www.sci.edu/public.html and www.nasm.edu) along the following lines. (i) Which is the agency that has launched this project? (ii) Why are scientists interested in collecting Stardust? (iii) Where from the Stardust is being collected?

ANSWER (project guidance) This is a research project; below is a model write-up you can verify and expand from the suggested websites and other reliable sources. (i) Agency: The Stardust mission was launched by NASA (the National Aeronautics and Space Administration of the USA). It was launched in 1999 and returned its samples to Earth in 2006. (ii) Why scientists are interested: Comets and interstellar dust are among the oldest, most primitive materials in the solar system — leftovers from the cloud that formed the sun and planets. By studying this “stardust”, scientists hope to understand the origin and early evolution of the solar system, the building blocks of planets, and possibly the origin of the organic molecules linked to life. (iii) Where it is collected from: Stardust collected dust samples from the coma (cloud) of Comet Wild 2 and also captured interstellar dust particles in space, trapping them in a light, sponge-like material called aerogel before returning the capsule to Earth.

Extra Practice Questions

Short Answer Type Questions

Q1. What is the Nebular Hypothesis?

ANSWERThe Nebular Hypothesis, proposed by Immanuel Kant and revised by Laplace in 1796, holds that the planets formed out of a cloud of material associated with a youthful, slowly rotating sun. Schmidt and Weizsacker later refined it using a solar nebula of hydrogen, helium and dust.

Q2. Define a light year.

ANSWERA light year is a measure of distance, not time. It is the distance light travels in one year at a speed of 300,000 km per second, which equals about 9.461 × 1012 km.

Q3. How were the oceans formed on the earth?

ANSWERAs the earth cooled, the water vapour released by degassing condensed. Carbon dioxide dissolved in rainwater, lowering the temperature further and causing more rain. This rainwater collected in depressions, giving rise to the oceans about 4,000 million years ago.

Q4. What is meant by accretion in the formation of planets?

ANSWERAccretion is the final stage of planet formation in which a very large number of small planetesimals collide and stick together under gravitational attraction, building up a few large bodies that become the planets.

Q5. What was Hoyle’s steady state concept?

ANSWERHoyle’s steady state concept was an alternative to the Big Bang Theory. It considered the universe to be roughly the same at any point of time. With growing evidence for an expanding universe, the scientific community now favours the Big Bang argument.

Long Answer Type Questions

Q1. Describe the stages in the formation of stars and planets.

ANSWERFormation of stars: Matter and energy were unevenly distributed in the early universe. These density differences created differences in gravitational force, drawing matter together to form the bases of galaxies. Within a galaxy, hydrogen gas accumulates as a huge cloud called a nebula. The growing nebula develops localised, denser clumps of gas, which keep growing into denser gaseous bodies that become stars; this is believed to have happened some 5–6 billion years ago. Formation of planets: (i) Stars are localised lumps of gas within a nebula; gravitational force forms a core to the gas cloud, around which a huge rotating disc of gas and dust develops. (ii) The gas cloud condenses and matter around the core gathers into small, rounded objects, which by cohesion grow into planetesimals; larger bodies form by collision and gravitational attraction. (iii) In the final stage, the large number of planetesimals accrete into a few large bodies in the form of planets.

Q2. Explain the three stages in the evolution of the earth’s present atmosphere.

ANSWERThe present atmosphere, chiefly nitrogen and oxygen, evolved through three stages. First stage – loss of the primordial atmosphere: The early atmosphere of hydrogen and helium was stripped off by solar winds. This happened to the earth and to all the terrestrial planets, which lost their primordial atmosphere through the impact of solar winds. Second stage – degassing: During the cooling of the earth, the hot interior released gases and water vapour through a process called degassing. Continuous volcanic eruptions added water vapour and gases such as nitrogen, carbon dioxide, methane and ammonia, with very little free oxygen. As the earth cooled further, water vapour condensed and carbon dioxide dissolved in rainwater. Third stage – modification by life: The composition of the atmosphere was modified by the living world through photosynthesis. Oceans first became saturated with oxygen, and around 2,000 million years ago oxygen began to flood the atmosphere, giving it its present life-supporting character.

MCQs & Assertion–Reason

1. The Big Bang event is generally accepted to have taken place about:

(a) 4.6 billion years ago    (b) 13.7 billion years ago    (c) 3.8 billion years ago    (d) 5–6 billion years ago

2. The Nebular Hypothesis was revised by Laplace in the year:

(a) 1796    (b) 1850    (c) 1920    (d) 1950

3. Who provided evidence in 1920 that the universe is expanding?

(a) Immanuel Kant    (b) Otto Schmidt    (c) Edwin Hubble    (d) Fred Hoyle

4. A large cloud of hydrogen gas in which stars begin to form is called a:

(a) galaxy    (b) nebula    (c) planetesimal    (d) singularity

5. The small, rounded objects that accrete to form planets are called:

(a) nebulae    (b) galaxies    (c) planetesimals    (d) comets

6. The process by which heavier materials sank to the centre and lighter ones rose to the surface of the earth is called:

(a) degassing    (b) accretion    (c) differentiation    (d) photosynthesis

7. The outpouring of gases and water vapour from the interior of the earth is known as:

(a) condensation    (b) degassing    (c) differentiation    (d) accretion

8. The earth’s oceans are estimated to be about how old?

(a) 2,000 million years    (b) 3,000 million years    (c) 4,000 million years    (d) 4,600 million years

9. The alternative to the Big Bang, holding the universe to be roughly the same at any time, was proposed by:

(a) Hubble    (b) Laplace    (c) Kant    (d) Hoyle

10. The light from the sun reaches the earth in about:

(a) 8.311 minutes    (b) 1 light year    (c) 13.7 minutes    (d) 300,000 seconds

Answer key: 1-(b), 2-(a), 3-(c), 4-(b), 5-(c), 6-(c), 7-(b), 8-(c), 9-(d), 10-(a).

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: The universe is considered to be expanding.

Reason: As time passes, galaxies move further and further apart, increasing the space between them.

A-R 2. Assertion: A light year is a unit of time.

Reason: It measures the distance light travels in one year at 300,000 km per second.

A-R 3. Assertion: The earth has a layered structure with crust, mantle, outer core and inner core.

Reason: Through differentiation, heavier materials sank towards the centre while lighter materials moved towards the surface.

A-R 4. Assertion: The present atmosphere of the earth is the same as its primordial atmosphere.

Reason: The early hydrogen and helium atmosphere was stripped off by solar winds.

A-R 5. Assertion: Photosynthesis played a role in modifying the earth’s atmosphere.

Reason: The living world released oxygen that saturated the oceans and eventually flooded the atmosphere.

Answer key: 1-(A), 2-(D), 3-(A), 4-(D), 5-(A).

Exam Tips & Common Mistakes

How to score full marks in this chapter

Memorise the key figures — the universe is about 13.7 billion years old, the earth about 4.6 billion years, oceans about 4,000 million years, and life began around 3,800 million years ago. For the Big Bang Theory, write its three stages in order (tiny ball → explosion and expansion → cooling and atomic matter). For the evolution of the earth, structure your answer as lithosphere → atmosphere → hydrosphere → life, and remember the three keywords differentiation, degassing and photosynthesis. Naming the scientists (Kant, Laplace, Schmidt, Weizsacker, Hubble, Hoyle) earns extra marks.

Common mistakes to avoid

  • Confusing the age of the universe (13.7 billion years) with the age of the earth (4.6 billion years).
  • Treating a light year as a unit of time — it is a unit of distance.
  • Mixing up differentiation (separation of the interior by density) with degassing (release of gases from the interior).
  • Writing that the present atmosphere is the original (primordial) one — the first hydrogen–helium atmosphere was stripped off by solar winds.
  • Confusing nebula (gas cloud), planetesimals (small rounded bodies) and accretion (their joining into planets).
  • Forgetting that photosynthesis, not just degassing, gave the atmosphere its oxygen.

Frequently Asked Questions

What is Chapter 2 of Class 11 Geography (Fundamentals of Physical Geography) about?

Chapter 2, The Origin and Evolution of the Earth, explains early hypotheses like the Nebular Hypothesis, the modern Big Bang Theory of the origin of the universe, the formation of stars and planets, and how the early earth evolved its lithosphere, atmosphere, hydrosphere and finally life.

What is the Big Bang Theory in simple words?

The Big Bang Theory states that all matter once existed as a “tiny ball” of infinite density which exploded about 13.7 billion years ago. The universe has been expanding ever since, with galaxies moving apart, as Edwin Hubble’s 1920 observations confirmed.

How old is the earth and when did life appear?

The earth is about 4.6 billion (4,600 million) years old. Oceans formed about 4,000 million years ago, and life is believed to have begun to evolve around 3,800 million years ago.

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