CBSE Class 11 Geography Chapter 2: The Origin and Evolution of the Earth NCERT Solutions

Reviewed by NCERT Help Editorial Team · Updated on 29 Jul 2026

NCERT Solutions PDF Class 11 PDF

CBSE Class 11 Geography, Chapter 2, The Origin and Evolution of the Earth, delves into the fascinating journey of our planet's formation. This chapter explores the immense age of the Earth and the vast geological time scales, breaking down Eons, Eras, Periods, and Epochs. It explains how our atmosphere came to be and how it has evolved over time. Students will learn about the characteristics of the inner, rocky planets and explore major scientific theories about Earth's origin, such as the nebular hypothesis and the planetesimal hypothesis. A key concept covered is planetary differentiation, the process that led to the layering of Earth's interior. These explanations aim to provide a clear understanding of Earth's development and its early history, aiding students in mastering the subject matter.

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Quick info

Board	CBSE
Class	Class 11
Subject	Geography
Session	2026
Language	English
Type	NCERT Solutions
Chapter	2. The Origin and Evolution of the Earth

Chapter summary

This chapter's NCERT Solutions focus on the fundamental aspects of Earth's origin and evolution. It addresses the estimated age of the Earth, the hierarchical structure of geological time scales, and the factors influencing atmospheric development. The solutions also differentiate between inner and outer planets and critically examine major theories proposed for the Earth's formation, such as those by Kant, Laplace, Chamberlain, and Moulton. The concept of differentiation and its role in shaping Earth's layered structure is also explained, providing a comprehensive overview for students.

Learning outcomes

Understand the estimated age of the Earth.
Differentiate between geological time units like Eons, Eras, Periods, and Epochs.
Identify factors influencing the formation and evolution of Earth's atmosphere.
Distinguish between terrestrial and other types of planets.
Explain major theories on the origin of the Earth.
Define and explain the process of differentiation in planetary formation.

Topics covered

Paper topics

Age of the Earth
Geological Time Scale
Atmosphere Formation
Terrestrial Planets
Nebular Hypothesis
Planetesimal Hypothesis
Differentiation Process
Origin of Earth Theories

Important topics

Age of the Earth
Geological Time Scale Units
Atmosphere Formation Factors
Terrestrial Planet Characteristics
Major Earth Origin Theories
Process of Differentiation

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Questions and Solutions

Question 1

Which one of the following figures represents the age of the earth?

4.6 million years
13.7 billion years
4.6 billion years
13.7 trillion years

Solution: The currently accepted scientific estimate for the age of the Earth is approximately 4.6 billion years. This age is determined through radiometric dating of meteorites and the oldest known rocks on Earth and the Moon. Therefore, option (c) is the correct representation of the Earth's age.

Question 2

Which one of the following has the longest duration?

Eons
Period
Era
Epoch

Solution: The geological time scale is divided into hierarchical units. The largest and longest divisions are called Eons. These are further subdivided into Eras, which are then divided into Periods, and finally into Epochs. Thus, Eons represent the longest duration among the given options.

Question 3

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

Solar winds
Differentiation
Degassing
Photosynthesis

Solution: Differentiation is the process by which heavier elements sank to the center of the Earth, forming the core, while lighter elements rose to form the mantle and crust. This process is crucial for the internal structure of the Earth but is not directly involved in the formation or modification of the atmosphere. Solar winds, degassing (release of gases from the Earth's interior), and photosynthesis (production of oxygen) are all significant factors in atmospheric evolution.

Question 4

Which one of the following represents the inner planets?

Planets between the sun and the earth
Planets between the sun and the belt of asteroids
Planets in gaseous state
Planets without satellite(s)

Solution: The inner planets, also known as terrestrial planets, are Mercury, Venus, Earth, and Mars. They are located in the inner solar system, between the Sun and the main asteroid belt. These planets are characterized by their solid, rocky surfaces. Options (c) and (d) describe characteristics that are more typical of outer planets or are not exclusive to inner planets.

Question 5

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

13.7 billion
4.6 billion
3.8 million
3.8 billion

Solution: Scientific evidence, primarily from fossil records and geochemical analysis, suggests that the earliest forms of life appeared on Earth approximately 3.8 billion years ago. This is significantly after the formation of the Earth itself, which occurred around 4.6 billion years ago.

Question 6 (i)

Why are the terrestrial planets rocky?

Solution: The terrestrial planets, namely Mercury, Venus, Earth, and Mars, are called 'rocky' or 'terrestrial' because their composition is predominantly rock and metal, similar to Earth's. During the formation of the solar system, the intense heat from the young Sun in the inner solar system evaporated lighter elements like hydrogen and helium. This left behind heavier elements, primarily rock-forming materials and metals, which then accreted to form these inner, solid planets.

Question 6 (ii) (a)

What is the basic difference in the arguments related to the origin of the earth given by Kant and Laplace?

Solution: Immanuel Kant, in his 'Nebular Hypothesis' (1755), proposed that the Earth and other planets formed from the gradual accretion of small, cold particles in a primordial cloud. Later, Pierre-Simon Laplace (1796) revised this idea, suggesting that the planets originated from a hot, rotating gaseous cloud (nebula) associated with the young Sun. Laplace's version proposed that the Sun shed rings of hot gas, which then condensed to form the planets.

Question 6 (ii) (b)

What is the basic difference in the arguments related to the origin of the earth given by Chamberlain and Moulton?

Solution: Thomas Chamberlin and Forest Moulton proposed the 'Planetesimal Hypothesis' (early 20th century). They argued that a rogue star passed close to our Sun. The gravitational pull of this passing star caused tidal bulges on the Sun, ejecting streams of solar material. These ejected materials then cooled and condensed into smaller solid bodies called planetesimals, which eventually aggregated to form the planets.

Question 6 (iii)

What is meant by the process of differentiation?

Solution: Differentiation refers to the process during the early formation of a planet, like Earth, where materials separate based on their density. Initially, the Earth was in a molten or semi-molten state. Denser materials, such as iron and nickel, sank towards the center to form the core, while lighter silicate materials rose to the surface, eventually forming the mantle and crust. This process resulted in Earth's layered internal structure.

Common mistakes

Confusing millions and billions in age estimations.
Misunderstanding the hierarchy of geological time scales.
Incorrectly associating processes like differentiation with atmospheric modification.
Confusing the characteristics of terrestrial planets with gas giants.

Revision tips

Memorize the age of the Earth and the approximate time of life's appearance.
Create a table to compare the different geological time units (Eons, Eras, Periods, Epochs).
Draw diagrams to illustrate the concepts of Kant's and Laplace's theories, and Chamberlain-Moulton's theory.
Focus on understanding the 'why' behind terrestrial planets being rocky.
Review the definition and significance of the differentiation process.

Practice MCQs

Q1. What is the currently accepted approximate age of the Earth?

Q2. Which of the following geological time units represents the longest duration?

Q3. Which process is NOT directly related to the formation or modification of Earth's present atmosphere?

Q4. The inner planets, also known as terrestrial planets, are characterized by being:

Q5. Approximately when did life first appear on Earth?

Frequently asked questions

What is the accepted age of the Earth according to NCERT?

According to the NCERT solutions, the accepted age of the Earth is approximately 4.6 billion years.

What are the main divisions of geological time?

The main divisions of geological time, from longest to shortest duration, are Eons, Eras, Periods, and Epochs.

Why are the inner planets called terrestrial planets?

The inner planets (Mercury, Venus, Earth, and Mars) are called terrestrial because they are primarily composed of rock and metal, similar to Earth, and formed in the inner, hotter region of the solar system.

What is the difference between Kant's and Laplace's theories on Earth's origin?

Kant proposed that Earth formed from small, cold particles, while Laplace revised this, suggesting planets formed from a cloud of material associated with the young Sun (nebular hypothesis).

Explain the process of differentiation in Earth's formation.

Differentiation is the process where Earth's constituent materials separated into layers (crust, mantle, core) based on their density during its formation.

How can these NCERT solutions help in exam preparation?

These solutions provide clear, concise answers to all questions in Chapter 2, helping students understand complex concepts, revise key theories, and practice answering questions accurately for exams.

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