The Origin and Evolution of the Earth – NCERT Solutions for Class 11 Geography

1. Multiple choice questions.

i. Which one of the following figures represents 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

Answer: (c) 4.6 billion years

ii. 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

Answer: (b) Differentiation

iii. 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) 3.8 billion

Answer: (d) 3.8 billion

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 materials got separated into different layers based on their densities. Heavier materials, like iron, sank towards the center, while lighter materials moved towards the surface, resulting in the formation of core, mantle, and crust.

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

Answer: The earth’s surface was initially barren, rocky, and hot. It had a thin atmosphere composed mainly of hydrogen and helium and was far different from the present-day earth, having no water or conditions suitable for life.

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

Answer: The initial gases that formed the earth’s atmosphere were mainly hydrogen and helium. Later, as the earth cooled, gases like water vapour, nitrogen, carbon dioxide, methane, ammonia, and very little free oxygen were released through volcanic eruptions.

3. Answer the following questions in about 150 words.

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

Answer: The Big Bang Theory explains the origin of the universe. According to this theory, all matter of the universe was concentrated in a “tiny ball” (singular atom) with extremely small volume and infinite temperature and density. About 13.7 billion years ago, this ball exploded violently, resulting in a huge expansion. As the universe expanded, some energy was converted into matter, and within fractions of a second, the first atoms began to form. Within 300,000 years, the universe cooled to about 4,500 K, allowing atomic matter to appear and making the universe transparent. The expansion of the universe means an increase in space between galaxies; galaxies themselves do not expand. The Big Bang Theory replaces earlier ideas, like the steady state theory, by providing evidence of an evolving, expanding universe—this expansion continues even today.

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

Answer: The evolution of the earth occurred in several stages:

• Primordial Stage: Earth began as a hot, barren, rocky body with a thin atmosphere of hydrogen and helium.
• Layer Formation: Differentiation occurred, causing heavier materials to sink and form the core, while lighter elements formed the crust, resulting in a layered structure.
• Atmosphere and Hydrosphere Evolution: Volcanic activity released gases and water vapor, leading to the evolution of atmosphere and oceans. Early atmosphere had little oxygen; oxygen increased due to photosynthesis later.
• Origin of Life: Life began around 3.8 billion years ago in oceans as a result of chemical reactions forming organic molecules, and gradually, photosynthetic organisms released oxygen into the atmosphere.

Key Concepts of The Origin and Evolution of the Earth – Class 11 NCERT Solutions 2025-26

Dive into the Origin and Evolution of the Earth with NCERT's Class 11 Geography. Mastering stages like the Big Bang, formation of atmosphere, and layered earth structure helps students build a strong foundation for future topics and exams.

Clear understanding of earth’s differentiation, early atmosphere, and the origin of life is crucial for scoring high in school and competitive exams. Breaking down each phase makes tough terminology and complex processes easy to grasp for every student.

Practice regularly and focus on core concepts like nebular hypothesis, star formation, and Big Bang theory. Reviewing concise NCERT solutions ensures concept retention and boosts your exam confidence for the 2025-26 session.