Embark on a fascinating journey through cosmic history with our expertly crafted resource designed around the New NCERT Class 11 Geography Chapter-2: The Origin and Evolution of The Earth Solutions Pdf. Tailored for students aiming for academic excellence, these detailed solutions offer clear explanations, accurate diagrams, and structured answers to help you conquer board exams and competitive tests with total confidence.
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
- Explanation: The Earth was formed approximately 4,600 million years ago, which equals 4.6 billion years. Note that 13.7 billion years represents the age of the universe (Big Bang event).
(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
- Explanation: Differentiation is the process by which materials inside the hot Earth separated into distinct interior layers (crust, mantle, core) based on density. Solar winds stripped the primordial atmosphere, degassing released gases from the interior, and photosynthesis added oxygen to the atmosphere.
(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
- Explanation: Life began to evolve in the oceans approximately 3,800 million years ago (3.8 billion years ago).
2. Answer the following questions in about 30 words.
(i) What is meant by the process of differentiation?
Answer: Differentiation is the process where Earth’s internal materials separated into distinct density layers during its volatile early stage. Heavier elements (like iron) sank to the core, while lighter silicates rose, forming the crust, mantle, and core.
(ii) What was the nature of the earth surface initially?
Answer: Initially, the Earth’s surface was rocky, barren, and extremely hot. It existed in a volatile, molten state without liquid oceans, surrounded by a thin primordial atmosphere composed mostly of hydrogen and helium.
(iii) What were the gases which initially formed the earth’s atmosphere?
Answer: The primordial atmosphere was initially dominated by light gases, primarily hydrogen and helium. After solar winds stripped these away, early volcanic degassing released water vapor, carbon dioxide, nitrogen, methane, ammonia, and negligible free oxygen.
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 prevailing cosmological model explaining the origin of the universe. Promoted by modern scientists after Edwin Hubble’s 1920 evidence of an expanding universe, it outlines three distinct stages of universal evolution:
- Singularity: Initially, all matter in the universe existed at a single point termed a “tiny ball” or singular atom, characterized by unimaginably small volume, infinite temperature, and infinite density.
- The Explosion: Approximately 13.7 billion years ago, this singular atom exploded violently, initiating rapid expansion that converted energy into matter. The first basic atoms began forming within the first three minutes following the explosion.
- Cooling and Transparency: Within 300,000 years post-explosion, expansion slowed and temperatures dropped to 4,500 Kelvin, giving rise to atomic matter and making the universe transparent.
The theory maintains that space between galaxies continues to expand today, causing galaxies to move progressively further apart.
(ii) List the stages in the evolution of the earth and explain each stage in brief.
Answer:
The Earth evolved from a hot, barren, rocky planet into a life-sustaining world through three major interconnected stages:
- Evolution of the Lithosphere (Density Differentiation): Early internal heating caused denser materials (like iron) to sink toward the center, while lighter materials rose to the surface. Over time, the outer layer cooled, condensed, and solidified to form distinct layers: crust, mantle, outer core, and inner core.
- Evolution of Atmosphere and Hydrosphere (Degassing and Rain): Solar winds stripped away the early primordial hydrogen and helium atmosphere. Subsequent cooling and volcanic eruptions released trapped gases—primarily water vapor, nitrogen, carbon dioxide, methane, and ammonia—through a process called degassing. Condensed water vapor fell as heavy rain, dissolving atmospheric carbon dioxide and filling deep surface depressions to create oceans around 4,000 million years ago.
- Origin and Biological Evolution of Life: Life originated around 3,800 million years ago in the oceans through complex chemical reactions. Photosynthetic organisms evolved between 2,500–3,000 million years ago, gradually saturating the oceans and eventually flooding the atmosphere with free oxygen around 2,000 million years ago.
Project Work
- Collect information about the project “Stardust” (website: www.sci.edu/public.html and www.nasm.edu) along the following lines.
Project Stardust:
1. (Which is the agency that has launched this project?
- Agency: NASA (National Aeronautics and Space Administration).
- Mission Type: Robotic sample-return mission under NASA’s Discovery Program.
2. Why are scientists interested in collecting Stardust?
- Why Collect Stardust?
- Comets are composed of primitive material left over from the formation of the solar system 4.6 billion years ago.
- Collecting stardust provides fresh insights into the early building blocks of planets and the origin of water and organic molecules on Earth.
- Unlike materials on Earth, comet material has remained preserved in a deep-freeze state in space.
3. Where from the Stardust is being collected?
- Collection Target: Comet Wild 2 (pronounced “Vilt 2”).
- Mechanism: The spacecraft flew through the dusty coma of Comet Wild 2, using a unique low-density solid material called aerogel to trap dust particles traveling at high speeds without damaging them.