The Origin and Evolution of the Earth
NCERT Solutions • Class 11 Geography • Chapter 21. Multiple Choice Questions
(i) Which one of the following figures represents the age of the earth?
(c) 4.6 billion years
Note: The universe is estimated to be 13.7 billion years old, while the Earth formed significantly later.
Note: The universe is estimated to be 13.7 billion years old, while the Earth formed significantly later.
(ii) Which one of the following is not related to the formation or modification of the present atmosphere?
(b) Differentiation
Reason: Differentiation is the process responsible for the separation of the earth into layers (crust, mantle, core) based on density. Solar winds, Degassing, and Photosynthesis are directly related to the atmosphere’s evolution.
Reason: Differentiation is the process responsible for the separation of the earth into layers (crust, mantle, core) based on density. Solar winds, Degassing, and Photosynthesis are directly related to the atmosphere’s evolution.
(iii) Life on the earth appeared around how many years before the present?
(d) 3.8 billion
Note: The oldest evidence of life (blue-green algae/cyanobacteria) dates back to roughly 3,800 million years ago.
Note: The oldest evidence of life (blue-green algae/cyanobacteria) dates back to roughly 3,800 million years ago.
2. Short Answer Questions
(i) What is meant by the process of differentiation?
Differentiation is the geological process by which the earth’s interior separated into layers of different densities. While the earth was in a molten state, heavier materials (like iron and nickel) sank towards the center (core), while lighter materials (like silica) floated towards the surface (crust).
(ii) What was the nature of the earth surface initially?
Initially, the earth was barren, rocky, and extremely hot. It had a thin atmosphere primarily of hydrogen and helium. There were no oceans or life forms, and the surface was volatile due to extensive volcanic activity.
(iii) What were the gases which initially formed the earth’s atmosphere?
The primordial atmosphere consisted chiefly of Hydrogen and Helium. However, these were stripped away by solar winds. The early secondary atmosphere, formed through volcanic degassing, consisted mainly of water vapour, nitrogen, carbon dioxide, methane, ammonia, and very little free oxygen.
3. Long Answer Questions
(i) Write an explanatory note on the ‘Big Bang Theory’.
The Big Bang Theory, also known as the expanding universe hypothesis, is the most widely accepted theory regarding the origin of the universe. Proposed by Edwin Hubble in 1920, it postulates:
- The Singularity: In the beginning, all matter and energy in the universe existed in one tiny point (singularity) with infinite temperature and density.
- The Explosion: Around 13.7 billion years ago, this tiny point exploded violently. This led to a massive expansion that continues today.
- Formation of Matter: As the universe expanded, it cooled down. Energy converted into matter, eventually forming the first atoms (Hydrogen and Helium), which later clumped together to form stars and galaxies.
(ii) List the stages in the evolution of the earth and explain each stage in brief.
The evolution of the earth occurred in three main stages:
- 1. Formation of Lithosphere (Accretion & Differentiation): Earth formed by the accretion of planetesimals. As density increased, the temperature rose, turning the earth molten. Through differentiation, heavy materials sank to form the Core, and lighter materials formed the Crust.
- 2. Evolution of Atmosphere & Hydrosphere: The primordial atmosphere (H, He) was stripped by solar winds. Cooling of the earth led to Degassing, releasing water vapour and gases from the interior. Condensed water vapour caused rains, filling depressions to form oceans.
- 3. Origin of Life (Biosphere): Around 3.8 billion years ago, complex chemical reactions in the oceans generated complex organic molecules, leading to the first unicellular life forms (Blue-green algae), which eventually evolved into modern life.
Project Work: Stardust
Topic: Project Stardust
(i) Agency: NASA (National Aeronautics and Space Administration).
(ii) Interest in Stardust: Scientists are interested because comets (the source of stardust) are remnants from the formation of the solar system. Analyzing these particles helps reveal the chemical composition and conditions that existed 4.6 billion years ago when the Earth was forming.
(iii) Collection Source: The Stardust spacecraft collected samples from the coma (dust tail) of the Comet Wild 2 and also collected interstellar dust flowing through the solar system.
(ii) Interest in Stardust: Scientists are interested because comets (the source of stardust) are remnants from the formation of the solar system. Analyzing these particles helps reveal the chemical composition and conditions that existed 4.6 billion years ago when the Earth was forming.
(iii) Collection Source: The Stardust spacecraft collected samples from the coma (dust tail) of the Comet Wild 2 and also collected interstellar dust flowing through the solar system.