Class 11 Geography NCERT Solutions Chapter 2 The Origin and Evolution of the Earth
The Origin and Evolution of the Earth is the second chapter of Class 11 Geography NCERT. We have prepared the Class 11 Geography NCERT Solutions Chapter 2 for your ready reference.
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
The correct answer is: (c) 4.6 billion years
The age of the Earth is approximately 4.6 billion years. This estimation is based on scientific evidence and dating techniques used by geologists and astronomers to study the formation of the Earth and the Solar System.
(ii) Which one of the following has the longest duration?
The correct answer is: (a) Eons
In the geological time scale, an eon is the largest division of time and has the longest duration. It is followed by eras, periods, and epochs, in descending order of time duration.
(iii) Which one of the following is not related to the formation or modification of the present atmosphere?
(a) Solar winds
Ans: (b) Differentiation
Differentiation refers to the process during the early stages of Earth’s formation when heavier elements sank to the core, and lighter elements, including gases, rose to the surface. This process played a significant role in shaping the composition of the Earth’s interior and atmosphere.
(iv) Which one of the following represents the inner planets?
(a) Planets between the sun and the earth
(b) Planets between the sun and the belt of asteroids
(c) Planets in gaseous state
(d) Planets without satellite(s)
Ans: (b) Planets between the sun and the belt of asteroids
The inner planets are the ones located between the Sun and the belt of asteroids in our solar system.
(v) 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.
Ans: The correct answer is: (d) 3.8 billion
Life on Earth appeared around 3.8 billion years before the present. This estimation is based on scientific evidence, including the discovery of fossilized microorganisms, that suggests the presence of early life forms on Earth dating back billions of years.
2. Answer the following questions in about 30 words.
(i) Why are the terrestrial planets rocky?
Answer: Terrestrial planets are rocky due to their proximity to the Sun, allowing higher temperatures that led to the formation of dense, solid materials.
(ii) What is the basic difference in the arguments related to the origin of the earth given by :
(a) Kant and Laplace
(b) Chamberlain and Moulton
(a) Kant and Laplace: Kant proposed the nebular hypothesis, suggesting that a rotating cloud of gas and dust gradually condensed to form the solar system. Laplace expanded on this, proposing that a rotating nebula flattened into a disk, with the Sun forming at the center and planets from the material in the disk.
(b) Chamberlain and Moulton: Chamberlain and Moulton proposed the planetesimal hypothesis, suggesting that a passing star’s gravitational forces disrupted the Sun, causing solar material to condense into small planetesimals. These planetesimals then collided and merged to form planets, including Earth.
(iii) What is meant by the process of differentiation?
Answer: Differentiation refers to the process by which a planet or celestial body develops distinct layers with varying compositions due to variations in density. This process occurs during the early stages of a planet’s formation when denser materials, like metals, sink towards the center, forming a core, while lighter materials, like silicates, rise to the surface.
(iv) What was the nature of the Earth’s surface initially?
Answer: The initial nature of Earth’s surface was extremely hot and molten due to intense heat generated during its accretion and the bombardment by celestial bodies during the early stages of its formation. This molten surface gradually cooled and solidified over time to form the Earth’s crust.
(v) What were the gases which initially formed the Earth’s atmosphere?
Answer: The early Earth’s atmosphere is believed to have been primarily composed of hydrogen, helium, methane, ammonia, and water vapor. These gases were released from the interior through volcanic activity and were eventually modified by various geological and biological processes to form the present-day atmosphere.
3. Answer the following questions in about 150 words.
(i) Write an explanatory note on the ‘Big Bang Theory’.
Ans: The Big Bang Theory is a widely accepted scientific explanation for the origin of the universe. It proposes that the universe originated from an immensely hot and dense state approximately 13.8 billion years ago. According to this theory, all matter, energy, and space itself were initially compressed into an extremely tiny, infinitely dense point known as a singularity. Then, in an explosive event known as the Big Bang, the singularity rapidly expanded, initiating the creation of space, time, and all the fundamental forces of nature.
As the universe expanded and cooled, subatomic particles formed, eventually leading to the formation of atoms, stars, galaxies, and other cosmic structures. The Big Bang Theory is supported by observations of cosmic microwave background radiation, the abundance of light elements, and the redshift of distant galaxies, among other pieces of evidence. It has revolutionized our understanding of the universe’s origins and evolution, providing a foundation for cosmology.
(ii) List the stages in the evolution of the earth and explain each stage in brief.
Ans: Stages in the evolution of the earth and their explanation:
- Accretion and Differentiation: During the early stages of the solar system, dust and gas particles began to accumulate due to gravitational forces, forming planetesimals. These planetesimals collided and merged, gradually forming the Earth. As the Earth grew in size, heat generated by radioactive decay led to differentiation, where denser materials sank to form the core, and lighter materials rose to form the mantle and crust.
- Heavy Bombardment: After its formation, the young Earth experienced intense bombardment by asteroids and comets. This period, known as the Late Heavy Bombardment, had a significant impact on the planet’s surface and may have contributed water and volatile compounds.
- Formation of the Oceans and Atmosphere: Volcanic activity released water vapor, carbon dioxide, and other gases from the Earth’s interior. As the planet cooled, water vapor condensed to form oceans, while volcanic outgassing contributed to the formation of the early atmosphere, primarily composed of water vapor, carbon dioxide, methane, and ammonia.
- Emergence of Life: Conditions in the oceans favored the emergence of simple organic molecules through processes like abiogenesis. Over time, these molecules evolved into more complex structures, eventually leading to the first living organisms.
- Oxygenation and Photosynthesis: Cyanobacteria, through photosynthesis, began to release oxygen into the atmosphere, leading to the Great Oxygenation Event. This oxygenation had a profound impact on the development of more complex life forms.
- Continental Drift and Evolution of Life: Continental drift and the formation of supercontinents influenced Earth’s climate, ocean currents, and habitats. Evolutionary processes led to the diversification of life forms, from single-celled organisms to multicellular plants and animals.
- Ice Ages and Human Evolution: The Earth experienced several ice ages, shaping landscapes and influencing the evolution of life. Human ancestors emerged, developed tools, and migrated across the globe.
These stages represent the dynamic and intricate processes that have shaped the Earth over billions of years, leading to the diverse and complex planet we inhabit today.
Project “Stardust”: Project “Stardust” is a space mission conducted by NASA, the United States space agency, with the primary goal of collecting samples from a comet and interstellar dust particles. The mission was launched on February 7, 1999, and its main objective was to gain insights into the early solar system’s composition and the building blocks of planets.
The main components of the project are as follows:
- Comet Sample Collection: The spacecraft, named Stardust, was designed to fly by Comet Wild 2 (pronounced “Vilt-2”) and collect samples from its coma, which is the cloud of gas and dust surrounding the comet’s nucleus. The spacecraft approached the comet and used a special collector made of aerogel, a low-density material, to capture the dust particles from the comet’s coma.
- Interstellar Dust Collection: In addition to collecting samples from Comet Wild 2, the mission aimed to capture interstellar dust particles passing through our solar system. These particles are remnants of ancient stars and are believed to carry valuable information about the formation of the solar system.
- Sample Return: After collecting the comet and interstellar dust particles, Stardust stored them in a sample return capsule. On January 15, 2006, the capsule re-entered the Earth’s atmosphere and safely landed in the Utah desert. The collected samples were then transported to laboratories for analysis.
- Scientific Studies: Scientists analyzed the collected samples to learn about the comet’s composition and the nature of the interstellar dust particles. The findings provided valuable data on the origins of the solar system and the processes that occurred during its formation.
The Project Stardust was a groundbreaking mission, as it was the first spacecraft to collect samples from a comet and return them to Earth. It provided important insights into the composition of comets, the presence of organic compounds, and the role of comets in delivering water and other volatile substances to Earth during its early history. The mission’s success has significantly contributed to our understanding of the solar system’s evolution and the broader field of planetary science.
(i) Which is the agency that has launched this project?
Ans: The agency that launched the Project “Stardust” is NASA, the National Aeronautics and Space Administration. NASA is the United States government agency responsible for the nation’s civilian space program and for aeronautics and aerospace research.
(ii) Why are scientists interested in collecting Stardust?
Ans: Scientists are interested in collecting Stardust, which refers to the dust particles and debris from comets and interstellar space, for several reasons:
- Understanding Solar System Formation: Stardust provides valuable information about the early solar system’s formation. Comets are considered remnants of the early solar system, and their composition can shed light on the conditions and materials present during the solar system’s birth.
- Origins of Life: Comets contain organic molecules, which are the building blocks of life. By studying these molecules, scientists hope to gain insights into the origins of life on Earth and the potential for life elsewhere in the universe.
- Cosmic Evolution: Interstellar dust particles carry information about the evolution of stars and galaxies. Analyzing these particles helps astronomers understand the processes occurring in distant regions of the universe.
- Composition of Comets: Studying the composition of comets helps scientists understand their structure, dynamics, and behavior. This knowledge is crucial for predicting their trajectories and potential impacts on Earth.
- Water and Volatile Delivery: Comets are believed to have delivered water and other volatile substances to Earth during its early history. Understanding the composition of comets helps scientists trace the sources of these essential components of life on Earth.
- Space Mission Technology: Collecting Stardust requires advanced space mission technology, including sample collection and return capabilities. Developing and testing such technology is essential for future space missions, including potential sample return missions from other celestial bodies.
- Planetary Defense: Studying comets and interstellar dust particles contributes to our understanding of potentially hazardous objects in space and helps in developing strategies for planetary defense against impact events.
Overall, collecting Stardust provides a unique opportunity to learn about the history and evolution of the solar system and the universe, as well as gain insights into fundamental questions about life’s origins and our place in the cosmos. It represents a significant contribution to the fields of planetary science, astrophysics, and astrobiology.
(iii) Where from has the Stardust been collected?
Ans: The Stardust spacecraft collected its samples from two different sources:
- Comet Wild 2 (pronounced “Vilt-2”): The primary target of the Stardust mission was Comet Wild 2, a short-period comet that orbits the Sun. The spacecraft flew close to the comet and used a special collector called the “comet coma sample return” to collect dust particles and debris from the coma, which is the cloud of gas and dust surrounding the comet’s nucleus.
- Interstellar Dust Particles: In addition to collecting samples from Comet Wild 2, the spacecraft also collected interstellar dust particles. These particles are believed to originate from other parts of the galaxy and pass through our solar system. Stardust’s collector was designed to capture these interstellar dust particles during its journey through space.
After collecting the samples from Comet Wild 2 and interstellar space, the spacecraft stored them in a sample return capsule. The capsule then re-entered the Earth’s atmosphere and safely landed in the Utah desert on January 15, 2006. The collected samples were subsequently transported to laboratories for analysis, providing valuable insights into the composition and origins of the early solar system.
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