GEOGRAPHY- CLASS-11: FUNDAMENTALS OF PHYSICAL GEOGRAPHY
CHAPTER-2
The Origin and Evolution of the Earth
1. Multiple Choice Questions
(i) Which one of the following figures represents the age of the Earth?
Answer: (a) 4.6 million years
Correct Answer: 4.6 billion years
Explanation: The Earth was formed about 4.6 billion years ago. (The option in the question appears to have a printing error. The correct answer is 4.6 billion years.)
(ii) Which one of the following is not related to the formation or modification of the present atmosphere?
Answer: (a) Solar winds
Explanation: Solar winds removed the early atmosphere but were not involved in the formation or modification of the present atmosphere. Differentiation, degassing and photosynthesis contributed to the present atmosphere.
(iii) Life on the Earth appeared around how many years before the present?
Answer: (d) 3.8 billion
Explanation: Scientific evidence suggests that life first appeared on Earth about 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 by which the Earth's interior separated into different layers according to density. Heavier materials like iron and nickel moved to the core, while lighter materials formed the mantle and crust.
(ii) What was the nature of the Earth's surface initially?
Answer:
Initially, the Earth's surface was extremely hot, molten and rocky. Frequent volcanic eruptions and meteorite impacts made the surface unstable. As the Earth cooled, a solid crust gradually formed.
(iii) What were the gases which initially formed the Earth's atmosphere?
Answer:
The early atmosphere mainly consisted of hydrogen and helium. Later, volcanic eruptions released gases such as water vapour, carbon dioxide, nitrogen, methane and ammonia, which formed the secondary atmosphere.
3. Answer the following questions in about 150 words.
(i) Write an explanatory note on the 'Big Bang Theory'.
Answer:
The Big Bang Theory is the most widely accepted explanation for the origin of the universe. According to this theory, the universe began about 13.7 billion years ago from an extremely hot and dense state called a singularity. A massive explosion, known as the Big Bang, caused the universe to expand rapidly in all directions. As the universe expanded, it cooled, allowing tiny particles to combine and form atoms. Over millions of years, these atoms gathered together under the force of gravity to form stars, galaxies and other celestial bodies. The solar system, including the Earth, formed much later from a cloud of gas and dust. Even today, the universe continues to expand, which supports the Big Bang Theory. This theory explains the origin and evolution of the universe based on scientific observations and evidence.
(ii) List the stages in the evolution of the Earth and explain each stage in brief.
Answer:
The evolution of the Earth took place in several important stages. First, the Earth formed about 4.6 billion years ago from a cloud of gas and dust surrounding the young Sun. Initially, it was extremely hot and molten due to frequent collisions and radioactive decay. As the Earth gradually cooled, heavier elements such as iron and nickel sank towards the centre, while lighter materials formed the mantle and crust. This process is known as differentiation. Volcanic eruptions released gases that formed the early atmosphere. As the temperature decreased further, water vapour condensed to form oceans. Simple forms of life appeared about 3.8 billion years ago. Over time, photosynthetic organisms released oxygen into the atmosphere, making it suitable for more complex life forms. Thus, the Earth gradually evolved into the habitable planet we know today.