The Origin and Evolution of the EarthClass 11 Fundamentals of Physical Geography NCERT Solutions
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Q1EXERCISES
(i) Which one of the following figures represents the age of the earth? (a) 4.6 million years (b) 13.7…
(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
(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
(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
Solution
(i) (c) 4.6 billion years
Explanation: The source text mentions that the period between 4,600 million years ago and the present led to the evolution of life on the planet. 4,600 million years is equivalent to 4.6 billion years, which represents the approximate age of the Earth.
(ii) (b) Differentiation
Explanation: The text describes three stages in the evolution of the atmosphere: the stripping of the primordial atmosphere by solar winds, the contribution of gases from the Earth's interior through degassing, and the modification of the atmosphere by the process of photosynthesis. Differentiation is the process by which the Earth's material separated into different layers like the crust, mantle, and core, and is related to the evolution of the lithosphere, not the atmosphere.
(iii) (d) 3.8 billion
Explanation: According to the chapter, modern scientists believe life began to evolve sometime around 3,800 million years ago. This is equivalent to 3.8 billion years before the present.
Q2EXERCISES
(i) What is meant by the process of differentiation? (ii) What was the nature of the earth surface initially?…
(i)
What is meant by the process of differentiation?
(ii)
What was the nature of the earth surface initially?
(iii)
What were the gases which initially formed the earth's atmosphere?
Solution
(i) What is meant by the process of differentiation?
The process of differentiation refers to the separation of the Earth's forming material into different layers based on their densities. During the Earth's primordial stage, it was in a volatile state. Due to immense heat, materials inside started to separate; heavier materials like iron sank towards the centre of the Earth, while lighter materials moved towards the surface. This process led to the formation of the Earth's layered structure, consisting of the crust, mantle, outer core, and inner core.
(ii) What was the nature of the earth surface initially?
Initially, the planet Earth was a barren, rocky, and hot object. It had a thin atmosphere composed primarily of hydrogen and helium. This initial state is vastly different from the present-day Earth, which is a vibrant planet with abundant water and a life-supporting atmosphere.
(iii) What were the gases which initially formed the earth's atmosphere?
The initial, or primordial, atmosphere of the Earth was composed of hydrogen and helium. This early atmosphere was very thin and is believed to have been stripped off as a result of solar winds. This process affected not only Earth but all the terrestrial planets.
Q3EXERCISES
(i) Write an explanatory note on the 'Big Bang Theory'. (ii) List the stages in the evolution of the earth…
(i)
Write an explanatory note on the 'Big Bang Theory'.
(ii)
List the stages in the evolution of the earth and explain each stage in brief.
Solution
(i) Write an explanatory note on the 'Big Bang Theory'.
The Big Bang Theory, also known as the expanding universe hypothesis, is the most popular scientific argument regarding the origin of the universe. In 1920, Edwin Hubble provided evidence that the universe is expanding, meaning galaxies are continuously moving further apart from each other.
The theory outlines the following stages in the development of the universe:
- The Singularity: In the beginning, all matter that forms the universe existed in one place as a "tiny ball" or a singular atom. This singularity had an unimaginably small volume, infinite temperature, and infinite density.
- The Expansion: Approximately 13.7 billion years ago, this tiny ball exploded violently, an event known as the Big Bang. This led to a huge and rapid expansion. As the universe expanded, some energy was converted into matter. The expansion has slowed down since but continues to this day.
- Formation of Atoms: Within the first three minutes after the Big Bang, the first atoms began to form. Over time, the universe continued to cool. Within 300,000 years, the temperature dropped to about 4,500 K, which allowed for the formation of atomic matter and made the universe transparent.
This theory is now widely accepted by the scientific community, supported by evidence of the continuously expanding space between galaxies.
(ii) List the stages in the evolution of the earth and explain each stage in brief.
The evolution of the Earth from a hot, barren rock to a planet teeming with life occurred over several stages. The key stages are the evolution of the lithosphere, atmosphere and hydrosphere, and the origin of life.
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Evolution of the Lithosphere: In its primordial stage, the Earth was in a volatile, hot state. A process called differentiation occurred, where materials separated based on density. Heavier elements like iron sank to the center to form the core, while lighter materials rose to the surface. Over time, the Earth cooled and solidified, forming the outer crust. This process created the layered structure of the Earth: the crust, mantle, and core.
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Evolution of the Atmosphere and Hydrosphere: This occurred in three phases.
- First, the primordial atmosphere of hydrogen and helium was stripped away by solar winds.
- Second, as the Earth cooled, gases and water vapour were released from the planet's interior through volcanic eruptions in a process called degassing. This new atmosphere contained water vapour, nitrogen, carbon dioxide, methane, and ammonia.
- Third, further cooling caused the water vapour to condense and fall as rain, collecting in depressions to form the oceans. Carbon dioxide dissolved in the rainwater, reducing atmospheric temperatures. Life, which evolved in the oceans, began the process of photosynthesis, releasing oxygen. Eventually, the oceans became saturated with oxygen, and about 2,000 million years ago, oxygen began to fill the atmosphere.
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Origin of Life: This is the final stage in Earth's evolution. Life is thought to have originated from a chemical reaction that created complex organic molecules capable of duplicating themselves. The earliest evidence of life, found in fossils, dates back to approximately 3,800 million years ago.