The Origin and Evolution of Earth - Chapter 2 Class 11 NCERT Geography Solutions

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

(ii) Which one of the following has the longest duration?

(a) Eons

(b) Period

(c) Era

(d) Epoch

(iii) 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

(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)

(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

2. Answer the following questions in about 30 words.

(i) Why are the terrestrial planets rocky?

The planets that falls under the title "terrestrial" planets are Mercury, Venus, Earth and Mars . They are similar to Earth in composition. And these planets are also nearer to the sun. Due to extreme heat from the Sun evaporated lightweight elements like hydrogen and helium from these terrestrial planets leaving behind rocky and metallic elements.

(ii) What is the basic difference in the arguments related to the origin of the earth given by :

(a) Kant and Laplace

German philosopher Immanuel Kant was well known for his argument on Nebular Hypothesis. Then in 1796 Mathematician Laplace revised it. According to Laplace, the planets were formed out of a cloud of material associated with a youthful sun and that cloud was known as Nebula.

(b) Chamberlain and Moulton

In 1904, Chamberlain and Moulton proposed the planetesimal hypothesis. They considered that:

1. Sun always existed way before the planets were formed.
2. Then a wandering star came closer to the sun.
3. Due to gravitational pull of the star, a cigar-shaped extension of material was separated from the solar surface.
4. As the passing star moved away, the material separated from the solar surface continued to revolve around the sun and it slowly condensed into planets.

(iii) What is meant by the process of differentiation?

It is a process in which the materials that formed the layers of the earth which are - crust, upper mantle and lower mantle, outer core and inner core. These layers got separated based on their material densities.

(iv) What was the nature of the earth surface initially?

The planet earth initially was a barren, rocky and hot object with a thin atmosphere of hydrogen and helium.

(v) What were the gases which initially formed the earth’s atmosphere?

Hydrogen and Helium.

3. Answer the following questions in about 150 words.

(i) Write an explanatory note on the ‘Big Bang Theory’.

The other name of Big Bang Theory is the expanding universe hypothesis. It is referred as the modern theory when it comes to the origin of earth. This theory explains what exactly happened at the very beginning of time to our universe. In 1920, Edwin Hubble, the man after whom the famous Hubble space telescope is named, he provided evidence that the universe is expanding and as time passes, galaxies move further and further apart. While Edwin Hubble was correct with his observation that galaxies were moving apart, but other scientists believed that there is no evidence that supports the galaxies themselves are expanding.

(ii) List the stages in the evolution of the earth and explain each stage in brief.
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