Short Question Answers : The Origin and Evolution of the Earth
Q. 1. Name the philosopher who first proposed the Nebular Hypothesis.
Ans. German philosopher Immanuel Kant (revised by mathematician Laplace in 1796).
Q. 2. What is the Nebular Hypothesis?
Ans. It considered that the planets were formed out of a cloud of material associated with a youthful sun which was slowly rotating.
Q. 3. Who revised the Nebular Hypothesis in 1950?
Ans. Otto Schmidt (Russia) and Carl Weizsäcker (Germany).
Q. 4. What is the most popular theory regarding the origin of the universe?
Ans. Big Bang Theory (also called expanding universe hypothesis).
Q. 5. According to the Big Bang Theory, when did the event take place?
Ans. 13.7 billion years before the present.
Q. 6. What does a "light year" mean?
Ans. A light year is a measure of distance and not of time. Light travels at a speed of 300,000 km/second. The distance light will travel in one year is taken to be one light year (9.461 × 10¹² km).
Q. 7. How many stages are there in the formation of planets?
Ans. Three stages.
Q. 8. Name the unique planet where life exists (as per the chapter).
Ans. Earth (life began to evolve on Earth around 3,800 million years ago).
Q. 9. Who forwarded the Nebula Hypothesis ?
Ans. Immanuel Kant and Pierre-Simon Laplace.
Q. 10. What are planetesimals?
Ans. Small-rounded objects formed by the process of cohesion; larger bodies start forming by collision and gravitational attraction.
Q. 11. What was the nature of the Earth surface initially?
Ans. The planet Earth initially was a barren, rocky and hot object with a thin atmosphere of hydrogen and helium.
Q. 12. How were oceans formed on the Earth?
Ans. As the Earth cooled, water vapour released from the interior condensed. Rainwater collected in depressions to give rise to oceans. The Earth's oceans were formed within 500 million years from the formation of the Earth (so oceans are about 4,000 million years old).
Q. 13. Which scientist of Russia modified the Nebular Hypothesis in 1950.
Ans. Otto Schmidt.
Q. 14. What is the process of differentiation?
Ans. Due to increase in density and temperature, heavier materials (like iron) sank towards the centre and lighter ones moved towards the surface. This led to the development of the layered structure (crust, mantle, outer core, inner core).
Q. 15. Which is the most popular theory regarding the origin of the Universe.
Ans. Big Bang Theory.
Q. 16. How much distance is travelled by light in a light year ?
Ans. 9.461 × 1012 km.
Q. 17. What do you mean by a 'light year' ?
Ans. A light year is a measure of distance, not of time. Light travels at a speed of about 300,000 km/second. The distance travelled by light in one year is called a light year and equals 9.461 × 1012 km. The mean distance between the Sun and the Earth is about 149,598,000 km; light takes approximately 8.31 minutes to travel this distance.
Q. 18. From which cloud were the planets formed? When did star formation begin?
Ans. Planets were formed through the process of accretion from a disk-shaped cloud (solar nebula). The formation of stars is believed to have taken place some 5-6 billion years ago.
Q. 19. How were oceans originated ?
Ans. Water vapour in the early atmosphere condensed as the Earth cooled, forming heavy rains. Dissolved gases such as carbon dioxide reacted with water and rocks, while rainwater collected in low-lying depressions to form the oceans. Oceans were formed within roughly 500 million years after the Earth formed, so they are about 4.1 billion years old.
Q. 20. Describe the different stages in the evolution of present day atmosphere.
Ans. There are three main stages in the evolution of the present atmosphere.
First stage: Loss of the primordial atmosphere that the Earth may have had immediately after formation.
Second stage: Outgassing from the hot interior of the Earth released water vapour, carbon dioxide, nitrogen and other gases, forming a secondary atmosphere.
Third stage: Biological activity, especially photosynthesis by early life forms, increased oxygen levels and changed the composition to the present atmosphere with significant free oxygen.
Q. 21. (i) What is a Nebula ?
Ans. Nebula is a slowly rotating cloud of gas and dust in space; it contains hot and cold gaseous matter and dust particles.
(ii) What are planetesimals ?
Ans. Planetesimals are small solid bodies formed by the accumulation and collision of dust and ice particles inside the rotating protoplanetary disc; they are the building blocks that later accreted to form planets.
(iii) Who first proposed Nebular Hypothesis ?
Ans. The Nebular Hypothesis was first proposed by Immanuel Kant in 1755.
(iv) What were the three stages in the evolution of the present atmosphere?
Ans. (i) Loss of primordial atmosphere (stripped off by solar winds).
(ii) Outgassing from the hot interior of the Earth (degassing).
(iii) Modification by the living world through the process of photosynthesis.
Q. 22. Describe the modification proposed in Nebular Hypothesis by Otto Schmidt.
Ans. In the mid-20th century Otto Schmidt (Russia) and Carl Weizsäcker (Germany) revised the nebular hypothesis. They suggested that the Sun was surrounded by a solar nebula made mostly of hydrogen and helium with dust. Friction and collisions among particles in the nebula caused it to flatten into a disc, and the planets formed by gradual accretion of material within this disc.
Q. 23. Describe the process of Star Formation.
Ans. The distribution of matter and energy in space was not uniform in the early Universe. Small density differences produced gravitational attraction that drew matter together, leading to the formation of galaxies and large gas clouds called nebulae. Within a nebula, localised clumps of gas grew denser and collapsed under gravity to form protostars. As the core of a protostar became hotter and denser, it ignited nuclear fusion and became a star. The Sun, for example, formed about 4.6 billion years ago by this process.
Q. 24. List the stages in the evolution of the Earth and briefly explain each.
Ans.
- Evolution of Lithosphere: Material separated according to density; heavier sank, lighter rose; formed crust, mantle, outer core and inner core.
- Evolution of Atmosphere and Hydrosphere: Three stages - loss of primordial atmosphere, degassing, photosynthesis. Water vapour condensed and formed oceans.
- Origin of Life: Chemical reactions produced complex organic molecules; life began around 3,800 million years ago.
Q. 25. Describe the three stages in the development of planets.
Ans. (i) Stars are localised lumps of gas within a nebula. Gravitational force leads to formation of a core and a huge rotating disc of gas and dust around it.
(ii) The gas cloud condenses and matter around the core develops into small-rounded objects called planetesimals.
(iii) Planetesimals accrete to form a fewer large bodies in the form of planets.
FAQs on Short Question Answers : The Origin and Evolution of the Earth
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