Important Questions: The Origin & Evolution of the Earth | Geography Class 11 - Humanities/Arts PDF Download

Very Short Answer Type Questions

Q1: Who first proposed the Nebular hypothesis?
Ans: The German philosopher, Immanuel Kant, proposed the Nebular hypothesis in 1755.

Q2: Name all the nine planets in their order from the sun.
Ans: They are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

Q3: Name two scholars who had identical views on the origin of planets.
Ans: Immanuel Kant, a German scholar and Laplace, a French mathematician, expressed identical views on Nebular hypothesis.

Q4: Name the planet with a maximum number of satellites in our solar system.
Ans: Saturn has the maximum number of satellites (20) in our solar system.

Q5: What are the various stages the sun has passed through during its formation?
Ans: They are Nebula → Supernova → Protostar → Infant Sun → Sun.

Q6: What is a meteorite?
Ans: A meteorite is a piece of rock or metal from outer space that hits the earth’s surface.

Q7: When did drifting start in Pangea?
Ans: In the upper carboniferous age about 300 million years ago.

Q8: Why does earth appear as a round ball that shines bright and blue when viewed from space?
Ans: Because a large part of the earth’s surface is covered with water, which is blue in colour.

Short Answer Type Questions

Q9: Explain Heterogenous Accretion Hypothesis.
Ans: According to Heterogeneous Accretion Hypothesis, the composition of the material from which the earth accreted changed r with time giving rise to the layered structure of the earth. According to this model, the earth formed ‘ inside out’ with an, oxidised and volatile-rich nucleus and a more metal-rich and depolarised outer rings.

Q10: What do you mean by plate tectonics?
Ans: Plate tectonics is a theory. According to it, the crust and mantle (lithosphere) are divided into plates and blocks. Different tectonic movements take place along their edges. These plates drift due to convection currents. Continents also drift along with these plates, known as tectonic plates.

Q11: Why are inner planets heavier than the outer ones?
Ans: Initially, the nebula was revolving in the form of a flat disc. Due to high temperature, the heavy materials of the flat disc condensed in the inner part of the disc. These include iron and aluminium. Thus, inner planets Mercury, Venus, Earth and Mars were formed.

Q12: What do you understand by a light-year?
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 that the light travels in one year is taken to be one light year. This is equal to 9.461 xlO12 km. The mean distance between the sun and the earth is Y‘ 149,598,000 km. In terms of light-years, it is 8,3 31 minutes.

Q13: What do you understand by the birth of the solar system?
Ans: The entire solar system forms a very small part of the galaxy that consists of many stars. Our galaxy is called the Milky Way. The gaseous cloud exploded to form a supernova. The explosion caused shock waves that caused the denser portion to collapse under its own gravity. In the process, the hot core developed into a protostar. Finally, the protostar became the infant sun.

Q14: Write a note on Heterogenous Accretion Hypothesis.
Ans: This hypothesis explains the layered structure of the earth. According to this theory, the earth is formed by the accretion of different ‘ types of materials. The materials changed with time. The earth formed from inside out due to the change of materials. It had an oxidised and hot, nucleus and more metal-rich rings.

Long Answer Type Questions

Q15: Discuss the various hypotheses for the evolution of the planets.
Ans: There are two hypotheses :

Nebula hypothesis: In 1755, German philosopher Immanuel Kant, hypothesised that slowly rotating cloud of gas, called Nebula, in some unspecified manner, condensed into a number of discrete and globular bodies. The great French mathematician Laplace also proposed, more or less, the same theory in 1796.
According to Kant and Laplace, the original mass of gas-cooled and began to contract. The rotational speed increased as a consequence of the law of conservation of angular momentum. Then, successive rings of gaseous material were spun off from the central mass by centrifugal force. In the final stage, the rings condensed into planets.

Collision hypothesis: Sir James Jeans and Sir Harold Jeffreys gave this hypothesis. According to this hypothesis, gaseous material was pulled away from the pre-existing sun by the gravitational force of a passing star. By collision and gravitational attraction, the larger planetesimals swept up the smaller pieces and thus were formed the planets.

Q16: Describe the origin of life and die cause for its origin.
Ans: Modern scientists refer to the origin of life as a kind of chemical reaction, which first generated complex organic molecules and then assembled them. This assemblage was such that they could duplicate themselves converting inanimate matter into living substance. The record of life that existed on this planet in different periods is found in rocks in the form of fossils. The microscopic structures closely related to the present form of blue algae have been found in geological formations that are much older than some 3000 million years. It can be assumed that simpler forms precede these. Scientists consider that life began to evolve sometime 3800 million years ago.
The last phase in the evolution of the earth relates to the origin and evolution of life. The initial or even the early atmosphere of the earth was not conducive for the development of life.

Q17: Write short notes on:
(i) Collision Hypothesis
Ans: Sir James Jeans and Sir Harold Jeffreys gave this hypothesis. According to this hypothesis, gaseous material was pulled away from the pre-existing sun by the gravitational force of a passing star. By collision and gravitational attraction, the larger planetesimals swept up the smaller pieces and thus were formed the planets.

(ii) Homogeneous Accretion Hypothesis
Ans: This hypothesis maintains that the earth accreted from an intermate mixture of silicate particles and metal particles. The material was assumed to have been formed in the solar nebula by a complex series of chemical and physical processes, which had occurred prior to the accretion of planets. According to a hypothesis, accretion of the earth occurred over a sufficiently long period (10—10s years) so that its gravitational potential energy was efficiently radiated away and it formed in an initially ‘cool’ and unmelted condition.

(iii) Origin of the Moon
Ans: Radiometric dating of the rocks from the moon shows that it was born along with the earth. Apparently, there are two possibilities. It either came out of the sun in a gaseous form but being too small was attracted by the earth, or it flew out of the earth due to a huge meteorite falling on the earth. The area where the meteorite fell, a huge hollow was created, which is now filled up by an ocean and the landmass plunged to outer space to create the moon.

Q18: Describe the evolution of the Solar system.
Ans: The entire solar system consists of the sun, the nine planets and their various satellites. The sun is a large brilliant star in the centre of the solar system. It is thought to be about 5 billion years old. The pressure and temperature at the centre of the Nebula (cloud of gas) that produced the solar system became so great that it triggered a nuclear reaction. Some of the hydrogen in the cloud fused into helium, releasing a great amount of energy.
The gaseous cloud exploded to form a supernova. The explosion caused shock waves that pushed the denser portion of the cloud to collapse under its own gravity. The dense core grew larger and hotter as its gravity attracted more material. In the process, the hot core developed into a protostar, that finally became the sun.

Q19: Describe in short the evolution of atmosphere and hydrosphere (oceans).
Ans: There are three stages in the evolution of the present atmosphere. The first stage is the loss of the primordial atmosphere. In the second stage, the hot interior of the earth contributed to the evolution of the atmosphere. The third stage in the composition of the atmosphere was modified by the living world through the process of photosynthesis. The early atmosphere, with hydrogen and helium, has been stripped off as a result of the solar winds. All the terrestrial planets are supposed to have lost their primordial atmosphere through the impact of solar winds. During the differentiation and cooling of the earth, gases and water vapour were released from the interior solid earth. This started the evolution of the present atmosphere. The early atmosphere largely contained water vapour, nitrogen, carbon dioxide, methane, ammonia and very little of free oxygen.
The process through which the gases were outpoured from the interior is called degassing. Continuous volcanic eruptions contributed water vapour and gases to the atmosphere. As the earth cooled, the water vapour released started getting condensed. The carbon dioxide in the atmosphere got dissolved in rainwater and the temperature further decreased causing more condensation and more rains, The rainwater falling on the surface got collected in the depressions to give rise to oceans. The earth’s oceans were formed within 500 million years from the formation of the earth. Oceans began to have the contribution of oxygen through the process of photosynthesis.

Q20: Describe in short the evolution of atmosphere and hydrosphere (oceans).
Ans: There are three stages in the evolution of the present atmosphere. The first stage is the loss of the primordial atmosphere. In the second stage, the hot interior of the earth contributed to the evolution of the atmosphere. The third stage in the composition of the atmosphere was modified by the living world through the process of photosynthesis.
The early atmosphere, with hydrogen and helium, has been stripped off as a result of the solar winds. All the terrestrial planets are supposed to have lost their primordial atmosphere through the impact of solar winds. During the differentiation and cooling of the earth, gases and water vapour were released from the interior solid earth. This started the evolution of the present atmosphere. The early atmosphere largely contained water vapour, nitrogen, carbon dioxide, methane, ammonia and very little of free oxygen.
The process through which the gases were outpoured from the interior is called degassing. Continuous volcanic eruptions contributed water vapour and gases to the atmosphere. As the earth cooled, the water vapour released started getting condensed. The carbon dioxide in the atmosphere got dissolved in rainwater and the temperature further decreased causing more condensation and more rains, The rainwater falling on the surface got collected in the depressions to give rise to oceans. The earth’s oceans were formed within 500 million years from the formation of the earth. Oceans began to have the contribution of oxygen through the process of photosynthesis.