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Long Question Answers : The Origin and Evolution of the Earth | Geography Class 11 - Humanities/Arts PDF Download

Q. 1. Describe the Nebular Hypothesis regarding the origin of the Planets.
Ans. Nebular Hypothesis. Some Monistic Theories (One Star Theories) explain the origin of planets. A German Philosopher, Immanuel Kant, proposed the Nebular Hypothesis. This Hypothesis was based on Newton’s Laws of motion.
Outlines of Hypothesis : 
(i) According to Kant, the primordial matter was scattered in the space.
(ii) This matter was supernaturally created.
(iii) There was a slowly rotating cloud of gas called Nebula.
(iv) The original cold  and motionless Nebula became a hot and spinning Nebula under the gravitational attraction. The French mathematician, Laplace proposed more or less, same theory in 1796.
(v) The rotational speed increased under Law of conservation of angular momentum. The centrifugal force then increased.
(vi) Thus, successive rings of gaseous matter were thrown off from the central mass (Equator) by centrifugal force.
(vii) The rings later on condensed to form planets.

The residual central mass remained as the sun.
Criticism :
(i) It was the forerunner of Laplace theory.
(ii) Heat and motion cannot be produced in cold Nebula without some external force.
(iii) Kant, despite criticism went to say ‘‘Give me matter and I can create the earth.”
Q. 2. Describe the collision Hypothesis proposed by Sir James Jeans and Sir Harold Jeffreys.
Ans. This theory belongs to Dualistic (Two Stars) Theories. This theory was forwarded by British scientists Sir James Jeans and Sir Harold Jeffreys in 1926.

According to this theory, planets are bi-parental in origin. It is also known as Tidal Hypothesis.
Outline of Hypothesis: 
(i) The sun was originally a very hot gaseous mass in the space.
(ii) Another star, several times bigger than the sun came close to the sun and caused Tidal disruptions.
(iii) Due to gravitational pull of the approaching star, gaseous material was pulled away from the preexisting sun. The ejected matter, called Filament was cigar shaped.
(iv) This filament was broken into small chunks called planetesimals.
(v) By collision and gravitational attraction the larger planetesimals collected the smaller bricks and condensed into planets.
Merits and Demerits: It is the most accepted Hypothesis. The present arrangement of planets confirms this idea. The number of satellites also proves the theory. The smaller planets have less satellites.

But this theory fails to explain the location of the planet Mars. The temperature of the Sun is too high for the formation of planets.

Q.3 Compare the inner planets and outer planets.
Ans. Of the eight planets Mercury, Venus, Earth and Mars are called as inner planets as they lie between the Sun and the belt of asteroids called the asteroid belt. The other four planets, lining up after the asteroid belt are Jupiter, Saturn, Uranus and Neptune are called outer planets. Alternatively the first four are called ‘Terrestrial’, meaning Earth like, as they are made up of rock and metals and have relatively high densities. The rest four are called Jovian or Gas Giant planets. Jovian means Jupiter like. Most of them are much larger than the terrestrial planets and have a thick atmosphere mostly of helium and hydrogen. All the planets were formed in the same period, some time about 4.6 billion years ago.

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FAQs on Long Question Answers : The Origin and Evolution of the Earth - Geography Class 11 - Humanities/Arts

1. What is the origin of the Earth?
Ans. The Earth formed approximately 4.6 billion years ago through the process of accretion, where dust and gas in the early Solar System came together to form a planet. Over time, these materials collided and merged, eventually creating the Earth.
2. How did the Earth evolve over time?
Ans. The Earth's evolution can be divided into several stages. Initially, it underwent differentiation, where denser materials sank towards the center to form the core, while lighter materials rose to the surface. This led to the formation of tectonic plates, which resulted in the creation of continents and oceans. The Earth's atmosphere also evolved, gradually developing oxygen through processes like photosynthesis.
3. What evidence supports the theory of Earth's evolution?
Ans. Scientists have gathered various types of evidence to support the theory of Earth's evolution. Fossil records provide insights into the existence of ancient life forms and their changes over time. Geological data, such as the age of rocks and the arrangement of layers, help establish the timeline of Earth's evolution. Additionally, the study of isotopes in rocks and ice cores provides information about past climates and atmospheric conditions.
4. How did life originate on Earth?
Ans. The exact origin of life on Earth is still a topic of scientific investigation. However, one popular hypothesis is that life emerged through a process called abiogenesis, where simple organic molecules combined and eventually formed self-replicating molecules, such as RNA. These early life forms gradually evolved, leading to the diverse range of species present on Earth today.
5. How have humans impacted the evolution of the Earth?
Ans. Human activities have had a significant impact on the Earth's evolution, particularly in recent centuries. Deforestation, pollution, and the burning of fossil fuels have contributed to climate change and the loss of biodiversity. Additionally, human actions have caused changes in ecosystems, leading to the extinction of certain species and the introduction of invasive species. Understanding and mitigating these impacts is crucial for the sustainable future of our planet.
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