View More


 

GEOGRAPHY: CHAPTER - 1: THE ORIGIN AND EVOLUTION OF THE EARTH

 

1. Origin of the Earth:

a. Nebular Hypothesis

  • Nebular hypothesis considered that the planets were formed out of a cloud of material associated with a youthful sun, which was slowly rotating.

  • The central region, Nebula became sun.

  • German Philosopher, Immanuel Kant and French Mathematician Laplace revised it in 1796. It is known as Nebular Hypothesis.

b. Binary Hypothesis:

The formation of planets, Sir Harold Jeffrey supported this argument. At a later date, the arguments considered of a companion to the sun to have been coexisting. These arguments are called binary theories. 

 

2. Modern Theories:

a. Origin of the Universe:

It is also called expanding universe hypothesis.

  • The most popular argument regarding the origin of the universe is the Big Bang Theory. Edwin Hubble, in 1920, provided evidence that the universe is expanding & became transparent.

  • The Big Bang Theory considers the following 3 stages in the development of the universe.

  1. In the beginning, all matter forming the universe existed in one place in the form of a “tiny ball” (singular atom) with an unimaginably small volume, infinite temperature and infinite density.

  2. At the Big Bang the “tiny ball” exploded violently. This led to a huge expansion. It is now generally accepted that the event of big bang took place 13.7 billion years before the present. The expansion continues even to the present day. As it grew, some energy was converted into matter. There was particularly rapid expansion within fractions of a second after the bang. Thereafter, the expansion has slowed down. Within first three minutes from the Big Bang event, the first atom began to form.

  3. Within 300,000 years from the Big Bang, temperature dropped to 4,500 K (Kelvin) and gave rise to atomic matter.

 

b. The Star Formation:

A galaxy starts to form by accumulation of hydrogen gas in the form of a very large cloud called nebula. Eventually, growing nebula develops localized clumps of gas.

  • The formation of stars is believed to have taken place some 5-6 billion years ago. These formed the bases for development of galaxies.

  • The mean distance between the sun and the earth is 149,598,000 km. In terms of light years, it is 8.311minutes. Light travels at a speed of 300,000 km/second.

(Note: A light year is a measure of distance and not of time.)

 

c. Formation of Planets: 
The 3 stages in the development of planets as a,

  1. The gravitational force within the lumps leads to the formation of a core to the gas cloud and a huge rotating disc of gas and dust develops around the gas core.

  2. In the next stage, the gas cloud starts getting condensed and these small-rounded objects by the process of cohesion develop is called planetesimals.

  3. In the final stage, these large number of small planetesimals accrete to form a fewer large bodies in the form of planets.

 

d. Evolution Of The Earth:
The Earth began to receive more heat from the Sun in the Proterozoic eon.

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

  • The earth has a layered structure. From the outermost end of the atmosphere to the center of the earth.

  • The evolution of life on the surface of the planet with ample amount of water and conducive atmosphere favoring the existence of life. The period, between the 4,600 million years and the present.

 

e. Evolution of Lithosphere:

Lithosphere consists mainly of mafic crust and ultramafic mantle (Peridotite)

  • The earth was mostly in a volatile state during its primordial stage. Due to gradual increase in density the temperature inside has increased.

  • As a result the material inside started getting separated depending on their densities. This allowed heavier materials (like iron) to sink towards the center of the earth and the lighter ones to move towards the surface. With passage of time it cooled further and solidified and condensed into a smaller size. This later led to the development of the outer surface in the form of a crust

  • During the formation of the moon, due to the giant impact, the earth was further heated up. It is through the process of differentiation that the earth forming material got separated into different layers.

 

f. Evolution of Atmosphere and Hydrosphere:

Earth’s atmosphere is chiefly contributed by nitrogen and oxygen.

There are three stages in the evolution of atmosphere. 

  1. The loss of primordial atmosphere 

  2. The hot interior of the earth contributed to the atmosphere 

  3. The composition of the atmosphere.

The earth’s oceans were formed within 500 million years from the formation of the earth, Life began to evolve around 2,500-3,000 million years before the present.

 

g. Origin of Life:

The origin of life on Earth is a set of paradoxes.

  • Origin of life as a kind of chemical reaction, which first generated complex organic molecules and assembled them. 

  • The microscopic structures closely related to the present form of blue algae have been found in geological formations much older than some 3,000 million years. It can be assumed that life began to evolve sometime 3,800 million years ago.

Posted By:

Kundan Patel

COMMENTS

View 0 more comments

The great mentor Leaderboard

Copyright @ 2018 | Star Universal Mentors LLP | All Rights Reserved.