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Earth- Origin and Evolution (summary notes) Notes - UPSC

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THE ORIGIN AND EVOLUTION OF THE EARTH

Early Theories:

Nebular Hypothesis

  • Immanuel Kant, a German philosopher, gave this theory.
  • In 1796, a mathematician Pierre-Simon Laplace reexamined it.
  • According to this hypothesis, the planets were moulded out of a cloud of material associated with a young Sun, which was rotating slowly.

Binary theories

  • As per these theories, the sun had a companion.

Revised Nebular Hypothesis

  • Revised Nebular Hypothesis was propounded by Carl Weizascar in Germany and Otto Schmidt in Russia.
  • They regarded that a solar nebula surrounded the sun and that the nebula comprised of chiefly hydrogen, helium and something called dust.
  • The collision of particles and the friction caused a disk-shaped cloud to be formed and then the planets were created via the accretion process.

Modern theories:

Big Bang Theory

  • Alternatively called the expanding universe hypothesis.
  • As per this theory, in the beginning, all matter or substance forming this universe existed at one place as a tiny ball. This tiny ball had an extremely small volume, infinite density and temperature.
  • At the Big Bang, this ball blasted fiercely and forcefully and started a substantial process of expansion which continues to this day.
  • Now it is accepted that this event took place 13.7 billion years ago.


ORIGIN OF EARTH

Formation of Planets

The following are regarded as the stages in the planets’ development:

  • The stars are localised gas lumps inside a nebula.
  • A core to the gas cloud as well as a spinning disc of dust and gas are created because of the gravitational force within the lumps.
  • After this, the cloud of the gas condenses and the matter over the core is changed into tiny rounded objects.
  • These small round objects develop into what are called planetesimals by a cohesion process.
  • The smaller objects start forming larger bodies by colliding with one another and they stick together because of gravitational force.
  • In the last stage, these large number of small planetesimals aggregate to develop into a smaller number of large bodies called planets.
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