Saturday, March 28, 2015

origin and evolution of the earth

There are various scientific theories of origin and evolution of the earth
  1. Nebular Hypothesis
  2. Planetesimal Hypothesis
  3. Gaseous Tidal Hypothesis
  4. Binary Star Hypothesis
  5. Gas Dust Cloud Hypothesis

Nabular Hypothesis

  1. German philosopher, Kant and French mathematician, Laplace
  2. Earth, planets and sun originated from Nebula.
  3. Nebula was large cloud of gas and dust. It rotates slowly.
  4. Gradually it cooled and contracted and its speed increased.
  5. A gaseous ring was separated from nebula
  6. Later the ring cooled and took form of a planet
  7. On repetition of the process all other planets came into being
  8. The central region, nebula became sun.

Objections:Interior of the earth

  • Sun should have the greatest angular momentum because of its mass and situated in the center, however, it has only two percent of momentum of the solar system
  • How the hot gaseous material condensed in to rings

Planetesimal Hypothesis

  1. Chamberlin and Moulton proposed the theory in 1904
  2. The sun existed before the formation of planets
  3. A star came close to the sun.
  4. Because of the gravitation pull of the star, small gaseous bodies were separated from the sun
  5. These bodies on cooing became small planet's
  6. During rotation the small planets collided and form planets


  • The angular momentum could not be produced by the passing star.
  • The theory failed to explain how the planetesimals had become one planet

Gaseous Tidal Theory

  1. Jeans and Jeffrey proposed the theory in 1925
  2. Large star came near the sun. Due to gravitational pull a gaseous tide was raised on the surface of the sun.
  3. As the star came nearer, the tide increased in size.
  4. Gaseous tide detached when star move away.
  5. The shape of the tide was like spindle.
  6. It broke into pieces-forming nine planets of the solar system

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