Chapter 2: The Origin & Evolution of the Earth

Origin of Earth: Early Theories

  • According to Nebular Hypothesis (by Laplace, 1796), planets were formed out of a cloud of material associated with a youthful sun, which was slowly rotating.
  • Later, in 1950, Otto Schmidt & Carl Weizascar opined that the sun was surrounded by solar nebula containing mostly the hydrogen & helium along with dust. The friction and collision of particles led to the formation of a disk shaped cloud & the planets were formed through the process of accretion.

Origin of Earth: Modern Theories

  • Earth Origin

    Origin of Universe: BIG BANG THEORY

     It is also called as expanding universe hypothesis.

     According to this theory the space between the galaxies is increasing.

     Though the space between the galaxies is increasing, the size of the galaxies is constant.

    Stages of development of universe:

    1. In the beginning, all matter forming the universe existed in one place in the form of a "tiny ball" with extremely small volume, infinite temperature and infinite density.
    2. Around 13.7 billion years before the present, the tiny ball exploded violently. This lead to huge expansion.
    3. Within 3,00,000 tears from the Big Bang, temperature dropped to 4,500 K (Kelvin) and gave rise to atomic matter.

  • S

    The Star Formation

    • Formation of stars is believed to have taken place some 5-6 billion years ago

       

  • Planet

    Formation of Planets

    Stage-1:

    • The stars are localised lumps of gas within a nebula.
    • 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

    Stage-2:

    • The gas cloud starts getting condensed and the matter around the core develops into small rounded objects.These small rounded objects by the process of cohesion develop into what is called planetesimals.
    • Larger bodies start forming by collision, and gravitational attraction causes the material to stick together. Planetesimals are a large number of smaller bodies.

    Stage-3:

    • These large number of small planetesimals accrete to form a fewer large bodies in the form of planets.

Our Solar System