NCERT Class 11 Geography Chapter 2: The Origin and Evolution of the Earth Part 2 YouTube Lecture Handouts

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Origin of Earth – Early Theories

  • Nebular Hypothesis - Kant & revised by Laplace

  • Chamberlain & Moulton – Cigar Shaped star - Planetesimal Theory

  • Jeans & Jefferys – Tidal Theory

  • Otto Schimdt – Dust Cloud (revised nebular hypothesis)

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Origin of Earth – Modern Theories

  • Big Bang Theory – Expanding universe hypothesis (Hubble in 1920 proved expanding universe)

  • Hoyle – Steady state

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Origin of Earth - Modern Theories For Geography Image - 1

Origin of Earth - Modern Theories for Geography Image - 1

Origin of Earth - Modern Theories For Geography Image - 1

Origin of Earth - Modern Theories For Geography Image - 2

Origin of Earth - Modern Theories for Geography Image - 2

Origin of Earth - Modern Theories For Geography Image - 2

Star Formation

  • Density difference lead to diff. in gravitational force

  • Galaxy – many stars – spread over many light years

  • Diameter of galaxy: 80,000 to 1,50,000 light years (distance)

Planet Formation

  • Star localized in nebula – core & disc formed

  • Gas cloud condense around core – by cohesion – planetesimals

  • Planetesimal accrete to form planets

Solar System

  • Nebula collapsed 5-5.6 billion years ago

  • Planets formed 4.6 billion years ago

  • Inner or Terrestrial Planets (till Mars) – too warm for gas to condense, solar winds were intense, small & low gravity couldn’t hold gas

  • Outer or Jovian or Gas Giant Planets: H & He

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Moon

  • Natural Satellite of earth

  • Darwin – earth & moon originated from single body – dumb-bell shaped body that broke

Evolution of Earth

Origin of Life

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Origin of Life for Geography Image - 3

Origin of Life For Geography Image - 3