NCERT Class 11 Geography Chapter 2: The Origin and Evolution of the Earth YouTube Lecture Handouts
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NCERT Class 11 Geography Part 1 Chapter 2: Origin & Evolution of Earth
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)
- Early Theories of Origin of Earth
Origin of Earth – Modern Theories
- Big Bang Theory – Expanding universe hypothesis (Hubble in 1920 proved expanding universe)
- Hoyle – Steady state
- Modern Theories of Origin of Earth
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
- Solar System
Moon
- Natural Satellite of earth
- Darwin – earth & moon originated from single body – dumb-bell shaped body that broke
Evolution of Earth
Origin of Life
✍ Manishika