NCERT Class 11 Geography Part 1 Chapter 4: Distribution of Oceans & Continents YouTube Lecture Handouts

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Watch Video Lecture on YouTube: NCERT Class 11 Geography Part 1 Chapter 4: Distribution of Oceans & Continents

NCERT Class 11 Geography Part 1 Chapter 4: Distribution of Oceans & Continents

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Continental Drift

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Continental Drift

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  • Abraham Ortelius: Dutch map maker – 1st proposed possibility of joining America, Europe & Asia in 1596.

  • Antonio Pellegrini: Drew a map showing 3 continents together

  • Alfred Wegener: German meteorologist gave this theory in 1912 – Pangea & Panthalassa. 200 mya – Pangea spit into Laurasia and Gondwanaland

Continental Drift – Evidences

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Continental Drift

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  • Jigsaw fit of continents – best fit of Atlantic by Bullard in 1964 by computer program & was tried at 1000 fathom line

  • Rocks of same age across oceans – radiometric dating – South America & Africa rock of Jurassic age (before that no oceans)

  • Tillite – Gondwana sedimentary rock deposit of glaciers provide evidence of palaeoclimates and drifting of continents

  • Placer Deposits – gold in Ghana but absence of source & gold bearing veins in Brazil

  • Fossil distribution - India, Madagascar and Africa (called Lemuria) – Lemurs occurred & linked them. Mesosaurus - Southern Cape province of South Africa and Iraver formations of Brazil which are presently 4800 km apart

Continental Drift – Forces of Drifting

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Forces in Continental Drift

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  • Pole Flee drift – rotation of the earth (bulged at equator)

  • Tidal drift – attraction of moon & sun cause tides on ocean waters

Post-Drift Studies

  • Convection Current Theory: Holmes – convection in mantle caused by radioactive elements causing thermal differences in mantle

  • Ocean Floor – submerged mountain ranges & trenches, mid-oceanic ridge had volcanic eruptions. Ocean crust is younger than continents.

  • Continental margin – includes shelf, slope, rise and trench

  • Mid-oceanic ridge – interconnected chain within mountain – rift system at crest is zone of intense volcanic activity

  • Abyssal plains – b/w margin and ridge

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Sea Floor Spreading – Henry Hess (1961)

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Sea Flood Spreading

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  • Along mid oceanic ridge volcanic eruption were common & brought lava to surface (cause spread)

  • Rocks equidistant from crest on both sides showed similarity, closer to mid-oceanic ridge there are of normal polarity & youngest

  • Ocean crust (200 mya) is younger than continental crust

  • Ocean sediments were thin

  • Deep trenches have deep seated earthquake but mid-oceanic ridge have shallow earthquake

Plate Tectonics

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Plate Techtonics

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  • 1967: McKenzie and Parker & also Morgan

  • Plate moves over asthenosphere as rigid units

  • Lithosphere includes crust & upper mantle (5-100 km in oceanic parts & 200 km in continental areas)

Plate Tectonics

  • Divergent – pull away, spreading sites, Mid Atlantic ridge

  • Convergent – destroyed, subduction zone

  • Transform – Slide, perpendicular to mid-oceanic ridge

Indian Plate Movement

  • subduction zone along the Himalayas – continent convergence

  • Rakinyoma Mountains of Myanmar towards the island arc along the Java Trench (Eastern – spreading site)

  • Western - Kirthar Mountain of Pakistan & extends along Makrana coast – spreading site

  • B/w India & Antarctica is divergent

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