CLASS LECTURES: GEOGRAPHY

Lecture 1

Content :

  • INTRODUCTION TO GEOGRAPHY, DEFINITION AND ITS USEFULNESS.
  • ORIGIN OF UNIVERSE, ORIGIN OF EARTH

PHYSICAL GEOGRAPHY

SECTION  1  GEOMORPHOLOGY

CHAPTER 01 THEORY: ORIGIN OF EARTH SURFACE

CHAPTER 02 INTERIOR OF THE EARTH

CHAPTER 03 EARTH MOVEMENTS

CHAPTER 04 CLASSIFICATION OF MOUNTAINS

CHAPTER 05 VOLCANISM

CHAPTER 06 EARTHQUAKES

CHAPTER 07 ROCKS –DIFFERENT KINDS OF ROCKS

CHAPTER 08 LANDFORMS AND CYCLE OF EROSION

CHAPTER 09 LAKES

CHAPTER 10 PLATEAU

 

SECTION  2  CLIMATOLOGY

CHAPTER 1. LATITUDES AND LONGITUDES

CHAPTER 2 MOTIONS OF THE EARTH: ROTATION AND REVOLUTION

CHAPTER 3 ATMOSPHERE

CHAPTER  4 TEMPERATURE DISTRIBUTION ON EARTH

CHAPTER  5 PRESSURE SYSTEMS

CHAPTER 6 GENERAL CIRCULATION OF THE ATMOSPHERE

CHAPTER 7 WATER CYCLE – HYDROLOGICAL CYCLE

CHPATER 8 JET STREAMS

CHAPTER 9 AIR MASSES

CHAPTER 10 FRONTS

CHAPTER 11 TROPICAL CYCLONES

CHAPTER 12 TEMPERATE CYCLONES

CHAPTER 13 EL NINO

CHAPTER 14 CLIMATIC REGIONS

 

SECTION 3  OCEANOGRAPHY

CHAPTER 1 OCEAN RELIEF

CHAPTER 2 OCEAN CURRENTS

CHAPTER3 TEMPERATURE DISTRIBUTION OF OCEANS

CHAPTER 4 TIDES

CHAPTER 6 CORAL REEFS

CHAPTER 7 RESOURCES FROM THE OCEAN

CHAPTER 8 JURISDICTION OVER THE SEAS

 

 

 

 

CHAPTER 1 THEORY: ORIGIN OF EARTH SURFACE

 

 

 

Important theories

  1. Polar wandering (Similar to Continental Drift Theory)
  2. Continental Drift Theory (CDT)
  3. Convectional Current Theory (CCT)
  4. Sea Floor Spreading Theory (SFST)
  5. Plate Tectonics (PT)

 

POLAR WANDERING

  • Polar wandering is the relative movement of the earth’s crust and upper mantle with respect to the rotational poles of the earth.
  • Continental drift refers to the movement of the continents relative to each other.
  • Convectional current theory forms the basis of SFST and PT.
  • Sea floor spreading describes the movement of oceanic plates relative to one another.
  • Plate tectonics is simply the movement of crustal plates relative to each other.

 

 

Continental Drift Theory (Alfred Wegener, 1922)

  • This theory was suggested by Alfred Wegener in 1920’s.
  • According to Wegener’s Continental Drift Theory, there existed one big landmass which he called Pangaeawhich was covered by one big ocean called Panthalassa.
  • A sea called Tethys divided the Pangaea into two huge landmasses: Laurentia(Laurasia)to the north and Gondwanaland to the south of Tethys.
  • Drift started around 200 million years ago (Mesozoic Era), and the continents began to break up and drift away from one another.

 

Force for Continental Drift

The drift was in two directions-

  1. equator wards due to the interaction of forces of gravity, pole-fleeing force and buoyancy(ship floats in water due to buoyant force offered by water), and
  2. westwards due to tidal currents because of the earth’s motion (earth rotates form west to east, so tidal currents act from east to west.
  • Wegener suggested that tidal force also played a major role.
  • The polar-fleeing force relates to the rotation of the earth. You are aware of the fact that the earth is not a perfect sphere; it has a bulge at the equator. This bulge is due to the rotation of the earth. [Greater Centrifugal force at the equator. Centrifugal force increases as we move from poles towards equator. This increase in centrifugal force has led to pole fleeing].
  • Tidal force is due to the attraction of the moon and the sun that develops tides in oceanic waters.
  • Wegener believed that these forces would become effective when applied over many million years.
  • According to Wegener, the drift is still continuing.

Evidence in support of Continental Drift

Apparent Affinity of Physical Features

  • South America and Africa seem to fit in with each other, especially, the bulge of Brazil fits into the Gulf of Guinea.
  • Greenland seems to fit in well with Ellesmere and Baffin islands.
  • The east coast of India, Madagascar and Africa seem to have been joined.
  • North and South America on one side and Africa and Europe on the other fit along the mid-Atlantic ridge.
  • The Caledonian and Hercynian mountains of Europe and the Appalachians of USA seem to be one continuous series.

Criticism

  • Coastlines are a temporary feature and are liable to change.
  • Several other combinations of fitting in of landforms could be attempted.
  • Continental Drift Theory shifts India’s position too much to the south, distorting its relation with the Mediterranean Sea and the Alps.
  • The mountains do not always exhibit geological affinity.

Causes of Drift

  • Gravity of the earth, buoyancy of the seas and the tidal currents were given as the main factors causing the drift, by Wegener.

Criticism

  • This is illogical because for these factors to be able to cause a drift of such a magnitude, they will have to be millions of times stronger.

Botanical Evidence

  • Presence of glossopterisvegetation in carboniferous rocks of India, Australia, South Africa, Falkland Islands (Overseas territory of UK), Antarctica, etc. can be explained on the basis of the fact that parts were linked in the past.

Criticism

  • Such vegetation is also found in the northern parts like Afghanistan, Iran and Siberia.
  • Similar vegetation found in unrelated parts of the world.

Rocks of Same Age Across the Oceans

  • The belt of ancient rocks of 2,000 million years from Brazil coast matches with those from western Africa.

Criticism

  • Rocks of same age and similar characteristics are found in other parts of the world too.

Distribution of Fossils

  • The observations that Lemurs occur in India, Madagascar and Africa led some to consider a contiguous landmass “Lemuria” linking these three landmasses.
  • Mesosaurus was a small reptile adapted to shallow brackish water. The skeletons of these are found only in South Africa and Iraver formations of Brazil. The two localities presently are 4,800 km apart with an ocean in between them.

Drawbacks of Continental Drift Theory

  • Wegener failed to explain why the drift began only in Mesozoic era and not before.
  • The theory doesn’t take oceans into consideration.
  • Proofs heavily depend on assumptions and are very general in nature.
  • Forces like buoyancy, tidal currents and gravity are too weak to be able to move continents.
  • Modern theories (PT) accept the existence of Pangaea and related landmasses but give a very different explanation to the causes of drift.

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