Branches of Geography

Physical Geography

  • Astronomical geography
  • Geomorphology
  • Climatology
  • Soil geography
  • Oceanography
  • Bio-geography

Human Geography

  • Population Geography
  • Anthropogeography
  • Political Geography
  • Social Geography
  • Cultural Geography
  • Economic Geography
  • Agricultural
  • Trade
  • Transport
  • Industrial
  • Historical Geography
  • Settlement Geography
  • Rural
  • Urban

Regional Geography

  • Macro Region
  • Meso Region
  • Micro Region

Origin of the Earth

Earlier Theories

  • Geocentric Theory

This theory is its final form was given by Ptolemy of Alexandria, Greece

  1. The earth is at the centre of the universe.
  2. Sun, the stars and all other heavenly bodies revolve around the earth.
  • Heliocentric Theory

This theory was first propounded by Nicolas Copernicus of Poland in his book “De Revolutionibus Orbium Coelestium”

  1. Sun is at the centre of the universe
  2. Earth and other planets revolve around the Sun

Galileo Galilei and Sir Issac Newton supported this theory against geocentric theory

Modern theories

  • Buffon’s Hypothesis
  • Proposed by Comte de Buffon, a French naturalist
  • Earth originated as the result of a collision between the sun and a comet
  • Gaseous Mass Theory
  • Proposed by Immanuel Kant
  • Earth and other planets originated from a rotating nebular mass of gas
  • This theory is based on Newton’s laws of gravitation
  • Nebular hypothesis

Proposed by Laplace de Marquis in his book “Exposition du systeme du monde”

  1. Intensely hot and rotating Nebular gaseous mass cooled
  2. Rotation and subsequently its centrifugal force increased further due to decrease in volume of the mass
  3. Due to centrifugal force, a ring of mass separated out of nebula and transformed into planetary bodies
  • Planetesimal Hypothesis
  • Proposed by T.C Chamberlain & F.R. Moulton
  • A star passed by the Sun and drew out some material which later condensed into planetary bodies
  • Tidal Hypothesis
  • Proposed by Jeans James and Jeffreys, H
  • Tides of gaseous mass from the sun, created as a result of higher gravitational force from an approaching star, condensed to form planets
  • Electromagnetic Hypothesis

Proposed by Dr. Hannes Alfven

  1. Electromagnetic field around the sun attracted the dust and gaseous mass
  2. The dust and gaseous mass revolved around the Sun and condensed into planets
  3. At a later stage the planets grew their own magnetic fields around them
  • Binary Star Hypothesis
  • Proposed by Russell and Lyttleton
  • Super Nova Hypothesis
  • Proposed by Hoyle and Lyttleton
  • Revised Nebular Hypothesis

Proposed by Otto Schmidt of Russia and Carl Weizascar of Germany

  1. The sun was surrounded by solar nebula containing hydrogen, helium and dust
  2. The friction and collision of particles led to the formation of a disk-shaped cloud
  3. The planets were formed through the process of accretion from the clouds

Big Bang Theory

  • “Expanding universe hypothesis”
  • Edwin Hubble, in 1920, provided evidence that the universe is expanding
  • Big Bang took place 13.7 billion years before the present
  • Explosion of a small mass at an extremely high density and temperature, led to the origin of the universe
  • The expansion still continues and; as it expands, some energy is converted into matter
  • There was a rapid expansion within fractions of a second after Big bang and thereafter, the expansion has slowed down
  • Within 300,000 years from the Big Bang, temperature dropped to 4500 K and gave rise to atomic matter

Expansion of the universe is supported but not the expansion of galaxies

 

Shape of the Earth

Oblate spheroid

  • slightly flattened at the poles and bulging at the equator

 

Layers of the Earth

  1. Crust
  • Outermost layer of the Earth
  1. Continental crust
  2. Oceanic crust
  • Composition
  • Made of solid rocks
  • made of the lighter elements
  • silicon, aluminium and oxygen
  • known as sial or felsic
  • Element by percentage
  1. Oxygen 47%
  2. Silicon 28%
  3. Aluminium 8%
  4. Iron 5%
  5. Calcium 3.5%
  • Compounds by percentage
  1. Silica
  2. Alumina
  3. Lime

2 – Mantle

  • Layer below the crust
  • Composition
  • Made of
  • silicon, oxygen and Magnesium
  • known as sima or mafic
  • The density of the Mantle increases gradually with depth
  • Layers
  1. Upper mantle
  • solid base of the crust
  • made of the heavy rock peridotite
  1. Upper aesthenosphere
  • layer is fluidic due to high pressure and temperature
  • leads to movement of continental plates
  1. Lower aesthenosphere
  2. Lower mantle

3- Core

  • Innermost layer of the earth
  • Composition
  • core is made of solid iron and nickel
  • known as NIFE
  • Layers
  1. Outer core
  • molten layer below the mantle
  1. Inner core
  • solid due to high pressure

 

Discontinuities

are the boundaries between layers of earth – found by analysis of the seismic waves

  1. Control discontinuity
  • Between Upper crust and lower crust
  • named after Victor Conrad
  1. Mohorovicic discontinuity
  • Between Crust and Asethenosphere
  • named after Andrija Mohorovicic
  • It lies at a depth of about
  • 20 miles under the continents
  • 4 to 6 miles under the oceans
  1. Repetti discontinuity
  • Between the upper mantle and the lower mantle
  1. Gutenberg discontinuity
  • Between lower mantle and the core
  1. Lehman discontinuity
  • Between outer core and the inner core

 

Important Points

Lithosphere = Crust+ Upper mantle

  • Thickness of continental crust is higher than oceanic crust
  • Mantle is the largest layer by mass and volume, followed by crust and core respectively
  • Earth’s density increases gradually from crust to core
  • Oceanic crust is denser than continental crust

Rotation of the Earth

Movement

  • Earth rotates on its axis from west to east
  • the reason for the apparent motion of the sun from east to west
  • Earth rotates once in every 23 hours, 56 minutes, 4.0916 seconds

Apparent rotations

  • From the North Pole, the direction of Earth’s rotation is perceived as counter clockwise or anti clockwise direction
  • from the South Pole, the direction of Earth’s rotation is perceived as clockwise direction

Velocity of the rotations

  • The rotational velocity at the poles is almost equal to zero
  • The greatest rotational velocity is found at the Equator
  • The rotational velocity at the 600 latitudes is equal to half of the velocity found at the equator

Effects

  1. Day and Night
  • Part of earth facing the sun experiences day
  • Part of earth facing the sun experiences Night
  • The line around the Earth separating the light and dark halves is called “The circle of illumination”
  1. Circulations
  • Atmospheric circulation
  • Circulation of atmospheric along its layers
  • Coriolis force
  • Oceanic circulation
  • Movement of waters in ocean
  • Ocean cycle
  • takes 10,000 years to complete a cycle