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
- The earth is at the centre of the universe.
- 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”
- Sun is at the centre of the universe
- 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”
- Intensely hot and rotating Nebular gaseous mass cooled
- Rotation and subsequently its centrifugal force increased further due to decrease in volume of the mass
- 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
- Electromagnetic field around the sun attracted the dust and gaseous mass
- The dust and gaseous mass revolved around the Sun and condensed into planets
- 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
- The sun was surrounded by solar nebula containing hydrogen, helium and dust
- The friction and collision of particles led to the formation of a disk-shaped cloud
- 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
- Crust
- Outermost layer of the Earth
- Continental crust
- Oceanic crust
- Composition
- Made of solid rocks
- made of the lighter elements
- silicon, aluminium and oxygen
- known as sial or felsic
- Element by percentage
- Oxygen 47%
- Silicon 28%
- Aluminium 8%
- Iron 5%
- Calcium 3.5%
- Compounds by percentage
- Silica
- Alumina
- 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
- Upper mantle
- solid base of the crust
- made of the heavy rock peridotite
- Upper aesthenosphere
- layer is fluidic due to high pressure and temperature
- leads to movement of continental plates
- Lower aesthenosphere
- Lower mantle
3- Core
- Innermost layer of the earth
- Composition
- core is made of solid iron and nickel
- known as NIFE
- Layers
- Outer core
- molten layer below the mantle
- Inner core
- solid due to high pressure
Discontinuities
are the boundaries between layers of earth – found by analysis of the seismic waves
- Control discontinuity
- Between Upper crust and lower crust
- named after Victor Conrad
- 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
- Repetti discontinuity
- Between the upper mantle and the lower mantle
- Gutenberg discontinuity
- Between lower mantle and the core
- 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
- 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”
- 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