Introduction, History, Branches, Origins of Earth and Theories

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Two Approaches to Study Geography

  • Regional Approach: The regions of the earth are different, and these differences must be studied. Descriptive discipline.
  • Systemic Approach: Though all places differ in some respects, yet there are similarities between different parts of the world. The aim of the geographer should be to identify these similarities. Analytical discipline.


First geographers: Hecateus and Theophrastus

Kant differentiated between history and geography by proposing that geography is a chorological science while history is a chronological science.


Main branches

  • Physical G: Physical environment and processes of changes on the earth. Consists of geomorphology (similar to geology) , climatology, oceanography, biogeography (relationships of organisms with their environment.
  • Human G: Study of pattern and activities of human occupancy on earth. Population geography, cultural geography, settlement geography (urban and rural geography) , political geography (geopolitics and electoral geography)
  • Economic G: Offshoot of human geography. Study of spatial patterns of various economic activities. Consists of agricultural & nutritional geography, industrial geography, transport geography, resource geography, geography of development. Besides, there can be historical g, military g, radical g, medical g, gender g etc.

Origins of Earth

Came into existence 4.6 billion years back


  • Gaseous Hypothesis: (Kant) Clouds of gases flattened down under gravity to create earth.
  • Nebular Hypothesis: (Laplace) Formed by solidification of a ring thrown away by a rotating nebula (sun)
  • Tidal Hypothesis: (Jeans and Jeffreys) Proposed effects of two nebulas in forming the earth. A larger nebula came close to the smaller one (sun) . The gravitational pull caused tidal upsurge on the surface of sun. As the larger nebula moved away, small rings of nebula separated from the smaller nebula and formed the earth and other planets.

Nature of Earth

  • Layered structure: Crust, mantle, core
  • Crust: sial (silica and aluminium)
  • Mantle: sima (silica and magnesium)
  • Outer Core: (nickel and iron)
  • Core: Iron

Time Line

  • Age estimated through carbon-dating
  • Three Eras: Palaeozoic (542 to 241 million years ago) , Mesozoic (240 to 64 million years ago) and Cenozoic Era (63 million to 10000 years ago) . The era before the Palaeozoic era is called the Pre-Cambrian period.
  • Earlier forms of life have existed as long ago as 3.5 billion years back. Human species came into existence around 2 million years back.

Solar System

  • Sun and eight planets
  • All planets rotate on their axis from west to east except Venus and Uranus which rotate from East to West. Direction of revolution around the sun is also west to east.
  • Jupiter has the largest number of satellites (63) while Mercury and Venus have none.
  • Asteroids and planetoids: Bodies revolving around the sun that are small to be classified as planets. Asteroid belt between the orbits of Mars and Jupiter. Jupiter Trojans are asteroids revolving around the sun in Jupiter՚s orbit.
  • Near-earth objects: perihelion distance < 1.3 AU.
  • Geocentric View: Ptolemy; Heliocentric View: Copernicus
  • Inner planets: Mercury, Venus, Earth and Mars. Rest are outer planets.
  • Mercury and Venus which are closer to the sun that earth is called inferior planets. Venus is the closest planet to earth.
  • Brightest: Venus
  • Smallest: Mercury
  • Most elliptical orbit: Pluto. It intersects with Neptune՚s orbit.

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