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Summary
Geography Class 08

Geomorphology (5:09 PM)

  • It is the study of the physical features of the earth and the process by which those features are formed.
  • Origin of the earth: Earth originated from a gaseous nebula.
  • As the nebula cooled rings of matter ejected resulting in planets.
  • Evolution of earth: The planet earth was initially barren, rocky, and in a volatile state.
  • This primordial earth gradually evolved into the present stable one with a thick atmosphere.
  • Formation of interior layers of the earth: 
  • Due to a gradual cooling down of the earth, the heavier elements started to sink toward the centre and the lighter ones moved toward to surface through the process of density separation.
  • With the gradual increase in density at the centre, the interior temperature increased
  • With time as the earth cooled further, it condensed into a smaller size(condensation).
  • The further process of differentiation led to the formation of different layers in the earth's interior.
  • Evolution of atmosphere and hydrosphere:
  • The early thin atmosphere with hydrogen and helium was stripped off due to solar winds.
  • During the cooling of the earth, gasses and water vapour were released from the earth's interior.
  • And the process through which these gases outpour into the atmosphere is called Degassing.
  • The volcanic eruption released more gasses and water vapour.
  • The important gases at this stage were carbon dioxide, nitrogen, methane, water vapour, and every little oxygen.
  • As the earth cooled further the water vapour started to condense and the CO2 in the atmosphere got dissolved in rainwater and was brought down to the surface.
  • This further reduced the temperature of the atmosphere which led to more condensation and more precipitation.
  • The rainfall from the atmosphere got collected in the depressions on the surface forming oceans which were completed around 4000 million years ago.
  • Life evolved in the oceans 3800 million years ago as Non-photosynthesis micro-organisms.
  • Between 3000-2000 million years ago, blue-green algae emerged in ocean water which released oxygen through photosynthesis.
  • By 2000 million years ago ocean was saturated with oxygen and oxygen started flooding the atmosphere.

Geological time scale (6:13 PM)

  • Proterozoic Eon: Soft body marine organism.
  • Hadean Eon: Ocean and continent were forming.
  • Archean Eon: Blue-green algae evolved.
  • Phanerozoic Eon: It is divided into 3 different eras:
  • Palaeozoic era: It means old life.
  • It includes periods Cambrian(no terrestrial life), Ordovician(1st fish), Silurian(1st plant),  Devonian(Amphibians), Carboniferous(286-360 Million years)(1st reptile), and Permian(domination of reptiles).
  • Mesozoic era: It means medium life.
  • This era includes the Triassic, Jurassic (208-144 million years)(Age of dinosaurs), and Cretaceous Periods(extinction of dinosaurs).
  • Cainozoic era: The Cainozoic era is divided into periods of tertiary(evolution of mammals, Himalayas, and apes) and Quaternary(the period of homo-sapiens).
  • We are currently in the Holocene epoch (0-11700 years).

Holocene epoch (7:13 PM)

  • Ages of Holocene: Greenlandian age:
  • The 1st age is called Greenlandian (8200-11700 years ago)
  • Northgrippean age: 8200-4200 years ago is called as Northgrippean age.
  • Meghalayan age: 4200 years-Present is the Meghalayan age.
  • In Mawluh cave in Meghalaya, evidence of change of age was found thus the name of Meghalayan age.

The interior of the earth (7:28 PM)

  • The sources of study of earth's interior:
  • There are direct sources and indirect sources.
  • Direct sources:
  • Mining and Deep ocean drilling(the maximum depth up to which we were able to drill is 12 km).
  • Volcanic eruptions through which we can analyze the material from the earth's interior.
  • Indirect sources:
  • Density studies:
  • It is done by analyzing the average density of the earth( 5.5 gm/cm3) and its comparison to the density of the surface(2.7-3 gm/cm3) and the core.
  • we can conclude that the crust is lighter and the core is heavier.
  • Seismic study:
  • It is done by analyzing different earthquake waves, their speed, and their direction while passing through the earth's interior.
  • Tempratue and pressure:
  • The temperature increases by 1 degree celsius for every 32 meters near the surface.
  • With the increase in depth pressure increases and the melting point of rocks increases.
  • Using this correlation we can conclude about the earth's interior.
  • Meteorite: It is by analyzing the structure, and mineralogy of meteorites we can conclude about the earth's interior as meteorites are remanet of planets.

The topic of the next class:  The layers of the Interior of the earth.