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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.