Geography Class 08
Geomorphology
- 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
- 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
- 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
- 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.
Images
1. What is geomorphology?
- The study of the
physical features of the earth and the processes by which those features are
formed.
2. How did the earth originate?
- Earth originated
from a gaseous nebula.
3. What happened as the nebula cooled?
- Rings of matter
were ejected, resulting in planets.
4. Describe the initial state of the planet earth.
- The planet earth
was initially barren, rocky, and in a volatile state.
5. What caused the formation of the earth's interior layers?
- The heavier
elements sank toward the center, and the lighter ones moved to the surface
through density separation.
6. What happened to the temperature as the density increased
at the center of the earth?
- The interior
temperature increased.
7. What is degassing?
- The process
through which gases and water vapor are released from the earth's interior into
the atmosphere.
8. Which gases were important in the early atmosphere?
- Carbon dioxide,
nitrogen, methane, water vapor, and very little oxygen.
9. How were the oceans formed?
- Rainwater
collected in surface depressions as the earth cooled and the water vapor
condensed.
10. When did life first evolve in the oceans?
- 3800 million
years ago as non-photosynthesis microorganisms.
11. Which eon saw the emergence of blue-green algae?
- Archean Eon.
12. What did blue-green algae contribute to the atmosphere?
- Oxygen through
photosynthesis.
13. What are the major eons in the geological time scale?
- Proterozoic,
Hadean, Archean, and Phanerozoic.
14. What marks the Phanerozoic Eon?
- It is divided
into the Paleozoic, Mesozoic, and Cainozoic eras.
15. What periods are included in the Paleozoic Era?
- Cambrian,
Ordovician, Silurian, Devonian, Carboniferous, and Permian.
16. What era is known as the 'Age of Dinosaurs'?
- Mesozoic Era.
17. Which period saw the extinction of dinosaurs?
- Cretaceous
Period.
18. What periods are in the Cainozoic Era?
- Tertiary and
Quaternary.
19. What epoch are we currently in?
- Holocene Epoch.
20. Name the ages of the Holocene Epoch.
- Greenlandian,
Northgrippean, and Meghalayan.
21. What is the significance of the Mawluh cave in
Meghalaya?
- Evidence of the
change to the Meghalayan age was found there.
22. What are the direct sources for studying the earth's
interior?
- Mining and deep
ocean drilling, and volcanic eruptions.
23. What are the indirect sources for studying the earth's
interior?
- Density studies,
seismic studies, temperature and pressure correlations, and meteorite analysis.
24. How does seismic study help understand the earth's
interior?
- By analyzing
different earthquake waves, their speed, and direction.
25. What is the average density of the earth?
- 5.5 gm/cm³.
1)
Which of the following is not an epoch of Cainozoic era?
(a)Holocene
(b)Pleistocene
(c)Oligocene
(d)Cambrian
2)
Which of the following is the correct sequence in ascending order of the period with respect to the Geological Time Scale?
(a)Eon->Era->Period->Epoch->Ages
(b)Ages->Era->Period->Epoch->Eon
(c)Ages->Epoch->Period->Era->Eon
(d)Eon->Epoch->Period->Era->Ages
3)
Which of the following statement(s) is/are correct?
- The First trace of life on land was seen in the Silurian period.
- The Mesozoic era is dedicated to the age of dinosaurs.
- The Meghalaya age is the latest age of the Pliocene Epoch.
Select the correct answer using the codes given below.
(a)1 and 2 only
(b)2 and 3 only
(c)1 and 3 only
(d)1, 2 and 3
4)
Arrange the following Period of the Palaeozoic Era according to the geological time scale in chronological order
- Cambrian
- Ordovician
- Silurian
- Devonian
- Carboniferous
- Permian
Which of the following is the correct code?
(a)1-2-3-4-5-6
(b)2-1-4-3-5-6
(c)1-2-3-5-4-6
(d)1-3-5-2-6-4
5)
Which of the following is not an indirect source of information of earth"s interior?
(a)Density studies
(b)Temperature and Pressure studies
(c)Meteorite
(d)Volcanic Eruptions
6)
What do you understand by Geomorphology?
(a)It is the study of the physical features of the earth and the process in which those featured are formed.
(b)It is the study of rocks, and of the way they are formed.
(c)It is the study of solar system.
(d)None of the above.
7)
Which of the following gases mainly constituted the first/early thin atmosphere of the earth?
- Hydrogen.
- Helium.
- Nitrogen.
- Oxygen.
Select the correct answer from the codes given below:
(a)1 and 3 only.
(b)2 and 3 only
(c)1 and 2 only.
(d)1,2 and 3.
8)
Consider the following statements regarding the evolution of the Earth:
- Between 3000-2500 million years ago, blue-green algae emerged in ocean water which started to release oxygen through the process of photosynthesis.
- By 2000 million years ago ocean was saturated with oxygen and oxygen started flooding the atmosphere and a new atmosphere emerged.
- The oceans were completely formed around 4000 million years ago.
Which of the above statements is/are correct?
(a)1 and 2 only.
(b)2 and 3 only.
(c)1 and 3 only.
(d)1,2 and 3.
9)
Discuss the various direct and indirect sources which throw light on interior of the earth. (150 words / 10 marks)
10)
Give an account of the Geological time scale and associated major life events which occurred. (10 marks/150 words)
Answers
1) d
2) a
3) a
4) a
5) d
6) a
7) c
8) d
Describe the formation of the inner layer of the earth as well as the evolution of the atmosphere and hydrosphere with respect to the origin and evolution of the earth. (150 words/10 marks)
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