Exercise
A)
Do as directed.
1)
Complete the sentences by choosing the correct option.
Solution
(1)
The height of the landforms on the Earth's surface and the depth of the ocean floor start from 0.
(2)
The diameter of the Earth is approximately 12800 km.
2) Choose the incorrect statement.
Solution
Ans.
(3) A wide and shallow valley is called gorge.
3)
Choose the correct option of the pair.
‘Mountain’
(1)
The Rockies
(2)
The Ethiopian
(3)
The Alps
(4)
The Andes
(5)
The Altai
‘Continent’
(a)
South America
(b)
Australia
(c)
Asia
(d)
North America
(e)
Europe
(f)
Africa
Solution
Correct Option
(B)
1 – d, 2 – f, 3 – e, 4 – a, 5 – c
B)
Write the result.
1)
Movement of liquid metals in the outer mantle.
2)
Tremendous pressure on the Earth's centre.
3)
Friction between plates.
Solution
(1)
Movement of liquid metals in the outer mantle.
Ans.
Due to the movements of the metal in the liquid form in the outer mantle,
the magnetic field of the Earth is created which saves the biosphere from
solar winds.
(2)
Tremendous pressure on the Earth's centre.
Ans.
The Earth's centre is in a solid state because of the extreme pressure there.
(3)
Friction between plates.
Ans.
Friction between plates causes Earthquakes.
C) Explain the differences with the help of diagrams.
1)
Mountain Range and Mountain Chain
Mountain Range
(1)
Mountains which are similar and spread in the same direction are called a mountain range.
(2)
They are spread over a limited area.
(3)
Example : The Aravalli Range.
(4) Diagram :
Mountain Chain
(1)
Mountains which are varied and spread in different directions are called a mountain chain.
(2)
They extend over a large area.
(3)
Example : The Himalayan Mountain Chain.
(4) Diagram :
2)
Gorge and Valley
Gorge
(1)
A narrow and deep valley between two mountains or hills is called a gorge.
(2)
Gorges are comparatively steep.
(3)
Example : The Indus Gorge.
(4) Diagram :
Valley
(1)
The low-lying and elongated landform between mountains, hills and hillocks is called a valley.
(2)
Valleys are comparatively broad and not steep.
(3)
Example : The Kashmir Valley.
(4) Diagram :
3)
Continental Crust and Oceanic Crust
Continental Crust
(1)
Continental crust is the upper land part of the lithosphere.
(2)
The continental crust is composed of lighter elements such as Silica and Aluminium.
(3)
The continental crust is also called Sial.
(4) Diagram :
Oceanic Crust
(1)
Oceanic crust is the lower part of the lithosphere which is below the oceans.
(2)
The oceanic crust is composed of elements such as Silica and Magnesium.
(3)
The oceanic crust is called Sima.
(4) Diagram :
D)
Give reasons.
1)
Continental crust is called SiAl.
2)
The Core is called ‘NiFe’.
Solution
(1) Continental crust is called SiAl.
Ans.
- The Continental crust is mainly composed of lighter elements such as Silica (Si) and Aluminium (Al).
- The word SiAl is thus formed by Si (Silica) + Al (Aluminium) — SiAl.
- Hence, the continental crust is called SiAl.
(2) The Core is called ‘NiFe’.
Ans.
- Scientists have inferred that there must be heavy metals such as Nickel (Ni) and Ferrous (Fe) present in the core.
- The word NiFe is arrived from the words Nickel (Ni) and Ferrous (Fe).
- Hence, the core is called NiFe.
E)
Think and write an answer.
1)
Why are the maximum quantities of Ferrous and Nickel found in the Core?
2)
What are the reasons for the movements of plates other than the semi-fluid state of the outer mantle?
Solution
(1) Why are the maximum quantities of Ferrous and Nickel found in the Core?
Ans.
- In the early stage of its formation, the Earth was a very hot, gaseous sphere. With time, it gradually changed into a solid sphere.
- During this process, heavy elements such as Ferrous and Nickel, because of their high density, moved towards the centre of the Earth due to gravitational force.
- These heavy elements accumulated in large quantities at the centre. Therefore, the maximum quantities of Ferrous and Nickel are found in the Core.
(2) What are the reasons for the movements of plates other than the semi-fluid state of the outer mantle?
Ans.
In the outer mantle layer of the Earth, the substances become extremely
hot because of the intense heat and move upwards. As these substances
cool down, they move downwards. This continuous upward and downward
movement of substances in the outer mantle causes the movement of the
plates, apart from the semi-fluid nature of the outer mantle.
F)
Answer in brief.
1)
Write a note about the temperature in the Earth's interior.
2)
Explain the difference between the inner core and the outer core.
3)
Answer why the outer mantle is semi-fluid.
4)
How could the Earth's interior have been studied?
5)
Explain the impact of landforms on human life.
Solution
(1)
Temperature in the Earth's Interior
- The temperature increases gradually as we move from the Earth's surface towards its interior.
- As the depth increases, the temperature also rises. Approximately, the temperature increases by 1°C for every 32 metres of depth.
- The temperature of the mantle is about 1400°C to 3000°C.
- The temperature of the core is about 3000°C to 6000°C.
(2)
Difference between the Inner Core and Outer Core
- The inner core is the innermost layer of the Earth, whereas the outer core surrounds the inner core.
- The inner core remains solid because of extremely high pressure, while the outer core is in a molten or liquid state due to comparatively lower pressure.
- The density of the inner core is approximately 13 g/cm³, whereas the density of the outer core is approximately 10 g/cm³.
(3)
Why is the Outer Mantle Semi-fluid?
- The temperature of the outer mantle is very high and is close to the melting point of the rocks present there.
- Therefore, the rocks in this region are not completely solid and remain in a semi-molten condition.
- Hence, the rocks are neither completely solid nor completely liquid.
- The rocks melt slowly because of the high temperature, making the outer mantle semi-fluid.
(4)
How could the Earth's Interior have been studied?
- The distance from the Earth's surface to its centre is about 6400 km.
- Therefore, it is not possible to directly reach the centre of the Earth using available tools.
- Geologists study the Earth's interior mainly by observing earthquake waves and their propagation through the Earth.
- They also obtain information about the increasing temperature, density of elements and materials released during volcanic eruptions.
(5)
Impact of Landforms on Human Life
- The major landforms include mountains, plateaus, hills, hillocks, valleys and plains.
- These landforms greatly influence human settlements, agriculture, transport, climate and economic activities.
- The soil of the Ganga Plains is very fertile, supporting agriculture and leading to dense population.
- In the Himalayas, steep slopes make agriculture and transport difficult, so the population is comparatively sparse.
G)
Perform group discussion.
1)
Have you ever been on a trip? Discuss in a group the differences between the landforms found in your area and the area you visited.
Solution
(1)
Yes, I have been on a trip. The landforms in my area are mostly plains, while the place I visited had hills and mountains.
(2)
The differences in landforms affect the climate, settlements, agriculture and transportation of the two areas.
(3)
Plains are generally suitable for agriculture, settlements and easy transportation, whereas hilly and mountainous areas have steep slopes and limited transportation facilities.
Activity
1)
Create a model showing the main layers of the Earth's interior:
Crust, Mantle, Outer Core and Inner Core.
Use different colours and label each layer clearly.
2)
Landforms found in my area:
Hills, plateaus and plains are found in my area.
Hills are elevated areas with slopes, plateaus are raised flat-topped
areas, and plains are broad areas of comparatively level land.
3)
Landforms not found in my area:
Mountains, valleys and deserts are examples of landforms that may not
be found in my area but are present in other parts of the world.
Their characteristics can be collected with the help of parents and
presented in class.
Activity
1)
Prepare a model showing the different layers of the Earth's interior.
Answer
A model of the Earth's interior can be prepared using different coloured materials to show the four main layers: Crust, Mantle, Outer Core and Inner Core.
Each layer should be clearly labelled and arranged from the outermost layer to the innermost layer.
2)
Find out the landforms found in your area and note them down.
Answer
In Maharashtra, important landforms include mountains, hills and plateaus.
The Sahyadri (Western Ghats) is an important mountainous region of Maharashtra. Hills and plateaus are also found in different parts of the state.
3)
Collect information about such landforms with the help of your parents and present it in class.
Answer
A desert is a dry landform that receives very little rainfall and has very little vegetation. It may have sand, rocks or gravel over large areas.
The Thar Desert is an important desert in India. It is mainly located in Rajasthan. It has a hot and dry climate with very little rainfall.
We collected this information with the help of our parents and presented it in the class.
Activity
1)
Observe the above picture and identify the landforms.
Solution
The landforms shown in the picture are:
1.
Mountains
2.
Plateau
3.
Valley
4.
Plain
5.
Island