Std 8 Social Science: Chapter 03 In Search of Earth's Secrets - Questions and Answers

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Class 8 Social Science Questions and Answers - Chapter 03: In Search of Earth's Secrets- Questions and Answers
1.What are the limitations in collecting information about the mysteries of the Earth's interior directly?
- The temperature and pressure inside the Earth increase with depth.
- The variations in pressure are due to the weight exerted by the overlying layers.

2.What are the different sources from which we get information on the Earth's interior?
- From the materials reaching the Earth's surface through volcanic eruptions.
- Data collected from mines.
- Analysis of the propagation of waves generated during earthquakes.

3.Observe the given figure and identify earth layers.
- Crust
- Mantle
- Outer Core
- inner Core

4. lists out the features of the different layers of the Earth.
- Based on the analysis of the waves generated during earthquakes, the Earth has been divided into different layers
i) Crust
•The comparatively thin outer shell of the Earth.
•Approximately 40 km thick.
•Two parts- continental crust oceanic crust.
Continental crust and oceanic crust
- As silica and alumina are the chief contents, the continental crust is also known as SIAL.
- As silica and magnesium are the chief contents, the oceanic crust is also known as SIMA.
ii) Mantle
•Located beneath the crust.
•Extends up to 2900 km from the crust.
•Two parts- upper mantle, lower mantle.
Upper mantle and Lower mantle
Upper mantle
- The upper mantle, made up of silicon compounds, is in a solid state.
Lower mantle
- The lower mantle, located beneath the upper mantle, is in a semi-liquid state.
iii) Core
•Central part of the Earth.
•From 2900 km to 6371 km
•Two parts- outer core, inner core.
Outer core and inner core
- The materials in the outer core are in a molten state.
- Due to the high pressure prevailing at the centre, the inner core is in a solid state. As it is mainly made up of the minerals nickel (Ni) and iron (Fe), it is also known as NIFE.

5. The inner core of the earth remains solid. Why?
- Due to the high pressure prevailing at the centre, the inner core is in a solid state.

6. Write a note on the lightest layer of the earth layer.
- Lightest layer - crust 
- Approximate thickness 40 km 
- Two parts -Continental crust and oceanic crust.

7. Which of the following is the deepest layer of the Earth?
(Mantle, outer core, crust, inner core)
- Inner Core

8. Below are the names of the different layers of the earth’s interior. Arrange them in order from surface to interior. 
(Outer core, Inner core, Crust, Mantle)
- Crust - Mantle -Outer core- Inner core

9. Explain the terms Lithosphere and Asthenosphere.
-  The crust and the upper part of the mantle together are known as the lithosphere.
-  The part beneath the lithosphere, where the materials exist in a partially molten state is known as the asthenosphere.

10. Write a short note – Lithosphere
-  The crust and the upper part of the mantle together are known as
the lithosphere.
- The lithosphere is made ('lithos' means rock) of rocks.
-  Rocks of different colours and hardness. This diversity is due to its
constituents.
- The constituents of rocks are called minerals.
- More than two thousand minerals such as silica, mica, hematite, bauxite, etc have been identified on earth.

11. Classify the rocks based on the mode of formation.
• Igneous rocks- Formed by the molten rock material rising through
the fissures in the crust and solidifying either on the surface of the Earth or within the crust itself.
 Eg:- granite, basalt.
• Sedimentary rocks- Rocks undergo weathering in course of time. The
debris so formed will be deposited in the low regions as layers. These materials gradually get lithified and transformed into sedimentary rocks.
 Eg:- sandstone, limestone.
• Metamorphic rocks - When rocks undergo physical and chemical changes due to high temperature and pressure metamorphic rocks are formed.
- Eg:- marble, slate.

12. Why Igneous rocks are called primary rocks?
- All other rock types are formed from igneous rocks, they are also
called primary rocks.
13. Sedimentary rocks are also called stratified rocks. Why?
- The sedimentary rocks are formed in layers, so they are also known
as stratified rocks.

14. Which type of rock is prominent in Kerala?
- Metamorphic rocks.

15. What is the rock cycle?
- The rocks may not remain in their original form forever.
- They are subjected to several changes over time.
-  Rocks from one form to other


16. What is weathering?
- Disintegration or decomposition of rocks is known as weathering.

17. Make a flowchart showing different types of weathering.

18. What are the human activities that lead to the weathering of
rocks?
- Quarrying
- Destruction  of hills
- Minning
- Construction of buildings

19. Weathering helps humans in many ways. Write examples.
-Minerals in rocks get extracted
- Helps in mining
- Causes soil formation

20. Explain how flora and fauna can affect weathering.
- By penetration the roots of plants into the gaps of the rocks
- Through the decomposition of flora and fauna
- Burrowing of animals

21. How is soil formed?
- The soil is formed by prolonged processes like weathering of rocks
and decomposition of organic matter.

22. What are the different factors influencing soil formation?
- Climate
- Topography
- Parent rocks
- Time
- Plants and Animals

23. What are the uses of soil?
- For construction purposes
- Making clay pots
- Agriculture purpose
- Making of bricks
- Making ornaments

24. Write the importance of soils.
- Without soil, there won't be any plants or animals.
-  Soil is one of the important factors that makes life on the earth
possible.
-  The green plants absorb nutrients from the soil and prepare food with the help of sunlight. Humans and other animals consume these plants.
- When plants and animals die, they return to the soil.
- For the function of a food chain 

25. Soil gets depleted due to various human activities. List out some activities.
- Deforestation,
- Destruction of hills
-  Unscientific agricultural activities.
- Non-degradable materials like plastic cause soil pollution.
- Overuse of chemical fertilizers that alter the structure of the soil.
- Unscientific construction and quarrying.
- Use of agricultural land for non-agricultural purposes.
- Draining wastewater into the soil on a large scale.
- Overgrazing.
26. Conservation of soil is essential for the sustenance of life. Justify.
- Once the topsoil is lost what is left behind is barren land or rocky
surface.
- It will take thousands of years for the topsoil to regenerate.
- Topsoil is essential for the continued sprouting of life.
- For this conservation is the only solution.

27. Write different steps to conserve soil.
- Check deforestation
- Terrace farming
- Crop rotation
- Terrace farming along hill slopes
- Construction of check dams.
- Planting of trees.

28. Which day we celebrate World Soil Day? Write its importance.
- 5th December.
- For creating awareness among the people about the importance of soil.

29. Which year we celebrated as International Year of Soils?
- 2015

30. Read the indicators and identify the rock type. Give an example for each.
(i) Formed by the lithification of rock debris deposited in the lower regions.
- Sedimentary rocks-limestone
(ii) Formed by the solidification of molten rock materials.
- Igneous rocks-basalt.

31. The carbon dioxide dissolved in rainwater causes weathering of rocks on the Earth's surface. Identify the type of weathering.
- Chemical weathering.

32. Find out different types of soil in India and in Kerala. Make a table.


33. What kind of weathering is most active in the desert? Why?
- Physical weathering
- High temperature causes the expansion of minerals and thereby disintegrate.

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