DAV Class 7 SST Solution Chapter 3 The Surface and Interior of the Earth
DAV School Books Class 7 SST Solution Chapter 3 The Surface and Interior of the Earth all Question Answer. DAV Class 7 3rd Chapter The Surface and Interior of the Earth full Chapter explanation by expert teacher.
DAV School Books Class 7 SST Solution Chapter 3 The Surface and Interior of the Earth:
(A) Tick the correct option.
(1) Living organisms do not survive inside the earth due to –
(a) High temperature
(b) Cool temperature
(c) Presence of gases
(d) Excessive water
Ans: (a) High temperature.
(2) Earthquakes and volcanoes are caused by –
(a) Internal disturbance
(b) External disturbance
(c) Over-population
(d) Gradation
Ans: (a) internal disturbance
(3) Respective layers of the earth from top to bottom are –
(a) Crust, core, mantle
(b) Crust, mantle, core
(c) Core, crust, mantle
(d) Core, mantle, crust
Ans: (b) Crust, mantle, core
(4) The full form of SIMA is –
(a) Silica and mica
(b) Silica and magnesium
(c) Silica and magma
(d) Silica and Magnetite
Ans: (b) Silica and magnesium
(5) The original rock from which Gneiss formed is –
(a) Limestone
(b) Shale
(c) Granite
(d) Quartzite
Ans: (c) Granite
(B) Fill in the blanks.
(1) Earth was formed about ______ million years ago.
Ans: 4600
(2) The behaviour of _____ waves tell us about the earth’s interior.
Ans: Seismic.
(3) The ____ of crust varies from place to place.
Ans: Thickness.
(4) Rocks are classified into three groups on the basis of their _____.
Ans: Formation.
(5) The _____ of the earth is rich in iron and nickel.
Ans: Core.
(D) Answer the following questions in brief –
(1) What is the special feature of sedimentary rocks?
Ans: Special features of sedimentary rocks are-
(i) formed by the deposition of the small rock particles, carried away by the rivers.
(ii) fossil fuels such as coal, oil, natural gas are found over here. They are formed after getting trapped or buried under the layers .
(iii) clay, shale, chalk are such examples of sedimentary rocks.
(2) How are metamorphic rocks formed?
Ans: Formation of metamorphic rock- internal heat and pressure change the character and appearance of the igneous and sedimentary rocks. These changed rocks are called metamorphic rocks. For example, – from granite to genesis.
(3) What is lava?
Ans: Lava- Temperature inside the earth is too high and it can convert all the solid rocks into molten state. When this kind of molten semi liquid material comes through the cracks of the earth crust is called lava.
(4) Why are igneous rocks called the primary rocks?
Ans: Igneous rocks are called primary rocks because on the earth surface the rock which was formed very first was igneous rocks. It was formed by cooling and solidification of Magma came from the earth crust due to intensive heat and pressure.
(5) What are sediments?
Ans: Broken small pieces of igneous rock due to weathering and denudation carried away by the river and are deposited on the river or sea bed. These small deposits are called sediments.
(E) Answer the following questions –
(1) Differentiate between the P-Wave and the S-Wave.
Ans: Differences between P wave and S wave-
They both are seismic waves. P waves are called primary waves and S waves are called secondary waves. P waves are faster than the secondary waves. P waves can pass through the solid and liquid medium while S waves can pass through only solid medium.
(2) Write two characteristics of each of the following:
(a) Crust
(b) Mantle
(c) Core
Ans: Crust –
(i) Crust is the thin layer covered the outside of Earth.
(ii) Crust is thin under the ocean floor and thick under the continents.
The Mantel –
(i) It is the layer exists under the Crust .
(ii) It is not a homogeneous layer.
The Core –
(i) it is the inner most layer of the Earth.
(ii) rich variety of Nickel and iron can be found over here.
(3) What are fossil fuels? Name any two fossil fuels and specify their importance.
Ans: Fossil fuels -coal ,oil and natural gas are called fossil fuels. Remaining of animals and plants who got burried or trapped under the layers and later on converted into coal, oil and natural gas are called fossil fuels. These fossil fuels have much economic importance. Such as the energy emitted from the coal is used in the power plants. Again in transport system, factories etc. Oil is most essential element.
(4) Why is the knowledge of the earth’s interior based on indirect observation?
Ans: Knowledge of Earth’s interior is based on indirect observation because of the temperature of the Earth. The temperature of the earth is very high at the interior and the intensive heat does not allow anyone to dig the ground and get entered.
(5) What are minerals? On what basis can the minerals be identified? Give examples.
Ans: Minerals-solid inorganic substance made by natural process is called minerals. On the basis of the structure and features different minerals can be identified. Such as black greasy and softest mineral grafite is identified by its colour, hardness and lustre.
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