Kerala Syllabus Class 7 Social Science: Chapter 05 Our Earth - Questions and Answers | Teaching Manual 


Questions and Answers for Class 7 Social Science (English Medium) നമ്മുടെ ഭൂമി | Text Books Solution Social Science (English Medium) Chapter 05 Our Earth - Teaching Manual | Teachers Handbook
ഈ അധ്യായത്തിന്റെ Teachers Handbook, Teaching Manual എന്നിവ ഡൗൺലോഡ് ചെയ്യാനുള്ള ലിങ്ക് ചോദ്യോത്തരങ്ങളുടെ അവസാനം നൽകിയിട്ടുണ്ട്.

ഈ ബ്ലോഗ് ഉടമയുടെ രേഖാമൂലമുള്ള അനുമതിയില്ലാതെ ഈ ബ്ലോഗിൽ നൽകിയിരിക്കുന്ന ചോദ്യോത്തരങ്ങൾ, ഇതേരീതിയിലോ പി.ഡി.എഫ് രൂപത്തിലോ, മറ്റേതെങ്കിലും ഡിജിറ്റലോ, പ്രിന്റഡ് ഉൾപ്പെടെയുള്ള ഏതെങ്കിലും രൂപങ്ങളിലേക്കോ മാറ്റി മറ്റൊരു വെബ്സൈറ്റിലോ, ബ്ലോഗിലോ, യുട്യൂബ്, സോഷ്യൽ മീഡിയാ ഗ്രൂപ്പുകളിലോ ഉൾപ്പെടെ ഒരിടത്തും പ്രചരിപ്പിക്കാൻ പാടില്ലാത്തതാകുന്നു.

Std 7: Social Science Chapter 05: Our Earth - Questions and Answers
♦ What is the temperature at the center of the interior?
• 5500 degree Celsius 

♦ What is the distance from the surface to the center of the Earth?
• 6371 km

♦ How did we get the information about the interior of the earth? 
• By examining materials that reach the Earth’s surface through volcanic eruptions
• From the information collected from mines
• By analyzing the motion of waves generated during earthquake

♦ Observe the picture. 
What information do you get about the interior of the Earth?
• The interior of the earth is divided into different layers.
• The outermost layer is the Crust.
• Mantle is the layer below the crust.
• The layer below the mantle is the core. It is divided into outer core and inner core.

♦ Prepare a note on the interior of the earth.
i. The Crust
• The crust is the outermost and relatively thin layer of the earth. 
• This layer is made up of solid rocks.
• The crust has two parts namely continental crust and oceanic crust.
• Continental crust is thicker than the oceanic crust. The average thickness is
about 30 kilometres. 
• In mountain areas, continental crust has a thickness of about 70 kilometres, but the average thickness of the oceanic crust is 5 kilometres. 

ii. The Mantle
• Mantle is the layer below the crust. This is relatively thick. 
• It extends up to about 2900 kilometres.
• The part of the earth that comprises crust and upper part of mantle is called lithosphere. 
• The part below the lithosphere, which is in a molten state due to the melting of rock particles (magma) is known as asthenosphere.
• The portion below the asthenosphere is in solid state. 

iii. The Core
• The layer below the mantle is the core. 
• It is divided into outer core and inner core.
• The outer core is in liquid state while the inner core is in solid state. 
• The core is mainly made up of metals like Nickel (Ni) and Iron (Fe). Hence the core is also known as NIFE. 
• The temperature in the inner core is about 5500 degree Celsius.

♦ Which of the following is the deepest layer of the Earth?
(Mantle, outer core, crust, inner core)
• Inner Core

♦ 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

♦ Core is also known as NIFE. What could be the reason?
• The core is mainly made up of metals like Nickel (Ni) and Iron (Fe). Hence the core is also known as NIFE. 
♦ Explain the terms Lithosphere and Asthenosphere.
• The part of the earth that comprises crust and upper part of mantle is called lithosphere. 
• The part below the lithosphere, which is in a molten state due to the melting of rock particles (magma) is known as asthenosphere.

♦ Complete the given diagram by including the features of each layer of the earth’s interior.
♦ The features of each layer of the Earth’s interior are given in the table. Draw ‘😊’ towards the correct ones and ‘☹️’ towards the wrong ones.

• The crust is the outermost solid part of the earth which is made up
  of rocks.		 😊
• Lithosphere is made up of crust and upper mantle 😊
• The asthenosphere is the molten part formed by the molten rock
  particles (magma) 		 😊
• The outer core is in liquid state 😊 
• The continental crust and the oceanic crust are the two parts of the
  crust.		 😊
• The core is also known as NIFE 😊

♦ What is the atmosphere?
The gaseous blanket that covers the earth is known as the atmosphere.

♦ How did the Earth and it's atmosphere transform in the way organisms could survive?
• The Earth which was in a molten hot state at the time of origin, slowly cooled over
in billions of years. 
• This process, released the gases inside the earth. 
• Eventually, an atmosphere of air composed of many gases formed around the Earth
• With the origin of plants, the atmosphere became rich in oxygen as a result of photosynthesis.

♦ How did the gases in the Earth's interior come out?
• The Earth which was in a molten hot state at the time of origin, slowly cooled over
in billions of years. This process released the gases inside the earth. 

♦ How is the atmosphere rich in oxygen?
With the origin of plants, the atmosphere became rich in oxygen as a result of photosynthesis.

♦ It is estimated that 97% of the total atmospheric air is located above the Earth's surface up to an altitude of about -----------. 
29 km

♦ Name the atmospheric gases that play a vital role in sustaining life on Earth.
• Oxygen and carbon dioxide

♦ Apart from Oxygen and Carbon dioxide what are the other gases present in the atmosphere?
• Nitrogen
• Argon
• Neon
• Helium
• Krypton
• Xenon
• Hydrogen
♦ Which is the most abundant gas present in the atmosphere?
Nitrogen

♦ What is the combined percentage of Nitrogen and Oxygen to the total atmospheric composition?
99%

♦ What is evaporation?
The process by which water from the earth’s surface heated by the sun and reaches the atmosphere as vapour is called evaporation.

♦ The presence of water vapour in the atmosphere is only up to ------------ from the earth’s surface. 
90 km

♦ Why fine dust particles in the atmosphere are called Hygroscopic nuclei?
Water vapour condenses around fine dust particles in the atmosphere to form clouds. Hence these fine dust particles in the atmosphere are called Hygroscopic nuclei. 

♦ How do dust particles reach the atmosphere.?
• Lifted from the earth by wind
• Coming out during volcanic eruptions
• Ash produced during burning of meteors
• Dust generated by construction activities 
• Ash and dust generated by wildfires

♦ How the atmosphere helps in the survival of life on earth.
• Causes atmospheric phenomena 
• Protects from harmful sun rays 
• Regulates atmospheric temperature 
• Provides oxygen to living organisms 
• Protects the Earth from meteorites

♦ Write down how each of the following factors helps to sustain life on the earth.
• Atmospheric air - Oxygen, the life-giving gas for humans and other living things, and Carbon dioxide that helps the survival of plants are obtained from the atmosphere.
• Water particles in the atmosphere - Causes cloud formation and rain.
• Dust particles in the atmosphere - Water vapour condenses around fine dust particles in the atmosphere to form clouds.

♦ What is atmospheric pollution?
The mixing up of smoke, toxic gases and other chemicals in the air that alters the composition of atmosphere is known as atmospheric pollution.

♦ What activities cause atmospheric pollution?
• Smoke from industries
• Increasing number of vehicles
• Burning of waste including plastics 
• Burning of agricultural crop residues 
• Use of fireworks 
• Volcanic eruption 
• Use of chemical pesticides

♦ What causes an increase in the level of atmospheric pollution in industrial cities?
Noxious gases emitted from industries, increased number of vehicles, construction activities and high population density all contribute to high levels of air pollution.
♦ What can we do to reduce atmospheric pollution?
• Use public transport 
• Control electricity usage 
• Practice walking and cycling 
• Avoid using large vehicles when travelling alone
• Avoid firewood as much as possible 
• Do not burn garbage 
• Plant more trees
• Reduce the use of fossil fuels  
• Use solar energy

♦ ----------- is a blend of smoke and fog.
Smog

♦ List the layers of the atmosphere?
The atmosphere is classified into five different layers based on temperature conditions.
• Troposphere 
• Stratosphere 
• Mesosphere 
• Thermosphere 
• Exosphere

♦ What are the features of the troposphere?
• It’s the lowermost layer of the atmosphere. It has an average height of 13
kilometre from the earth's surface. 
• The height ranges about 8 kilometre at the poles to 18 kilometre at the equator. This is because the temperature is high in the equatorial region.  
• Dust particles and water vapour are most abundant in this layer. Atmospheric
phenomena such as cloud formation, rain, snow, wind etc. occurs in this layer.
• An important feature of troposphere is that the temperature of the atmosphere
decreases at the rate of 1 degree Celsius for every 165 metres from the surface
of the earth. This is called Normal Lapse Rate.

♦ Why the troposphere is called the most important layer of the atmosphere?
Dust particles and water vapour are most abundant in this layer. Atmospheric
phenomena such as cloud formation, rain, snow, wind etc. occurs in this layer.

♦ Why the high-altitude regions like Ooty, Munnar, Kodaikanal etc. feel cold?
The temperature in the troposphere decreases at 1 degree Celsius for every 165 meters from the surface of the Earth. This is why high-altitude regions like Ooty, Munnar, and Kodaikanal feel cold.

♦ What are the features of the stratosphere?
• It is the layer of atmosphere just above the troposphere. 
• The average height is about 50 kilometres from the earth’s surface. 
• In the stratosphere, the temperature increases after a specific height. 
• The ozone layer is in the stratosphere. It stands at an altitude of about 25 kilometres from the surface. 

♦ The atmosphere layer known as Earth’s Shield?
Ozone layer

♦ In which atmospheric layer is ozone found?
The stratosphere

♦ What is the significance of the Ozone layer?
• The presence of ozone gas in the atmosphere protects the earth by blocking the harmful ultraviolet rays from the sun. 
• If ultraviolet rays reach the earth's surface at an increased rate, it is harmful to living organisms and ecosystems.

♦ What harm does ultraviolet rays cause on the Earth?
• Collapse of the food chain
• Crop damage
• Stunting of plant growth
• Early aging
• Blindness, Cataract
• Skin cancer

♦ Which day is Ozone Day?
September 16

♦ What are the features of the Mesosphere?
• This atmospheric layer extends from about 50 kilometre to 80 kilometre above stratosphere. 
• The phenomenon of decrease in temperature with the increase in height is present in this layer also. 
• At an altitude of about 80 kilometre from the surface, the temperature drops to -100 degrees Celsius. 
• The lowest temperature in the atmosphere is experienced here. 
• Most of the meteors that enter the Earth’s atmosphere burn down in this layer.

♦ Which layer of the atmosphere experiences the lowest temperature of the atmosphere -100 degrees Celsius?
Mesosphere
♦ What are the features of the Thermosphere?
• The thermosphere is the layer of atmosphere that lies about 80 to 400 kilometre
above the mesosphere. 
• The temperature increases with an increase in altitude.
• The lower part of the thermosphere is called the Ionosphere.

♦ In which atmospheric layer is the ionosphere found?
Thermosphere 

♦ Which atmospheric layer enables long-distance transmission of radio waves?
Ionosphere

♦ What are the features of the Exosphere?
• It is the uppermost layer of the atmosphere. 
• The presence of air molecules in the exosphere, which lies above 400 kilometre from the surface, gradually decreases and the layer becomes a part of the outer space. 

♦ The atmospheric layers and their features are given below. Match them correctly.
• Exosphere
- Air molecules gradually reduce and dissolve into space

• Thermosphere
- Located at an altitude of 80 to 400 kilometre 

• Mesosphere
- The layer with the lowest temperature
- The layer where meteors burn to ash

• Stratosphere
- Temperature increases with increase in altitude
- Zone where ozone is present

• Troposphere
- The layer in which temperature decreases at a certain rate according to the increase in height




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