In NCERT Class 7 Geography Chapter 3 Our Changing Earth, students learn about the dynamic processes that shape the Earth’s surface. It talks about concepts like weathering, erosion, and deposition, shedding light on how they influence landscapes. The chapter emphasizes the role of natural forces, such as wind, water, and glaciers, in sculpting the Earth’s features. Students learn about different landforms, like mountains, plateaus, and plains, and the processes responsible for their formation. The chapter also touches upon the Earth’s structure, including the core, mantle, and crust, providing a basic understanding of the planet’s composition. It also introduces the concept of earthquakes and volcanoes, explaining their causes and effects. By the end of the chapter, students gain a comprehensive understanding of the dynamic forces that continually shape and transform the Earth’s surface.
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Important Definitions in NCERT Class 7 Geography Chapter 3
- Lithospheric plates: The earth’s crust consists of several large and some small, rigid, irregularly shaped plates which carry continents and the ocean floor.
- Volcano: A volcano is a vent in the earth’s crust through which molten material erupts suddenly.
- Earthquakes: When the Lithospheric plates move, the surface of the earth vibrates. The vibrations can travel all around the earth. These vibrations are called earthquakes.
- Focus: The place in the crust where the movement starts is called the focus.
- Epicentre: The place on the surface above the focus is called the epicentre.
- Glacial moraines: As the ice melts they get filled up with water and become beautiful lakes in the mountains. The material carried by the glacier such as rocks big and small, sand and silt gets deposited. These deposits form glacial moraines.
- Mushroom rocks: An active agent of erosion and deposition in the deserts is wind. In deserts, you can see rocks in the shape of a mushroom, commonly called mushroom rocks.
- Erosion: Erosion is the wearing away of the landscape by different agents like water, wind and ice. The eroded material is carried away or transported by water, wind, etc. and eventually deposited.
Important Questions and Answers in NCERT Class 7 Chapter 3 Our Changing Earth
1. Answer the following questions.
(i) Why do the plates move?
Ans. The movement of molten magma inside the earth results in the movement of plates.
(ii) What are exogenic and endogenic forces?
Ans. The movement of these plates causes changes on the surface of the earth. The earth’s movements are divided on the basis of the forces which cause them. The forces which act in the interior of the earth are called Endogenic forces and the forces that work on the surface of the earth are called Exogenic forces.
(iii) What is erosion?
Ans. Erosion is the wearing away of the landscape by different agents like water, wind and ice. The eroded material is carried away or transported by water, wind, etc. and eventually deposited.
(iv) How are floodplains formed?
Ans. At times the river overflows its banks. This leads to the flooding of the neighbouring areas. As it floods, it deposits layers of fine soil and other material called sediments along its banks. This leads to the formation of a flat fertile floodplain.
(v) What are sand dunes?
Ans. When the wind blows, it lifts and transports sand from one place to another. When it stops blowing the sand falls and gets deposited in low hill–like structures. These are called sand dunes.
(vi) How are beaches formed?
Ans. The sea waves deposit sediments along the seashores. This results in the formation of beaches.
(vii) What are oxbow lakes?
Ans. When the river enters the plains, it twists and turns forming large bends known as meanders. In due course of time, the meander loops start to cut off the river and form cut-off lakes, known as the oxbow lakes.
2. Tick the correct answer.
(i) Which is not an erosional feature of sea waves?
(c) Sea cave
(ii) The depositional feature of a glacier is:
(iii) Which is caused by the sudden movements of the earth?
(iv) Mushroom rocks are found in:
(b) River valleys
(v) Ox bow lakes are found in:
(b) River valleys
3. Match the following.
|(i) Glacier||(a) Seashore|
|(ii) Meanders||(b) Mushroom rock|
|(iii) Beach||(c) River of ice|
|(iv) Sand dunes||(d) Rivers|
|(v) Waterfall||(e) Vibrations of earth|
|(vi) Earthquake||(f) Sea cliff|
|(g) Hard bedrock|
|(i) Glacier||(c) River of ice|
|(ii) Meanders||(d) Rivers|
|(iii) Beach||(a) Seashore|
|(iv) Sand dunes||(h) Deserts|
|(v) Waterfall||(g) Hard bedrock|
|(vi) Earthquake||(e) Vibrations of earth|
4. Give reasons.
(i) Some rocks have the shape of a mushroom.
Ans: Some rocks have the shape of a mushroom because, in deserts, wind erodes the lower section of the rock more than the upper section, which makes the base of the rock narrow and the upper part wide, giving it the shape of a mushroom.
(ii) Flood plains are very fertile.
Ans: Flood plains are very fertile because at times when river water overflows, it results in the flooding of the neighbouring areas. This deposits a layer of fine soil and other sediments on the banks of the river, which leads to fertile flood plains.
(iii) Sea caves are turned into stacks.
Ans: When the cavities in the sea caves become bigger and bigger, only the roof of the caves are left, which forms sea arches. Further, due to erosion, the roof vanishes and only the walls stay intact, turning the sea caves into stacks.
(iv) Buildings collapse due to earthquakes.
Ans: When the lithospheric plates move, the surface of the earth vibrates and then these vibrations travel outwards from the epicentre in the form of waves, which leads to sudden movement and results in the collapse of buildings.
📌Check out Class 6 Geography Notes:
Ans: The earth’s crust consists of several large and some small, rigid, irregularly shaped plates which carry continents and the ocean floor.
Ans: A volcano is a vent in the earth’s crust through which molten material erupts suddenly.
Ans: When the Lithospheric plates move, the surface of the earth vibrates. The vibrations can travel all around the earth. These vibrations are called earthquakes.
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