Textbook Solutions: The Changing Face of Earth | Window on the Word Class 7: Solutions, Notes & Worksheets PDF Download

A. Choose the correct answer.

1.
Ans: (c)

2.
Ans: (b)

3.
Ans: (b)

4.
Ans: (a)

5.
Ans: (c)

6.
Ans: (c)

7.
Ans: (a)

8.
Ans: (c)

B. Mark the sentences as True or False. Correct the statements that are false.

1.
Ans: False
Earthquakes and volcanoes are caused by endogenic processes.

2.
Ans: True.

3.
Ans: False.
The point inside the Earth at which the earthquake originates is the focus

4.
Ans: False.
A sand dune is a feature of wind erosion.

5.
Ans: False.
U-shaped valleys are created by glaciers.

C. Give reasons for the following statements

1.
Ans: The surface of the Earth is in a state of constant change due to the action of endogenic and exogenic forces. Endogenic forces that originate deep below the Earth's surface cause the formation of new landforms like mountains, volcanoes, and rift valleys. Exogenic forces that act on the surface shape the Earth by forming river valleys, plains, deserts, and beaches.

2.
Ans: The edges of the Pacific Ocean are called the Ring of Fire because over two-thirds of the world's volcanoes lie along these edges. This area is prone to high volcanic activity and earthquakes due to the movement of tectonic plates.

3.
Ans: Some rocks in deserts have the shape of a mushroom because of the action of wind. Wind is a potent agent of erosion and deposition in deserts. It can shape rocks into different forms, including a mushroom shape, due to its uninterrupted force.

D. Answer In one or two sentences

1.
Ans: Endogenic forces originate deep below the Earth's surface and are responsible for the formation of landforms like continents and mountains, while exogenic forces originate and act on the Earth's surface, forming landforms like river valleys and deserts.

2.
Ans: Tectonic plates are several pieces into which the Earth's lithosphere is broken up, including the crust and the upper mantle.

3.
Ans: Fold mountains are formed when two tectonic plates push towards each other, causing the land between them to be thrown up in a series of massive folds.

4.
Ans: The focus of an earthquake is the point inside the Earth where the earthquake originates, while the epicenter is the point on the Earth's surface directly above the focus.

5.
Ans: Gradation is the process of making the land level or flat, and the agents of gradation are natural forces like water, wind, and ice that act on the Earth's surface.

6.
Ans: Sand dunes are landforms created by the movement of sand by wind or water, and they are typically found in deserts.

7.
Ans: Sea cliffs, beaches, and sand bars are three landforms formed by sea waves.

8.
Ans: Glaciers are slow-moving rivers of ice formed by the accumulation and compaction of snow over a long period of time.

E. Answer in a paragraph

1.
Ans: Tectonic plates are pieces into which the Earth's lithosphere, consisting of the crust and the upper mantle, is broken up. These plates are constantly in motion due to heat energy released from deep inside the Earth. This heat from the Earth's liquid outer core creates massive convection currents in the semi-liquid lower mantle, which push the tectonic plates floating on the mantle in different directions.

2.
Ans: Block mountains and rift valleys are formed when two tectonic plates move away from each other. This movement causes fractures or faults to appear on the Earth's surface. When the land between two parallel faults drops, a rift valley is formed. Conversely, when the land between two faults is pushed upwards, a block mountain is created. The process can be visualized as two parallel lines (the faults) with the area between them either rising (forming a block mountain) or falling (forming a rift valley).

3.
Ans: A volcano is an opening or vent in the Earth's crust through which magma, ash, and smoke erupt. Magma that flows onto the Earth's surface is called lava, which solidifies over millions of years to form volcanic mountains. A typical volcano has features such as a vent, a crater, a magma chamber, and layers of solidified lava and ash. Volcanoes are generally found along the boundaries of tectonic plates.

4.
Ans: The three stages of a river are the upper course, middle course, and lower course. In the upper course, the river flows swiftly through mountains, eroding the land. In the middle course, the river's speed decreases as it enters plains, forming meanders and floodplains. In the lower course, the river's flow slows down further as it approaches the sea, depositing sediments and forming distributaries.

5.
Ans: Waterfalls are formed when a river flows over a steep drop, while sea stacks are formed by the erosion of cliffs by waves. Wave-cut platforms are formed when waves erode the base of coastal cliffs, and U-shaped valleys are formed by the erosive action of glaciers.