Chapter-3: Our changing Earth

These NCERT Class 7 Geography Chapter 3 notes explain how the surface of the Earth is constantly changing due to natural forces. The chapter helps students understand that the Earth is dynamic and not fixed.

Our Changing Earth introduces endogenic forces that act inside the Earth and exogenic forces that act on the Earth’s surface. It also explains important processes like earthquakes, volcanoes, weathering, erosion and deposition.

This chapter builds a clear understanding of how various landforms are created and modified over time.

1. Introduction

• The Earth is not fixed and its surface keeps changing continuously.
• Changes happen due to forces acting inside the Earth and on the surface of the Earth.
• Internal pressure raises or builds landforms over time.
• External forces cut, wear and reshape the land surface.
• The Earth changes slowly but constantly over long periods.

2. Endogenic forces

• Endogenic forces act inside the Earth.
• These forces are responsible for building or raising landforms.
• They cause sudden movements like earthquakes.
• They lead to volcanic eruptions and mountain building.
• Plate movements are a result of endogenic forces.

3. Exogenic forces

• Exogenic forces act on the surface of the Earth.
• These forces wear down existing landforms.
• Rivers play an important role in erosion and deposition.
• Wind reshapes land in dry and desert regions.
• Sea waves and glaciers also modify the land surface.

4. Earthquakes

• An earthquake is a sudden shaking of the Earth’s surface.
• It is caused by movement of tectonic plates inside the Earth.
• Energy is released along fault lines.
• Earthquakes are measured using a seismograph.
• The Richter scale measures the intensity of earthquakes.

5. Bhuj earthquake case study

• A major earthquake occurred on 26 January 2001.
• The epicentre was Bhuj in Gujarat.
• The earthquake measured 6.9 on the Richter scale.
• Thousands of people lost their lives.
• Buildings, roads, water supply and electricity were badly damaged.

6. Earthquake preparedness

• Earthquakes cannot be predicted in advance.
• Preparedness can reduce loss of life and property.
• Staying under strong tables provides safety.
• Standing near inner walls is safer than open areas.
• Avoid windows and heavy objects during earthquakes.

7. Volcanoes

• A volcano is an opening in the Earth’s crust.
• Lava, ash and gases come out during eruptions.
• Volcanoes help in the formation of new landforms.
• Volcanic soil is often very fertile.
• Volcanic eruptions can also cause destruction and air pollution.

8. Weathering

• Weathering is the breaking of rocks into smaller pieces.
• It happens at the same place without movement of material.
• Heat and cold cause physical weathering.
• Rainwater leads to chemical weathering.
• Roots of plants cause biological weathering.

9. Erosion

• Erosion is the wearing away of the land surface.
• The eroded material is carried away from its original place.
• Running water is a major agent of erosion.
• Wind erodes land in dry regions.
• Ice and sea waves also cause erosion.

10. Deposition

• Deposition is the process of laying down eroded material.
• It occurs when the transporting force becomes weak.
• Rivers deposit soil in plains.
• Deposited material increases soil fertility.
• Deposition creates new landforms over time.

11. Landforms made by rivers

• Rivers shape land differently in different stages of flow.
• In the upper course, rivers form waterfalls and gorges.
• In the middle course, rivers create meanders.
• In the lower course, rivers form flood plains.
• Rivers also form deltas at their mouths.

12. Work of wind

• Wind plays a major role in shaping desert regions.
• Strong winds carry loose sand particles.
• Sand dunes are formed due to deposition by wind.
• Mushroom rocks are created by wind erosion.
• Wind action is common in deserts like Rajasthan.

13. Work of sea waves

• Sea waves continuously hit coastal landforms.
• Sea caves are formed by wave erosion.
• Sea arches and sea stacks develop over time.
• Waves also deposit sand along coastlines.
• Beaches are common depositional features.

14. Work of glaciers

• Glaciers are slow-moving rivers of ice.
• They are found in mountain regions like the Himalayas.
• Glaciers erode land as they move downhill.
• U-shaped valleys are formed by glacial erosion.
• Moraines are deposits of rock debris left by glaciers.

15. Importance of earth-shaping processes

• These processes help in the formation of plains, mountains and plateaus.
• They play an important role in soil formation.
• Natural resources are distributed due to these processes.
• They shape the surface of the Earth continuously.
• Without these forces, the Earth would be lifeless and flat.

16. Important keywords

• Endogenic force acts inside the Earth.
• Exogenic force acts on the Earth’s surface.
• Earthquake is sudden shaking of the Earth.
• Seismograph measures earthquake waves.
• Richter scale measures earthquake intensity.
• Volcano, weathering, erosion and deposition shape landforms.

Understanding NCERT Class 7 Geography Chapter 3 is important to learn how natural forces shape the Earth’s surface continuously. The chapter clearly explains the role of rivers, wind, glaciers and sea waves in forming different landforms.

The ideas discussed in Our Changing Earth help students understand physical geography concepts and are highly useful for school examinations and foundation-level preparation.

Continue reading NCERT Class 7 Geography Chapter 4 – Air to understand the composition of the atmosphere, weather and climate.

FAQs

Q1. What are endogenic forces?
Endogenic forces are internal forces that act inside the Earth and create landforms.

Q2. What are exogenic forces?
Exogenic forces act on the Earth’s surface and wear down landforms.

Q3. What is an earthquake?
An earthquake is a sudden shaking of the Earth’s surface caused by movement inside the Earth.

Q4. What is weathering?
Weathering is the breaking of rocks into smaller pieces at the same place.

Q5. Why is this chapter important for exams?
It explains Earth-shaping processes and landforms, making it important for school exams and foundation-level preparation.