Chapter 3 Our Changing Earth Summary with NCERT Solution 2025

Class 7 Social Science Geography NCERT Solution with Summary

Class 7 Chapter 3 Our Changing Earth

Summary of "Our Changing Earth"

The Earth is constantly changing, and these changes are caused by forces that work both inside and on the surface of the Earth. The chapter explains how these forces shape the landforms we see today.

1. Forces that Change the Earth

There are two main types of forces:

- Endogenic Forces: These are forces that come from inside the Earth, like the movement of molten magma in the Earth's mantle. This movement causes the Earth's crust (the outer layer) to break into large pieces called lithospheric plates. These plates move very slowly, just a few millimeters each year, but their movement can cause big changes like earthquakes and volcanoes.

- Exogenic Forces: These are forces that work on the surface of the Earth, like wind, water, and ice. They wear down the land through processes called weathering (breaking down rocks) and erosion (carrying away the broken pieces). 

 2. Earthquakes and Volcanoes

- Earthquakes: When the lithospheric plates move, they can cause the ground to shake. This shaking is called an earthquake. The point inside the Earth where the earthquake starts is called the focus, and the point directly above it on the surface is called the epicenter. Earthquakes can cause a lot of damage, especially near the epicenter.

- Volcanoes: A volcano is an opening in the Earth's crust through which molten rock (called magma) erupts. When magma reaches the surface, it is called lava. Volcanoes can also cause destruction, but they also create new landforms.

3. Landforms Created by Rivers

Rivers play a big role in shaping the land. Here’s how:

- Waterfalls: When a river flows over hard rocks, it can create a waterfall.

- Meanders: As a river flows through a plain, it twists and turns, forming loops called meanders.

- Ox-bow Lakes: Over time, the loops of a meander can get cut off from the main river, forming a ox-bow lake.

- Floodplains: When a river floods, it deposits fine soil and sediments along its banks, creating a flat, fertile area called a floodplain.

- Deltas: When a river reaches the sea, it slows down and deposits sediments, forming a delta.

 4. Landforms Created by Sea Waves

Sea waves also shape the coastlines:

- Sea Caves: Waves erode rocks to form hollow caves.

- Sea Arches: When caves get bigger, they can form arches.

- Stacks: When the top of an arch collapses, it leaves behind tall rock pillars called stacks.

- Beaches: Waves deposit sand and sediments along the shore, forming beaches.

5. Landforms Created by Ice

Glaciers, which are like "rivers of ice," also change the landscape:

- They carve out deep hollows in the mountains, which can turn into lakes when the ice melts.

- The rocks and sediments carried by glaciers get deposited, forming glacial moraines.

 6. Landforms Created by Wind

In deserts, wind is a powerful force:

- Mushroom Rocks: Wind erodes the lower part of rocks more than the top, creating mushroom-shaped rocks.

- Sand Dunes: Wind carries sand and deposits it in low hill-like structures called sand dunes.

- Loess: Fine sand carried by wind over long distances can form large deposits called loess.

 7. Earthquake Preparedness

Earthquakes cannot be predicted, but we can prepare for them. During an earthquake, it’s important to take shelter under strong furniture like tables or desks and stay away from windows, mirrors, and heavy objects that could fall.

~~The END~~

Chapter 3 Our Changing Earth

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