B. Fill in the Blanks
- Earth was formed about 4,600 million years ago.
- The behaviour of seismic waves tells us about the earth’s interior.
- The thickness of the crust varies from place to place.
- Rocks are classified into three groups on the basis of their formation.
- The core of the earth is rich in iron and nickel.
C. Give a Single Term for Each of the Following Statements
- It is the hardest substance.
Answer: Diamond - The molten rock material present inside the earth.
Answer: Magma - Rocks which are formed due to cooling and solidification of magma inside the earth.
Answer: Intrusive Igneous Rocks - Shaking and trembling of the earth’s surface.
Answer: Earthquake - A naturally occurring solid substance made up of a mixture of minerals.
Answer: Rock
D. Answer the Following Questions in Brief
Chapter: The Earth and Changes on It (Tata DAV Class 7 Social Science)
1. What is the special feature of sedimentary rocks?
Answer:
Sedimentary rocks are formed by the deposition and compaction of sediments in layers. Their special feature is that they are arranged in distinct layers or strata and often contain fossils of plants and animals.
2. How are metamorphic rocks formed?
Answer:
Metamorphic rocks are formed when existing igneous or sedimentary rocks undergo changes due to intense heat and pressure inside the Earth. For example, limestone changes into marble and granite changes into gneiss.
3. What is lava?
Answer:
Lava is the molten rock material that comes out onto the Earth’s surface through volcanic eruptions. Inside the Earth, this molten material is called magma.
4. Why are igneous rocks called the primary rocks?
Answer:
Igneous rocks are called primary rocks because they were the first rocks to be formed from the cooling and solidification of molten magma. All other types of rocks are directly or indirectly derived from them.
5. What are sediments?
Answer:
Sediments are small particles of rocks, minerals, and organic matter that are formed by the weathering and erosion of rocks. These particles are carried by wind, water, or glaciers and get deposited in layers, eventually forming sedimentary rocks.
E. Answer the Following Questions
Chapter: The Earth and Changes on It (Tata DAV Class 7 Social Science)
1. Differentiate between the P-Wave and the S-Wave.
| Basis | P-Waves (Primary Waves) | S-Waves (Secondary Waves) |
|---|---|---|
| Full Form | Primary Waves | Secondary Waves |
| Speed | Travel the fastest and reach first | Travel slower and reach after P-waves |
| Nature | Longitudinal waves; particles move back and forth in the direction of the wave | Transverse waves; particles move at right angles to the direction of the wave |
| Medium | Can travel through solids, liquids, and gases | Can travel only through solids |
| Importance | Help scientists understand the Earth’s internal structure | Their inability to pass through liquids proves that the outer core is molten |
Humanistic Understanding:
The study of P-waves and S-waves shows how scientific observations help us understand the hidden interior of our planet. This knowledge enables scientists to study earthquakes better and develop safety measures that protect human lives and property.
2. Write two characteristics of each of the following:
(a) Crust
- The crust is the outermost and thinnest layer of the Earth.
- It is made mainly of rocks and minerals and forms the continents and ocean floors.
(b) Mantle
- The mantle lies below the crust and is the thickest layer of the Earth.
- It consists of hot, semi-molten rocks called magma, which cause volcanic and tectonic activities.
(c) Core
- The core is the innermost and hottest layer of the Earth.
- It is mainly composed of iron and nickel (NIFE) and has extremely high temperatures.
Humanistic Understanding:
Each layer of the Earth performs a vital role in making our planet dynamic and suitable for life. Understanding these layers helps us appreciate the complexity of nature and encourages us to use Earth’s resources wisely and responsibly.
3. What are fossil fuels? Name any two fossil fuels and specify their importance.
Answer:
Fossil fuels are fuels formed from the remains of plants and animals that lived millions of years ago and were buried under layers of sediments. Over time, heat and pressure converted these remains into fuels.
Two examples of fossil fuels are:
- Coal
- Petroleum
Importance of Fossil Fuels:
- They are major sources of energy for homes, industries, and transportation.
- Coal is used for generating electricity and in industries.
- Petroleum is refined into petrol, diesel, kerosene, and other products used in vehicles and industries.
Humanistic Understanding:
Fossil fuels have greatly contributed to human development by powering industries and transportation. However, they are exhaustible and their excessive use causes pollution. Therefore, every individual should use energy responsibly and promote renewable sources of energy to protect the environment for future generations.
4. Why is the knowledge of the Earth’s interior based on indirect observation?
Answer:
The Earth’s interior is extremely hot and lies thousands of kilometres below the surface. It is impossible for humans to directly observe or reach the deeper layers of the Earth. Therefore, scientists study the Earth’s interior through indirect methods, such as:
- The behaviour of seismic waves generated during earthquakes.
- Information obtained from volcanic eruptions and deep mining activities.
These observations help scientists estimate the composition and structure of the Earth’s interior.
Humanistic Understanding:
This shows the remarkable ability of human beings to gain knowledge through observation, reasoning, and scientific inquiry. Even without direct access to the Earth’s interior, scientists continue to deepen our understanding of our planet and help society prepare for natural disasters.
5. What are minerals? On what basis can the minerals be identified? Give examples.
Answer:
Minerals are naturally occurring inorganic substances found in the Earth’s crust. They have a definite chemical composition and specific physical properties.
Minerals can be identified on the basis of their:
- Colour
- Hardness
- Lustre (shine)
- Streak
- Density
- Cleavage or fracture
Examples of minerals:
- Quartz
- Mica
- Feldspar
- Diamond
- Iron ore
Humanistic Understanding:
Minerals are precious gifts of nature that provide the raw materials needed for our daily lives and industrial development. Since mineral resources are limited and take millions of years to form, it is our responsibility to use them carefully, avoid wastage, and promote conservation for the benefit of future generations.
Also read: Components of Environment Class 7 SST Chapter 1 DAV Solutions, Notes, Question Answers & MCQs
class 6: Class 6th Science
Tata DAV Class 7 Social Science Chapter 2: The Earth and Changes on It Solutions – Summary
Tata DAV Class 7 Social Science Chapter 2, The Earth and Changes on It, explains how our planet is continuously changing due to various natural processes. This chapter helps students understand the structure of the Earth and the forces that shape its surface. The chapter is an important part of the Tata DAV Class 7 Social Science curriculum and is frequently searched by students looking for complete solutions and question answers.
The Earth consists of different layers, namely the crust, mantle, and core. The crust is the outermost layer where we live, while the mantle lies beneath it. At the centre is the core, which is extremely hot and composed mainly of iron and nickel. Understanding these layers is essential for answering many questions from DAV Class 7 SST Chapter 2.
The chapter also discusses the internal and external forces that bring changes to the Earth’s surface. Internal forces originate from within the Earth and cause events such as earthquakes and volcanic eruptions. These forces can lead to the formation of mountains, plateaus, and valleys. External forces, on the other hand, work on the Earth’s surface through weathering, erosion, and deposition. Wind, water, and glaciers continuously reshape landforms over long periods.
Another important topic covered in The Earth and Changes on It Solutions Class 7 is the movement of tectonic plates. The Earth’s crust is divided into large plates that move slowly. Their movement can cause earthquakes and volcanic activities. Students often find questions related to tectonic plates and natural disasters in examinations.
The chapter further explains different landforms and how they are created. Mountains are formed due to folding and faulting of the Earth’s crust. Plateaus are elevated flat lands, while plains are formed through the deposition of sediments by rivers. These concepts are crucial for understanding geography and environmental changes.
Studying The Earth and Changes on It Question Answers for Class 7 helps students develop awareness about natural disasters and the importance of disaster preparedness. By learning about earthquakes, volcanoes, and erosion, students gain knowledge about the dynamic nature of our planet and the need to protect the environment.
The Tata DAV Class 7 Social Science Chapter 2 Complete Solutions provide easy explanations, textbook question answers, and important notes that simplify complex geographical concepts. These solutions enable students to revise quickly, improve conceptual understanding, and perform better in examinations. Regular practice of the chapter’s questions and answers can help students master the concepts and score excellent marks in Social Science.