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Page No 9:

Question A.1:

Which are the three layers of the earth?

Answer:

Following are the three layers of the Earth:

1. Crust: It is the outermost layer of the Earth's surface. It extends from 5 to 8 kilometres beneath the oceans and about 35 kilometres beneath the continental masses.
2. Mantle: It is the layer that lies below the crust. The thickness of mantle is 2,900 kilometres.
3. Core: It is the innermost layer of the Earth  and is 3,500-kilometres thick.

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Question A.2:

What are minerals? Name two rock-forming minerals.

Answer:

The naturally occurring inorganic compounds found in the Earth's crust are known as minerals. Minerals are made up of one or more elements that have definite chemical composition and physical properties.

The two common rock-forming minerals are quartz and feldspar.

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Question A.3:

What are sediments?

Answer:

Rocks on the surface of the Earth constantly break into smaller pieces due to the force of running water, ice, winds and waves. These smaller fragments of rocks are known as sediments. Sediments are of various sizes, ranging from sand, silt and clay to gravel. 

Page No 9:

Question A.4:

Define fossils? Name two fossil fuels found in sedimentary rocks.

Answer:

The dead remains of plants or animals that are preserved in the sedimentary rocks are known as fossils. These remains are from the prehistoric times and are very rare because their formation involves a long process. 

The two fossil fuels found in sedimentary rocks are natural gas and petroleum.

Page No 9:

Question A.5:

What do you understand by the term 'rock cycle'?

Answer:

Rocks go through a cycle of transformation. Magma rises to the Earth's surface and solidifies to form igneous rocks.The igneous rocks are broken down into smaller pieces by the forces of water, wind and waves to form sediments. These sediments consolidate to form sedimentary rocks. The igneous and sedimentary rocks change into metamorphic rocks due to extreme pressure and heat. These rocks melt to form new magma. This process is called the rock cycle. 

Page No 9:

Question B.1:

Magma and lava

Answer:


                                     Magma                               Lava
1. The hot molten material present in the interior of the Earth is known as magma. Lava is the material that reaches the Earth's surface from it's interior through cracks and crevices.
2. Magma gets collected in a magma chamber beneath the volcanoes. Lava erupts from cracks or crevices on the Earth's surface to form volcanoes.

Page No 9:

Question B.2:

Rocks and ores

Answer:

 
        Rocks                 Ores
1. It includes all the solid material present on the Earth's crust. There are minerals that are found inside a rock that can be extracted economically.  These rocks are known as ores.
2. The Earth's outer layer is made up of rocks. The ores are made up of several minerals.

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Question B.3:

Intrusive and extrusive igneous rocks

Answer:

 

Intrusive Igneous Rocks Extrusive Igneous Rocks
1.The igneous rocks found below the surface of the Earth are known as intrusive igneous rocks. The igneous rocks found on the surface of the Earth are known as extrusive igneous rocks.
2.These are formed when the magma cools and solidifies below the Earth's surface. These are formed when the lava cools and solidifies after reaching the Earth's surface during a volcanic eruption.
3. Examples: Granite and dolerite  Examples: Basalt and obsidian

Page No 9:

Question C.1:

We have knowledge about the earth's interior.

Answer:

We have knowledge about the interior of the Earth because of the information and clues provided to via means of the occurrence of earthquakes, volcanic eruptions and deep mines. These help us in knowing the composition and nature of the Earth's interior.


 

Page No 9:

Question C.2:

In the earth's core, iron is found in a liquid state.

Answer:

The temperature of the outer core of the Earth is 2,200 °C. Therefore, the iron present in this layer is in molten state.

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Question C.3:

Igneous rocks are called primary rocks.

Answer:

The magma or lava cools down and solidifies to form igneous rocks. Sedimentary rocks as well as metamorphic rocks are formed from the igneous rocks. Therefore, the igneous rocks are called primary rocks.

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Question C.4:

Sedimentary rocks are also called stratified rocks.

Answer:

The sediments of rocks are compressed and cemented together due to heavy pressure to form sedimentary rocks. This formation takes place in layers. Therefore, sedimentary rocks are also known as stratified rocks.

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Question C.5:

Sometimes igneous and sedimentary rocks are changed into metamorphic rocks.

Answer:

Sometimes igneous and sedimentary rocks undergo changes in their characteristics and form, resulting in the formation of metamorphic rocks. This change happens because the rocks are subjected to extreme heat and pressure, volcanic activities or movements on the Earth's surface.

Page No 9:

Question D.1:

Describe the interior of the earth, explaining any one layer in detail. Illustrate your answer with a diagram.

Answer:

The Earth is made up of several layers. While the crust is its outermost layer, the interior of the Earth consists of the mantle, which is a 2,900-km-thick layer lying beneath the Earth's surface. The core is the innermost layer of the Earth, which lies below the mantle.

The innermost layer, called the core, stretches to about 3,500 km. The core is divided into outer core and inner core. The outer core is a 2,300-km-thick layer that lies below the mantle. This layer is in a molten state due to the extreme temperature of 2,200 oC and is made up of iron and nickel, collectively known as NiFe. The inner core, which is about 1,200-km-thick, lies below the outer core. Although the temperature is 5,000 oC, the NiFe is in a solid state. This is due to the extreme pressure exerted by the rocks of the layers lying above the inner core.

The layers of the interior of the Earth have been illustrated with the following diagram:

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Question D.2:

Explain the formation of different types of rocks. Give examples of each.

Answer:

On the basis of their formation, rocks are classified into the following three categories:
 
1. Igneous rocks: Lava is the hot molten magma that reaches the Earth's surface through cracks and crevices during a volcanic eruption. This cools down and solidifies below the Earth's surface or on it to form rocks. These rocks are known as igneous rocks.
Examples: Granite and basalt

2. Sedimentary rocks: The igneous rocks are broken down into smaller fragments by running water, waves, winds and moving ice. These fragments of rocks, known as sediments, are carried by rivers and are deposited at the floor of the lakes, oceans and seas. These fragments get compressed and cemented together due to extreme pressure, thereby, forming rocks. These rocks are formed in layers and are known as sedimentary or stratified rocks.
Examples: Sandstone and gypsum

3. Metamorphic rocks: Igneous and sedimentary rocks undergo a change in their characteristics and forms when they are subjected to extreme heat and pressure, volcanic activities or movements in the Earth's surface. The change leads to the formation of rocks known as metamorphic rocks.
Examples: Quartzite and marble

Page No 9:

Question D.3:

What do you know about the rock cycle? Explain with a help of a diagram.

Answer:

Ans. Rocks go through a continuous process of change or transformation. It begins with formation of igneous rocks due to the cooling down and solidification of the hot molten magma which reaches the earth's crust. the rocks are then broken down into smaller fragments or sediments by the forces of running water, moving ice and waves. The sediment are carried along by the rivers and are deposited at the bottom of lakes, oceans and seas. these are compressed and cemented due to extreme force and form a sedimentary rocks.When subjected to extreme heat and pressure,the igneous and sedimentary rocks undergo a change in their characteristics and form . This results into the formation of metamorphic rocks. This cycle of change from one rock to another is known as rock cycle.

The diagram explaining the rock cycle is as follows:

Page No 9:

Question E.1:

The temperature in the lower mantle is

(a) 2000 °C
(b) 2100 °C
(c) 2200 °C
(d) 2300 °C

Answer:

The correct answer is (c).

Explanation: The temperatures of the outer mantle and the lower mantle are 870 oC and 2,200 oC, respectively. The temperature increases with each layer beneath the Earth's crust.

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Question E.2:

The core of the earth is made up of

a. silicon
b. aluminium
c. magnesium
d. nickel and iron

Answer:

The core of the Earth is made up of (d) nickel and iron.

Explanation: Nickel and Iron present in the inner core of the Earth are together known as NiFe. The extreme pressure exerted on the inner core by the rocks of the layers lying above causes the NiFe to be in a solid state.
 



Page No 10:

Question E.3:

Haematite is an ore of

a. copper
b. iron
c. aluminium
d. manganese

Answer:

The correct answer is option (b).

Haematite is an ore of iron.

Explanation: Iron is the metal that is extracted for economic use from haematite. It is used in pharmaceutical, heavy machinery and automobile industries.
 

Page No 10:

Question E.4:

This is plutonic rock

(a) granite
(b) gypsum
(c) basalt
(d) gneiss

Answer:

The correct answer is option (a).

Granite is a plutonic rock.


Explanation: Granite is a plutonic or an intrusive igneous rock, which means that it is found beneath the Earth's crust. Granite is granular in texture and is used in construction of buildings.

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Question E.5:

Sedimentary rocks are also called

(a) stagnant
(b) sedentary
(c) stratified
(d) solidified rocks

Answer:

The correct answer is option (c).

Explanation: The smaller fragments of igneous rocks or sediments compress and get cemented due to extreme pressure. These rocks are formed in layers. Therefore they are known as stratified rocks.

 

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Question E.6:

Quartzite is formed from

(a) limestone
(b) shale
(c) sandstone
(d) slate

Answer:

Quartzite is formed from (c).

Explanation: Quartzite is a metamorphic rock. It is formed when sandstone is exposed to extreme heat and pressure. Quartzite is used as railway track ballast because of its hardness and angular shape.

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Question F:

Classify the following rocks into Igneous, Sedimentary and Metamorphic.
Granite, sandstone, basalt, coal, marble, quartzite, limestone, obsidian, gypsum, gneiss, slate, dolerite

Igneous Rocks Sedimentary Rocks Metamorphic Rocks



 
   

Answer:

The rocks mentioned above have been classified in the following table:
 

Igneous Rocks Sedimentary Rocks Metamorphic Rocks
Granite, basalt, obsidian, dolerite Sandstone, coal, gypsum, limestone Quartzite, marble, gneiss, slate

Explanation

Igneous rocks: Granite, basalt, obsidian and dolerite have been classified as igneous rocks. This is because they were formed due to the cooling and solidification of lava beneath or on the Earth's surface.

Sedimentary rocks: Sandstone, coal, gypsum and limestone have been classified as sedimentary rocks. This is because they were formed by the consolidation of the sediments, one layer after the other.

Metamorphic rocks: Quartzite, marble, gneiss and slate have been classified as metamorphic rocks. This is because they were formed after igneous and sedimentary rocks underwent a change in their physical form and characteristics . This occurred due to being subjected to extreme heat and pressure.



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