| Reference Book | Ratna Sagar Integrated Social Science |
| Class | Class 7 |
| Category | Geography |
| Chapter Number | Chapter 2 |
| Chapter Name | Inside Our Earth |
A) Tick (✓) the correct answers.
1) The thinnest layer of the Earth is the
a) Crust ✓
b) mantle
c) outer core
d) inner core
2) The average radius of the mantle is about
a) 2300 Km
b) 2900 Km ✓
c) 3500 Km
d) 3900 Km
3) What is the outer name of core?
a) Lithosphere
b) Asthenosphere
c) Barysphere ✓
d) Biosphere
4) Which layer of the Earth is made up of iron and nickel?
a) Core ✓
b) crust
c) mantle
d) Lithosphere
5) Granite, chalk, clay and salt are examples of
a) rocks ✓
b) minerals
c) fossils
d) metals
6) The rocks which are formed from molten magma called _______ rocks.
a) sedimentary
b) igneous ✓
c) metamorphic
d) metallic
7) The fossil fuels are found in _______ rocks
a) igneous
b) sedimentary ✓
c) metamorphic
d) volcanic
8) Which of the following is not a metamorphic rock?
a) Quartzite
b) Marble
c) Granite ✓
d) Slate
B) Fill in the blanks
1) The average density of the earth is about 5.5 g per cubic cm.
2) The solid outermost layer of the earth is called crust
3) Limestone is metamorphosed into marble.
4) The rock cycle has neither a beginning nor an end.
C) Classify the names of the rocks given below into igneous, sedimentary and metamorphic.
| Igneous | Sedimentary | Metamorphic |
| Granite | Sandstone | Marble |
| Dolerite | Limestone | Slate |
| Basalt | Coal | Quartzite |
| pumice | Shale | Gneiss |
D) Write True or False
1) The geographers study the interior of the earth. False
2) The earth is composed of uniform materials. False
3) Salt is an example of chemically formed sedimentary rock. True
4) The change of one type of rock into another is known as mineral cycle. False
E) Match the columns
| Column A | Column B |
| 1) Sima | made up of Silica and magnesium |
| 2) Rocks | the materials of the Earth’s crust |
| 3) Minerals | have definite chemical composition |
| 4) Shale | changes into slate |
F) Distinguish between the following
1) Crust and core
| Crust | Core |
| 1) This is the outermost layer of the Earth. | 1) This is the innermost layer of the Earth. |
| 2) It is called Lithosphere | It is called Barysphere. |
| 3) It is termed as SIAl and SIMA | It is termed as NIFE |
| 4) It is made up if silica, aluminium and magnesium. | It is made up of nickel and iron. |
2) Sial and Sima
| SIAl | SIMA |
| 1) It is composed of silica and aluminium | It is composed of silica and magnesium |
| 2) The continental crust is made up of SIAL. | The oceanic crust is made up of SIMA. |
| 3) It is the upper part of the Earth’s crust. | It is the lower part of the Earth’s crust. |
| 4) Its thickness is nearly 20 Km. | Its average thickness is nearly 20 Km -35 Km. |
| 5) It is not a continuous layer. | It is a continuous layer |
3) Rocks and minerals
| Rocks | Minerals |
| 1) A rock is inorganic and a solid naturally-formed substance without any chemical composition or atomic structure. | A mineral is also a solid, inorganic, substance as that of the rock which has a definite crystalline structure as well as chemical composition. |
| 2) Rock comprises minerals. | A Mineral does not comprise rocks |
| 3) These occur in solid form on the earth’s crust. | Minerals are said to occur as mineral deposits. |
| 4) Example- Marble, slate, limestone | Example – quartz, copper, iron, gold etc. |
4) Intrusive and Extrusive rocks
| Intrusive rocks | Extrusive rocks |
| 1) They are formed below the surface of Earth. | They are formed above the surface of Earth. |
| 2) These rocks have large size crystals due to slow cooling. | Crystals are not formed due to rapid cooling of lava. |
| 3) Example – Granite | Example -Basalt |
| 4) They are usually dark and dense. | They are usually light coloured and low density. |
G) Give short answers for the following questions.
Que 1) Name the main types of rocks with one example of each.
Ans The three types of rocks are :
a) Igneous Rock – Granite
b) Sedimentary Rock – Sandstone
c) Metamorphic Rock – Marble
Que 2) How are extrusive and intrusive igneous rocks formed?
Ans When molten lava comes out of volcanoes, reaches the Earth’s surface and cools down rapidly to become a solid piece of rock, extrusive igneous rocks are formed. These rocks have large size crystals due to slow cooling.
For example – Basalt.
When the molten lava solidifies deep inside the earth’s crust, the rocks sp formed are called intrusive igneous rocks. As the pace of cooling is slow, the crystals formed are large.
For example – granite
Que 3) How are metamorphic rocks formed?
Ans The metamorphic rocks are actually igneous or sedimentary rocks which have been changed due to excessive heat and pressure inside the earth. Excessive heat and pressure can change the original properties of rocks such as their colour, hardness, texture and mineral composition. Such changed rocks are called metamorphic rocks. The act of metamorphism takes hundreds of years. In due course of time, limestone can change into marble, shale into slate, granite into gneiss, sandstone into quartzite. Gems can be found in these rocks.
Que 4) How are rocks and minerals useful to us?
Ans
Uses of Rocks and Minerals
1) In ancient times, rocks were used to make tools and weapons.
2) Rocks are widely used in the construction of roads, houses and buildings.
3) Minerals like coal and petroleum provide the sources of power. :
4) Chemicals found in some sedimentary rocks are used to make fertilizers.
5) Soil is formed from rocks.
H. Give long answers for the following questions.
Que 1) What do you know about the structure of the earth?
Ans On the basis of varying density and other physical and chemical properties of rocks, the earth can be divided into three concentric layers — crust, mantle and core.
a) Crust
1) The crust is the solid outermost layer. It is also called the lithosphere. It is a relatively thin layer.
2) The upper part of the crust is called continental crust (about 35 km thick). The lower part is called oceanic crust (about 5 km thick).
3) The continental crust is made up of silica (si) and aluminia (al), so it is also called sial. The oceanic crust is made up of silica (si) and magnesium (ma), and therefore also called sima. The average density of the crust is about 3.0g per cubic cm.
4) The outer crust has soil. It also provides with most of the minerals.
b) Mantle
1) Just beneath the crust is a 2,900 km thick layer called the mantle. It lies between the crust and the core.
2) It is made up of dense and heavy materials, such as iron and magnesium.
3) The average density ranges between 3.5 to 5.5 per cubic cm.
4) The temperature in the mantle is very high. Magma is found in this layer.
c) Core
1) The core lies below the mantle and around the centre of the earth. It is also called barysphere.
2) The average radius of the core is about 3,500 km.
3) It is made up of heavy metals, such as nickel and iron. Therefore, it is also called nife (‘ni’ stands for nickel and ‘fe’ for iron).
4) The temperature of this layer varies between 2,200 °C and 5,000°C.
5) The average density ranges between 5.02 and 13.0g per cubic cm.
Que 2) What are the main features of the mantle and the core?
Ans
Features of mantle
1) Just beneath the crust is a 2,900 km thick layer called the mantle. It lies between the crust and the core.
2) It is made up of dense and heavy materials, such as iron and magnesium.
3) The average density ranges between 3.5 to 5.5 per cubic cm.
4) The temperature in the mantle is very high. Magma is found in this layer.
Features of core
1) The core lies below the mantle and around the centre of the earth. It is also called barysphere.
2) The average radius of the core is about 3,500 km.
3) It is made up of heavy metals, such as nickel and iron. Therefore, it is also called nife (‘ni’ stands for nickel and ‘fe’ for iron).
4) The temperature of this layer varies between 2,200 °C and 5,000°C.
5) The average density ranges between 5.02 and 13.0g per cubic cm.
Que 3) What are the main characteristics of sedimentary rocks?
Ans
The main characteristics of sedimentary rocks are :
1) These rocks are softer than igneous rocks.
2) These rocks have horizontal layers, arranged one above the other.
3) These rocks are mostly formed under water and have marks of waves and mud-cracks.
4) These rocks also contain remains of animal and plants, called fossils, between the layers.
5) The important examples are sandstone, limestone and coal.
Que 4) Explain the working of the rock cycle.
Ans The change of one type of rock into another type under certain conditions in a cyclic manner is known as the rock cycle.
The rock cycle has neither a beginning nor an end. In this process, the matter of the earth’s crust is not lost. The rock cycle operates in the following ways:
1) The hot and molten magma forms igneous rocks on cooling.
2) These igneous rocks are exposed to different agents of weathering and erosion on the earth’s surface.
3) The broken rock fragments, when transported and deposited in basins, form sedimentary rocks.
4) The leftover igneous rocks and the newly formed sedimentary rocks are subjected to intense heat and pressure. They change into metamorphic rocks in due course of time.
5) The sedimentary and metamorphic rocks are buried again and melt to form magma.
6) This magma again cools down and forms igneous rocks.
Throughout the geological period of millions of years, rocks and minerals have been changing due to the working of the rock cycle.
Que 5) Why can’t we go to the centre of the earth?
Ans It is impossible to reach the centre of the earth because the temperature inside increases with the increase in depth. The temperature at the centre is estimated to be about 5,000°C. Thus, it is not possible to access direct information about the interior of the earth.
Que 6) Why can’t we get direct information about the interior of the earth?
Ans We can’t get direct information about the interior of the earth because it is impossible to reach the centre of the earth because the temperature at the centre is estimated to be about 5,000°C. Most of our knowledge about the earth’s structure and interior is based on the density of materials and the behaviour of the earthquake waves. These waves reveal that the earth behaves like a solid body up to a depth of about 2,900 km from the surface. The average density of the earth is about 5.9g per cubic cm. The earth is not composed of uniform material. The materials of the inner layers are heavier than that of the outer layer. The density of rocks increases towards the centre.
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