Chapter 2 Inside Our Earth

NCERT CLASS 7^TH GEOGRAPHY  OUR ENVIRONMENT

1. Consider the following languages: (UPSC / IAS  2014)

1. Gujarati
2. Kannada
3. Telugu

Which of the above has/have been declared as ‘Classical Language/Languages’ by the

Government?

 a) (i) and (ii) only

 b) (iii) only

 c) (ii) and (iii) only

 d) (i), (ii) and (iii)

2. Which one of the following was given classical language status recently? (UPSC / IAS  2015)

 a) Odia

 b) Konkani

 c) Bhojpuri

 d) Assamese

3. Which one of the following was given classical language status recently? (UPSC / IAS  2015)

 a) Odia

 b) Konkani

 c) Bhojpuri

 d) Assamese

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Question 1 of 3

Summary

Chapter 2 Inside Our Earth

NCERT CLASS 7^TH GEOGRAPHY  OUR ENVIRONMENT

• Lithosphere is the solid crust or the hard top layer of the earth.
• Lithosphere is made up of rocks and minerals and covered by a thin layer of soil.
• The uppermost layer over the earth’s surface is called the crust.
• About 98 per cent of the total crust of the earth is composed of eight elements like oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium.

INTERIOR OF THE EARTH

crust.

• The uppermost layer over the earth’s surface is called the crust.
• crust. is the thinnest of all the layers.
• crust. is about 35 km. on the continental masses and only 5 km. on the ocean floors.
• The main mineral constituents of the continental mass are silica and alumina.
• It is thus called sial (si-silica and al-alumina).
• The oceanic crust mainly consists of silica and magnesium; it is therefore called sima (si-silica and ma-magnesium)
• Half of the earth’s crust is composed of feldspar (It has light cream to salmon pink colour. It is used in ceramics and glass making).
• SOME MAJOR MINERALS in crust  (Feldspar , Pyroxene , Amphibole, Mica )
• The earth’s crust is composed of rocks. A rock is an aggregate of one or more minerals
• When magma in its upward movement cools and turns into solid form it is called igneous rock. The process of cooling and solidification can happen in the earth’s crust or on the surface of the earth.
• The earth’s crust is dynamic. it has moved and moves vertically and horizontally.
• All processes that move, elevate or build up portions of the earth’s crust come under diastrophism.
• The crust forms only 1 per cent of the volume of the earth, 84 per cent consists of the mantle and 15 per cent makes the core.
• The radius of the earth is 6371 km.

The Major Elements of the Earth’s Crust

mantle

• The innermost layer of the earth  is the core and it is mainly made up of nickel and iron .
• The upper portion of the mantle is weak It is the main source of magma that finds its way to the surface during volcanic eruptions.
• The crust and the uppermost part of the mantle are called lithosphere.
• Just beneath the crust is the mantle which extends up to a depth of 2900 km. below the crust.
• The innermost layer is the core with a radius of about 3500 km.
• It is mainly made up of nickel and iron and is called nife ( ni – nickel and fe – ferrous i.e. iron).
• The central core has very high temperature and pressure.
• The Mantle The portion of the interior beyond the crust is called the mantle.
• The mantle extends from Moho’s discontinuity to a depth of 2,900 km.
• The upper portion of the mantle is called asthenosphere. The word astheno means weak. It is considered to be extending upto 400 km. It is the main source of magma that finds its way to the surface during volcanic eruptions.
• It has a density higher than the crust’s (3.4 g/cm3). The crust and the uppermost part of the mantle are called lithosphere. Its thickness ranges from 10-200 km. The lower mantle extends beyond the asthenosphere. It is in solid state.

ROCKS AND MINERALS

• The earth’s crust is made up of various types of rocks. Any natural mass of mineral matter that makes up the earth’s crust is called a rock.

• Rocks can be of different colour, size and texture.

There are three major types of rocks: igneous rocks, sedimentary rocks and metamorphic rocks.

Igneous Rocks

• As igneous rocks form out of magma and lava from the interior of the earth, they are known as primary rocks.
• The igneous rocks (Ignis – in Latin means ‘Fire’) are formed when magma cools and solidifies.
• You already know what magma is. When magma in its upward movement cools and turns into solid
• The process of cooling and solidification can happen in the earth’s crust or on the surface of the earth.
• Igneous rocks are classified based on texture. Texture depends upon size and arrangement of grains or other physical conditions of the materials.
• . Granite, gabbro, pegmatite, basalt, volcanic breccia and tuff are some of the examples of igneous rocks.

There are two types of igneous rocks: intrusive rocks and extrusive rocks.

intrusive rocks

• the molten magma cools down deep inside the earth’s crust.
• Solid rocks so formed are called intrusive igneous rocks.
• Since they cool down slowly they form large grains.
• Granite is an example of such a rock.
• Grinding stones used to prepare paste/powder of spices and grains are made of granite.

.

extrusive rocks

• Lava is actually fiery red molten magma coming out from the interior of the earth on its surface.
• When this molten lava comes on the earth’s surface, it rapidly cools down and becomes solid. Rocks formed in such a way on the crust are called extrusive igneous rocks.
• They have a very fine grained structure. For example, basalt. The Deccan plateau is made up of basalt rocks.

Sedimentary Rocks

• Rocks roll down, crack, and hit each other and are broken down into small fragments. These smaller particles are called sediments.
• These sediments are transported and deposited by wind, water, etc. These loose sediments are compressed and hardened to form layers of rocks.
• These types of rocks are called sedimentary rocks.
• For example, sandstone is made from grains of sand.
• These rocks may also contain fossils of plants, animals and other microorganisms that once lived on them. Igneous and sedimentary rocks can change into metamorphic rocks under great heat and pressure . For example, clay changes into slate and limestone into marble.

Metamorphic Rocks

• Metamorphic Rocks is  formed out of existing rocks undergoing recrystallisation.
• when the molten magma cools; it solidifies to become igneous rock.
• These igneous rocks are broken down into small particles that are transported and deposited to form sedimentary rocks.
• When the igneous and sedimentary rocks are subjected to heat and pressure they change into metamorphic rocks.
• The metamorphic rocks which are still under great heat and pressure melt down to form molten magma. This molten magma again can cool down and solidify into igneous rocks .
• Mica. is commonly found in igneous and metamorphic rocks. It is used in electrical instruments.

metamorphic rocks include phyllite, schist, gneiss, quartzite and marble.

sedimentary rocks include sandstone, limestone, and shale. 
Examples of igneous rocks  Granite.,Basalt. ,Pumice. ,Gabbro.

Fossils: The remains of the dead plants and animals trapped in the layers of rocks are called fossils.

Q 2. Tick the correct answer.

(i) The rock which is made up of molten magma is

(a) Igneous   (b) Sedimentary    (c) Metamorphic

Answer: a

(ii) The innermost layer of the earth is

(a) Crust   (b) Core  (c) Mantle

Answer: b

(iii) Gold, petroleum and coal are examples of

(a) Rocks  (b) Minerals  (c) Fossils

Answer: b

(iv) Rocks which contain fossils are

(a) Sedimentary rocks  (b) Metamorphic rocks   (c) Igneous rocks

Answer: a

(v) The thinnest layer of the earth is

(a) Crust   (b) Mantle   (c) Core

Answer: a

(i) Core                                                (e) Innermost layer

(ii) Minerals                                           (d) Has definite chemical composition

(iii) Rocks                                               (b) Used for roads and buildings

(iv) Clay                                                  (f) Changes into slate

(v) Sial                                                    (c) Made of silicon and alumina