Download UNIT II INTERIOR OF THE EARTH

CBSE-i
CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
UNIT II
INTERIOR OF THE EARTH
CONTENT
The Earth’s Interior
Its structure - Its layers and characteristics
Rocks Classification
Types of rocks based on mode of
formation –

Igneous

Sedimentary

Metamorphic

Their formation and characteristics
Rock Cycle
Definition, Process and Significance
Uses of Rocks
Economic Significance for Man
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CBSE-i
CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
UNIT -II
INTERIOR OF THE EARTH
INTRODUCTION
Rocks, metals, minerals, water etc., have something common in relation to earth, the third
planet from the Sun in our Solar System. These are the components that largely form the
earth and make it one of the known, densest rocky planet that was formed 4.5 billion years
ago. Man has always wondered about the occurrence of phenomena like earthquakes,
tsunamis, volcanoes etc. The answer to this lies in the study of the interior of the earth. The
interior of this rocky planet differs completely in nature which becomes evident from the
information obtained from the study of different sources.
It is the planet we evolved on. Our planet's rocks, soils, and the various processes that create
and transform them, produce resources and materials that sustain our life.
The Interior of the Earth – An Overview
The earth comprises of three main realms – the lithosphere (the solid inorganic section),
hydrosphere (the liquid section) and the atmosphere (the gaseous realm). The solid earth
actually has a concentric layer structure comprising of the crust, the mantle and the core. The
temperature within the earth increases with the depth at the rate of 1 oC for every 32 metres
depth. This makes the average temperature at the centre of the earth touch 5000oC.
The Layers of the Earth
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1. The Crust: The outermost layer also known as lithosphere. It is the thinnest layer of the earth
that is 5 – 40 km thick. It is the most significant part of the earth’s surface with its name
lithosphere being derived from Latin word ‘lithos’ meaning ‘rocks’ or ‘stones’.
The crust is subdivided into two distinct parts according to its composition known as Sial and
Sima.
Sial: The topmost layer consists of granite rocks which on an average forms first 25 km of
the crust and is lighter. It consists of silicates and aluminium along with other lighter metals.
This layer is thick over the continents but is thin or absent on the ocean floors.
Sima: It lies below the sial layer. A dense layer with an average thickness of 35 km, it
consists pre-dominantly of silicates of magnesium, iron and other denser metals. It is a zone
of basaltic rocks forming the ocean floors.
Though these two layers are in a solid state, the lighter sial is considered as floating on denser
sima layer.
Do You Know?
Scientists have discovered a large area
thousands of square kilometres in extent in
the middle of the Atlantic where the Earth’s
crust appears to be missing. Instead, the
mantle - the deep interior of the Earth,
normally covered by crust many kilometres
thick - is exposed on the seafloor, 3000m
The Crust
below the surface.
Fact File
Earth is the only known planet in the Solar System with crustal plates. The outer
crust of the Earth is broken up into regions known as tectonic plates. These are
floating on top of the magma interior of the Earth and can move against one
another.
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2. The Mantle: Below the crust lies the mantle that extends up to a depth of about 2900 km. It
is composed of mineral matter in a solid state, the chief constituents being silicates of iron
and magnesium. Both the temperature and the density of the mantle increases with the
increasing depth towards the centre of the earth. The zone of separation between the crust
and the mantle is called Moho Discontinuity. (Moho, a simplification of the name of the
Croatian seismologist Mohorovicic who discovered it). Moho marks the lower limit of the
earth’s crust. It occurs at an average depth of 8km beneath the oceans and 32km beneath the
continents. The mantle has two parts:
(a)Upper Mantle: The thickness of the upper mantle is about 670 km. The top layer of the
upper mantle is solid. Below this layer lies a soft mobile layer. This soft layer of the upper
mantle is called asthenosphere (from the Greek word asthenes meaning weak). The lithosphere
that consists of the crust and the hard uppermost part of the mantle floats over this
asthenosphere.
(b)Lower Mantle: This is about 2200 km thick. This part of the mantle is a solid region starting
at about 700 km. It is composed of rocks of uniform thickness.
The Mantle
Do You Know?
Heat in the earth's interior causes the magma in the mantle to expand and rise.
As the magma spreads out beneath the plates, the plates are dragged along and
move away from each other. As the magma cools and sinks, plates are dragged
towards each other. The repeated heating
4 and rising of the magma sets up
continuous convection currents in the mantle causing the plates to move.
CBSE-i
CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
3.
The Core: Scientists believe that as we go deep within the earth, there’s a huge ball of
liquid and solid iron, which is the earth’s core. The thickness of the core is about 3500 km. It
is the densest layer. When the earth was first formed, 4.6 billion years ago, it was a hot ball of
molten rock and metal. And since it was mostly liquid, heavier elements like iron and nickel
were able to sink down into the planet and accumulate at the core.
The core is believed to have two parts: a solid inner core, with a radius of 1,220 km, and a
liquid outer core that extends to a radius of 3,400 km. The two most abundant elements found
in the core are iron and nickel. This is why it is called as NIFE. The inner core is solid, but
the outer core is a hot liquid. At the core of the earth, temperatures may be as high as 5000oC.
The Liquid Outer Core
The Solid Inner Core
Fact File
The Gutenberg Discontinuity is the name given to the core – mantle boundary
about 1800 miles below the surface.
The Layers of the Earth
Material required: An apple, a knife
Procedure: The teacher will cut the apple
with a knife and ask the students to
observe........
Conclusion: The seed area of the
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apple is the core, the flesh of the apple
is the mantle and the peel is the crust.
An apple used to show the layers of
the Earth
CBSE-i
CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
Do You Know?
 According to some scientists, at the centre of the earth, there is a nucleus of high
density atoms that descended from the atoms that were the beginning of our solar
system.
 The deepest hole ever drilled is in the north – west centre of Russia for scientific
research. It reached to a depth of about 7.6 miles. The temperature at this depth
was 180oC at which point the rock became more like plastic than a solid,
stopping further drilling.
 Earth’s greatest source of heat, besides the sun, is its interior, which conducts a
hundred billion calories of energy to the surface each year. So much energy
radiates from inside the earth that it could satisfy all human energy needs three
times over.
Rocks: The earth’s crust is majorly composed of rocks. Rocks are combinations of one or
more minerals that we find in nature. They have been an integral part of mankind since time
immemorial. Rocks were initially used as tools for hunting and later as building materials to
construct shelters and monuments. The different kinds of minerals and metals that we find in
rocks have contributed significantly to human prosperity.
Classification of Rocks on the basis of Mode of Formation
Rocks Classification (On
the basis of Mode of
Formation)
Igneous Rocks (Primary
rocks)
Sedimentary Rocks
(Secondary Rocks I)
Metamorphic Rocks
(Secondary Rocks II)
Igneous Rocks: All the rocks on the earth were initially igneous in nature. The term
“igneous” comes from the Latin word ignis that means fire. Igneous rocks are formed as a
result of cooling and solidification of the hot magma that originates from far below the
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CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
earth’s surface. On the basis of their occurrence, igneous rocks can be classified into two
categories (i) Extrusive rocks (ii) Intrusive Rocks
Extrusive Igneous Rocks are formed by cooling of lava on the surface of the earth. The
cooling process takes place quite rapidly leading to the formation of small crystals and have
fine grain particles. Such types of rocks are called extrusive rocks. These rocks are also called
volcanic rocks. Basalt is the most common example of an extrusive igneous rock is basalt.
Basalt
Rhyolite
Andesite
Obsidian
Intrusive Igneous Rock are formed when magma solidifies below the surface of the earth.
The rate of cooling below the earth’ surface is very slow which leads to the formation of
large crystals and have coarse grains. Such types of rocks are called as plutonic or intrusive
rocks. The most common example of an intrusive igneous rock is granite. Other examples
include gabbro, dolerite etc.
Granite
Dolerite
Gabbro
Do You Know?
Granite is the signature rock of the continents. More than that, granite is the
signature rock of the planet Earth itself. The other rocky planets—Mercury,
Venus and Mars—are covered with basalt, as is the ocean floor on Earth. But
only Earth has this beautiful and interesting rock type in abundance.
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CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
Sedimentary Rocks: The various agents of erosion like running water, wind and moving ice
carry small particles of rock. These particles of rocks are deposited on land or on the beds of
oceans and rivers forming sediments. The sediments are deposited in layers.
Over the years these sediments get harden due to the weight of the layers above. In the ocean
or the river beds, the weight of the water also helps in hardening the layers. Such rocks that
are formed by the deposition and the hardening of the layers of the sediments are called as
sedimentary rocks. The most common example of sedimentary rock is coal. Other examples
include sandstone, limestone, shale, gravel, clay etc.
Limestone
Conglomerate
Sandstone
Shale
Case Study – The Neighbourhood Rock
Coal is an organic sedimentary rock that is
Formed mainly from plant debris. The plant
Debris usually accumulates in a swamp
environment. Sometimes we find coal in the soil
near our home, along railroad tracks, or along
beaches. Coal is combustible and is mainly used
as a fuel.
Coal
 Can you name a few areas where coal is used as a fuel?
 Find out the largest producer of coal in the world.
 Locate the major coal producing regions on a world map.
Metamorphic Rocks: The word ‘metamorphosis’ means change of form. The igneous and
sedimentary rocks are transformed by the action of intense heat and pressure deep inside the
earth’s surface. The changed rock that is formed is called as metamorphic rock. In course of
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CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
time shale may change into slate and schist, limestone to marble, sandstone to quartzite and
granite to gneiss.
Marble
Quartzite
Gneiss
Do You Know?
 Some rocks such as chalk, red sandstone and limestone have pores, cracks
and joints in them which let water drained easily. They are known as
permeable rocks. The size of the particles in the rocks and the way they are
arranged affects how permeable they are.
 Rocks that do not let water pass through them are impermeable rocks. Mica,
granite, slate are some examples of impermeable rocks.
Case study – A Visit To Agra
Felix was very excited as he was visiting his grandmother in India for the first time. He had
read about India in his seventh grade history book and wanted to see the famous Taj Mahal.
As he was going to miss his school for few days, his geography teacher gave him a special
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Taj Mahal
project based on types of rocks that were used to build monuments
Agra Fort in India.
A Visit to Agra – A City known for its Mughal architecture was the subject of study for
Felix. Accompanied by his parents, Felix reached Agra and saw the Famous Taj Mahal and
CBSE-i
CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
The Rock Cycle: All the three types of rocks are formed in different ways. The rock cycle is
the process that makes and recycles rocks. We know that most of the rocks on earth began as
igneous rocks. Igneous rocks are formed from cooling and solidification of the magma.
When igneous rocks are exposed on the surface due to erosion and weathering the rock
breaks down into smaller and smaller pieces. Wind and water carry these smaller pieces of
igneous rocks as sediments and deposit them in the ocean or the river beds. Over time the
sediment beds get buried and the pieces of rock become cemented together to form a new
type of rock called a sedimentary rock. It is the igneous rock that has changed into a
sedimentary rock. If the sedimentary rock is exposed at the surface, it can be eroded away
and eventually changed into new sedimentary rock. However, if the sedimentary rock gets
buried deep in the Earth, due to excessive heat and pressure, metamorphosis takes place and
the rock changes into a metamorphic rock. Metamorphosis can happen to igneous rocks as
well.
The metamorphic rocks due to weathering and erosion change into sedimentary rocks. If the
metamorphic rock is forced deeper into the Earth, the rock melts and becomes magma and
form the igneous rock. Igneous rocks and sedimentary rocks can also be forced down into the
earth and melt into magma and form the igneous rocks.
.
10 Cycle
The Rock
CBSE-i
CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
In short, the rock cycle includes the processes that forms and recycles the different types of
rocks found in or on the surface of the earth. Rocks begin the cycle as igneous rocks, erode
into sedimentary rocks then change into metamorphic rocks; finally the rocks melt back to
magma and start the process again
Uses of Rocks: Rocks and minerals have played an important role in the development of
human civilization. Rocks and stones have been used in making tools and implements and for
construction of buildings and monuments. For the better understanding of the importance of
rocks, the following are the uses of rocks:
1. Soils: Soils are derived from rocks. Soils are essential for all plant growth. Soils provide
suitability for agricultural products.
2. Mineral Service: Rocks are a store house of mineral. Igneous and metamorphic rocks are
rich in metallic minerals like iron, lead, copper, gold, silver, diamond etc. Sedimentary
rocks contain valuable deposits of coal, oil and natural gas. These are needed for all
industrial and economic activities.
3. Source of Building Material: Rocks are the source of different types of building materials.
Rocks provide us building stones like marble, sandstone or granite. Limestone and
gypsum are used for the manufacture of cement.
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CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
4. Source of Raw Materials: Rocks provide raw material for large number of mineral based
manufacturing industries like iron & steel, aluminium and other metals along with
petroleum that forms the basis for petrochemical industries.
5. Precious Stones: Precious stones and metal are obtained from different metamorphic or
igneous rocks. Diamond, gens, rubies etc are used in jewellery.
Various Uses of Rocks
Following are the examples of uses of different types of rocks:
Coal from China's Xuan Wei County, widely
used for Cooking and Heating
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Clay a sedimentary rock is used in
making pottery. (Pottery)
CBSE-i
CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
Red Sandstone
Limestone
* Coal a sedimentary rock is used as a domestic fuel and in power plants to make electricity.
* Limestone a sedimentary rock, is used in the production of lime, manufacture of paper,
petrochemicals, insecticides, fibreglass, glass, carpet backing and as the coating on many
types of chewing gum.
* Sandstone a sedimentary rock is used chiefly for construction.
Gabbro
Granite
Gneiss
Basalt
Gabbro an igneous rock is widely used as crushed stone for concrete aggregate, road metal,
railroad ballast, etc.
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CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
Basalt an igneous rock is used in construction, making cobblestones and in making statues.
Gneiss a metamorphic rock is used as building stones and other structural purposes.
Green Marble
Marble a metamorphic rock is quarried for use as
dimension stone for statuary, architectural and
ornamental purposes.
In spite of the rock cycle a single layer of sedimentary
rock may take centuries to build. This brings us to the
important concern of sustainable use of this resource
keeping the need and requirement of future generation
in mind.
GLOSSARY:
Asthenosphere: A thin semi-fluid layer of the earth below the lithosphere, forming part of
the mantle and thought to be able to flow vertically and horizontally, enabling sections of the
lithosphere to move.
Atmosphere: The envelope of the air surrounding the earth.
Biosphere: The life-bearing layer of the earth.
Crust - The rigid, rocky outer surface of the Earth composed mostly of basalt and granite.
The crust is thinner under the oceans.
Hydrosphere: The water-bearing layer of the earth.
Igneous Rock: The rocks that are formed due to cooling and solidification of hot lava on the
earth’s surface and magma in the earth’s surface.
Inner core - The solid iron-nickel center of the Earth that is very hot and under great
pressure.
Lava: When the hot magma flows on the earth’s surface.
Lithosphere: The rock-bearing layer of the earth.
Magma: The molten rock material under the earth’s crust from which igneous rock is formed
by cooling.
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CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
Mantle - A rocky layer located under the crust - it is composed of silicon, oxygen,
magnesium, iron, aluminum, and calcium. Convection (heat) currents carry heat from the hot
inner mantle to the cooler outer mantle.
Metamorphic Rock: Rocks that change their form due to intense heat and pressure.
Moho discontinuity: It is the boundary between the crust and the mantle. Also called
‘Moho’.
Outer core - the molten iron-nickel layer that surrounds the inner core.
Rocks: Rocks are naturally occurring solid aggregates of minerals.
Sedimentary Rock: Rock formed from consolidated clay sediments.
Seismology: The science that studies the earthquake waves.
WORKSHEETS
WORKSHEET-I
Name of the Student:
Class:
Section:
 Label the given diagram showing the layers of the earth’s interior.
 Write two interesting facts about each layer.
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STUDENTS’ MANUAL
A_____________________________________________________________________
______________________________________________________________________
B_____________________________________________________________________
______________________________________________________________________
C_____________________________________________________________________
______________________________________________________________________
D_____________________________________________________________________
______________________________________________________________________
______________________________________________________________________
WORKSHEET-II
Name of the Student:
Class:
Section:
Collect rock samples from your neighbourhood and prepare a report under the following
headings:
i.
Name of the rock
ii.
Identify the rock as igneous or sedimentary or metamorphic
iii.
Observe and record the characteristics of your rock sample
iv.
State the use of your rock sample.
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
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CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
WORKSHEET-III
Name of the Student:
Class:
Section:

Create a fact file about major types of rocks.
Paste your picture of Igneous Rock
State two facts related to Igneous Rocks
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CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
Paste your picture of Sedimentary Rock
State two facts related to Sedimentary Rocks
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
Paste your picture of Metamorphic Rock
State two facts related to Metamorphic Rocks
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CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
___________________________________________________________________________
___________________________________________________________________________
___________________________________________________________________________
__________________________________________________________________________
WORKSHEET-IV
Name of the Student:
Class:
Section:
Match the following terms with their explanation:
1. Lava
(a) An example of a sedimentary rock
2. Basalt
(b) Tiny pieces of rocks
3. Sediments
(c) Melted rock above the earth’s surface
4. Magma
(d) An example of an igneous rock
5. Limestone
(e) Melted rock beneath the earth’s surface
6. Identify the following rocks:
WORKSHEET-V
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CBSE-i
CLASS VII GEOGRAPHY
STUDENTS’ MANUAL
Name of the Student:
Class:
Section:
1. Complete the given diagram of the rock cycle by colouring the arrows according to the
given colour code:

Weathering and Erosion: Blue

Heat and Pressure: Red

Melting: Purple

Cooling: Yellow

Compaction and cementation: Green
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2. Complete the given extract regarding the rock cycle by using the words given in the
box against the appropriate blank:
Recycle means to take something old and change into something new. So
some of these old rocks that have been around for more than four billion
years are being changed into different rocks. Of course, that doesn't happen
overnight. It takes millions of years. To better understand how this happens,
let's take a journey through the ______________.
Journey of the rocks begins in the mantle. Here there is
some red hot _________ that is being pushed up
towards the _________. Some of this magma creeps
into the cracks of the volcano; while, the rest is forced
out of the top of the volcano. Once the magma is out
of the volcano, it is called lava. The lava ______ and
forms ______________rocks.
Then some of the igneous rocks roll down the mountains formed by the
volcanoes and eventually end up in the ocean. As they roll, bits and
pieces of the igneous rocks are broken and form ___________. Layer
after
layer
of
sediments
are
pressed
and
cemented
together
forming ______________________________.
Some of the sedimentary rocks lying deep under the overlying layers get
hot because of the ____________ and change to _________________
rocks. When the metamorphic rock is buried deeper, it gets hotter and
melts. Once again, it becomes magma and may eventually be pushed up
and out of a volcano.
The rock cycle _______________ all over again!
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Magma
Rock cycle
Cools
Crust
Pressure
Sediments
Igneous
Metamorphic
Sedimentary
Begins
WORKSHEET-VI
Name of the Student:
Class:
Section:
1. Identify the activity in relation to the uses of rocks being depicted in the given picture
(a)
(b)
(c)
(d)
_(a)___________________________________________
_(b)___________________________________________
_(c)___________________________________________
_(d)___________________________________________
_(e)___________________________________________
(e)
2. Give an account of how are rocks useful to man?
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
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_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
Resources:
 A textbook of Geography – Class 9 –Rita Rajen
 Our World – Then and Now – Part II – S.Mukherjee, K.K.Maltiar, S.R.Maltiar
and V.Shukla
 http://www.jgms.ccs.k12.nc.us/WindJammers/Jones/_overlay/plates/1bookpgs/FTT01AAD.pdf
 http://www.geography4kids.com/files/earth_intro.html
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http://www.gisthai.org/resource/article/systematic_geo_eng.html
http://www.ehow.com/info_8746061_earths-layers-science-project-ideas.html
http://geology.com/nsta/earth-internal-structure.shtml
http://www.kidsgeo.com/geology-for-kids
http://www.universetoday.com
http://ratw.asu.edu/aboutrocks_igneous.html
http://tlc.howstuffworks.com/home/pottery2.htm
http://www.lung-cancer-blog.com/blogs/permalinks/1-2010/lung-cancermystery.html
sandstone.stoneworthindia.com
indiamart.com
flexiblelearning.auckland.ac.nz
ed101.bu.edu
geology.about.com
kishangarhmarble.com
http://www.mrsciguy.com/rocks.html
(http://www.rocksforkids.com/RFK/uses.html)
http://www.coaleducation.org/lessons/wim/20.htm
(http://www.sciencedaily.com/releases/2007/03/070301103112.htm)
http://library.thinkquest.org/20035/newpage4.htm
http://facts.randomhistory.com/2009/09/17_earth.html
http://geology.com/rocks/sedimentary-rocks.shtml
http://geology.about.com/od/more_igrocks/a/granite.htm
www.thefreedictionary.com
http://www.computerclipart.com/
tnsindia.net
india-server.com
westernreservepublicmedia.org
education.com
www.cotf.edu
wn.com
oceanworld.tamu.edu
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indiatalkies.com
www.visitjohnstownpa.com/.../
Google Images
mii.org
soil-net.com
csmres.jmu.edu
pitt.edu
eurasian.in
galleries.com
www.swisseduc.ch/.../glossary/basalt-en.html
rocks-rock.com
vijayacement.com
www1.newark.ohio-state.edu
flexiblelearning.auckland.ac.nz
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