Learning-Science-PartI.pdf

7/27/2019 Learning-Science-PartI.pdf

1/91

LEARNING SCIENCEPart 1

Universe, Solar System, Earth

Indumati RaoC. N. R. Rao

JAWAHARLAL NEHRU CENTRE FOR

ADVANCED SCIENTIFIC RESEARCH,

BANGALORE


2/91

About the Authors

Mrs. Indumati Rao has received degrees from the Universities of Mysore,Kanpur and Purdue (U.S.A.) and certificate in Education from Oxford University

(U.K.). She has worked for over four decades in the field of education. She has

contributed to developing new methods of teaching and teaching aids. Mrs.

Rao has worked as a geography expert in many institutions. She has participated

in several teacher orientation programs conducted by the Karnataka State. She

has authored books in Geography. At present, she is working as the Honorary

coordinator of the multimedia group at Jawaharlal Nehru Centre for Advanced

Scientific Research.

C. N. R. Rao is Linus Pauling Research Professor at the Jawaharlal Nehru

Centre for Advanced Scientific Research and honorary professor at the Indian

Institute of Science. He was at the Indian Institute of Technology, Kanpur, and

has been a visiting professor at University of California, Santa Barbara. He is a

member of many science academies including the Indian National Science

Academy, the Royal Society, London, U.S. National Academy of Sciences,

Russian Academy, French Academy, Pontifical Academy and Japan Academy.He was President of the International Union of Pure and Applied Chemistry,

and is now President of the Third World Academy of Sciences.

He has received several medals and prizes which include the Marlow Medal of

the Faraday Society, Centenary Fellowship of the American Chemical Society,

Einstein Gold Medal of UNESCO, the Centenary Medal of the Royal Society

of Chemistry, London and the Hughes medal of the Royal Society. He has

published more than 1300 papers in the areas of Chemical Spectroscopy,

Molecular Spectra and Chemistry of Advanced materials. He has authored 38books and has been active in science education. He was awarded the Karnataka

Ratna in 2001 by the Karnataka Government. He is the first recipient of the

India Science Prize, the highest scientific award recently instituted by the

Government of India and the Dan David International Prize for Science (2005).

He was recently awarded the Chevalier de la Legion dHonneur, the highest

civilian award of France (2005). He was also named the `Chemical Pioneer of

2005 by the American Institute of Chemists, USA.


3/91

LEARNING SCIENCE

Part 1

Universe, Solar System, Earth

Indumati Rao

C. N. R. Rao

JAWAHARLAL NEHRU CENTRE FOR

ADVANCED SCIENTIFIC RESEARCH,

BANGALORE - 560 064.

With the assistance of

Jatinder Kaur

Sanjay S. R. Rao


4/91


5/91

Preface

Science has become a part of our lives. Applications of science haveprovided us many benefits, and a better quality of life. The world today

uses a language which has a lot of science in it. Without knowing, we use

many words and phrases derived from science. We are also becoming

conscious of our environment as well as our economy. Science has much

to do with both these aspects. It is, therefore, important to learn the language

of science. Children and adults alike have to know the rudiments of science

and must be able to use the language of science where necessary. Theymust be able to apply the lessons learnt from science in daily life.

It is for this purpose that we have produced a book entitled Learning

Science in four parts. The book has the following four parts:

Part1: Universe, Solar System, Earth

Part2: The world of physics and energy - Learning physical principles

Part3: The world of chemistry: Of molecules and materials,

Air around us, All about Water.

Part4: Biology and life

It describes various aspects of science in simple language. It is hoped that

this will be useful to school children as supplementary reading material

and to all others who want to learn science and partake in the excitementof this experience.

Bangalore Indumati Rao

2005 C. N. R. Rao


6/91


7/91

CONTENTS

Preface (iii)

1. Understanding the Universe 1

Objectives 1

What is the universe? 2

Light-Year 6

Stars 9Constellations 14

2. Exploring the Solar System 18

Objectives 18

How did the solar family begin? 19

Getting to know the sun 26

Planets - chips of the old block 31

Special features of planets 38

3. Earth - the unique planet 49

Objectives 49Our unique planet 50

The earth - our home planet 57

Motions of the earth and seasons 78


8/91


9/91

2 Learning Science

What is the universe?We will try to understand the meaning of universe

by taking an imaginary journey through space.

Your spaceship is now blasting off into space.

You are 1.6 million (1.6 x 106) kilometres into

space. The earth looks big and bright in the

darkness of space. The moon looks small.

You also see some familiar stars

and constellations. The stars,

however, remain unchanged.

Second stage of the journey, ~1.6 x 109 km into space.

Now you can see Mercury,

Venus, Earth and Mars close to

the sun. They look bigger than

they actually are. The stars do

not show any change in size or

position.


10/91

Learning Science 3Deeper into space 1.6 x 1011 km into space.

You are 25 times farther from the

sun than Pluto, the planet

farthest from the sun. You can

see all the planets. The sun looks

prominent and the earth looks

small. You can see the Milky

Way clearly.

Now you are very far into space. The distance from the earth can no longer

be measured in kilometres. It has to be measured in light-years.

One light-year = 9.41 x 1010

kilometres. You are 16 light-

years into space. The Milky Way

dominates your view. The sunand the planets look tiny. You

can see some stars which are

close to the sun shining brightly.

1.6 million light-years into intergalactic space.

Our sun is just a speck. It is

almost lost in the group ofmillions of other stars. You can

see many new clusters of stars

that you cannot see from the

earth.


11/91

4 Learning Science

As you continue on yourimaginary journey through inter

galactic space, the view from

your spacecraft may look like

this.

All things from microscopic

particles to the biggest galaxies

are part of the universe.

You are a citizen of the universe

Give your address in full;

How was the universe formed?In the beginning, there was just a point of infinite density and energy. Some

15 billion years ago, a fiery explosion now called the Big Bang occurred.

Immediately after the explosion, the universe expanded rapidly from the size

of a pin to about 2,000 times the size of the sun. When the universe was less

than a second old, it was dense as iron and it was also opaque. After 500,000

years, the universe gradually cooled to ~3,0000K. The elementary particles

fused to form hydrogen andhelium gas - the life blood of the universe.

Name

House number, Street,

Block number, City - pin code,

State,

Country,

Continent,

Planet,

Universe.


12/91

Learning Science 5Hydrogen and helium formed gas pockets at random. In these pockets proto-galaxies began to form. Between one and two billion years after the Big

Bang, the proto-galaxies gave birth to galaxies, stars and other members

of the universe.

Is the universe expanding?

The ever expanding universe

Till the early part of the twentieth century, astronomers believed that the

universe, was infinitely large, but did not change its size or shape.

However, towards the end of the 1920s, Edwin P. Hubble showed that, the

galaxies were moving away from each other and moving in all directions.

That is, the universe is expanding all the time in all directions.

Edwin Powell Hubble (1889-1953)

Hubble is considered to be the founder of extragalactic astronomy - the

branch of astronomy that studies the existence of other galaxies. He was

the first to observe the evidence of the expansion of the universe. He

discovered that all nebulae in the sky are not part of the Milky Way

galaxy. Until his observation in 1924, astronomers believed that all the

nebulae were part of our galaxy.


13/91

6 Learning Science

Hubble made his second major discovery - In 1927 - that the galaxies heobserved were moving away from our galaxy. In 1929 - the universe was

expanding. Hubble received many honours for his outstanding

contributions to astronomy. The most advanced telescope to study

intergalactic world is named after him.

After the Big Bang, Big crunch?

Will the universe expand forever? Or will it collapse at some point of

time to signify the end?The density of the hydrogen atoms/m3 and the fate of the universe

Some, modern astronomers believe that: if the density of the universe is less

than 3 hydrogen atoms/m3, its gravity is not enough to hold the matter together;

i.e. the universe will expand forever. If its density is more than this, the gravity

will cause the collapse of the universe and the big crunch will occur.

Light-Year

Measuring distances between starsWhen we look at the sky, the stars look close

enough to each other to form patterns in the

sky. Actually, some of them are millions of

kilometres apart. How can we measure the

distance between them, or for that matter,

their distance from the earth?

Measuring distances

We can measure the distance between A and B in

centimetres (or inches).

We can measure

the distance in

metres (or feet)

as in swimming

or athletics.

A B


14/91

Learning Science 7The distance between two cities or continentsis measured in kilometres (or in miles). Each

unit of measurement has a specific use.

For example, we do not measure the distance

between A and B in ki lometres or the

distance between New Delhi and London in

centimetres.

The problem of measuring the distance between

stars

It is not possible to measure the distance of a star or any other object in the

sky from the earth by the usual methods because,

of the enormous distance of the stars from the earth.

it is not possible to use a physical scale.

To measure this distance, therefore, scientists have found a method of using

light rays that come from the stars or any celestial object in the sky.


15/91

8 Learning Science

The sun - our nearest starThe distance between the sun and the earth is ~ 150,000,000 km. So, the

light rays from the sun have to travel 150,000,000 km to reach the earth.

Astronomers have found that a ray of light from the sun covers this

distance in 8.3 minutes.

What is the distance covered by the light

rays (from the sun) in a second?

What is a light-year?

A ray of light from any

celestial object covers

9.41 x 1010 km in a year.

This distance is called

the light-year. The light-

year is the unit used tomeasure the distance

between celestial

objects in the sky and

the earth. Proxima

Centauri is the next

nearest star from the

earth. It is 4.2 light-years

from us.

~ 150,000,000 km


16/91

Learning Science 9How old are the light rays from the stars?The light from the sun that reaches our eye at any

instant will have left the sun 8.3 minutes earlier. If

you see the sunlight at 7 a.m., you are actually

seeing the sunlight of 6:52 a.m.

When we see the light

from the star Proxima

Centauri, they are

already 4.2 light-yearsold. A light ray from the

Andromeda galaxy that

you see, is 2.2 million

years old.

Stars

This is how the night sky might

look on a clear moonless night.

Hundreds of stars twinkling in the

night sky. If you observe carefully,

you can see some bright objects not

twinkling at all. These are the

planets.

Our earth is also a part of the star-

lit sky. If we were to look at the

night sky from the moon or Mars,

the earth would not be twinkling.

Planets

Ancient sky-watchers or astronomers noticed that stars that did not

twinkle wandered through the sky. They called these stars, wanderers

orplanets (Greek word).


17/91

10 Learning Science

They named them after their gods - Venus, Jupiter, Mars. According to them,the sun and the moon were also planets! Now we know better. Planets

shine steadily. They do not have light of their own. They merely reflect

suns light. They do not twinkle, because their flat discs reflect a lot of

light. We can view the surface of a planet through a telescope.

On a cloudless new moon

night, we can see a faint band

of white light glimmering

across the sky.

This band consists of millions

and millions of stars. The stars

appear in groups or clusters.

Group or clusters of stars

are called galaxies.

The white band of stars seen

across the sky is the Milky

Way galaxy.Our sun is in its outer arm.

Galaxies

Galaxies are systems or families containing millions of stars. In addition

to stars, galaxies also contain cosmic dust and gases. Sir William Herschel,

the famous 18th century astronomer, called them islands in the sky. There

are millions of galaxies in the universe. Galaxies are millions of light-

years apart from each other. There is vast empty space between them.


18/91

Learning Science 11Milky Way galaxy

The Milky Way galaxy contains around 200

billion stars. The stars are too far away from us

to be seen individually or by the naked eye. The

light from these stars forms a glowing haze in

the sky as their light blends with the inter-

stellar dust and gas.

This glow obviously has been seen by people

from the early times. The ancient Egyptianscalled it the Road of Souls and the bushmen of

the Kalahari desert called it the Backbone of Night. In India, it is called

Akash Ganga. Astronomers call it the Milky Way galaxy, our home in

the vast universe.

There are millions of galaxies in the universe

All the galaxies do not have the same

shape,

size and number of stars.

Depending on the shape, galaxies are classified as: Spiral galaxy, Elliptical

galaxy. The classification is called Hubble classification, named after the

famous astronomer Hubble. Have you heard of the Hubble telescope?


19/91

12 Learning Science

What are the stars made of?

You must have wondered about the twinkling stars in the sky. Remember

the nursery rhyme, Twinkle Twinkle Little Star? Remember the story of

Dhruva?It is now known that stars are actually made up of hot gases - mostly

hydrogen and helium. Hydrogen is being continuously changed to helium

in the stars. The stars glow due to enormous heat and light energy produced

by this reaction.

Why do stars twinkle?

Stars are far away from the earth. The light rays from

a star have to pass through the earths atmosphere.

In doing so, they undergo bending or refraction.When there is a wind, the amount of bending of the

light rays changes. This makes the star twinkle.

Stars in the sky

There are stars of different sizes, brightness and even colour. Also, the stars

are not evenly distributed in the sky. They are not as close to each other as

they appear to us from the earth.


20/91

Learning Science 13Brightness of stars

Strike a match and hold it close to your eye. It blinds you as if you are

looking at a powerful light. It is the same with the stars. The brightness of

a star depends on its shape, temperature and most importantly its distance

from the earth. The stars that appear merely as faint points of light may

be actually bright, but appear faint because of the distance.

Colours of stars

All stars do not have the same

colour. Some are reddish, some

yellowish and some are whitish

or bluish white. The colours

indicate the temperature of the

stars. When we heat a metal bar,

it first turns red, then orange,

then yellow and finally white.

The range of colours of stars

also follow the same pattern.

Red stars are the coolest and

bluish white stars are the hottest. Our sun is a yellow star.

How are stars born?

Stars are born out of a fast rotating cloud of gases and dust particles. The

cloud of gases and the cosmic dust particles constitute a nebula. A nebula is

a star nursery.


21/91

14 Learning Science

Do stars die?Anything that is born has to die after completing its life cycle. Some insects

die within a day of being born.

Redwood trees live for hundreds of years. An elephants average life span is

about 70 years. Human life span is

approximately 100 years.

A star too has its own life cycle, but it

spans billions of years. At the end of its

life cycle, the beautiful twinkling star

loses all its light and heat, and becomes

a cold black dwarfin the sky. Our sun

is a middle aged star.

Constellations

Some star groups form recognisable patterns. During the course of the night,

they appear to change their positions in the sky. But the stars forming the

pattern remain together. The star forming patterns in the sky are called

constellations. There are altogether88 constellations.

Our ancestors were great sky-watchers. They

noticed patterns in the sky and gave names to

them.

There is a group of stars occupying a fairly large

patch of the sky. This is the well known

constellation Ursa Major or the Great Bear.

The Big Dipper is a part of this constellation.


22/91

Learning Science 15There are seven prominent starsforming the tail and the back of the

Great Bear. Join these stars with

imaginary lines. You can see the

shape of a pan with a handle.

This is called the Big dipper or the

Plough. It is also called the

Saptarishi or the Seven Sages. The

last two stars in the pan of the Big

Dipper are called the Pointers.

Constellations do not remain in the same position

The earth rotates from the west to

the east. Therefore, the stars and

constellations appear to move across

the sky from the east to the west.

Also, the earth revolves around the

sun. As a result, different constellations

are visible during

different seasons.

Ursa Minor or the little BearThere is another well known group of stars

or constellation close to Ursa Major. This

constellation also has a group of seven

stars. The stars form a Dipper. The Little

Dipper is smaller and less bright than the

Big Dipper. The last star in the handle of the Little Dipper is the Polestar.

This constellation is also known as the polestar constellation.


23/91

16 Learning Science

The polestar

The polestar always appears in the same position in the night sky.

Different stars have occupied the polestar position during different

periods of time. The change of stars takes place once in ~ 2,400 years!

The polestar now is Polaris. The next one will be Vega. The polestar is

also known as Dhruva Nakshatra.

Orion

The constellation Orion has also been known to

sky-watchers since prehistoric times. Orion has

some of the brightest stars. Orion is called the

Hunter with the unbreakable club.

Orion is easily recognised with its belt of three

bright stars and the bright stars of the Sword.

Orion is visible clearly during winter in the

Northern Hemisphere.

The largest constellation - Hydra, the Sea Serpent

This constellation is visible more clearly in the southern sky. It occupies

nearly one-fourth of the sky. It stretches from Gemini to the south of Virgo.


24/91

Learning Science 17It is long and winding. No wonder then, it looked like a serpent to ourancestors. January to February is the best time to view this constellation.

Legend of Hydra

According to Greek mythology, Hydra was a nine-

headed sea monster serpent (much like Kalinga in

the Hindu mythology?).

It was dreaded as it had the unique power to grow

back a severed head. In the end, Hercules killedHydra with the help of Iolas. Iolas cauterised the

neck of the severed head with a hot iron.

The smallest constellation- the southern cross

It cannot be seen by observers in the Northern Hemisphere.

Southern Cross nestles at the feet ofCentaurus. Sailors used the position

of the Southern Cross to know their location.


25/91

18 Learning Science

2

Exploring the Solar System

Objectives

In this module, we learn about the sun and the planets.

In the entire solar system, it is only on earth we find diversity in life.

The sun is responsible for the diversity and evolution of life.

We depend so much on the sun, that it is important that we know

something about the solar system.


26/91

Learning Science 19The sun is only one of the millions of stars moving through space. Yet, whatmakes this average star special?

It is the only star known to have a family of its own. Wherever the sun goes

in the celestial sky, its family follows it.

How did the solar family begin?

About 5 billion years ago, there was no

sun. Therefore, there was no earth andno moon.

Instead, only gases and cosmic dust

were drifting in the darkness of space.

There are two theories about the

birth of the solar system.


27/91

20 Learning Science

According to an earlier theory, astronomers believed that long ago, a starpassed very close to our sun. The star andour sun nearly collided.

As a result, large quantities of various materials were thrown off into space.

After a long time, these materials formed the planets. The sun held the planets

in place. This theory has serious drawbacks.

According to modern astronomy, the solar system

was formed from a slowly spinning cloud of gas

and dust.

Gradually, the cloud began to spin faster and

faster. This formed a large spinning disk about

the size of the solar system - with a large spinning

whirl at the centre and smaller whirls surrounding

it at various distances.

The huge and heavy centre became hot enough to start the thermonuclear

reaction. As a result, the centre began to glow and became oursun.

Modern astronomers believe that everything in the solar system has the same

source material.


28/91

Learning Science 21Planets or wanderersThe smaller whirls attracted more and more

particles from the cloud of dust and gases and

grew in size. They were like snowballs rolling

down a snow-covered mountain. Finally, they

formed the nine planets at varying distances

from the sun.

The four planets - Mercury,

Venus, Earth and Mars are

closer to the sun. They are called

the inner planets and the other

five planets - Jupiter, Saturn, Uranus,

Neptune and Pluto are called the outer

planets.

The planets are independent of each other and

they move in their own respective paths or

orbits around the sun.

Solar family or the solar system

Apart from the nine planets, solar family includes

tiny sand-like objects as well as gigantic rocks.

moons.

thousands of asteroids.

millions of meteors.

millions of comets.

All the members of the solar system

revolve around the sun along their

respective paths at varying speeds.


29/91

22 Learning Science

The Moons

The moons are the natural satellites revolving around the planets in the

solar system. Except Mercury and Venus, all the other planets have moons.

While the Earth andPluto have one moon each, Uranus has 15, Jupiter

16, andSaturn 18. The size and composition of the moons vary. Some

moons are only a few kilometres in diameter, while others are larger than

the planet Mercury.

While the earths moon is rocky, Saturns Enceladus is ~ 50% ice. Satellites,

Io, Europa, Ganymede and Callisto of Jupiter are Galilean moons.

They were discovered by Galileo in 1610.

Asteroids - A ring of space rocks

What are asteroids?

Between the orbits ofMars (the last of

the inner planets) andJupiter (the first

of the outer planets), asteroids orbit

around the sun.Astronomers believe that

The asteroids are pieces of a planet that came too

close to Jupiter.

The enormous gravitational force of Jupiter broke up

this object into pieces of rock and metal.

And these pieces of varying sizes continued to

revolve around the sun.

Asteroids

Asteroids are too small and too far from the earth to be seen without a

telescope, Even through a telescope, they look like faint stars.

Guiseppe Piazzi, an Italian astronomer, discovered the first asteroid. He

called it Ceres after the Roman goddess of agriculture. It is the biggest

asteroid and yet it takes 5000 Cereses to balance the earth in a gigantic

balance!


30/91

Learning Science 23What are meteors?Meteors are the stony or metallic pieces travelling around the

sun. There are billions of meteors in the solar system.

Meteors can be as small as sand grains or as big as

boulders.

They travel alone around

the sun or travel together in swarms of billions

of particles.

Meteors travel at great speeds around the sun.

Sometimes when a meteor comes close to the

earth, the meteor is pulled towards the earth by the gravitational force of the

earth. When a meteor enters the earths atmosphere, it streaks across the sky

as a shooting star. While most of the meteors burn out in the earths

atmosphere, some big ones land on earth. Those that land on earth are called

meteorites.

Comet - the mysterious member of the solar family

A comet streaking across the sky has

inspired awe and fear in people from

ancient times. The orbits of comets are very

large with the sun off centre. Comets come

closer to the sun at one end and go almost

to the edge of the solar system at the other

end.


31/91

24 Learning Science

A comet has no light of itsown. Its light is entirely

reflected sunlight. Comets do

not streak across the sky. Even

though they travel at great

speed, they stay visible in the

sky for weeks as they are far

away from us.

Comets return to view at

regular intervals.

Edmund Halley,

of England was

the first to observe this phenomenon.

Halleys comet is the most famous comet. It visits the earth once

in 76 years. Its most recent visit was in 1986. Halleys comet

was first observed in 240 BC by Chinese astronomers.

Hale-Bopp is the brightest comet that was seen in the 20th century.

It was discovered in 1997 by Alan Hale andThomas Bopp ofUSA.

The shape and structure of a comet

A comet is shaped like a thin torpedo.

It has two distinct parts; a nucleus or

head and a tail.

The head of a comet is made up of

frozen gases, cosmic dust and ice. It

looks like a dirty snow ball.

When a comet comes close to the sun,

the outer layers of the head begin to

evaporate. The winds from the sun

blow the gas and dust particles away

from the sun. This looks like a bright tail. The comet develops a long tail

extending millions of kilometres into space.

nucleus or head

tail


32/91

Learning Science 25The revolving planets do not fly into space. Why?The sun is a very powerful

master. He keeps all the

members in place. How does the

sun do it? We will try to

understand it by a simple

activity.

Take a string about 3 metres. Tie a small round object to one end. Stand in an

open place and rotate the string horizontally as fast as you can.

Let go of the string. What do you notice? The stone flies off. As long as youwere holding the string, the stone was moving in a circle.

This is how the sun holds his family together

Nearly 99% of the total mass of the

solar system is in the sun. This gives

the sun an enormous force of

attraction. The force produced by the

revolution of the planets is balanced

by the suns gravitational force.

This balance of forces keeps the

members of the solar family in

place. Sitting in the centre, the

sun perhaps keeps an eye on

them!


33/91

26 Learning Science

Getting to know the sunThe sun is literally the star of the family. Like all stars,

the sun is a huge ball of hot gases.

Its temperature is

so high that all

the elements in

the sun are in the

gaseous state.

The sun consists mostly of hydrogen.The other element present in large

quantities is helium.

How old and how many more years to go?

The sun is 4.6 billion years old and has ~ 10 billion years to go. The stages in

the life of our sun (or any other star) are:

Main sequence of a star

The main sequence stage is the longest and

perhaps the most important stage in the life cycleof a star. The contracting nebula has a central

bulging core in which thermonuclear reactions

cause the nebula to shrink and finally end itself.

Then the hot centre begins to glow with its own

light and changes into a star that is stable. At

this stage, the star gives out its own heat and

light. Our sun is in its main sequence now.

Main sequence Red giant stage White dwarf stage Black dwarf stage

The sun is in the main

sequence stage now.


34/91

Learning Science 27Based on the surface temperature of the sun, it is classified as a yellow starwhich is in the middle of its main sequence.

The red giant stage

In this stage, the sun expands upto 100 times of its original size. Its surface

resembles a red hot burning charcoal due to the high temperature. Then the

sun emits enormous solar energy, as a result of which the planets close to the

sun could melt and turn into a liquid state.

On earth, all the water in the oceans could evaporate and form giant clouds

of vapour.

The white dwarf stage

The red giant stage cannot last forever. When the

fuel in the red giant, i.e. hydrogen, is exhausted the

red giant becomes unstable. Its outer layers begin

to separate and disappear in space. The centre ofthe sun gradually cools and the light becomes dim.

Then the sun becomes a white dwarf.

The black dwarf stage

After a billion years, the white dwarf cools and gradually the light fades.

Lastly, the sun which gave heat and light to all the members of the solar

family and was responsible for the evolution and sustenance of life on earth,


35/91

28 Learning Science

itself loses all the heat and light to become a black dwarf. This is the laststage in the life cycle of the sun.

Layers of the sun

The sun we see day in and day out is only one layer of the sun. Let us find out

about the different layers of the sun.

Core, the engine room

All the energy of the sun is producedhere. It is deep inside the sun. The

energy released in the core travels to

the outer layers. Thetemperature in

the core is ~15,000,0000C

Photosphere - the sphere of light

Photosphere is what we see. Its surface temperature is around 60000C. It is a

thin layer. Its thickness is ~544 km. Sunspots were first discovered by Galileo

in the 16th century. Photosphere has dark patches. They are calledsunspots.

Galileo

Galileo discovered

that the surface of the moon was not smooth.

that the Milky Way consisted of millions of stars.

that Venus also had phases.

the rotation of the sun.

the sunspots covering the face of the sun.

the moons of Jupiter.

Galileo was the first to actually see the moons of Jupiter

when he focussed his telescope on Jupiter in 1610. He also

saw the rings around Saturn. He discovered all these by

looking through his telescope night after night!!


36/91

Learning Science 29Sunspots

Sunspots are the dark patches of different sizes and

shapes that are seen on the photosphere of the sun.

Galileo was one of the first to observe the sunspots

through his telescope in the 17th century. The sunspots

have two distinct parts the umbra or the dark core

and the surrounding penumbra.

Chromosphere - the sphere of colourChromosphere is a transparent layer. It is much

hotter than the photosphere. Chromosphere can

be seen only during total solar eclipse.

Chromosphere is seen as a thin red ring around

the dark disk of the sun.

Corona - the crown

Corona is the outermost layer of the sun.It stretches millions

of kilometres into

space.

The temperature of

the corona is around

2,200,0000C. Corona

can be seen only

during total solar

eclipse.

Corona presents a

spectacular sight as

white streamers or

white petals around a

darkened sun.


37/91

30 Learning Science

Suns motionsAsk your friend, `Does the sun have motion? Your friend is likely to laugh

and reply `Have you not seen the sun move across the sky from sunrise to

sunset?

The sun has two motions. They are:

Rotation on its axis and

Circular movement among its neighbouring stars

and constellations.

Its rotation period at its equator is 25 earth

days and at its poles, it is 35 earth days. (1

earth day = 24 hours)

The sun seems to be in a hurry to visit its

friends, for, it travels at 250 km per sec. The

sun does not move across the sky from

sunrise to sunset.

Vital statistics of the sunAge ~4.6 billion years

Mass 330,000 (earth = 1)

Density 1.41(water = 1)

Waist (diameter at the equator) 1,400 million km.

Average distance from earth ~150 million km.

Surface temperature 60000C

Core Temperature ~15 million 0C

Rotation period

at the equator 25 Earth days

at the poles 35 Earth days


38/91

Learning Science 31Planets - chips of the old block

Planets are made of the same elements as the sun.

Planets have

solid rocks / gases.

varying amounts of water as

water / water vapour / frozen ice

(depending on their distance

from the sun),

and an atmosphere comprising of various gases.

It is only on earth that

water is found in all the

three states i.e. ice (solid

state), water (liquid state),

and water vapour

(gaseous state).

Same, yet differentThe planets vary in size, their distance from the sun and in their structure.

Jupiter is the largest planet and Pluto is the smallest. The sun is ~600

times bigger than Pluto, but only ~10 times bigger than Jupiter.

Jupiter

Sun

Pluto


39/91

32 Learning Science

Nearest and the farthestMercury is nearest to the

(57.9 million kms) sun and

Pluto is farthest from the sun

(5,900 million kms)

Pluto is a lonely planet. Its

closest neighbour Neptune is

nearly 1,414 million km

from it.

Mercury, Venus, Earth and

Mars are relatively close to the

sun. They are grouped together

as terrestrial planets.

Mercury

Mercury is the closest planet to the sun. It is difficult to spot mercury in

the night sky as it is very close to the sun. Mercury is a small planet. Its

mass is 0.055 (Earth = 1). Its surface temperature ranges from very cold to

very hot (-1800C to 4300C). Mercury revolves fastest around the sun (47.9

km/s). It rotates slowly (58.65 earth days to complete one rotation). Itssurface is scarred by craters. It has a huge iron core.

Terrestrial planets

Terrestrial means earth-like. Mercury, Venus, Earth and Mars - the

terrestrial planets, are also called inner planets. Venus and Earth are

about the same size. They are also calledtwin planets.


40/91

Learning Science 33Giant planets or the outer planetsJupiter, Saturn, Uranus and Neptune are called the giant planets or the

gaseous planets. They

are massive.

rotate faster.

have many moons.

They are so far away from the sun that they retain most of the volatile elements

from the original cosmic cloud. Water seems to be frozen on their rocky

cores.

The moon - earths satellite

What is special about the earths satellite

(moon) in the solar system? According to our

present knowledge, in the entire solar system,

man has set foot only on the moon.

In 1969, Neil Armstrong of

USA was the first to set foot

on the moon. His foot prints

will remain for thousands of

years on the moons surface.

Why? (Clue: there is no

atmosphere on the moon)


41/91

34 Learning Science

A day on a planetA day is the time taken by a

planet to complete one rotation

on its axis. Duration of a day is

not the same on all planets.

A day is shortest on Jupiter.

It is a 10 hour day on Jupiter.

It is difficult to know the duration

of a day on Venus because of itsdense atmosphere.

The smaller

planets closer to the sun have

longer days.

Each planet has its own day i.e. the time taken to complete one rotation.

Still `a day of any planet is expressed in terms of the earth day (24 hourperiod).

A day in a planet

Planet Duration of a day

Mercury 88 earth days

Venus around 30 earth days

Mars 24 hours 15 m

Jupiter less than 10 hrsSaturn 10 hours 15 m

Uranus 11 hours

Neptune 16 hours

Pluto 6 days and 9 hours

Jupiter

Earth

Venus


42/91

Learning Science 35Is life possible on other planets?The sun provides light and heat energy to all other planets. Why is

development of life not possible on other planets? Some planets are too hot

(Mercury) while some are too cold (Pluto).

Some lack an atmosphere while others are covered

by an atmosphere that has little life-supporting gases.

Life supporting

soil and water

(in liquid state)

are not available

in other planets.

What are the criteria for

evolution of life on a planet?

The two important criteria for evolution of life on a planet are: (i) the distance

of a planet from the sun and (ii) the size of the planet.


43/91

36 Learning Science

The distance of a planet from the sun:If the planet is too close to the sun, chemical compounds cannot remain

stable. If it is too far from the sun, water will be frozen and chemical

reactions cannot take place there.

The size of a planet:

If the planet is too small, its gravitational pull

will not be enough to hold the atmosphere.

If the planet is too big, its gravitational

pull holds a very thick layer of

atmosphere. This dense atmosphere

will not let solar energy reach the planet.

Only the earth is at the ideal distance

from the sun and has the ideal size to

support life.

Is there life on Mars?

Why do scientists believe that Mars is the only other planet

which can support life? Detailed studies of Mars have revealed

that

the length of a day on Mars is almost the

sameas an earth day.

the martian year and its seasons are twice

as long as ours.

it is green during its spring and brown

during its autumn.

its polar caps grow larger during its

winter and shrink during its summer.

But its atmosphere is thinner, seems to have very little

oxygen and water vapour.


44/91

Learning Science 37Is there life elsewhere in the Universe?There are billions of stars in the universe. Astronomers strongly believe that

there are many stars similar to our sun in

the universe and these stars are likely to

have planetary systems.

if even one planet is at the ideal distance

from its star, and has the right size, there

can be living organisms on the planet.

How can we find out if there

is anyone else in the universe?

In principle, every television

programme or radio broadcast can be

heard - many light-years later ofcourse - on the other stars.

Carl Sagan

the famous

radio astronomer was convinced that we were not

alone in the universe. His group sent an image signal

in 1974 towards the Great Cluster of stars 25,000

light-years away.

The reply will arrive 50,000 light-

years later if our friends reply assoon as they receive the greetings.

The search for extra-

terrestrial intelligence

Radio signals or clapping hands? How

do you catch your friends attention in a

crowded room?


45/91

38 Learning Science

You can either shout or clap your hands. As these sounds donot blend with the other sounds in the crowded room, you

can catch your friends attention.

Likewise, a signal from an alien from another world may be

a sound that is different from any otherearth sound or may

be, he/she will send a photo image! digital of course.

Special features of planets

Distance of the planets from the sun

The nine planets are arranged at varying distances from the sun. Earth is

~150,000,000 km from the sun. This is taken as the astronomical unit (AU).

Bodes law:

In 1770, Bode of Germany, put forward a strange law to calculate the distanceof a planet from the sun. He allotted numbers at random to the planets. Mercury

= 0, Venus = 3, Earth = 6, Mars = 12, ..........

He added 4 to these numbers and divided the sum by 10. The resulting value

gave the distance in astronomical unit.

Planet Distance of the planet Actual distance

(According to Bode) of the planet

Mercury 0.4 0.39

Venus 0.7 0.72

Earth 1.0 1.0

Mars 1.6 1.52

Jupiter 5.2 5.22

Saturn 10.0 9.59

Uranus 19.6 19.36

Neptune 38.8 30.10

Pluto 77.2 39.78


46/91

Learning Science 39But according to knowledge available then, there was no planet in the positionof 24 and 192. Later, astronomers found asteroids in the position of 24 and in

1781, they discovered Uranus in the position of 192.

Only Neptune and Plutos distances did not conform to Bodes law. Even

though modern astronomers may consider Bodes law as a coincidence, this

law is one of the profound statements about the laws of nature.

Inclination of the axes of planets

The planets (except Pluto)

revolve around the sun in

approximately the same

plane. Their axes point to the

celestial north. However,

their axes are tilted in

varying degrees. Only the

axis of Mercury is almost

perpendicular to the plane of

its orbit or its inclination is 0

0

.Planets and the inclination of their axes

Mercury 00 Jupiter 30 07

Venus 2042 Saturn 26044

Earth 23027 Uranus 82008

Mars 25021 Neptune 29034

Orbits of all the planets are not the same

Orbits of the planets are not circular.They are elliptical or eccentric in

varying degrees. As the eccentricity

increases, the orbit becomes more

elliptical. Eccentricity of a circle is

zero.

The eccentricity of the orbit of Venus is

the least. (Its orbit is almost circular.)


47/91

40 Learning Science

The eccentricity of the orbit of Pluto is thegreatest. (It is elliptical.) In the solar system,

the orbits of comets are most eccentric.

Density of planets

The main difference between the gaseous giant

planets and the inner planets is in their

densities.

Density of a substance tells us how tightly the

matter in a body is packed.

Density of a substance = mass of the substance

volume of the substanceDensity of water is taken as the standard to measure the density of a substance.

Density of planets

Mercury 5.4 Jupiter 1.3 (mass = 318e)

Venus 5.2 Saturn 0.7 (mass = 95e)

Earth 5.5 Uranus 1.3 (mass = 14.5e)

Mars 3.9 Neptune 1.8 (mass = 17.2e)

Density of Pluto = 2.1(?)

The individual special characteristic of planets: a

brief look

Mercury - the planet that is hurtling around

the sun.

Mercury is closest to the sun. Naturally, it is the

hottest planet. Why does it hurtle at ~170,000

km around the sun?


48/91

Learning Science 41If it did not move at this great speed, the tremendous gravitational attractionof the sun would have pulled the planet towards its centre. What would have

happened?

Venus, the earths twin

Earlier, astronomers believed that there

was an abundance of life on Venus. But,

the reality is different. Venus is a violent

planet with violent storms and acid rain.

Venus is the brightest planet.

It shines as the morning star in the

constellation Taurus and as the

evening star in Libra. The highest

mountain in the solar system, Maxel mounts, is on this planet. This planet

rotates from east to west. The Mayans based their calendar on the revolution

of the planet Venus.

Venus, the greenhouse planet

The atmosphere here

consists mainly ofcarbon

dioxide and clouds of

sulfuric acid. As a result,

incoming solar insolation

is trapped. The dense layer

of CO2

and clouds of

sulfuric acid in the

atmosphere of Venusabsorb and trap enough

incoming solar radiation

to keep Venus hot even

through its 4 month long

night. As a result, this

planet has the greatest

greenhouse effect.


49/91

42 Learning Science

Oxygen

CO2

It gives this warning to us: If we do not mend our irresponsible ways,our planet also will hurtle towards the same fate.

Earth, the home of lifeforms

In the entire solar system,

life as we know it, exists

only on earth. This is due,

among other factors, to

the water cycle.

the rock cycle.

the carbon

dioxide cycle.

the oxygen

cycle.

The solar rays and

earths atmosphereThe sun provides heat and light to all the members

of the solar system. But the suns radiation

includes harmful gamma rays, x-rays and ultra-

violet rays. The earths atmosphere protects the

earth from the harmful gamma rays radiation.


50/91

Learning Science 43Gift of the earths atmosphere

At a height of approximately 50 km, the ozone layer

protects all life on earth from the harmful ultra-violet

rays. Clouds and

dust particles

absorb the infra-

red radiation to a

large extent and

reflect it.A small portion of

the white light

coming through the atmosphere is

scattered by clouds and dust particles. This scattering

of white light makes the sky appearblue during the day

andorange at sunrise and sunset.

In 1930, Professor C.V. Raman received the Nobel Prize

in physics for his work on the scattering of light. This is

also known as the Raman effect.

Jupiter - the planet with the red spot

Astronomers had observed the red spot

on Jupiters surface around 300 years ago.

But, its nature and cause have been

understood only recently.

In the lower

atmosphereof Jupiter,

there are

al ternate

belts of

rising and falling gases. They circulate in

opposite directions.


51/91

44 Learning Science

The red spot is actually a huge stormbetween two rising belts. It gets its red

colour from a chemical in the lower

atmosphere. This chemical rises with the

rising air currents and turns red in

sunlight. The red spot rotates in an

anticlockwise direction. Its period of

rotation is six earth days. How many

hours does it take to complete one rotation?

Could Jupiter have become a star?

The mass of the sun is 99% of the total

mass of the solar system. The mass of

Jupiter is 99% of the remaining 1%. This

is the only reason why the sun became a

star and Jupiter remained a planet.

Astronomers believe that if the mass of

Jupiter had been 100 times more than itsactual mass, the temperature in its core

would have been high enough to start

nuclear fusion.

About 4.6 billion years ago, when

the solar system began to form,

Jupiter was a huge ball of cosmic

cloud and dust. But, its mass was not

sufficient to exert great pressure on

its core. As a result, the heat

generated there was not enough to

start nuclear fusion.

Gradually, Jupiter cooled and

became a planet. Jupiter is cooling

down even today. It is the only planet that radiates more heat than the isolation

it receives from the sun.


52/91

Learning Science 45Comparison between Jupiter and the Sun

Sun Jupiter

Mass 3,30,000 318

(Earth as standard)

Volume 1,304,000 1,316

(Earth as standard)

Core temperature 1,50,00,0000K 30,0000K

Pressure 200 billion earth 100 million earthatmospheres atmospheres

Miniature models of solar system within the

solar system

The gas

g i a n t s

Jupiter and

Saturn have16 and 18

s a t e l l i t e s .

These two

planets have

held their satellites in place by their

gravitational force just as the sun holds

them in their place in the solar system.


53/91

46 Learning Science

However, unlike the sun, Jupiter andSaturn do not give heat and light to their

satellites. The sun is the source of heat

and light of these satellites also.

Why does Uranus rotate

almost on its side?

Astronomers give many explanations to the strange inclination of Uranuss

axis. According to one of the explanations, when Uranus was being formed,

a round object, an intruder from space, hit the young planet near one of its

poles. The force of this collision turnedUranus on its side and the intruding

object broke into pieces of rock and ice. The pieces of rocks, clouds of steam

and gases began to orbit around the plane of Uranuss equator. Gradually,

these became the planets, rings and satellites.

Neptune - the stormiest planet in the solar system

For a long time, astronomers believed

that Neptune was a calm blue planet.

But Neptune is the windiest planet,

with winds blowing upto 2,400 km per

hour. The width of some of the storms

is wider than the earth.


54/91

Learning Science 47How were the moons formed?The mental picture we get of the moon is the beautiful milky white object in

the night sky. But moon actually is the satellite of a planet.

Astronomers believe that after the main planets were formed, the remaining

small bits came together and became moons. They became the satellite of

the planets which held them by their gravitational attraction. All moons

are not the same. Let us look at some unusual moons.

Io, the moon with active volcanoes

The Galilean moons of Jupiter are Io, Europa, Callisto and Gyanmede.

There are at least 10 volcanoes on Io. The volcanoes on Io spew out

liquid sulfur and silicate rocks.

What is the difference between volcanic eruption on the earth and on Io?

Io Europa Callisto Gyanmede


55/91

48 Learning Science

Triton - the satellite with cold volcanoesCold volcano may sound like

a contradictory term. We are

used to hot lava pouring out of

the volcanoes here on earth but

the volcano on Triton spews

out liquid nitrogen.

As its temperature is very low,

liquid nitrogen gets frozen.

Titan - the sole satellite with atmosphere

Titan is the biggest satellite of Saturn. There is atmosphere only in this

satellite in the entire solar system. Its atmosphere consists mostly of nitrogen

and traces of methane. As the satellite is far away from the sun, methane is in

liquid form.


56/91

Learning Science 493

Earth - the unique planet

Objectives

What is unique about our planet? forms the theme of this module.

The rock and minerals, the motions of the earth and the seasons are

explored in this module.


57/91

50 Learning Science

Our unique planetOur earth is just a minor planet revolving around an average star. Looking

from the vastness of space, our planet may be no more than a speck.

Yet, this is the only member of the vast universe to have life.

Seeing is not believing - shape of the earth

For a long, long time, people believed in only what they could see, and they

did not see the round shape of the earth.


58/91

Learning Science 51The ancient Babylonians, the Egyptians, the Greeks, the Indians and theChinese had their own ideas about the shape of the earth.

The turtle, the elephants and the serpent:

The Indian idea of the earth

According to one idea, the earth was held

up by elephants. The elephants stood on

a turtle. The turtle was one of the ten

incarnations of Vishnu, the supreme God.The turtle rested on a cobra with its tail

in its mouth.

As the cobra symbolised water, the earth

was surrounded by water. Whenever the

elephants shifted their legs, earthquakes

took place.

The circular disc, the mountain and the

travelling sun - the Chinese ideaThe earth was a circular disc with the ocean surrounding it. There was a

great mountain in the centre of the circular disc (the earth). Once a day,

the sun went round the mountain going behind the western side of the

mountain in the evening. After travelling behind the mountain throughout

the night, the sun came out on the eastern side in the morning.


59/91

52 Learning Science

Changing shape of the earthIf you look at the earth from the top of a mountain, it will lookconical. If you

go down a wide valley and look at the earth, it will look like the inside of a

bowl. Ordinarily, if you look at it from where you are the earth will lookflat.

The round earth - early Greek idea

Pythagoras, the renownedGreek mathematician suggested that the earth

was round. Around 350 BC, Aristotle taught his pupils

that the earth was round.

Around 250 BC, Eratosthenes

calculated the circumference of

the earth for the first time by usingthe idea of a round earth.

Astronomers of ancient and medieval India were also aware

of the true shape of the earth.

Pythagoras 580 BC - 500 BC

Pythagoras was perhaps one of the greatest mathematicians of all time. He

contributed to the development ofmathematics andwestern philosophy.

He started a school or brotherhood. He believed that reality was mathematicalin nature, and that it was possible for the soul to achieve union with the divine.

Why did Pythagoras conclude that the earth was round?

According to mathematicians, a sphere is the most perfect shape. Like all

Greek philosophers and mathematicians, Pythagoras believed that the earth

was a perfect body.

He concluded, therefore, that the earth was round. He was nearly correct

in his conclusion about the shape of the earth.


60/91

Learning Science 53How did Eratosthenes calculate the

circumference of the earth?

Eratosthenes was the first to actually calculate the circumference of the

earth. Eratosthenes lived in Alexandria, an Egyptian town. There was a

deep and dry well in Syene, a town ~5000 stadia ( 800 km) to the south of

Alexandria. Eratosthenes came to know that on summer solstice day

(June 21), one could see the bottom of the well as there was no shadow at

noon on that day.

On the same day, he noticed that the sun at noon time was not vertical but

cast a shadow at Alexandria. Using Pythagoras idea of a round earth he

calculated the circumference of the earth.

Actual shape of the earth

The earth is not a perfect sphere.

It bulges at the equator and is slightly flattened

at the poles. This shape is called an oblate

spheroid.

This is the result of the earth

spinning or rotating very

fast on its axis,

and

rotating faster at its

equator than at its poles.

Isaac Newton was the first to suggestthis. The earths shape is also called

geoid.

Picture of the exact shape of the earth

The model suggested by Newton was not completely correct. Information

from space gave the exact shape of the earth.


61/91

54 Learning Science

Vanguard I in 1958 confirmed that the earths bulgeis:

not uniform.

not exactly at the

equator.

slightly more at

some places in the

southern hemisphere and at the north pole

Nearly 4.6 billion years after the earth wasformed, we finally know the shape of the earth.

If the earth is round, why do we see it as a flat earth?

We will find the answer to this question through a simple activity.

Take a sheet of foolscap paper, a pencil and a piece

of string at least 120 cm long.

Tie the string to the sharpened end

of the pencil. Fix the paper to the

top of a drawing board or a flat

table. Draw arcs of circles of

radius 5 cm, 35 cm and

110 cm on the paper.

Compare the curvatures of

the arcs of the three circles.

What can you conclude?

The biggest arc is curved least.

It is for the same reason that the

round earth appears flat. If you

want to draw the arc of the earths

surface, you will need a string ~6400 km long!


62/91

Learning Science 55Why is the earth round?Even the smallest particle of dust in the

vast universe has the power to attract

other things. At the time the earth was

being formed, particles of dust etc.,

attracted each other to form the tightest

possible shape - a sphere. This force of attraction is called

gravity or gravitational force.

Gravitational force

Do you know the story of Newton and falling apple?

London was hit by the plague

epidemic. So, Newton went to a quiet

village. While sitting under a apple

tree, an apple fell on his head. He

wondered why the apple fell down?

Working on this problem, Newtongave the Law of gravitation.

Gravitational force is the force of

attraction between objects.

All things big and small, including the

tiniest dust particle or atom in the

universe, experience this force. The

strength of this force depends upon

the weight of the object- the heavier

the object, the stronger is the force.

Centre of the earth and gravity

As in a sphere, the particles of matter of the earth are

crowded at its centre. Therefore, the force of attraction or

gravity is strongest at the centre of the earth.


63/91

56 Learning Science

Why dont we fall off the sides and bottom of around earth?

The reasons for us not falling off the round earth into space are:

there is no top or bottom or sides of the earth.

Everything that we see on earth is on its

outside, or the surface.

all objects on the surface are attracted

towards the inside or the centre of the earth. this force, or the earths gravity, holds

all things on the outside or on the surface of

the earth, and prevents them from falling off.

Why do things weigh a little more at the poles than

at the equator?

Gravitational force decreases as the distance from the centre of gravity

increases. Remember! Weight of a body = mass x acceleration due to gravity;W = m x g

The earth is not a perfect sphere. It

is slightly flattened at the poles.

Therefore, the poles are slightly

closer to the centre of the earth. As

a result, a person weighs slightly

more at the poles.

Armstrong, the first man to land on the moon, weighed

on the moon 1/6th his weight on earth. Why?

Can we escape from the grip of earths gravity?

We can do this, provided we are prepared to live in

a spaceship beyond the reach of earths gravity.

Why are the astronauts attached to the spaceship

by a long rope when they carry out repairs outside

the spaceship?


64/91

Learning Science 57Escape from earths gravity

To escape the pull of the earths gravity, we must reach the limits of the

atmosphere. Then, we have to enter into space. To do this, the spacecraft

with you in it has to travel at a speed of ~40,000 km per hour or 11.2 km

per second! This speed is called the escape velocity.

The earth - our home planet

We have explored space successfully. We have gathered evidence of whatlies beneath the waves.

It is strange but true that we know little about what lies beneath our feet.

Getting to know our planetIt is now known that the radius of the earth

is ~6400 km. The deepest mine, the

Champion Reef mine in Kolar Gold

Fields, (Karnataka) is

only ~2 km deep. One of

the deepest oil wells in

Pecos Oil Field in Texas

(USA) is only 8 km deep.

They are merely like

scratches on the earths

surface.

How can we get evidence about the earths interior?

We cannot take a pickaxe and dig through the layers of the earth. We do not

have any instruments to look through the layers. We cannot drill through the

Kolar


65/91

58 Learning Science

layers of the earth to its centre and get samples. It is, therefore, not possible

to get direct evidence. We can only have indirect evidence.

Earthquake waves and the indirect evidence of the

earths interior

An earthquake is always associated with destruction. But the earthquake

waves have unlocked some secrets of the interior of the earth. By the manner

in which they travel through the different depths, they provide evidence of

the nature of the earths interior.

What is an earthquake?

An earthquake is the shaking of the ground under

your feet. This is caused by the sudden release of

energy stored in the rocks. This energy is released

in the form ofwaves. They are calledseismic waves.

The place where an earthquake originates is called

the focus and the point directly above the focus (on

the earths surface) is called the epicentre. An

earthquake can be felt when it occurs just a few

kilometres below the earths surface.

Earthquake waves or seismic waves

There are three types of seismic or earthquake waves. They are;

The P wave or the primary wave - This wave can travel through both the

solid and liquid forms of the material in the earths interior. These waves

reach the earths surface first.

Focus

Epicentre

Ground surface


66/91

Learning Science 59S wave or the secondary wave - Thiswave can travel only through solids.

Their speed is approximately half the

speed of the P waves.

L waves or the surface waves - These

waves move only on the surface. They

are slower than the P and S waves.

The earthquake waves start from the

focus of the earthquake and reach the

earths surface.

What do the earthquake waves reveal?

By studying the way earthquake waves travel through the earths interior, we

now know that:

the materials of the crust and the upper mantle are in the solid state.

there is a soft zone in the mantle.

the iron and nickel outer core is in the liquid state (This is due to the

melting of the substances at high temperatures). the iron-nickel inner core is in the solid state due to the tremendous

pressure there.

Tsunami

Tsunami literally means harbour wave in

Japanese language. It is also called seismic sea

wave. This is one of the most catastrophic natural

disasters. It is caused by an underwater

earthquake occurring less than 50 kilometres

below the seafloor. This takes place due to two

tectonic plates either converging or one plate

slipping under another plate. The magnitude of

the earthquake has to be greater than 5.5 on the

Richter scale for the tsunami waves to be generated.

Coastal or underwater landslide or underwater

volcanic eruption may also cause a tsunami.

P - waves

S - waves

S - waves

L - waves


67/91

60 Learning Science

Tsunami is a more catastrophic disasteras its destructive force can be felt in

coastal regions thousands of

kilometres away from the epicentre of

the underwater earthquake or volcanic

eruption. Immediately after the

earthquake, a train of waves travel over

great distances at the ocean surface in

ever- widening circles. This can be compared to the waves produced by a

pebble thrown into a shallow pool of water.

As the tsunami waves approach the continental coasts or coasts of islands,

increasingly shallow seafloor reduces the velocity of the waves. This in turn

makes the coastal water rise as high as 30 m in 10 to 15 minutes and giant

waves come crashing inland. The effects of the tsunami waves depends upon

the bottom topography near the shore and nature of the coast. As result, their

effects vary widely from place to place.

Often, the first sign of the arrival of a tsunami at a coast is the water receding

and exposing the shallow seafloor. Lisbon, Portugal witnessed such aphenomenon on November 1, 1755. This unusual event attracted many curious

people to the bay; many were swept away by the tsunami wave that arrived

only minutes later. Tsunami that struck Awa in Japan killed more than 100,000.

As tsunamis are common in the Pacific Ocean, a tsunami early warning system

has been put in place there.

The most catastrophic tsunami occurred on the morning of

26 December 2004. This was caused by an underwater

earthquake measuring 8.5 on the Richter scale off the coast

ofSumatra, Indonesia. Within minutes it devastated Aceh,Sumatra, and moved with great speed and hit Thailand, Car

Nicobar, Nicobar and Andaman Islands, India in the Bay

of Bengal, southern part of the Tamil Nadu coast on the

mainland and eastern and southern coasts of Sri Lanka.

More than 220,000 people died in Indonesia alone. India

and Sri Lanka also suffered casualties in tens of thousands. Tsunami was not

known to strike the coasts in the Indian Ocean and The Bay of Bengal. Here


68/91

Learning Science 61also, as in Lisbon, many paid with their lives when curiosity drew them to the

beaches. The tsunami of 26 December 2004 is perhaps the greatest human

tragedy as it killed nearly 300,000 people and destroyed the coastal regions

of the affected countries.

The layers of the earth

The earth has four layers.

The crust is the topmost layer. It is found

both under the continents and the oceans.

The mantle is found between the crust

and the core. It stretches from ~40 km to

~2900 km.

The outer core is in a molten state. This contains mostly iron and nickel.

The inner core stretches from a depth of ~5200 km to ~6400 km.

From a molten rocky mass to a layeredplanet

How did this happen? We have to look into the

earths distant past to understand its present layeredinterior. Earth scientists have established that in

the beginning, primitive earth was a mixture of

molten rocky material. There were no continents

or oceans. As the earth cooled, the densest materials

(iron and nickel) sank to the centre of the earth.

This formed the core of the earth.

It begins at a depth of ~2900 km and stretches to the centre of the earth. The

lighter materials floated to the top and on further cooling formedthe crust.

The residual material formed a layer, calledthe mantle, in the middle.

Comparative distribution of the elements in the earth as

a whole and in the earths crust

Percentage of minerals in the whole of the solid earth

* Sulfur 1.9% Calcium 1.1% Aluminium 1.1% Rest < 1%

Nickel

2.4%

*Others

Magnesium

13%

Silicon

15%

Oxygen

30%

Iron

35%

The Mantle

Outer core

The Crust

Inner core


69/91

62 Learning Science

Percentage of minerals in the earths crust

~ 82 % of the crust is made up of just three elements - oxygen, silicon and

aluminium. Oxygen occurs only in combination with other elements in

the solid part of the earth. Most of the 35% of iron is found in the core.

Evolution of the earth is the result of the internal and the external heat

engines simultaneously driving the earth.

Role of internal heat

The internal heat

melts rocks.

throws out magma.

supplies energy to build and move

continents around.

pushes up the mountains.

Role of the external heat engine

In the beginning, the earths external heat was the result of meteorites hitting

the earth with tremendous force. This heat contributed to the melting of the

young earth. Once the earth cooled, the earths external heat engine is driven

by the solar energy received by the earths surface. Now, external heat is

responsible for:

erosion by wind and rain. weathering.

weather and climate.

water cycle.

* Calcium 2.4% Potassium 2.3% Sodium 2.1% Rest < 1%

Oxygen

46%

Silicon

28%

Al

8%

Iron

6%

Mg

4%

*

Others

Weathering

Wind and rain

Weather and climateWater cycle


70/91

Learning Science 63Earths atmosphere, oceans andthecontinents evolved as result of the effectsof the external heat and the internal heat acting upon the primitive earth.

Atmosphere

Most earth scientists believe that the atmosphere was also formed when

the primitive earth began to cool. As the molten rocky mass of the infant

earth cooled, the lightest and the most volatile substances escaped as gases

from the earths interior. These gases formed the atmosphere.

The composition of the early or primitive atmosphere was very different

from the composition of the atmosphere now. Sunlight and plants were

mainly responsible for the change in the composition of gases in the earths

atmosphere.

Formation of continents

Scientists believe that the formation

of the continents started when the

magma started coming to the earths

surface. On reaching the earthssurface, the molten rock material

slowly cooled and solidified and

formed the earths crust.

Here also, the heavier materials sank to the bottom and lighter materials

floated to the top. The lighter crust was decomposed and broken into

fragments by forces of nature. These fragments were deposited in layers

at various sites to form different landforms of the primitive continents.

Birth of the oceanIt is hard to believe that in the

beginning, there was no water on our

planet. As the rock pieces from space

hit the young earth with great force,

many huge basins were formed on the

earths surface.


71/91

64 Learning Science

As the earth cooled, steam escaped from the interior and entered theatmosphere. Gradually, it cooled and formed clouds. At first, the clouds

brought incessant rains. The rain water filled the basins for tens of

thousands of years and eventually a super ocean was formed.

Lithosphere - the outer shell of the earth

Lithosphere is composed of the crust and the solid part of the upper mantle.

It is not an unbroken and continuous shell. It is made up of rock slabs

calledcrustal plates. The plates are in constant motion. The change in theshape of continents and oceans are the result of the motion of these plates.

Crustal plates

Earths crust is made up of many smaller pieces called crustal plates.

These are like pieces of a jigsaw puzzle. The crustal plates ride or float

over the soft layer of the mantle. The crustal plates are in constant motion.

They come together (convergent movement), move apart (divergent

movement) and slide under (subsidence). Movement of the crustal plates

(or plate tectonics) result in many natural phenomena.

How hot is the interior of the earth?

We know for certain that the temperatures in the borewells and the mines

increase by about 20 or 30C per 100 m depth. How can we know about the

temperatures below a depth of 8 km? You can imagine the difficulty when

we compare the depth of the deepest oil well (8 km) to the depth from the

crust to the centre of the earth (~6400 km). To find out about the earths fever

chart, the earth scientists have studied

the temperature of the lava as it emerges from the

interior of the earth.

the speed changes in the seismic waves

as they travel through the different

layers.

the melting points of various metals and

minerals.


72/91

Learning Science 65The earths fever chart

The temperature increase is not uniform throughout the interior of the

earth.

The temperature increases by ~120C

per km in the first 100 km and by

~20C between 100 km and 300 km.

The temperature increases to ~20000C

from 2900 km. This temperature is

higher than the melting point ofiron. (Hence the outer iron core is in a

liquid state).

The temperature of the inner core or

the centre of the earth is ~22000C to 27500C.

But the inner core is a solid because of the tremendous pressure there.

Many believe that the temperature of the core is as high as 50000C.

Atmospheric pressure at the core is ~ 4 million times greater than it is at

sea level.

Minerals: the gift of the lithosphere

What are minerals? Where are they found?

Minerals

are naturally occurring, non-living substances.

can be made up of elements or

of chemical compounds.

are found in the thin uppermost layer of the crust.

are sources of energy. can be metallic or non-metallic.

are the source of soil.

In fact, rocks are made up of minerals.

How many minerals are known to us?

Mineralogists have identified more than 2000 minerals which are distinct

from one another. All these minerals do not form rocks of the earths crust.


73/91

66 Learning Science

The main rock-forming minerals are the silicates, carbonates and sulfides.There may be only one mineral in some rocks (Limestone often consists only

of calcite). There may be more than one mineral in some other rocks. (Granite

contains quartz, feldspar and at least one other mineral.)

Identification of minerals

Minerals are generally identified on the basis of the following properties.

From salt to transistorsImportance of materials from the earth.

Some commonly used materials are:

stones for buildings.

chemical salts for fertilizers.

limestone for making cement.

sand (silica) for transistors and optical fibres.

clays for ceramics.gemstones

Can you imagine life without

common salt at home?

Uses of minerals

Man has used minerals in a variety of ways throughout history and in all

civilizations. Minerals have been used in the following ways:

Colour Transparency Lustre Streak

Crystal form Cleavage Hardness


74/91

Learning Science 67 for making rock shelters. for making weapons.

as mineral fuels.

as gemstones.

Gems - the beautiful minerals

Gems are beautiful, durable and rare. There are about 80 known gems.

The most precious and sought after ones are diamond, ruby, sapphire

and emerald. These beautiful gems are actually drab elements or

compounds. Diamond is carbon, ruby and sapphire are both forms of

aluminium oxide (corundum (Al2O

3)).

Ruby and sapphire are transformed to beautiful gems by certain impurities

in corundum (Al2O

3). Ruby is red because of chromium, sapphire is

cornflower blue because of iron and titanium.

How are gems useful?

Artificial diamond, ruby and sapphire have been made in the laboratoryby imitating the conditions under which they are formed in nature.

Gems are useful in industry as well. Ruby and sapphire are used in

grinding tools in industry. Large ruby crystals are used in lasers. Sapphires

are used in watches. Diamonds are used as tips in cutting tools.

Mineral wealth of India

Distribution of some of the important mineral ores in India

Haematite

Fe2O

3

Bauxite

Al2O

3. 2H

2O

Pyrolusite

MnO2

Ilmenite

FeTiO3

Monazite sands(rare earth elements)


75/91

68 Learning Science

Rocks

What are rocks?

Rocks make up the crust of the earth we live in,

are aggregates of minerals, are generally porous

but all porous rocks are not permeable.

They are necessary for soil formation and are

the key for understanding the evolution of the

physical earth through geologic time.

Rock dating or measuring geological time

At first geologic time was measured using

rate of deposition: It takes 4,000 to 10,000 years for a layer of ~1

foot thick sedimentary rock to be formed.

rate of erosion and salt in the ocean.

Modern methods of measuring geologic time are based on more reliable

radioactive clocks. These radioactive clocks measure the decay ofradioactive elements and the amount of radiocarbon present.

Radiocarbon dating: All plants and animals have a tiny amount of

radiocarbon. The radiocarbon content begins to decrease as soon as the

plant or animal dies.

Same minerals but different rocks!

Rocks are like cakes which may be made of

the same ingredients and minerals are like

nuts and dried fruits. Just as two pieces of a

cake may have different amounts of nuts, raisins and other

goodies, two different

samples of the same

rock may have

different proportions

of the minerals

making up the rock.


76/91

Learning Science 69Classification of rocksJust as we can prepare different things using the same ingredients but by

using different processes, rocks differ when they are formed by different

processes. Rocks are classified into three major groups. They are: Igneous

rocks, sedimentary rocks, metamorphic rocks.

Type of rock What is it made up of? What is the process?

Igneous rock Melted rocks in the earths Solidification of the rock

hot and deep crust and melt and crystallization.upper mantle.

Sedimentary rock Material from weathering Transportation,

and erosion of the earths sedimentation

surface. and lithification

Metamorphic rock Solid rocks in the earths Re-crystallization and

deep crust and mantle. formation of a new class

of rocks.

How are the three types of rocks distributed?

Rocks are not distributed with fixed and known boundaries, each in a separate

enclosure as it were. They occur together without any fixed boundaries.

Sedimentary rocks cover a greater percentage of land surface and ocean

floors. Igneous and metamorphic rocks make up most of the crustal volume.

Metamorphicrock Crustal Volume Surfacearea

Sedimentaryrock

Sedimentary

rock

Sedimentary

rock

Metamorphic

rock

Meta

morphic

rock

Igneous

rock Igneous

rock

Igneous

rock


77/91

70 Learning Science

Distribution of the three groups of rocks is different in the horizontaland vertical planes of the earths lithosphere.

H o r i z o n t a l

plane of the

earths crust

and the upper

mantle.

Vertical plane of the

earths crust and the

upper mantle.

On the horizontal plane of the crust and the upper

mantle sedimentary rocks make up 75% of the rocksfound. The continents and the ocean floors are made up

of sedimentary rocks upto 75%.

Distribution of rocks in the vertical plane

In the vertical plane, as one goes down from the crust to

the upper mantle, igneous and metamorphic rocks make

up 95% of the volume of the rocks.

Decoding the information in the rocks

Rocks may provide the key to unlock the geological secrets

of the earth, buried deep within it and strewn all around us

on the surface. In order to decode the information hidden

in the rocks, we need

to know when, where and how a rock is made and

to remember that the individual characteristics of a

rock is the result of its process of formation.

Crust

Upper mantle

Oceaniccrust

Continental

crust

Sedimentary

rocks

1 2 3 4 5 6 7 8 9

1 2 3 4 5 6 7 8 9

1 2 3 4 5 6 7 8 9

1 2 3 4 5 6 7 8 9

1 2 3 4 5 6 7 8 9

1 2 3 4 5 6 7 8 9

1 2 3 4 5 6 7 8 9

1 2 3 4 5 6 7 8 9

1 2 3 4 5 6 7 8 9

Igneous andmetamorphic

rocks

Sedimentary rocks


78/91

Learning Science 71Earth as a rock factoryIn this factory, rocks are made and unmade at all times without a break. The

raw materials are never in short supply here. There is never any power shut

down and the work force never quits.

Like most natural phenomena in our physical world, the formation of different

types of rocks also follows a cyclic pattern. Rock cycle is the result of certain

geological processes that have been going on for millions of years on our

planet. As result of these processes, the three types of rocks are continuously

changing from one type of rock to either of the other two types o

Learning-Science-PartI.pdf

Documents