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الثلاثاء، 30 سبتمبر 2014
اعطوهم حقهم ما ريك
الجمعة، 26 سبتمبر 2014
الأربعاء، 24 سبتمبر 2014
Whales
Q Is that a fountain of water coming
out of the blowhole?
A The whale opens its
blowhole to breathe out stale
air. When this air
comes in contact
with the colder
air outside, the
water vapour in
the atmosphere
condenses. This
looks like a
fountain or
spout.
Whales
Whales might live in the oceans and might even look like very
large fish, but they are mammals. Like most other mammals,
whales give birth to live young and breathe with their lungs.
Whales belong to a group of animals called marine mammals.
They are among the largest animals on the planet.
The Living Planet
Q Why do whales have holes on their heads?
A Whales do not have gills like fish. Instead
they take in air through nostrils like all the
other mammals. The nostrils of whales, called
blowholes, are located on top of their heads.
Every once in a while, whales come to the
surface of the water and open their blowholes
to breathe.
56
Quick Q’s:
1. What is blubber?
Blubber is a layer of
fat found between the
skin and flesh of all
whales. It preserves
body heat and stores
energy as well as
keeping whales afloat.
2. Do whales live as
a family?
Most whales are social
creatures. They travel
and feed in groups
called pods. Many of
them migrate long
distances in groups
between their feeding
and breeding grounds.
3. What do whales use
their tails for?
The tail of a whale is
divided into two parts,
called flukes. While
fish move their tails
sideways to swim,
whales swim by moving
their flukes up and
down in the water.
4. Which is the largest
whale in the world?
Blue whales are not
only the largest whales,
but also the largest
animals ever to live on
Earth. They can be as
long as 34 metres (112
feet). They are also the
loudest animals on
Earth – 1.5 times as
loud as a pneumatic
drill. But they use such
a low frequency that we
cannot hear them.
There she blows
Whale hunters and whale watchers spot whales by the
fountain of water coming out of their blowholes.
Killer whale
The killer whale or orca is the most common member of
the family of marine mammals that includes whales and
dolphins. They can be found in all the oceans of the
world. They are highly social animals and travel in stable
groups, led by the oldest female member of the group.
Odd Mammals
It’s a
mammal
The platypus lives
in and around rivers
in eastern Australia
and Tasmania. The male
has a spur on the hind
foot that can secrete poison.
Big jumper
The kangaroo can jump
so far that it is difficult
to catch one. Their
numbers have grown
many times in the absence
of predators in Australia,
where they live.
Odd Mammals
Most mammals share certain characteristics. The majority
of mammals give birth to live young and look after them,
and most of them (apart from some sea mammals)
have four limbs and live on land. But there are some
exceptions, such as platypuses, anteaters and bats.
QDo any mammals lay eggs?
A The duck-billed platypus and the spiny
anteater lay eggs. They are found in Australia,
Tasmania and New Guinea. They were among
the first mammals on Earth. Apart from
laying eggs, they are similar to other
mammals. They are warm-blooded, have hair
and produce milk to feed their young. But
neither anteaters nor platypuses have any
teeth. They have snouts that look like beaks.
QWhy do some mammals like kangaroos
carry their babies in a pouch on their bellies?
A Kangaroo babies are born early, before
they have finished developing. When the baby
is born, it climbs into its mother’s pouch
where it remains for several weeks until it
is strong enough to move about on its own.
The baby may remain in the pouch for more
than a year, climbing out to play more and
more often. Apart from kangaroos, koalas,
possum and wombats also carry their
babies in a pouch. All the mammals that
do this are known as marsupials.
Q How are bats able to fly?
A The front legs of bats act as wings. Each
leg has four long fingers to support the wing.
The wings have a double layer of skin
stretched between the finger bones and
attached to the side of the body and to the
hind legs. Bats have three pairs of flight
muscles, attached to the upper arms and
chest, that give them the power to fly.
Odd Mammals
55
Following its echo
Bats use a special sense of vibration, called
echolocation, to find food and to navigate.
They emit sounds that bounce back as echoes after
striking an object. Bats can identify the direction,
distance, speed, and sometimes, even the size of an
object by listening to this echo.
This special technique helps them to find food
and avoid obstacles in the dark.
Try these too…
South America
(112–113), Australia
and Oceania (114–115),
Europe (116–117),
Africa (118–119),
Asia (120–121)
Odd-toed Mammals
Q Does the tapir belong to the same family
as zebras and rhinos?
A Although it looks a lot like a pig, the
tapir is in fact closely related to zebras and
rhinos. This animal has a short, muscular
trunk and is about 1 metre (3.2 feet) tall.
It has splayed hooves, which help it to get
a firm grip on soft, muddy ground.
Odd-toed Mammals
Some mammals have an odd number of toes or hooves. This
group includes animals like horses, zebras, rhinoceros and
tapirs. Horses, zebras and donkeys have only one toe in each
foot, which is in the form of a hoof. A rhinoceros has three toes.
Tapirs have four toes in their front feet, three in their hind feet.
The Living Planet
Q How can you tell the different types of
zebra apart?
A There are three main kinds of zebra –
the plains, mountain and Grevy’s zebra. The
plains zebra, found in the African grasslands,
is the most common of all three species. It is
striped all over and its stripes are wider than
those of the other two species. Mountain
zebras are native to the mountainous regions
of southwest Africa. They have a white belly.
Grevy’s zebra is the largest of the zebra
species. It has a mane that stands up straight,
large ears and narrow, closely set stripes that
extend all the way down to its hooves.
Q How many species of rhinoceros are there?
A There are five species of rhinoceros in
the world today. They are the Sumatran,
Javan, Indian, white and black rhinoceros.
The white and black rhinoceros are found in
Africa, while the others live in Asia. All rhinos
have thick skin with folds. They have short,
thick legs and a tiny tail. They are solitary
animals that come together only during the
mating season.
54
Quick Q’s:
1. Where did the horse
come from?
The earliest ancestor of
the horse lived in
North America about
55 million years ago.
It was the size of
a small dog, and did
not look anything like
today’s horse. But its
teeth were like any
horse we know today.
This animal went
through many changes
over millions of years
before the modern
horse evolved.
2. Where are tapirs
found?
There are five species
of tapirs in the world.
Three of these are
found in the
rainforests of South
America, while the
other two inhabit parts
of southeast Asia and
Iran. All tapirs prefer
water to land and
spend a great deal of
time in lakes and
streams.
Mother and child
Baby tapirs are various
shades of pink and have
prominent stripes. Their
colour changes to grey
and white and the stripes
fade as they grow older.
Under threat
Indian rhinos have one horn, while African rhinos have
two. The horns are supposed to have healing properties
and are used in various forms of traditional medicine.
As a result, rhinos have been hunted and now their
numbers have grown alarmingly small. There are so few
Javan and Sumatran rhinos left that the species is under
threat of extinction.
Staying in a herd
Plains zebras are among
the most common animals
seen in the African
savannah. They usually
do not go very far
from watering holes.
Hoofed Animals
Hoofed Animals
The nails of some mammals are large and hard enough for them
to walk on. These nails are called hooves and such animals are
called hoofed animals, or ungulates. This group includes pigs,
hippopotamuses, camels, giraffes, goats and cattle.
QHow did the hippopotamus get its name?
A The word hippopotamus means river
horse in Greek. The hippopotamus spends
a large part of its day in shallow water and
usually comes out only at night.
QDo hippopotamuses sweat blood?
A Common hippos do not have sweat
glands, but their pores secrete a reddish-pink
fluid which is often mistaken for blood. This
fluid gives their skin a shiny appearance and
prevents it from cracking in the heat.
Q How many species of camels are there
in the world?
A There are two species of camels. They
are the Bactrian and the Arabian camel. The
Bactrian camel has two humps on its back,
while the Arabian camel has one. The humps
contain fat that provides the animal with
nutrients when food is not available.
Q How are llamas different from camels?
A Llamas are found in South America.
Although they are in the same family as
camels and even look a lot like them, llamas
do not have humps. They are usually white,
with black and brown patches. Alpacas are
similar to llamas but much smaller.
Q Is there any difference between antelope
and deer?
A All species of antelope have pointed,
hollow horns that are permanent. Deer have
branched antlers that they shed every year.
Deer antlers are solid and bony. Only male
deer grow antlers, while both male and
female antelope have horns.
Hoofed Animals
53
Living tall
The giraffe is the tallest living mammal.
An adult male giraffe can grow to a height
of about 6 metres (20 feet). In contrast, the
giraffe’s body is not as long as that of most
other hoofed animals. Its front legs are
slightly longer than its hind legs. Giraffes’
necks can be over 1.5 metres (5 feet) in
length, but only have seven vertebrae (neck
bones). Its long neck and extraordinary
height help the giraffe to pluck leaves that are
beyond the reach of other animals. Giraffes
also have tongues that can be extended as far
as 45 centimetres (18 inches)!
Two humps
The Bactrian camel (above) is found in the Gobi desert of
Mongolia. The Arabian camel is found in Asia and Africa.
Hollow weapon
Antelope horns are hollow
and light. But they are
still formidable weapons.
Camel’s cousin
The llama is found in the
Andes mountains.
Try these too…
North America
(110–111), South
America (112–113),
Africa (118–119), Asia
(120–121), Ancient
Americas (132)
Elephants
Q How are African elephants different
from Asian elephants?
A African elephants are larger and have
less hair. They have bigger, fan-shaped ears.
Both male and female African elephants have
tusks. In contrast, Asian elephants have lowerhanging
ears and only the male members
have tusks. The savannah
elephant is light grey,
while forest and Asian
elephants have dark
grey skin.
Q How do
elephants use their trunks?
A The elephant’s trunk is a combination
of its nose and upper lip. The elephant uses
its long, flexible trunk to grasp objects, pluck
leaves, break off branches and carry heavy
objects like logs. While strong, the trunk is
also very sensitive. Small, finger-like
projections at the end help elephants to pick
up small objects. The trunk is also used to
suck in water for drinking or to spray water
over the body for bathing. Elephants
pick up dust with their trunks in
the same way when they want to
have a dust bath. When lying in
water, the elephant sticks its trunk
out to breathe. Elephants use the
nostrils at the tip of the trunk to
capture the scent in the air.
The trunk is then placed in
their mouth, where special
organs identify the scent.
Elephants
Elephants are the world’s largest land animals. They are divided
into three different species – savannah, forest and Asian
elephants. Savannah and forest elephants are together known
as African elephants.
52
Quick Q’s:
1. Do the members of
a herd stick together?
The members of a
herd feed, bathe and
migrate together. They
usually stay very close
to the leader. They also
protect one another
from predators. The
young, sick and old are
especially well-defended
by the healthier
members. When faced
with danger, the head of
the herd leads the rest
away. When the leader
dies, the next oldest
female takes over.
2. Do elephants eat
a lot?
The elephant’s
digestive system is very
weak. It can digest
only 40 per cent of the
food it eats. It has to
make up by eating a
great deal. An adult
eats about 140–270
kilograms (300–600
pounds) of leaves and
grass every day.
3. How big are the
tusks of an African
elephant?
An African elephant’s
tusks are between
1.8–2.4 metres (6–8 feet)
in length and weigh
about 20–45 kilograms
(50–100 pounds).
Those of an Asian
male are only about
1.5 metres (5 feet)
in length and weigh
about 30 kilograms
(70 pounds).
Big pet
Asian elephants have
been domesticated by
people for centuries.
Tragic tusks
Elephants have often
been hunted for their
precious ivory tusks.
Moving in a herd
A herd of African elephants moves towards a watering
hole. Note how the young members of the herd are
surrounded by older and stronger members for
protection. Elephant herds are led by the oldest female.
The Living Planet
Q Are the elephant’s tusks really teeth?
A The tusks of an elephant are simply
elongated incisor teeth. A calf is born with a
pair of incisors that are replaced within 6 to
12 months. The second set grows into tusks.
Canines
Canines
The canine family includes dogs, wolves, foxes, coyotes, dingoes
and jackals. Though dogs were probably the first animals to be
domesticated by humans, wild canines can still be found in every
part of the world. Wolves and wild dogs live in large packs, while
the other canines are solitary or live in small groups.
The Living Planet
Q What makes canines good hunters?
A All canines have a keen sense of hearing
and smell. As a result, they can locate prey
a long way off. Wild canines are very
determined hunters, willing to chase prey
over long distances. They also have several
sharp teeth used for killing, feeding and
defence. Canines use their chisel-like incisors
for cutting food and grooming. These are
located in the front of the mouth. Next to
them is a pair of dagger-shaped canine teeth
used for fighting and hunting.
Q Can canines run fast?
A Canines can run extremely fast and have
a lot of stamina. This ability is due to their
long legs and ankle bones. Canines have a
highly flexible backbone that can be arched
as they run. Their feet are small, and all their
toes have strong but blunt claws. Their small,
light feet and limbs help them to
run more efficiently than other
animals with larger
legs. Wolf packs and
hunting dogs are
known to chase their
prey for hours.
They finally
overtake
animals
that may
be faster
than them
over short
distances.
50
Quick Q’s:
1. Which is the fastest
canine in the world?
Greyhounds are the
fastest canines in the
world. They have been
known to run at speeds
of up to 70 kilometres
per hour (44 miles per
hour). African hunting
dogs are also very fast
and can maintain
speeds of 50–60
kilometres per hour
(31–37 miles per hour)
for very long distances
while chasing prey.
2. What is unique
about fennecs?
Fennecs are the
smallest canines. These
tiny foxes are only 65
centimetres (2 feet)
long from the top of
their ears to the tips of
their tails, and weigh
less than 1.5 kilograms
(3.3 pounds). These
desert-dwellers have
huge ears that help
them to dispel excess
heat from their body.
Desert fox
Fennecs live in the hot Sahara desert. Their coats can
repel sunlight in the day and conserve heat at night.
Fierce hunters
Wild African hunting dogs
are feared by other
animals because they do
not give up the chase.
Q What is the structure of a wolf pack?
A Wolf packs have a breeding male, called
the alpha, which rules over the others in
the pack. He asserts his authority by using
dominant body posture, facial displays,
growls, barks, scent marking and at times,
even fighting. The alpha’s mate, called beta,
is the second in command.
Q Do foxes live in groups like wolves?
A Some species of fox, like the red fox,
live in small groups, but foxes usually hunt
alone. A male and female fox pair defends
the territory in which they hunt and raise
their young. Sometimes several female foxes,
usually a mother and her daughters, live in
a group with a single male. The younger
adults in a red fox group act as helpers,
assisting the breeding pair in defending
their territory and caring for the young.
Bears
Q Which is the largest of all
bear species?
A The polar bear is not only the
largest of all bears, but also the largest
carnivore on land. Found in the Arctic
regions, polar bears can grow to a
length of 2 metres (7 feet) and can
weigh up to a massive 800 kilograms
(1,760 pounds). They have creamy white fur
that blends in with the ice. Polar bears are
excellent swimmers and move quickly on land
and in water. They prefer to eat meat, and
their diet mainly consists of seals and young
walruses. During the summer when ice floes
(sheets of ice) melt and food is scarce, polar
bears feed on berries and bird eggs.
Bears
Bears can be found in a wide range of habitats, including
mountains and Arctic regions. There are eight species of bear –
the spectacled bear, the sun bear, the giant panda, the Asiatic
black bear, the American black bear, the brown bear, the sloth
bear and the polar bear.
The Living Planet
Q Do the eight species of bear
have any common features?
A All species are fairly
similar, although there
are slight differences in
size and diet. Bears have
stocky bodies, powerful limbs,
thick fur and a short tail. They
have elongated heads, rounded ears
and long snouts. They have a keen
sense of hearing and smell.
All bears, except the polar bear,
are omnivorous. Their varied diet
includes roots, nuts, fruit, berries,
honey, caterpillars and ants. Bear
teeth are small, and are mainly
used for defence or as tools. The
molar teeth are broad and flat,
suitable for shredding and
grinding fruit, nuts and berries.
Q Do bears have claws like cats?
A Bears have four limbs with
paws. Each paw has five long,
sharp claws. Unlike cats, bears
cannot retract their claws. They
use them to climb trees, open
termite nests and beehives, dig for roots,
and catch prey. All bears have long,
shaggy fur. The colour of
fur varies from
species to species.
48
Ferocious grizzly
The brown bear, known as the grizzly bear in
North America, is a ferocious predator. When
threatened or during a fight for a mate,
grizzlies stand up on their hind legs and
use their long-clawed forepaws to fight.
Great swimmers
Polar bears are
excellent swimmers
and spend almost
as much time in
water as they
do on land.
Sharp claws
Bears have pads on their
feet to help them walk
and sharp, curved claws.
Quick Q’s:
1. How do you know
when a bear is angry?
When threatened or
agitated, bears stand
up on their hind legs.
They probably do this
to appear larger to
their enemies. They
also use their clawed
paws to slash at
an attacker.
2. How does the giant
panda spend most of
its day?
The giant panda bear
eats about 18 kilograms
(40 pounds) of
bamboo leaves and
stems or about 40
kilograms (85 pounds)
of bamboo shoots each
day. It spends up to
14 hours just eating.
3. What is special about
the Kermode bear?
The Kermode bear is a
type of American black
bear. It inhabits the
rainforests of British
Columbia, Canada.
The Kermode bear is
the only black bear to
have a white coat.
4. Which is the smallest
bear in the world?
Sun bears are the
smallest of all bear
species. Even so,
they grow up to 1.5
metres (5 feet) in
length and weigh up
to 66 kilograms
(146 pounds).
big cats
Q What is special about the claws of a
big cat?
A All big cats – except the cheetah – have
retractable claws. These claws can be drawn
into the paw when the cat is not using them.
This prevents the cat from getting hurt while
grooming. The cheetah has short claws. It
uses them to get a good grip on the ground
while chasing its prey at high speeds.
Big cats
A big cat is a cat that can roar! This group includes the lion,
tiger, jaguar and leopard. They have large eyes, sharp teeth,
excellent hearing and powerful limbs with sharp claws. Most
have long tails and coats that are either striped or spotted. Big
cats are found in all continents except Australia and Antarctica.
The Living Planet
46
Quick Q’s:
1. What do cats use
their tongues for?
A cat’s tongue is rough
and covered with
sharp, hook-like
projections called
papillae. Cats use their
tongues to clean the
flesh from the bones of
their prey and to
groom themselves.
2. How does a jaguar
kill its prey?
The jaguar uses its
powerful jaws and
sharp teeth to pierce
the skull of its prey
between the ears.
Its strong teeth can
even break open
turtle shells.
3. Are white tigers
albinos?
White tigers are not
albinos. A true albino
would not have stripes,
but white tigers have
prominent stripes.
They are not a separate
species, but differentlycoloured
members of
the same species. Their
colour is caused by a
mutation in their
genes, which rarely
occurs naturally. In
recent times, the first
pair of white tigers was
found in a forest in
central India. Since
then, most white tigers
we know of have been
bred in captivity and so
can usually be seen
only in zoos.
Q Why do the eyes of a big cat glow in
the night?
A The eyes of a big cat – or any other cat,
for that matter – have a mirror-like tissue in
them that gather even the faintest light and
focus it on an object, making it clearly visible
to the cat. It is this mirror-like structure that
causes the cat’s eyes to glow in the dark.
Hidden weapons
Big cats usually draw their claws into the paw (left)
and extend the claws (right) when about to jump
on their prey.
Q Is the cheetah a big cat?
A The cheetah is not actually a big cat as it
cannot roar, but purrs like our domestic cat.
However, it has many other characteristics of
a big cat, and is sometimes regarded as the
smallest member of the big cat family. It is
the fastest of all land animals, and can run
at a speed of up to 110 kilometres per hour
(70 miles per hour) over a short distance.
Roaring apparatus
The flexible hyoid bone of the big cats allows them to roar.
Living in a pride
Lions are the only big cats that live in prides. Each pride
has one adult male with three or four lionesses and their
cubs. Male cubs are thrown out of the pride as soon as
they become semi-adults.
Q How are big cats different from
other cats?
A Big cats are similar to our pet cats in
many ways. However, only big cats can roar.
This is because of a difference in the
structure of a bone that is present in the
mouth of all cats. This bone, called the hyoid
bone, connects the tongue to the roof of the
mouth. In small cats, the hyoid is hard, while
in big cats the hyoid is flexible, helping them
open their mouths really wide and roar aloud.
Apes
Apes
Apes are primates with long arms, a broad chest, and no tail.
Early apes evolved several million years ago, long before humans.
Only six species of ape survive today. Gibbons, siamangs and
orangutans live in Asia, while gorillas, chimpanzees and bonobos
are African apes.
Q Which is the largest of all apes?
A Gorillas are the largest apes. Adult males
are about 1.8 metres (6 feet) tall and weigh
up to 170 kilograms (375 pounds). They have
huge heads, a bulging forehead and a crest
with thick muscles on top of the head.
Although they are portrayed as aggressive and
dangerous killers, gorillas are in reality shy,
peaceful vegetarians. They are extremely
intelligent and can learn complex tasks. Each
evening, gorillas make nests using leaves and
twigs in which they curl up and sleep.
44
Quick Q’s:
1. Which species
is known as the
crying ape?
Chimpanzees are
crying apes. They
bark and produce
loud calls to warn the
rest of the group about
approaching danger.
2. Is a siamang also
an ape?
The siamang is a
black-coloured gibbon
found in Malaysia and
Sumatra. The siamang
is one of the three
species that form the
group of lesser apes.
It is the largest of the
lesser apes, growing
to a height of about
1 metre (3 feet).
3. What are bonobos?
Bonobos are a species
of chimpanzee,
discovered in 1928 by
American scientist
Harold Coolidge. They
are the closest relatives
to humans. They walk
on two feet longer than
any other apes feet.
Some bonobos in
captivity have learnt to
speak a human
language. Unlike other
apes, a bonobo society
is controlled by a
female. Today, bonobos
are found only in the
forests of central Congo
in Africa. There are so
few of them that they
are in danger of
becoming extinct.
Gentle giant
Gorillas do not attack
anyone unless
provoked.
In danger
The siamang is distinct for two reasons.
First, two fingers on each hand are fused
together. The second is the large throat
pouch found among the males. The male
siamang can inflate this pouch to make
loud calls. The siamang is under serious
threat as forests are being cut down.
The Living Planet
Monkeys
Top of the forest
Colobus monkeys are usually found
at the top layer of branches in
African rainforests.
Q What does a monkey eat?
A Most monkeys will eat whatever
they come across, including birds’ eggs, fruit
and the sap from plants. Several species
of monkey will even attack and eat
other monkeys. Howler monkeys
of South America and colobus
monkeys of Africa eat
the leaves of any
type of tree. The
digestive system
of leaf-eating
monkeys is similar
to that of other
herbivores, like
deer and cows.
Monkeys
Monkeys belong to the group of mammals called primates,
which also includes apes and humans. All three species share
certain characteristics, such as narrow noses and five fingers
and toes. However, unlike apes and humans, many monkeys
have tails. Monkeys from Asia and Africa have noses that point
downwards, while monkeys from Central and South America
have broad noses and nostrils that open sideways.
The Living Planet
Q What are the common characteristics
of primates?
A All primates have a large brain, and their
eyes face forwards, allowing binocular vision.
Most of them have thumbs on both hands
and feet that can be used for grasping.
Their highly developed brain helps
them to remember things, and to
understand others.
Q How many primate
species are there in the world?
A There are more than
350 species of primates in the
world, divided into two groups.
Small to medium-sized
primates, such as lemurs and
lorises, have long whiskers
and well-developed senses of
smell and hearing. The rest
of the primates, including
humans, apes and other
monkeys, are part of the
‘humanlike’ category. This group
consists of about 175 species.
Most of these primates have flat
faces and a poor sense of smell.
42
Quick Q’s:
1. Why is the Japanese
macaque also known as
the snow monkey?
The Japanese macaque,
commonly known as
the snow monkey, is
one of the few primate
species that live in
cold regions. They are
found in the mountains
of Honshu in Japan.
When it is very cold,
these monkeys move
near hot springs to
keep themselves warm.
2. What is grooming?
Monkeys and apes
groom each other’s fur
using their hands. This
helps not only to get
rid of parasites and dirt
but is also an important
part of socializing.
3. Why are monkeys
called social animals?
Most species of
monkeys live in
groups. The size of
a group depends on
how much food is
available and if there
are predators around.
4. Do howler
monkeys howl?
Howler monkeys make
a peculiar barking
sound. They can
be heard up to
3 kilometres
(1.9 miles) away.
Ringed tail
Lemurs are easily
identified by their
ringed tails.
Big hug
Snow monkeys
are often found
huddling near hot
springs to keep
warm.
Hurricanes and Tornadoes
Hurricanes and Tornadoes
Sometimes the weather becomes wild. Blizzards, thunderstorms,
hurricanes and heatwaves are some examples of extreme
weather conditions. Such severe weather often causes a great
deal of damage to both life and property. Hurricanes and
tornadoes especially are very destructive.
Quick Q’s:
1. Can hurricane winds
be measured?
Hurricanes are divided
into five categories
depending on their
wind speeds. Category
5 hurricanes are the
worst, causing
maximum damage.
Winds of a category 5
hurricane can reach
speeds of about 250
kilometres per hour
(155 miles per hour).
Category 1 hurricanes
are much weaker, and
only travel at 119–153
kilometres per hour
(74–95 miles per hour).
2. What is a
storm surge?
Sometimes the strong
winds of a hurricane
can cause the water
level in the ocean to
rise. Huge waves hit
the coast along with
the storm, causing
severe flooding. This is
called a storm surge.
3. What is the
Fujita scale?
The Fujita scale is
used to measure the
intensity of a tornado.
It ranks tornadoes by
the damage caused to
man-made structures.
4. How did tornadoes
get their name?
The word tornado is
from the Spanish tomear,
meaning ‘to turn’.
40
Eye of the hurricane
This satellite image clearly shows the eye of the
hurricane, an area of calm in the middle of the storm.
Huge destroyer
In 2005, Hurricane Katrina, seen here in a satellite
image, destroyed large parts of the city of New Orleans
in the USA.
Q What is a hurricane?
A Hurricanes are large, violent storms that
form over the ocean near the equator. These
storms are accompanied by winds that travel
at an average speed of about 119 kilometres
per hour (74 miles per hour). Hurricanes
usually occur between June and November.
Q How does a hurricane form?
A When the air above the sea is heated it
rises, creating an area of low pressure. Cooler
wind moves in to take place of the warm air.
The Earth’s rotation causes the rising hot air
to twist and form a cylinder. As the warm air
rises higher, it cools down and forms huge
thunderclouds and finally becomes a
hurricane. Meanwhile, the cooler air at the
bottom also becomes warm, adding more
energy to the storm.
QWhat is the eye of a hurricane?
A The centre of a hurricane is called the
eye. The eye is an area of clear skies, light
winds and no rain. It is also the warmest part
of the storm and is surrounded by a wall of
heavy rain and strong winds. People faced
with a hurricane usually experience the heavy
rain and strong winds first, then there is a
period of calm as the eye passes over the area,
followed by more stormy weather.
Hurricanes and Tornadoes
Hurricanes and Tornadoes
Sometimes the weather becomes wild. Blizzards, thunderstorms,
hurricanes and heatwaves are some examples of extreme
weather conditions. Such severe weather often causes a great
deal of damage to both life and property. Hurricanes and
tornadoes especially are very destructive.
Quick Q’s:
1. Can hurricane winds
be measured?
Hurricanes are divided
into five categories
depending on their
wind speeds. Category
5 hurricanes are the
worst, causing
maximum damage.
Winds of a category 5
hurricane can reach
speeds of about 250
kilometres per hour
(155 miles per hour).
Category 1 hurricanes
are much weaker, and
only travel at 119–153
kilometres per hour
(74–95 miles per hour).
2. What is a
storm surge?
Sometimes the strong
winds of a hurricane
can cause the water
level in the ocean to
rise. Huge waves hit
the coast along with
the storm, causing
severe flooding. This is
called a storm surge.
3. What is the
Fujita scale?
The Fujita scale is
used to measure the
intensity of a tornado.
It ranks tornadoes by
the damage caused to
man-made structures.
4. How did tornadoes
get their name?
The word tornado is
from the Spanish tomear,
meaning ‘to turn’.
40
Eye of the hurricane
This satellite image clearly shows the eye of the
hurricane, an area of calm in the middle of the storm.
Huge destroyer
In 2005, Hurricane Katrina, seen here in a satellite
image, destroyed large parts of the city of New Orleans
in the USA.
Q What is a hurricane?
A Hurricanes are large, violent storms that
form over the ocean near the equator. These
storms are accompanied by winds that travel
at an average speed of about 119 kilometres
per hour (74 miles per hour). Hurricanes
usually occur between June and November.
Q How does a hurricane form?
A When the air above the sea is heated it
rises, creating an area of low pressure. Cooler
wind moves in to take place of the warm air.
The Earth’s rotation causes the rising hot air
to twist and form a cylinder. As the warm air
rises higher, it cools down and forms huge
thunderclouds and finally becomes a
hurricane. Meanwhile, the cooler air at the
bottom also becomes warm, adding more
energy to the storm.
QWhat is the eye of a hurricane?
A The centre of a hurricane is called the
eye. The eye is an area of clear skies, light
winds and no rain. It is also the warmest part
of the storm and is surrounded by a wall of
heavy rain and strong winds. People faced
with a hurricane usually experience the heavy
rain and strong winds first, then there is a
period of calm as the eye passes over the area,
followed by more stormy weather.
Earthquakes and Tsunamis
Earthquakes and Tsunamis
The Earth is made up of a boiling hot, liquid centre covered by
a crust. This crust is broken into pieces called tectonic plates,
which move around, sometimes colliding into each other. These
collisions lead to earthquakes, some so small that they are hardly
felt. But some earthquakes are so massive that they cause the
ground to shake violently, destroying houses and killing people.
Quick Q’s:
1. Which is the worst
earthquake in history?
In 1556, an earthquake
struck three provinces
in China. About
830,000 people were
killed in the disaster.
It was the worst
earthquake in history.
2. Can we predict
earthquakes?
No, we cannot. The
movements of the
Earth are too complex
for us to be able to
predict earthquakes.
But we do know the
lines along which the
Earth’s plates meet,
so we know the areas
that are more likely
to have earthquakes.
3. What is liquefaction?
Liquefaction is caused
by the violent shaking
of the ground during
an earthquake. Moist
soil or sand turns into
slurry, like quicksand.
This liquid can suck in
entire buildings.
4. Is a tsunami the
same as a tidal wave?
A tsunami is diffeerent
from a tidal wave.
A tidal wave is
generated by high
winds, but a tsunami is
caused by underwater
earthquakes, landslides
or volcanic eruptions.
Q Do earthquakes occur everywhere?
A Earthquakes usually occur along a region
called a fault, where broken rocks under the
Earth’s surface rub against each other and
cause tremors. Faults are marked by cracks on
the Earth’s surface, caused by the movement
of tectonic plates. Most faults are located near
the edges of the plates, but small faults can be
found far away from the boundaries.
Q How do faults produce earthquakes?
A Faults allow the rock fragments that form
the Earth’s crust to move about. Over a
period of time, plate movement builds up
pressure, causing rocks along a fault to bend
or break with a jolt. This sudden movement
releases energy that moves through the surface
of the Earth in the form of waves. This is an
earthquake. The energy moves out in a circle
from the point where the movement occurs.
38
Fault in the Earth
The San Andreas Fault in
California, USA, is one
of the few faults in the
Earth’s surface that can
actually be seen by any
observer on the ground.
Most of the other faults
are covered by soil or
water. These faults mark
the lines on the Earth’s
surface where two
tectonic plates of the
Earth meet. As a result,
areas around these faults
are the ones most prone
to volcanic activity
and earthquakes.
San Francisco 1906
The notorious San
Francisco earthquake
in 1906 destroyed
most of the large
buildings in the
city. Tramlines
were ripped up
as the roads
buckled
under
them.
Earthquakes and Tsunamis
Q Where is an earthquake most dangerous?
A The point inside the Earth where the
rocks first begin to break is the focus of the
earthquake. The point on the Earth’s surface
that lies directly above the focus is called
the ‘epicentre’. This is where the earthquake
is strongest. In a major earthquake, the
maximum damage takes place at the
epicentre, and there is less damage as you
get further away from it. The epicentre is
directly above the hypocentre, the actual
location of the energy released inside the
Earth. Seismic waves ripple out from the
hypocentre. After an earthquake, scientists
can find the centre by looking at the seismic
wave data from three separate locations.
The extent of the damage caused by an
earthquake may also depend on the
nature of the soil.
Volcanoes
Q How are volcanoes formed?
A Volcanoes are formed by tectonic plates
colliding with each other. The heavier plate
is usually forced down below the lighter one,
where part of it is melted by the heat of the
crash. The melting plate forms magma
or molten rock that collects below the surface
of the Earth in magma chambers. As the
amount of magma increases, the pressure
inside the chamber rises. This creates
a mountain, or volcano. The volcano has a
cone, from which gases and lava may trickle
out. When the pressure gets too high, the
whole chamber explodes, ejecting the
magma. This is a volcanic eruption.
Planet Earth
Volcanoes
A volcano is a mountain through which molten rock and gases
erupt from the Earth’s crust. Volcanoes are named after the
Roman god of fire, Vulcan.
Quick Q’s:
1. Which is the highest
volcano on Earth?
Mauna Loa in Hawaii is
the highest volcano on
Earth. It rises about 4
kilometres above sea
level; below that, it
extends to 5 kilometres
down before it reaches
the seabed. Its massive
weight has pushed the
volcano down a further
8 kilometres below the
seabed! So Mauna Loa
is 17 kilometres
(56,000 feet) from its
base to its summit.
2. Which is the most
active volcano?
Mount St Helens in
Washington State of
USA is the most active
volcano. It last erupted
in 1980.
3. What are geysers?
Geysers are jets of hot
water that erupt from
the Earth. When water
trickles down into the
hot molten rock under
the Earth’s crust, it is
heated up. As the water
becomes hotter, the
pressure builds up,
finally causing it to
spurt out.
36
Q Do volcanoes erupt regularly?
A Volcanoes may be active, intermittent,
dormant or extinct depending on how often
they erupt. Active volcanoes erupt often.
Intermittent volcanoes erupt at regular
intervals. Dormant volcanoes have been
inactive for a long time. They are the most
dangerous because they are merely ‘sleeping’
and can erupt without warning. Extinct
volcanoes have not erupted for thousands of
years. It is difficult to distinguish between
dormant and extinct volcanoes because some
volcanoes may remain quiet for a long time
before suddenly becoming active again.
Movements of the Earth
The tectonic plates that cover the Earth can move in
various ways, and are constantly rubbing against one
another, sometimes violently.
Hot water
Old Faithful is a geyser of hot water in the Yellowstone
National Park, USA. It erupts from the Earth every
90 minutes, on average.
Active volcano
Mount St Helens is the most active volcano in the world.
It last erupted in 1980.
Volcanic rocks
Hardened lava from
volcanoes forms new rocks.
Oceanic Crust
Continental
Crust
Mantle
Q What are the various things that happen
during a volcanic eruption?
A Magma, or molten rock, erupts through
the surface of Earth during an eruption.
Magma that comes out is called lava. It can be
thick and slow moving or thin and fast. Pieces
of rocks and ash also erupt from the volcano.
Pumice stone, a light rock full of air bubbles,
is formed in an explosive volcanic eruption.
These volcanic materials are called pyroclasts.
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