Knowing Master

8/14/2019 Knowing Master

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KnowledgeMASTERSTHE EARTH

Written byRoger Coote


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Have you ever wondered why volcanoes erupt, orwhere the coldest place on Earth is? This book willanswer these and other fascinating questions aboutour planet, Earth.Learn about oceans, rivers and climatechange and see how the Earthhas changed through theages. You will find outwhat is under theground and what ison the ocean floor.Discover why citiesare warmer thanthe countrysideand what causesacid rain.Packed withfacts and fullof colourfulillustrations,this book clearlyanswers yourquestions about Earth.


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it is aThe Earth weighs about6,000,000,000,000,000,000,000 t onnes .

Aplanet is a world that travels around, or orbits, a star. 0planet - the Earth - orbits a star that we call the Sun.Both the sun and the Earth are part of the solar SysteirQA

What is the Solar System?It is a group of planets and about60 moons in orbit around the Sun.

Theplanets are Mercury, Venus, Earth,Mars, Jupiter, Saturn, Uranus, Neptune,and Pluto. Twonewly discoveredplanets are called Smiley and Karla.There are also thousands of lumpsofrock, called asteroids, which also orbitthe Sun.

How was the Solar Systemformed?The Sun and its planets formedfrom a cloud of gas and dus twhirling in space. The cloud was pulledtogether by gravity and it became verythick. Most of the cloud turned intowhat is now the Sun, and the rest madethe planets, moons and asteroids.Moon Earth

Su n Venus

Mercury

QA

A re there any other planets inspace?The Solar System is a tiny part ofa galaxy - the Milky Way - whichcontains 100 billion s tars. The MilkyWay is jus t one of more than 10 billiongalaxies in the Universe. It is almostcertain that some other stars haveplanets, but they are hard to findbecause they are so far away . Scientiststhink they have fou nd one about thesame size as the E arth - it is abo u t300 million billion km away.Callisto

Asteroids

Mars

H ow old is*'/the Earth?Scientists think that the Universebegan 14 billion years ago.The Earth and the rest of the SolarSystem are mu ch you nger - mo rethan 4 billion years old.


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Th e Milky Way is a good example of a spiral galaxy.It measures almost 70,000 light years across.

Why do we have day and night?The Earth gets light and heat from the Sun.As the Earth travels around the Sun, it alsoon its own axis (an imaginary line joining

e North Pole, the centre of the Earth and thePole). When your part of the Earth isthe Sun you have daylight. When it turns away, darkness falls.

What is the right time?|It depends whereyouare,|because when ifs day in oneifs night somewhere else. There

zones around the world.time is different in each zone somust reset your watch when youfrom one zone to another.

NeptuneSmiley

PlutoKarla

Chanon

QAWhat shape isthe Earth?Our planet isalmost a round

sphere - like a ball - but notquite. The speed at which the

Earth spins causes the planet to bulgeat the Equator and flatten at the Poles.This shape is called a spheroid.

If the Earth is spinning, whydon't we fly off into space?W e are held down by gravity.Everything 'pulls' on everything

else with a force - gravity. For mostthings gravity is too weak to notice,but the Earth is so large that it has astrong pull of gravity towards itscentre. The Sun's gravity is evenstronger and it holds all the planetsin orbit.

QA


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The temperature of theEarth's inner core isabout 5,7000'C.

Barth

NOfy

The plates that makethe outer layers of thEarth move betweenand 10 cm each yea

QA

o one has dug down deep enough to be certain, but wthink that it is made of layers of rock and metal.Scientists have worked this out bystudying earthquakes.What is inside the Earth?There are four main layers. The outerone is a layer of solid rock calledthe crus t. Below this is the mantle.This is solid at the top, but deeperdown it is so hot that the rocks havemelted. Next is the outer core, madeof hot liquid metal. At the centre isthe inner core, which is solid metal.

QACould we dig a tunnel to theother s ide of the Earth?No. The inner coreof the Earth is far

A

too hot. The deepesthole dug into theEarth is about12 kmdeep. ^7)1 Is the Earth~magnetic?Yes, th e Earth acts as though it has ahuge bar magnet inside it, with amagnetic field andnorth and south poles.A compass needlepoints to the northmagnetic pole. TheEarth's magneticfield stretches

thousands ofkilometres into space.

Q What issoil made of?There are many types ofsoil. They are all made of amixture of pieces of rock,living particles, deadplant and animalmaterial, air and water.


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T h e Earth's crust is, onaverage, between 30 kmand 40 km thick beneathth e continents.

Under the oceans the crustis only 6 - 8 km thick.

millionago

Has the Earth always lookedthe same as it does now?No. The hard outer layers aresplit into large pieces, or plates.These plates have been movingvery slowly fo r millions ofyears, and have movedthe continents around.

AiHow are rocksmade?There are threetypes of rock onEarth and they are madein different ways. Igneousrocks are made when hotmelted material, calledmagma, bubbles up from themantle and hardens. Sedimentaryrocks are layers of tiny pieces ofrocks, or dead plants and animals,

gradually build up and becometogether. Metamorphic rockssedimentary or igneous rocksby great heat and pressure.

QA

What makes earthquakeshappen?Earthquakes occur when rocksmove along faults, or cracks inthe Earth's outer layers. Severeearthquakes happen when platesmove past each other or towards eachother. The rocks at the edges of theplates rub together, making theground shake. Sometimes the plates'stick' for a while and pressure buildsup. Then they break free suddenly,causing a hugeearthquake.


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8The deepest scuba diveever recorded was 13 3metres by John J. Grueneand R. Neal Watson.

here are four large oceans on Earth -the Pacific, the Atlantic, the Indianand the Arctic. There are also smallerareas of water called seas. Most seas are

actually part of the oceans or are joined on to them.QA

How big are the oceans?Oceans and seas cover aboutseven-tenths of the Earth's surface.The Pacific is the largest ocean, with anarea of about 166 million sq km,followed by the Atlantic, with about82 million sq km, and the Indian, atabout 74 million sq km. The ArcticOcean is the smallest at about12 million sq km.

Q Why is sea-water salty?The salty taste of sea-watercomes from minerals that havebeen washed into the sea by rivers.The most common mineral is salt.

A

Q What makes waves?

/ Howwere the oceans- ~ ~ J formed?IpNo-one is certain. Somescientists think that soon

after the Earth was formedit was surrounded by thickclouds. As the Earth cooleddown, rain fell and filled thehollows in the crust to formthe first oceans. When thecontinents drifted apart,water filled the gaps theyleft to form the modernoceans we know today.

A Waves are made by wind blowing_ across the surface of the water. Thewind pushes the water upwards,making a wave crest, and thengravity pulls it back down again,into a wave trough.

Continental crust

Trench

Ridaee

Magma


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Sea-water contains gold - about4 grams in every million tonnes ofwater. It also contains silver,calcium and sulphur.

Th e biggest wave ever recordedin the open sea was seen from aship during a storm in 1933. Itwas 34 metres high!

How does a coral reef grow?\Coral reefs form inwarm, shallow'waters. They are made by tiny

How are islands formed?Some islands are areas of landthat were joined to continents

long ago when the sea level waslower than it is now. The British Isles,for example, were once connected tomainland Europe. Other islands arethe tops of volcanoes that rise upfrom the sea bed. The island ofSurtsey, near Iceland, was formedin this way. Between November1963 and June 1967 the island rosemore than 289 metres from theocean floor, leaving it 170 metresabove sea level.

Volcanic island

animals called polyps, which have hard,cup-shaped shells. Thousands of polypslive side by side and their shells jointogether to form a reef. When the polypsdie, their hard shells remain. Morepolyps grow on top of them andgradually the reef grows.

QAIs the bottom of the ocean flat?No. The ocean floor has many hills, valleys, deeptrenches and high mountain ranges. The Mid-AtlanticRidge, which runs for 20,000 km down the centre of theAtlantic Ocean, is the longest mountain range in theworld. The deepest point is the Marianas Trench, in thePacific Ocean which plunges to 11,033 metres belowsea level.

Oceanic crust


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in Dorset is a A stack is a single column of rock. The Old Manof Hoy in the Orkney Islands is a famousexample of a stack.

How are beaches made?Beaches form along stretches ofcoast that are sheltered fromwaves, such as in bays. Mostsand is brought from inland byflowing into the sea. Some isrocks broken off by there worn down into smaller andpieces. Sand is dropped alongby waves and it builds upbeaches.

QACan we take back land fromthe sea?Yes. Coastal marshes and evenshallow bays can be reclaimedfrom the sea. The first step is usuallyto build a protective wall to stop thesea flooding the area. Then the saltwater is drained or pumped out,leaving dry land.

f*.

QA

Why do some beaches havegroynes?Groynes, or breakwaters, are builtstretching into the sea to stopbeaches being worn away by the sea.What causes high and low tides?Tides rise and fall twice in every24 hours and 50 minutes. They aremainly by the Moon. When theis overhead, it s gravitypullson the sea, away from thea bulge like a large wave.is low tide. As the Earth spins, thearound the planet, causing

Spring and neap tides occur twice a month. They are the highest and lowest high tides.


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12These are the five highestmountains in the world.

Mount EverestO/t 8,848 metres

T he first mountains may have been madesoon after the Earth was formed, butthey were worn away many millionsof years ago.The mountains we cane today are much younger.- - -

QA

Where are the world's highestmountains?The world's 20highest mountains(measured from sea level) are allin the Himalaya-Karakoram rangein Asia. Mount Everest is the tallest at8,848 metres. The highest mountainfrom top to bottom is the peak ofMau na K ea in the Hawaiian Islands. Itrises 10,203 metres from the ocean floor,but as over half of it is underwateronly 4,205 metres rises above sea level.

Q What is a rift valley?Where two faults run side by sidethe block of land between themmay sink down to form a rift valley. Thmost famous example is the Great RiftValley which runs fo r 6,400 kin from

Syria down through East Africa.Q

QADo mountains always stay thesame?No. Mountains are being wornaway by rain, wind, frost and othernatural forces. Some mountain ranges,such as the Alps, Himalayas and Andes,are still rising as the continental platesthey rgjfepn are pushed closer together.

AHow are mountains made?Some mountains are volcanoes.Others are dome mountainswhich were pushed up by hot melted,or molten, rock rising below thesurface. Some mountains formedwhen rocks were squeezed togetherand folded. Others are blocks of landforced up between huge cracks, orfaults, in the Earth's surface.

Volcanic Dome Folds Faul t


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Kangchenjunga8,597 metres

Act ive volcanoe s around

Lhotse8,511 metres

13Makalu I8,481 metres

QAW hy do high mountainshave snow on top?For every 1,000 metresthat you go up, thetemperature of the air fallsby about 5 C. The tops ofhigh mountains are alwayssurrounded by very coldair, even in summer.

QA

What is a volcano?A volcano is a hole inthe Earth's crust. Whena volcano erupts, hot moltenrocks from inside the Earthpour out of the hole on to thesurface. Volcanoes that erupt

often are called active, whilethose that might erupt sometime in the future are said tobe dormant. A volcano thathas stopped erupting is saidto be extinct.Q Where are therevolcanoes?

There are about 1,300active volcanoes (onesthat erupt) in the world,although only about 20 to 30erupt in any one year. Mostvolcanoes are in areas nearthe edges of the plateswhich make up the Earth'souter layers.


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14The deepest lake is LakeBaikal in Russia, which

10 metres

A

The water in rivers comes from rain, lakes,springs, and melting ice and snow. Riversoften begin high up on mountains and rundownhill to the sea. As they flow, they wear'

away the land to make valleys.Which is the **world's longest river?^

A The Nile is the longest, a6,695 km. It flows through

Why do rivers get larger as theyflow?A river usually starts as a tinytrickle called a rill. It flows

Qdownhill and is joined by other rills. Itgets larger and becomes a stream. Otherstreams flow into it to make a river. Ariver may have other rivers, calledtributaries, flowing into it and s o it getsbigger and bigger.

East Africa into the Mediterranean Sea.The river that contains the most wateris the Amazon in South America. Ever)second it carries about 120,000 cubicmetres of water into the Atlantic Ocean

QAHow is adelta formed?As a river rushesdownhill, it washeswith it mud, sand and evenboulders from its bed and bankAs the river approaches the sea, itflows over flat land and slows down,dropping the material. If tides don't washaway the sand and mud, it builds up to form

new land, called a delta.


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freshwaterIt covers

82,000 sq km in the

15Each year the Huang He, orYellow River, in China washesabout 2,000 million tonnes ofsoil down its valley.

How are lakes formed?Most of the world's lakes are inplaces where glaciers carved outvalleys in the land (see pagesSome lakes, such as Lakein Africa are in deepcalled rift valleys, whichby huge movementsformin the cratersof

when a riverits course.

7S1Why don't rivers run straight?A On their way downhill to thesea,rivers travel along the easiestroutes. If a river meets something in itsway, such as a boulder or a hill, itsimply flows around it.

AAre there rivers underthe ground?Yes, especially in areas,'where there is limestone.Rain-water can wear awaylimestone, making holes'and caves.A river on the surfacemay pour down a hole in the rock and flow through thecaves underground.

Underground river

How are waterfalls made?Most waterfalls formwhere a river flows over ahard rock and then overrock. The river wears awaye softer rock faster than the hard rock,a step. The step gradually gets deeper


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16Many plants andanima ls have adaptedto living in the deserts.

The saguarocactusca n grow up to15 metres high.

A area is called desert if, on average, it has less than25 centimetres of rain a year. Deserts are often inhot places, but not always. Most deserts are coveredwith rocks and stones rather than sand.QA

Where are the world's deserts?The world's largest deserts are inregions with high air pressure.

Winds blow outwards from these areasand moist winds from the sea veryrarely blow into them. Other desertsare far from the sea. By the time windsreach them, they have lost most of theirmoisture. Some deserts are on theinland, sheltered sides of mountainranges. Most of Antarctica is a frozendesert. It is a region of high pressureand little new snow falls inland.

AWhich is the world's driestdesert?Many deserts go without rain forseveral years at a time and thenhave a short downpour. The driest

desert is the Atacama in South America;until 1971 it had not rained there forfo ur hundred years.QA

What is an oasis?An oasis is an area of land in adesert whereplants are able togrow because there

is water from an v, jP -:undergroundspring or a well.

How do sand dunes move?Wind blows loose sand along theground and piles it up into hillscalled dunes. Sand grains are blown u

one side of a dune and rolled over thetop and down the steep face on theother side. Sand grains are always beiblown up and over the dune, movingacross the desert.


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DromedaryCholla

OcetilloKangaroo ra t

is the largest desert?Sahara desert, in North Africa, is

e biggest. It covers an area of aboutsq km. Only about a tenth of it is

with sand; the rest is rocky.r

QA

Can plants and animalslive in the desert?Yes. Plants and animalhave developed specialways of living in deserts.

Some plant seeds stay buriedin the sand for years until itrains. Then they grow quicklyand produce seeds of theirown before dying off whenthe sand dries out. Mostdesert animals hide duringthe day and come out atnight when it is cooler. Somecan store water in their bodiesfo r a long time.

1 Transveres2 Barchan

3 Star4 Ridge

Do deserts change size?Sometimes they growand at other times theyshrink. In 1987 the Sahara

spread 54 km south in onearea, but the following yearit retreated 96 km north.


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18Ice sheets ca n covervast areas duringan ice age.

X is a gi9 The ice in most glacisis between 200 and400 metres thick.

A glacier is like a river of ice. It formswhen snow piles up in a hollow ona mountainside. As the snow continuesto build up it gets squeezed togetherturning into ice. Finally, the ice spills outof the hollow and flows slowly downhill

as a glacier.What is an ice age?An ice age is a period in whichtemperatures are much lowerthan normal and ice sheets spreadacross large parts of the Earth. Ice ageshappen every few million years. Themost recent one ended about 10,000

years ago. Parts of North America, andEurope were covered by ice sheets.

Q How thick is an ice sheet?A The ice sheets that covered muchof North America and Europeduring the last ice age were up to3,000 metres thick. The ice coveringthe continent of Antarctica today iseven thicker - 4,800 metres in places.

A cross-section through an ice sheet.

A A re there any glaciersin the world today?Yes. There are glaciers inth e cold lands at the farnorth and south of the Earth,in northern Canada, Greenlandand Antarctica, for example.Glaciers also slide downvalleys in high mountainranges, such as the Himalayas,the Rockies and the Alps.

QA

Why do glaciers stopmoving?As a glacier slides downa mountain it movesinto warmer regions andbegins to melt. Eventuallyit gets to a point where itis melting at the bottomat the same rate that itis being fed by freshsnow at the top. Inthe cold north andsouth, glaciers mayflow straight intothe sea.A close up view of amelting glacier.


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The deep se a inlets, or f jords,along the coasts of Scandinaviawere made by glaciers.

How fast does a glacier move?Most glaciers move downhillquite slowly, at less than 30centimetres a day. The Quaraya glacierin Greenland is much quicker, speedingalong at around 24 metres a day. Someglaciers have short bursts of energyduring which they race down at up to120 metres a day. These bursts last for a

few months and then the glacier slowsdown again.What do glaciers and ice sheetsdo to the land?They wear away,or erode, the landthey move over. The icepulls pieces of rock

from the land beneathit . Rocks fall on to theice from above. All ofthese pieces of rockbecome frozen into the ice. As theglacier or ice sheet moves, therocks grind against the land,wearing it away. When theice melts, the rocks aredropped on the ground.These rocks are calledmoraine.QA

Where are the longestglaciers in the world?Most are in Antarctica,including the longestof all - the Lambert-FisherIce Passage - which is515 km in length.


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In 1958 the US Nasubmarine 'Nautiluactually travelledunderneath th eNorth Pole.

Antarctica conta ins90 per cen t of theworld's ice. The polar regions are at the farnorth and south of the Earth.

The Arctic lies inside the ArcticCircle, an imaginary line aroundthe North Pole. The Antarctic isa continent that surrounds the South Pole.

QA

How much of the world iscovered with ice?Ice covers more than one tenthof the Earth's land surface. The

Greenland ice sheet covers about1,800,000 sq km, while the ice sheetAntarctica is over 13,000,000 sq km.About three-quarters of all the worlfresh water is frozen in ice sheetsand glaciers.Q What are the North and SouthPoles?A The Poles are the places on the

Earth which are farthest northand south. If you stood at the NorthPole, which ever way you walkedyou would be going south.

Q What is underneath the polarice?A Beneath the ice in Antarctica -

lies a vast continent, r g ) f r . " with high mountains ^and deep valleys.The ice around theNorth Pole in theArctic is not restingon land but simplyfloating on the sea.


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21Here are three of the manydifferent shapes of icebergthat can be foundat the poles.

Slab

What is an iceberg?

Where ice sheets and glaciers flowdown into the sea,huge chunks of ice - icebergs - can break off and floatThe tallest one ever seen stood 167 metres above the water and extendedthan a kilometre below the surface. The largest iceberg ever seen was nearin 1956. It covered an area of more than 31,000 sq km.W hich is colder, the Arctic orthe Antarctic?The Antarctic gets far colderthan the Arctic.The coldest placeall is the Vostok base in Antarctica,to the South Pole. In July 1983temperature of -89.2C wasIs it always snowing in theAntarctic?No, the Antarctic actually getsvery little snow, especially in theThe air over the continent iscold and also very dry, and only50 mm of snow falls in a year.to the coasts, where it is not soand there is more moisture in themuch more snow falls.Does anyone live inAntarctica?No-one lives there permanently.There are a number of researchations where scientists live forat a time and study the area.from the coast, Antarctica haslife at all other than oneof tiny mite, several mosses andspecies of flowering plant.


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22Plants give off oxygenan d make th eatmosphere capable ofsupporting animal life.

The atmosphere is the layer of gas that surrounds the EarlThe atmosphere is made up of oxygen (which we allneed to breathe), nitrogen, water vapour and tinyamounts of other gases.

QAHow many layers are there in theatmosphere?The atmosphere is divided intofive layers - the troposphere,

QA

stratosphere, mesosphere,thermosphere and exosphere.QA

Why doesn't the atmosphere floataway into space?The force of gravity pulls thegases of the atmosphere towardsthe Earth and stops them from driftingaway. More than three-quarters of thegases are squashed into the tropo-sphere, and there are fewer and fewerthe higher you go. In the exospherethere are hardly any gases at all.

Does the atmosphere get coldethe higher up you go?Yes, and no. It gets colder as yoclimb through the troposphere,then warmer in the stratosphere,colder again in the mesosphere andthen warmer again in thethermosphere and exosphere.

Does air weigh anything?Yes scientists think thatthe weight of all the air around theEarth is about 5,200 million million tonnes.


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only makes up aboutt o f the atmosphere .

makes up 78 per cen tatmosphere .

23These are scientists' models

of oxygen and nitrogen.

Oxygen

Ntrogen

Where is the ozone layer?It is in the stratosphere, between15 and 30 km above the Earth. Itof a thin layer of ozone gas,is a type of oxygen. O zonemuch of the harm fu l ultravioletfrom the Sun, preventing itreaching the Earth. W ithout theall living things on Earth

be killed by the ultraviolet rays.layer is an invisible barrier protecting the Earth.

Why does air move about in theatmosphere?Moving air in the atmosphere isbetter known as wind. It is caused

QAWhat is atmospheric pressure?Because air has weight, it presseson the Earth and everything on it,including us . The more air there isabove us, the more it presses on everysqu are centimetre yor the higher theatmos pheric pressu re. So, the higher upwe go and the less air there is above us,the lower the pressure is.

differences in air temperature.air weighs less than cold air, andit to take it s place,winds.

1

\i


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24The winds in a hurricaneca n reach between 300and 450 km per hour.

weath

Al of the world's weather takes place in the lowest layerof the atmosphere - the troposphere. That is where theSun's heat causes air to rise, cool and sink down again.The movement of the air creates areas of high and lowpressure and winds.

QAWhat is an air mass?When a large amount of airstays for a long time in oneplace, it forms an air mass. They arewarm or cold, depending upon thetemperature of the land or sea below.When air masses start to move, theybring changes in the weather.

QA

What is aweather front?A front is the boundary betweena cold air mass and a warm airmass; it is where most weatherchanges happen.

Q Do all clouds bringrain or snow?No. All clouds areCirrus - high, wispy clouds(possible rain)

made of water vapour, _ .Cirrostratus - mm, whitishbut don't always bring douds (possib|e rain orrain or snow. There are s n o w )ten different types ofCloud and theyCan help Cirrostratus - th in , whi t i shtO tell US What SOrt Of r'PP les (chan9ingweather)weather to expect.

Altocumulus - grey bluislayer of cloud (fineweather)

Altocumulus - likealtostratus, but lower inthe sky and fluffier(changing weather) Cumulus - fluffy, whi

clouds (good weathe


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25every hurricane is given a nameidentify it. The names ar e chosen

and change from femaleto male names for each n ew storm.

Why do hurricanes happen?Hurricanes are verypowerful storms thatin warm areas ofe world. They start neare Equator when warm,over the sea risesd forms giant columns of v%~full ofwater vapour. ,air rushes in below the if feair and beginsspiral around at up to ^MB0 km perhour. When a ^freaches land, it canenormous destruction.

Where is the snowiestplace on Earth?The most snow in ayear - 31.1 metreson ParadiseWashingtonUSA in

- thick,storm clouds

high into the(rain)

Stratocumlus - unevenpatchy clouds (dryweather)

Stratus - low layer of greycloud (rain or snow)

Nmbostratus - dark greylayer (rain or snow)

What makes rain and snow?When water in oceans and rivers is heated^by the Sun, it turns into an invisible gasOcalled water vapour. As this warm, moist ai0Arises, it cools and the vapour turns to tinywater droplets which group together to forrrra^^clouds. The droplets get bigger until they areso heavy that they fall to the ground asrain. If it is very cold, the water dropletsfreeze into ice crystals and fall as snow.

* l .)

What causes thunder andlightning?When warm, moist air rises very quickly,deep cumulonimbus storm clouds form. Icecrystals and water droplets whirl around inside /; / ,the clouds and bump into each other, makingtiny electric charges. The charges build upuntil huge electric sparks flash from cloudto cloud or down to the ground and , &back. The lightning flash heats upthe air as it passes. The airexpands very rapidly and .mi^^Amakes the booming noisewe call thunder.


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26Siberia, in Russia,hasth e greatest range oftemperatures during ayear, from -7CP C to

T he type of weather that a place usually has from year toyear is called its climate. Some places are warm allyear round while others are always very cold. In someareas the temperature changes from season to season.

QA

Why do some places have hotterclimates than others?The hottest climates are usuallyin places closest to the Equator.The Sun's rays are more concentratedthere than they are further north orsouth, where the Earths roundedshape spreads the Sun's rays over alarger area.

QA

How many types of climate arethere?The world is divided into four maintypes of climate: polar, temperate,subtropical and tropical. Some areas,such as deserts and mountains, havetheir own special types of climate.

AWhat things canaffect climate?The climate of a particular placeis affected by a number of things.Places near the sea have milder climatesthan those far inland, which often havevery hot summers and freezingwinters. Ocean currents canmake climates warmer or colder

Mountains have colder climatesthan the lowlands around them.

Map showingvegetation regions

Do cities have their ownclimates?Yes, cities are often warmer thanthe surrounding areas. Concretebuildings absorb heat fromE^ the Sun during the day andrelease it at night, making

J H the air in the city warmer.


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27of

The seasons come atdifferent timesthe year indifferentplaces.

When it is summerin Europe it is

winter inAustralia.

What is a monsoon?A monsoon is a type of wind. Insome places near the Equator,airthe land heats up in summer andfrom the oceanin to take its place, bringingIn winter the winds

blows fromthe sea.

QA

Does climate affect whichplants grow where?Yes. Different types of plant preferdifferent climates. For example,rainforests grow in the hot, wet areasaround the Equator, and coniferousforests grow in the cold areas in thenorth. Farther north, where it is evencolder, only mosses and tiny flowerscan survive.

Temperate forest

(~} Mediterranean Desert and semi-desert

Why do we have seasons?As the Earth moves around theSun, different parts of it are tiltedthe Sun for a few months at aThe part leaning towards the Sunhas winter.


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28More than 20 per centof the world's oil comesfrom th e rocks beneathth e sea.

The first large scalenuclear plant wasbuilt in 1956.

Amost everything we use, suchas the fuel we burn, the woodand stone we use for building andthe food we eat, comes from theEarth in some way. These thingsare called natural resources.

QA What are fossil fuels?They are fuels, such as coal, oiland gas, that were formed fromthe remains of animals and plants thatlived and died millions of years ago.QA

QA

What are renewable energysources?When fossil fuels are used theycan't be renewed, or made again.Some energy sources will never run out(They are called renewable sources andinclude running water, the wind,energy from the Sun and even heatfrom the rocks deep inside the Earth.

How is nuclear power producedEverything in the Universe ismade of tiny particles, calledatoms. When atoms are broken apartthey give off heat, which can be used tproduce electricity. This is done insidenuclear power stations. The atoms mosoften used are uranium.

Solar panels store energyfron the sun

mmmmmmmmmm/ . " i '

Hydroelectric dams produce electricityfrom running water.

Wind turbinesuse th e wind toproduce electricity. Geothermal plants use energyfrom rocks below the groung.


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r : " '% ^ - t y"i * ' / * - & There are about 70,000different varieties of ricein the world.

29

Which food crops are the mostimportant?Cereals, or grain crops, are usedto feed more people in the worldany other type. Rice and wheat

QA

l!

What are staple foods?Your staple food is the one thatyou eat most often. In Asia, forexample, people eat more rice thananything else. Staple foods in Europeand North America include bread,potatoes and pasta.

What is amineral?Copper

Minerals are natural, non-living substancesthat are found in the Earth. There are abouttypes of mineral, each made fromwn special combination of atoms.minerals, such as diamonds,and emeralds are very rare andOthers, like quartz, arecommon.

Do the oceans have resources?Yes. The rocks of the sea-bedcontain minerals, including oilgas, and metals. W e catch fish tooceans, and the seawatercan be made into water forWaves and tides are alsoenergy sources.

QAHow many fish can be caught inone go?In 1986 a Norwegian fishing boathauled in a single catch weighingmore than 21,400 tonnes. It wasestimated to contain about120 million fish.


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30Th e USA has less than 5per cent of the world'speople, but uses 29 percent of the Earth'spetrol.

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e are damaging the Earth in a number of ways - bypolluting the air, soil and water, by destroying theplaces where plants and animals live, and byusing up its natural resources.

What is pollution?Pollution means spoiling our environmentby putting into the air, water or land

materials that will harm them. Humanshave always polluted the planet withsmoke, rubbish and other things.Pollution is now very seriousbecause there are many morehumans than ever before.

QAWhat is global warming?Some gases in the atmosphere,such as carbon dioxide, help totrap in heat from the Sun. Factories,cars and power stations produce a lotmore of these gases, and so more heatis being trapped in. If the Earth keepsgetting warmer, the Antarctic ice sheetmay begin to melt and the sea level

would rise, flooding some low coasts.

QA

Where does our rubbish go?Some is burned, which causes airpollution and adds to globalwarming. Most is either buried in holesin the ground or dumped at sea, causinmore pollution. Little is reusedor recycled, even though glass,metals, paper and plastics can

all be treated and reused.


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31be tween 5 million and 8 million di f fe rent spec ies of

n d an ima ls in the world. So far, only ] .6 million haverest may become ext inc t even

we discover them.

How does rainbecome acid?All rain-wateris very slightlyWhen fossil fuels are burnedr engines, factories and power- chemicals are produced whichthe mois ture in the air mu ch mo reEventu ally, this mo istu reto the ground as acid rain .

QA

W hy do people cut downrainforests?The world's tropicalrainforests are

Are there holes in the ozonelayer?The ozone layer protects us fromharmful ultraviolet radiation fromozone is being destroyedarein aerosols, fridges and somematerials. So far, thereany actual holes in the ozonebut it hasthin inManyes hav estoppedCFCs.view of the

layer. The pinkareas.

cu t down to makegrazing land forcattle and to use certain'hardwood trees formaking furnitu re.The forests arebeing destroyed at a rate of about 24square km every hour. If this continues,by the year 2050 they w ill al l have gone.

Q Does recy cling papersave rainforests?No, because thetrees used formaking paper arespecially grown.Recycling paper makes selisebecause it uses fa r less energy andwater than making new paper fromtrees. It also means that we throw lessaway, which reduces pollution. y


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30 32 Index

Acid rain 30Air 6, 22, 24-25, 30Air mass 24Air pollution 30Antarctica 16, 18-19, 20-21, 30Arctic 20Atoms 28Atmosphere 22-23, 24, 30Atmospheric pressure 23, 24Axis 5

Beaches 11Carbon dioxide 30CFCs 31Cities 26Cliffs 10Climate 26-27Clouds 8,24-25Coal 28Coastal marshes 11Coastline 10Coniferous forests 27Continents 6, 20Coral reef 9Crust 6, 8Day 5,17Deltas 14Deserts 16-17, 26Dome mountains 12Earthquakes 6Electricity 28Equator 5, 25, 26-27Exosphere 22Faults 6Fish 29Food crops 29Fossil fuels 28Gas 28-29Glaciers 15,18-19, 20Global warming 30Gravity 4-5, 8, 11, 22Groynes 10

r1Ice 14,18, 20Ice age 18Iceberg 20Ice crystals 25Ice sheet 18-19, 20, 30Inner core 6Islands 9Lakes 14Lava 10Lightning 25Magma 7Magnetic field 6Mantle 6-7Mesosphere 22Metal 6, 29, 30Mid-Atlantic Ridge 9Minerals 8, 29Molten rock 13Monsoon 27Moon, The 11Moraine 19Mountains 9, 12-13, 18, 26Natural resources 28, 30Night 5,17Nitrogen 22North Pole 5, 6, 20Nuclear power 28Oasis 16Oceans 8, 14, 27, 29Ocean floor 9Oil 28Outer core 6Oxygen 22Ozone 23Ozone layer 23, 31Plates 6Pollution 30Polyps 9

Rain 15, 16, 24-25, 26-Rainforests 27, 30Rain-water 31Recycling 31Renewable energy 28Rift valleys 12, 15Rill 14Rivers 8,14-15Rocks 6-7, 15, 16-17, 1Sahara 16Sand 10-11, 16-17Sand dunes 16Seas 8,10,11,14-15, 16Seasons 27Snow 13, 14, 18, 20, 24Soil 6, 30Solar System 4South Pole 5, 6, 20Springs 14Staple foods 28Storms 25Stratosphere 22Streams 14Sun 4, 5, 24, 26-27, 28Temperature 23, 26Thermosphere 22Thunder 25Tides 11, 15, 29Time zones 5Trench,ocean 9Tributaries 14Troposphere 22, 24Ultraviolet radiation 2Underground caves 1Underground springUniverse 4, 28Valley 9Volcanoes 9,10,12-13,1Water 6, 30Waterfalls 14Water vapour 22,24-2Waves 8,10-11, 29

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