My First Library of Knowledge
Our Planet
Earth
Orpheus
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THE EARTH is ahuge, spinning ball
of rock. It is one of nineplanets that travel roundthe Sun. It is the onlyworld we know where lifeexists. Its surface is madeup of oceans, which covermore than two thirds ofit, and land masses, calledcontinents.A layer of aircalled the atmosphere,surrounds the Earth.
CONTENTS INTRODUCTIONFirst published in 2005 by Orpheus Books Ltd.,
2 Church Green,Witney, Oxfordshire, OX28 4AW
Copyright © 2005 Orpheus Books Ltd.
Created and produced by Rachel Coombs,
Nicholas Harris, Sarah Harrison, Sarah Hartley and
Emma Helbrough, Orpheus Books Ltd.
Text Nicholas Harris
Consultant Susanna van Rose
Illustrated by Gary Hincks and Peter Dennis
All rights reserved. No part of this book may be
reproduced, stored in a retrieval system, or transmitted
in any form or by any means, electronic, mechanical,
photocopying, recording or otherwise, without the prior
written permission of the copyright owner.
ISBN 1 901323 XX X
A CIP record for this book is available from the
British Library.
Printed and bound in Singapore
4 INSIDE THE EARTH
6 TECTONIC PLATES
8 VOLCANOES
10 EARTHQUAKES
12 HOW ROCKS AREMADE
14 RIVERS
16 CAVES
18 GLACIERS
20 DESERTS
22 WATER
24 WEATHER ANDCLOUDS
26 STORMS
28 SEASONS ANDCLIMATES
30 GLOBAL WARMING
32 INDEX
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MAGMA
In the mantle, the temperature is 2000˚C. Here,the rock is partly melted. Known as magma, itflows like hot tarmac on a newly-surfaced road.Sometimes the magma is forced upwards from themantle. It can burst through weak points in theEarth’s crust. It erupts at the surface in a volcano.
INSIDE THE EARTH
THE EARTH has athin rocky shell on
the outside, called thecrust. Beneath lie severallayers, all extremely hot.The first layer, the mantle,is made of rocks so hotthey have partly melted.
Farther down is theouter core, made ofliquid metal.Theinner core, atthe Earth’scentre, is asolid ballof iron.
In this illustration, a largeslice of the Earth has
been cut away sowe can seethe layersinside.
Thecrust
beneaththe oceans
is a thin layerof volcanic rock.
The crust beneath thecontinents is thicker.
4
Innercore
Outer core
Mantle
Crust
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TECTONIC PLATES
THE EARTH’s surfaceis like a jigsaw puzzle
wrapped around a giantball. It is divided intoabout 15 jagged-edgepieces, called tectonicplates.They are alwaysshifting about, but onlygradually. Sometimesthey lock together for atime, then suddenly joltapart, causing earthquakes.
Some plates aremoving apart, othersare pushing together.In some places, oneplate slides downbelow another. Inothers, two platesslide past each other,moving in oppositedirections. When twoplates push together,the land slowlycrumples, formingmountains.
The white lines on this globemark some of the tectonic plateedges. One runs like an enormouscrack down the middle of theAtlantic Ocean.
This diagram is a cross-section throughthe Earth’s crust. The yellow arrowsshow which way the plates are moving.
Two plateedges pullaway fromeach other
Ocean floor
Oceantrench
NORTH
AMERICA
EUROPE
A T L A N T I C
O C E A N
Two plate edgespull away fromeach other
Two plate edgespush againsteach other
One plateedge slidesdownbeneaththe other
Two plate edgesslide past eachother
Mountains
Mid-oceanic ridgeFault
Magma rises frombelow the crust
Volcano
Rift valley
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TYPES OF VOLCANOAn active volcano erupts lava, ash anddust frequently.When a volcano has noterupted for many years, it is called adormant volcano. But this type ofvolcano may erupt again some time inthe future.When eruptions stopaltogether, the volcano is described asextinct. Some volcanoes blast out red-hot
lava and gas in spectacularexplosions. But in many othervolcanoes, the lava oozes out
gently, like boilingsyrup.
VOLCANOES
AVOLCANO isan opening in
the Earth’s crustthrough whichmagma erupts. Manyvolcanoes are cone-shaped mountainswith a crater at the
summit.In a violent eruption, thevolcano shoots hugeamounts of lava (eruptedmagma), ash and dustinto the air. Over time,many layers of lava and
Magma
Ancientlava flow
Dormantvolcano
Layers of lavaand ash frompreviouseruptions
Crater
Lavabombs
Ash cloud
Ancient lavaflow
Rock layersunder theground
Cloud of ash,dust andglowing gas
Extinctvolcano
Cooled magma
Vent
Magma mayrise throughthe crust andcool to formsolid rockunderground.
Magmaseepsthroughgapsbetween therock layers toform sheets ofvolcanic rock.
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XYZ XYZXyz xyz xyz
EARTHQUAKES
AN EARTHQUAKEis the trembling or
shaking of the ground. Itis caused by the suddenmovement of the rocks inthe Earth’s crust.Thishappens when the edge of
EARTHQUAKE DAMAGEIt is mostly in towns and citieswhere earthquakes cause largeloss of life.The sudden violentshaking of the ground may resultin the collapse of buildings andbridges, pipes bursting and cablesbreaking. Fire or flooding alsocreate great damage.
SHOCK WAVES
The place where the rocks snapis called the focus. Shock wavestravel out in all directions. In asmall earthquake, the groundwill tremble only slightly. In alarge one, it may shakeviolently for several minutes.
TSUNAMI!A tsunami is caused by anearthquake on the sea bed.Thesudden slip creates a series offast-moving waves.When theyreach coastal waters, they buildup to immense heights.
one tectonic plate (see page6) slides beneath or along-side another.The twoplates may lock togetherfor a while before thepressure becomes too muchand the rocks snap apart.
Focus
Shock waves
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HOW ROCKS ARE MADE
ROCKS are the hardmaterials that make
up the Earth’s crust.Theylie both beneath the soiland the depths of theocean.You can seethem in cliffsalong
This diagram shows part of the Earth’scrust. Wind, rivers and glaciers weardown all kinds of rocks into fragmentscalled sediments. These are washedaway into lakes and seas.
TYPES OF ROCKThere are many kinds of rocks.They can be divided into threegroups. Igneous rocks, such asgranite and basalt, result fromthe cooling of magma (see page8). Sedimentary rocks, such assandstone and limestone, aremade from sand, mud andother fragments of rock, or theremains of living things.Metamorphic rocks, such asmarble and slate, are formedwhen any kind of rock ischanged by great heat orpressure under the ground.
the seashore. Rocks are,themselves, made up froma solid mixture ofminerals.
Many sediments arewashed out to sea. Asmore layers settle ontop of each other, theweight presses thefragments together.Eventually, they formrocks. Over millionsof years, Earth move-ments may bring thesedimentary rocklayers to the surface.
When rising magma heatsnearby rocks, the rock is“baked”. They turn intometamorphic rocks. Earthmovements (see page 7) mayalso produce metamorphicrocks by squashing them.
Risingmagma
Layers ofsediments collecton the sea bed
Layers of rockin Earth’s crust
Igneousrock
Glacier carries awayrock fragments
Metamorphicrocks
Volcano eruptslava
Fragments ofrock blownaway by winds
Rivers wash awaysediments
Sedimentaryrock layers
Sediments laiddown at river’smouth
Undersealandslide
Sedimentaryrocks formed onsea bed
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RIVERS
RIVERS are naturalwater channels.
They carry rain or meltedsnow and ice downhill tolowlands, lakes andseas.
The force of runningwater wears away therocks.This is callederosion.
A river starts as a spring,rainwater collecting onsodden ground or melt-water from a glacier. Near itssource, the river, often calleda brook or stream, flowsquickly. Its waters washaway soil and mud so thatthe stream bed is bare rock.
Lower down, the riverflows more slowly. Itwidens as other smallerrivers, called tributaries,join it. Over flatterground, the river flowsin huge curves calledmeanders.
The RiverZambezi plunges128 m at theVictoria Falls insouthern Africa.
The river finally enters the seaat its mouth. It may divide intomany channels, forming a delta.
ESTUARIESWhere a river meets the sea as a singlechannel, it may widen to form anestuary. Here, fresh and salt waters mix,and rise and fall with the tides.
WATERFALLS
A waterfall forms where a river flowsover a cliff, or where the rocks in its bedbecome easier to wear away.The watercascades over a “lip” of hard rock.
Mountainlake
Estuary
Sea
Glaciermeltwater
Waterfall
Rapids
Ox-bowlake
Meanders
Delta
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LIMESTONE CAVESLimestone may look like solid rock, but it containsmillions of cracks. Rainwater seeps into these cracks.Over many years, the water dissolves the rock,widening the cracks and eventually forming caves.
STALACTITES ANDSTALAGMITESAs water drips from the ceiling of acave, the limestone dissolved in ithardens very gradually to formicicle-like stalactites. Stalagmitesgrow up from the floor where thedrips fall. Sometimes they join thestalactites to form columns of rock.
CAVES
CAVES are formedwhen water, flowing
below ground, hollowsout the rocks.You mayalso come across caves atthe seashore, where wavescrash against the cliffs.Limestone caves are oftenmade up of a series ofchambers, linked bytunnels and shafts. Somehave lakes.
Anundergroundstream flowsthrough this cave. Oneday, the water may drainaway, leaving a dry cave.
Swallowhole
Limestonepavement
Limestonehills
Columns
Undergroundstream
UndergroundlakeStalactites
Column
Stalagmite
Gorge
Rockfall
This is a cross-section throughan area oflimestone rock.
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GLACIERS
AGLACIER is a massof ice that moves
slowly downhill. It ismade from layers of snow.
As the layers build up, thesnow turns to ice.The icebecomes so thick andheavy, it starts to move.
RIVERS OF ICEAs a glacier grinds its way down avalley, it gouges out loose rocksand carries them downhill.Theserocks collect together in bandscalled moraines.Where twoglaciers meet, their moraines
merge together. Further down thevalley where the glacier melts (atits snout), all the rocks are dumpedin heaps known as end moraines.Where a glacier runs over steeperslopes, cracks, known as crevasses,form on its surface.
Snout
Glacier
Cirque (hollowwhere glaciers begin)
Crevasses(cracks inglacier)
End moraine
End moraine
Meltwaterstreams
Moraines fromtwo glaciers
meet
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DESERTS
DESERTS are foundin areas where very
little rain falls. Other thanat oases, fertile spots in adesert, there is little signof life. Many people thinkof deserts as vast areas of
Where the wind alwaysblows in the samedirection, it piles upsand in crescent-shapeddunes, called barchans.
sand. In fact, only abouta fifth of the world’s hotdeserts are sandy. Mostare just bare rock andgravel.Antarctica is alsoa desert: very little snowever falls there.
In deserts, strong windsmay blast tiny sandparticles at the rocks,carving out someincredible shapes. Insome desert landscapesyou can see rock arches.Mushroom-shaped rocksare made when wind-blown sand blasts awayat the base of a boulder,leaving a narrow neck.
When rainstormsdo occur, the fast-flowing waterquickly wears awaythe rocks to formsteep-sided gorgescalled wadis.
Some desert mountainranges have flat tops.They are called mesas.
Oasis
Sand dunes
Rock arch
Barchans
Mesa
Wadi
Mushroom-shaped rocks
Salt flat
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WATER
THE OCEANS holdabout 97% of the
world’s water. Some water iscarried in the air asclouds. It may fall tothe ground as rain orsnow.Then it flowsback to the oceanin rivers.Thishappens over andover again, all overthe world. It is calledthe water cycle.
THE WATER CYCLEWater evaporated from the oceansmay be carried as water vapouracross land.As it rises above highground, it condenses and falls toearth as snow or rain. Riverscarry the water on the land’ssurface back to the ocean and thecycle begins again.
EVAPORATION AND CONDENSATIONWhen water from oceans, rivers or lakes is heated by theSun, it evaporates: it turns into an invisible gas calledwater vapour.This rises into the air and is blown bywinds.As the air rises, it cools and starts to condense (turnsback into a liquid) around tiny dust particles in the air.Millions of water droplets gather together to form clouds.
Much of the waterevaporated fromthe oceans fallsdirectly back intothe oceans as rain.
Water mayseep down intothe rocks. Thisgroundwaterwill eventuallyflow down intothe oceans.
Water vapour in theair is carried by winds
Rivers carrywater acrossland’s surface
Ice or waterdroplets fall assnow or rain
Water evaporatesfrom rivers, lakesor vegetation
Cloudsform
Cloudsform
Rain fallsover oceans
Evaporationfrom oceans
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CLOUDS IN CLOSE-UPClouds consist of millions of tinywater droplets or ice particles.Whenwater vapour in the air condenses,water droplets form around dustparticles (see page 22). If thetemperature falls below freezing, thedroplets turn to ice.They float in theair until they become too heavy.They then fall as rain or snow.
A FOGGY DAYFog or mist (a thin fog) is cloudthat hugs the ground. It is oftenfoggy when moist air cools atnight, causing water droplets toform. Fog also forms when moistair is forced to rise over a hill.
are warmer than others.Warm air rises, so coolerair flows in to replace it,producing winds.Whenair moves, it carries watervapour from one area toanother (see page 22-23).
WEATHER AND CLOUDS
WEATHER is aword to describe
the what is happening inthe air: rain or snow, hotor cold, windy or still.TheSun’s heat is vital to ourweather. Some regions
At night, the ground cools quickly.Water vapour near the groundcondenses, forming dew. This soakseverything — including spiders’ webs.
Clouds form at differentheights above the groundand have differentshapes. They may bewispy, fluffy or flat.
If the temperature falls belowfreezing, the condensed water vapourturns into a layer of sparkling icecrystals, which we call frost.
Cirrus
Cirrostratus
Cirrocumulus
Altostratus
Altocumulus
Cumulonimbus
Stratocumulus
Cumulus
Stratus
Nimbostratus
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STORMS
STORMY weather means highwinds and heavy rain or snow.In some parts of the world, theextremely fast-moving winds ofhurricanes and tornadoes may bepowerful enough to cause severedamage and even loss of life.Heavy rainfall or blizzards mayalso result in floods, mudslides oravalanches in mountainous areas.
HURRICANESA hurricane is a storm thatoccurs in tropical regions. Itbegins when warm, moist airrises high above the oceans.Theair begins to swirl around in aspiral. Clouds form and massivedownpours follow.Very powerfulwinds rage around a calmcentre, called the “eye” of thestorm.When a hurricane movesacross land, it can cause greatdamage, including ripping uptrees and overturning cars.
LIGHTNINGThunderclouds formwhen warm, moist airrises quickly.As waterdroplets and ice crystalsbump together, theyproduce electricity.Wesee this as lightning.Theheat of the flash causesthe air around it toexpand rapidly, makingthe boom of thunder.
A tornado is a twisting column of air,swirling at up to 400 km per hour. Itsbase may be only 100 m across, butthe winds are so powerful they destroynearly everything in their path.
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SEASONS AND CLIMATES
INMANY parts of theworld, the weatherchanges according to thetime of year.These are thechanging seasons. Differentpatterns of weather,including rainfall, windsand temperature, are foundin different parts of theworld.These patterns arecalled climates.
THE SEASONSAs the Earth spins round, it is not uprightbut tilted.When the northern half (thenorthern hemisphere) leans towards theSun, the Sun is nearer. It is summer. Later inthe year, the southern hemisphere is nearerthe Sun and has its summer.The northernhemisphere is further away and has winter.
THE EARTH IN ORBITThe Earth orbits the Sun in justover 365 days.The Moon orbitsthe Earth in about 27 days.TheEarth spins once every 24 hours.
Regions close tothe Equator havetropical climates.Here it is hot andwet all year round.Deserts have verylittle rain.
EARTH’S CLIMATESHot climates are found nearthe Equator where the Sun isclosest. Polar regions, where theSun is furthest away, are thecoldest. In between aretemperate lands which havewarm summers andcool winters.
Tropical
Desert
Temperate
Cool temperate
Polar
Mountain
Equator
Sun
Earth’sorbit
Earth
Moon
21st June
22nd December
N O R T H
AM E R I C A
A U S T R A L A S I A
A S I A
E U R O P E
A F R I C A
S O U T H
AM E R I C A
Sun’srays
Sun’srays
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31
Sun’srays
Atmosphere
Greenhousegases inatmospheretrap heat
Heat reflectedback into space
Earth’s surface
30
WHY IS IT HAPPENING?Global warming is probablycaused by the greenhouse effect(see panel). Human activities haveresulted in a large increase ofgreenhouse gases, such as carbondioxide, in the atmosphere.Vehiclesand power stations give off exhaustgases from burning oil or coal(“fossil fuels”).These add billions oftonnes of carbon dioxide to theatmosphere. Plants will usually
absorb (take in) carbon dioxide aspart of their natural life cycle. Butthe destruction of forests aroundthe world means there are fewerplants to absorb the gas.
GLOBALWARMING
THE EARTH isgetting warmer.
Average temperaturesworldwide have risenduring the last centuryand there is no sign ofthis rise slowing.There isnow a high risk that theice caps will start to melt,raising sea levels every-where and changingworld climates.
If melted ice cause sea levels to rise, itmay result in many coastal cities beingflooded by sea water. To avoid this
catastrophe, people must reduce theamount of greenhouse gases in theair by burning fewer fossil fuels.
Sun’srays
Atmosphere
Greenhousegases inatmospheretrap heat
Heat reflectedback into space
Earth’s surface
GREENHOUSE EFFECTThe atmosphere contains gasesthat stop all the Sun’s heatescaping.These gases act like theglass in a greenhouse.They helpkeep the Earth’s surface warm.
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INDEXAair 24-25, 26-27Antarctica 20Atlantic Ocean 7atmosphere 30-31avalanches 26
Bbarchans 21basalt 13blizzards 26
Ccarbon dioxide 31caves 16-17cirque 18cliffs 12, 14, 16climates 28-29, 30clouds 22-23, 24-25,26-27
columns 16condensation 22-23, 25core 4-5crater 8-9crevasses 19crust 4-5, 7, 8, 10,12-13
Ddelta 15deserts 20-21, 29dew 25
EEarth 4-5, 6-7, 30,inside of the 4-5movements in the
6-7, 10, 12-13orbit of 28
earthquakes 7, 10-11electricity 26Equator 28-29erosion 14estuary 15evaporation 22-23
Ffaults 7flooding 11, 26, 31focus (of earthquake)11
fog 25fossil fuels 31frost 25
Gglaciers 13, 15, 18-19global warming 30-31gorges 17, 21granite 13greenhouse effect 30-31greenhouse gases 30-31groundwater 23
HIheat 24hemispheres 29hurricanes 26-27ice 14, 18, 23, 25, 26ice caps 30
Llakes 13, 14-15, 16-17,23
landslide 13lava 8-9, 12lightning 26limestone 13, 16-17
Mmagma 4, 7, 8-9, 12-13mantle 4-5marble 13meanders 14mesas 20-21mid-oceanic ridge 7minerals 12Moon 28moraines 18-19mountains 6, 8, 20
NOoases 20-21ocean floor 6-7ocean trench 6oceans 22-23, 27ox-bow lake 14
Pplants 31polar regions 28
Rrain 22-23, 24-25, 26,28-29
rainwater 15, 17, 21rapids 14rift valley 6rivers 12-13, 14-15,22-23
rock arches 20-21rock layers 13rockfall 17rocks 4, 10, 12-13,
14-15, 16-17, 19,20-21, 23
igneous 13melted 4, 8metamorphic 12-13sedimentary 13volcanic 5, 8-9
Ssalt flats 21sand 20-21sand dunes 21sandstone 13sea bed 11, 13sea levels, rising 30-31seas, 11, 13, 14-15seashore 12, 16seasons 28-29sediments 12-13shock waves 11
slate 13snout (of a glacier) 19snow 14, 18, 20, 22-23,24-25, 26
stalactites 16stalagmites 16storms 21, 26-27streams 15, 17, 18summer 29Sun 24, 28, 29-30,heat of the 22, 30
swallow hole 16
Ttectonic plates 6-7, 10temperate regions 28temperatures 25, 28, 30thunder 26tides 15tornadoes 26-27tributaries 14tropical regions 27,28-29
tsunami 11
VVictoria Falls 14volcanic ash 8-9volcanic eruptions 8-9,12
volcanoes 4, 6, 8
Wwadis 20-21water 14-15, 16-17,22-23, 25
water cycle 22-23water vapour 22-23,24-25
waterfalls 14-15weather 24-25, 28winds 12-13, 21, 22,24, 26-27, 28
winter 29
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