MyFirstLibraryofKnowledge Our Planet Earth

My First Library of Knowledge

Our Planet

Earth

Orpheus

YCE Earth FINAL:YCE Earth FINAL 10/26/10 12:45 PM

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

YCE Earth FINAL:YCE Earth FINAL 10/26/10 12:45 PM

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

5

YCE Earth FINAL:YCE Earth FINAL 10/26/10 12:47 PM Page 4

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

6 7


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.

8 9


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

10 11


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

12 13


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

14 15


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.

16 17


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

18 19


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

20 21


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

22 23


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

24 25


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.

26 27


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

28 29


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.


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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