1. 1. *Earth Sci Prelims (1-7).qxd 12/12/08 11:02 AM Page 1 SCIENCE VISUAL RESOURCESEARTH SCIENCEAn Illustrated Guide to Science The Diagram Group
2. 2. *Earth Sci Prelims (1-7).qxd 12/12/08 11:02 AM Page 2Earth Science: An Illustrated Guide to ScienceCopyright 2006 The Diagram GroupAuthors: Simon Adams, David LambertEditors: Gordon Lee, Jamie StokesDesign:Anthony Atherton, bounford.com, Christopher Branfield, Richard Hummerstone, Lee Lawrence, Tim Noel-Johnson, Phil RichardsonIllustration:Peter WilkinsonPicture research:Neil McKennaIndexer: Martin HargreavesAll rights reserved. No part of this book may be reproduced or utilized in any formor by any means, electronic or mechanical, including photocopying, recording, orby any information storage or retrieval systems, without permission in writing fromthe publisher. For information contact:Chelsea HouseAn imprint of Infobase Publishing132 West 31st StreetNew York NY 10001For Library of Congress Cataloging-in-Publication data,please contact the publisher.ISBN 0-8160-6164-5Chelsea House books are available at special discounts when purchased in bulkquantities for businesses, associations, institutions, or sales promotions. Please callour Special Sales Department in New York at 212/967-8800 or 800/322-8755.You can find Chelsea House on the World Wide Web athttp://www.chelseahouse.comPrinted in ChinaCP Diagram 10 9 8 7 6 5 4 3 2This book is printed on acid-free paper.
3. 3. *Earth Sci Prelims (1-7).qxd 12/12/08 11:02 AM Page 4ContentsMalestrom1 EARTH AND SPACE 8 Earths orbit18 The Moon: structure 9 Earths shape and size 19 Solar and lunar eclipses10 Day and night time zones 20 Structure of Earth11 The seasons21 Earths magnetic field12 Latitude and longitude 22 Earths magnetosphere13 The solar system 23 Meteors14 Structure of the Sun 24 Meteorites15 The Suns energy 25 Elements: universal16 The Moonabundance17 The Moon: surface2 EARTHS HISTORY26 Superposition41 Ordovician period27 Unconformities 42 Silurian period28 Complex rock sequences 43 Devonian period29 Paleomagnetic dating 44 Mississippian period30 How fossils form 45 Pennsylvanian period31 Fossil use in rock 46 Permian period correlation47 Triassic period32 Correlating rocks48 Jurassic period33 Tree of life 49 Cretaceous period34 Evolutionary clocks50 Paleocene epoch35 Mass extinctions 51 Eocene epoch36 Geologic time52 Oligocene epoch37 Archean eon53 Miocene epoch38 Proterozoic eon54 Pliocene epoch39 Phanerozoic eon55 Pleistocene epoch40 Cambrian period56 Holocene (recent) epoch
4. 4. *Earth Sci Prelims (1-7).qxd 12/12/08 11:02 AM Page 53 EARTHS ROCKS57Origins83 Metamorphism58Elements 84 Progressive59Internal heat metamorphism60Periodic table 85 The rock cycle61Atoms86 Continental drift: fit62Compounds87 Continental drift: geology63Isotopes and ions88 Continental drift: biology64Crystals and minerals89 Continental drift: polar65Crystal systems paths66Rock forming minerals90 Wegeners theory67Hardness 91 Continents: 250 million68Igneous rocks years ago69Intrusive igneous rocks92 Continents: 180 million70Magma productionyears ago71Volcanoes: active93 Continents: 60 million72Volcanic typesyears ago73Volcanoes: caldera 94 Lithospheric plates74Volcanoes: lava forms95 Plate tectonics75Volcanoes: central 96 Crust and lithosphere76Volcanoes: fissure 97 Oceanic crust77Volcanoes: shield98 Hawaiian Islands78Geysers and hot springs99 Dating the seafloor79Sedimentary rocks:100 Spreading ridgesformation 101 Continental crust80Sedimentary rocks: clastic102 Continent growth81Sedimentary rocks:103 Isostasyorganic and chemical104 Ore82Sedimentary rocks:105 Coalbedding 106 Oil and gas
5. 5. *Earth Sci Prelims (1-7).qxd 12/12/08 11:02 AM Page 64 AIR AND OCEANS107Atmosphere: structure 128 Hurricanes108Atmosphere: layers129 Tornadoes109Radio waves 130 Pressure systems110The nitrogen cycle131 Air masses111The carbon and oxygen 132 Water cycles133 Oceans112Heat transfer processes 134 Ocean temperatures113Sunshine135 The ocean floor114Temperature belts 136 Seafloor profiling115Pressure belts137 Tides116The Coriolis effect 138 Ocean currents117Wind circulation139 Wave features118Jet streams 140 Wave types119Coastal breezes 141 Bays and headlands120The Beaufort scale of 142 Sea cliffs wind speeds 143 Waves and beaches121Humidity144 Longshore drift122Fog 145 Spits and bars123Cloud types 146 Raised coastlines124Rain, snow, and sleet 147 Submerged coastlines125Rain types148 Coral reefs126Thunderstorm149 Atolls and guyots127Cyclones5 SHAPING THE SURFACE150Mechanical weathering 157 Soils of the USA151Mechanical and organic158 Mass movement weathering159 Slopes152Chemical weathering 160 Water cycle153Chemical weathering:161 Groundwater hydration 162 Chalk and limestone154From granite to sand163 Rivers155Soil formation164 Rapids and waterfalls156Soil textures 165 River transport
6. 6. *Earth Sci Prelims (1-7).qxd 12/12/08 11:02 AM Page 7166River flow 178 Ice sheets167River valleys179 Glacier features168Drainage 180 Glacial erosion169Watersheds 181 Glacial deposits170Meanders 182 Cold landscapes171Oxbow lakes183 Permafrost172Lakes184 Deserts173Flood plains 185 Deserts of the USA174Deltas 186 Desert landforms175River profiles 187 Wind erosion176River rejuvenation 188 Sand dunes177Hills and valleys189 Desertification6 COMPARISONS190Continents 195 Submarine features191Lakes196 Volcanoes and192Islandsearthquakes193Mountains197 Rivers194Seas and oceansAPPENDIXES198Key words205Internet resources207Index
7. 7. *Earth Sci Prelims (1-7).qxd 12/12/08 11:02 AM Page 3IntroductionEarth Science is one of eight volumes in the Science VisualResources set. It contains six sections, a comprehensive glossary,a Web site guide, and an index.Earth Science is a learning tool for students and teachers. Full-color diagrams, graphs, charts, and maps on every page illustratethe essential elements of the subject, while parallel text provideskey definitions and step-by-step explanations.Earth and space provides an introduction to the study of ourplanet in the context of the solar system. Issues such as Earthsdependence on the Sun, and reciprocal influence with the Moon,are illustrated and discussed, as the elementary concerns of theearth sciences are introduced.The concept of geologic timea timescale staggering by thestandards of human historyis expanded in Earths history.Reference is made to the fossil traces of past life that enablemodern paleontology to make deductions about the developmentof life-forms, while the land of the present-day USA is presented asa familiar point of reference in a story of unceasing change.Earths rocks introduces the elementary chemistry and physicsunderlying the geology of the planet, and discusses how mineralsform rocks. The three major classifications of igneous,metamorphic, and sedimentary rock are examined in detail beforethe chapter returns to the origins of Earths current surfacealignment and mineral resources.Air and oceans examines in detail Earths unique and life-sustaining atmosphere and surface water.Shaping the surface looks at the physical geography of the landand how it is naturally shaped by weather and water movement.Finally, familiar and significant geographical features of the worldare statistically compared in Comparisons.
8. 8. *01 Earth-space (8-25).qxd 12/12/0811:04 AM Page 8 8EARTH AND SPACEEarths orbit Key wordsGravity and inertia aphelionperihelion asteroidplanet comet gravitytendency orbitto moveactual orbitEarth, speedGravity and inertia 18.2 miles per second Theplanet Earth tries to speed(29.8 kmps)through space in a straight line. The force ofSuns gravitational force tries to pull gravitationEarth into the Sun. Inertiathetendency of an object to resist a forcechanging its speed or directionprevents this from happening. Instead,the captured Earth continually orbitsthe Sun. Earth orbits the Sun at a meandistance of 92,960,000 miles(149,600,000 km). Sun Earths orbital velocity is 18.5 milesper second (29.8 kmps).Earths path Earthrevolves around the Sun in acounterclockwise direction if viewedfrom space. Each years complete revolution tracesan elliptical orbit bringing Earthclosest to the Sun in January andEarths pathfurthest away in July. The point atannual circuitwhich a planet, comet, or asteroidmost closely approaches its sun istermed perihelion, while the pointfurthest away is aphelion. Earth At perihelion, about January 3rd,Earth comes within 91,400,000 miles(147,100,000 km) of the Sun. At aphelion, about July 4th, it is94,510,000 miles (152,100,000 km)from the Sun. Sunperihelion aphelion (about July 4)(aboutJanuary 3) Diagram Visual Information Ltd.
9. 9. *01 Earth-space (8-25).qxd 12/12/0811:05 AMPage 9 9Earths shape and size EARTH AND SPACEKey wordsEarths sizeellipsoidNorth PoleAlexandria, equatorSouth Pole AlexandriaSyene Egypt: pillarcasts shadow geoid of 7.5 Suns raysat noon, axislongest dayEarths sizeEarths Around200 BCEcenter Eratosthenes calculated Earths circumference bymeasuring angles equator made by the Suns rays at noon at two places a known distanceSyene, Egypt:Sun verticallyapart, one south of theover wellother. Parallel sunrays cast ashadow at midsummer noon, which atAlexandria, Egypt, was at 7.5 to theEarth: nearly an ellipsoidvertical. At the same time, in the southperfect sphereat Syene (present-day Aswan), theSuns rays fell vertically down a well. polar diameter Earth: nearly an ellipsoid Thedistance from the North Pole to the South Pole of 7,900 miles (12,714 km) is 26 miles (42 km) equatorial diameter shorter than the distance across the equator, which is 7,926 miles (12,756 km). The shape of Earth can be represented ellipsoid as a near-ellipsoid by visuallyThe diagram shows anellipsoid against a perfectexaggerating the differences betweensphere. Earth is almost an its polar and equatorial diameters.ellipsoid. The geoid: Earths actual shapeThe geoid Thegeoid is Earths actual shape North Polecalculated to take account of its mass, elasticity, and rate of spin. It follows +18.9 mean sea level in the oceans and is miles perfect ellipsoid slightly pear-shaped, with the NorthgeoidPole 18.9 miles (30 km) further from Earths center than other places and the South Pole 25.8 miles (42 km) nearer. Diagram Visual Information Ltd. The diagram stresses Earths pearlikeThe diagram shows ashape by visually exaggerating smallgeoidan approximation differences in distance from surfaceof Earths actual shapeagainst an ellipsoid. Theto center.geoid is visuallyexaggerated to illustrate-25.8its difference from an ideal miles South Poleellipsoid.
10. 10. *01 Earth-space (8-25).qxd12/12/0811:05 AMPage 10 10EARTH AND SPACEDay and night time zones Key words Day and night longitude meridian prime meridian Sun time zonemidnight noon Suns raysDay and night Earthspins like a spinning top, andcompletes one revolution every24 hours. As it spins, each place on itssurface moves into sunlight anddaytime, and then into the Sunsshadow and night. When North America faces away fromthe Sun it is night there. When North America faces the Sunit is day there.Time zonesmidnight noon Suns rays The world is divided into standardtime zones based on the prime (orGreenwich) meridian at 0 longitude. With local adjustments, each standardtime zone is a 15 degree band east orwest of the prime meridian andrepresents a difference in time ofone hour. sunriseInternational date line prime meridian World time zones 0 3 12 Diagram Visual Information Ltd.3 12 4 12 5 12 6 12 9 12 0 +1 +2+3+4 +5+6 +7 +8 +9+10 +11 +12 11109 8 7 6 5 43 2 10
11. 11. *01 Earth-space (8-25).qxd12/12/08 11:05 AMPage 11 11The seasonsEARTH AND SPACEKey wordsSummer solsticeequinoxJune 21rotationsolsticeof Earth North Pole rays ofArctic Circle the SunSun (6630 N)equator Seasons Earth Seasons are periods of the year with rays of the Sun orbitNightcharacteristic weather. Many tropicalDayand subtropical regions have only wet Earth orbit and dry seasons. Temperate regions such as North America and Europe have fourAutumnal (fall) equinoxseasons: spring, summer, fallSeptember 23 (autumn), and winter. North Pole Seasons result from the fact that Earths axis of rotation is not perpendicular to the plane of its rays of Sunthe Sun orbit around the Sun, but tilted by rays of 23.5 degrees. Earththe Sun This tilt means that Northern andorbitSouthern hemispheres receive moreEarthor less sunlight depending on whetherorbitthey are tilted toward or away fromequator the Sun. Seasons depend on the intensity of solar radiation, so the northern summer coincides with the southernWinter solstice winter and vice versa. The diagramsDecember 22 show seasons for the NorthernEarth orbitEarth North PoleHemisphere. orbitrotationof EarthArctic Circlerays of Summer (6630 N)Sunthe Sun Atthe summer solstice the NorthernHemisphere is tilted toward the Sun.Summer is the hottest time of year.rays ofthe Sun equatorFall (autumn) Atthe autumnal equinox, the Sun isdirectly overhead above the equator.In the fall daytime grows shorter,crops ripen, and deciduous treesVernal (spring) equinox shed leaves.March 21 rotation North Poleof EarthWinter Earth Atthe winter solstice, the NorthernArctic CircleorbitHemisphere is tilted away from the Diagram Visual Information Ltd. (6630 N) rays ofSun. Winter is the coldest time of year. the SunDaytime hours are shortest. Plantgrowth slows or stops.rays Sunof theSunequator Spring Atthe vernal equinox, the Sun isoverhead at the equator. In spring dayslengthen and plants grow.
12. 12. *01 Earth-space (8-25).qxd12/12/08 11:05 AM Page 12 12 EARTH AND SPACE Latitude and longitude Key wordsLatitudeLongitude Earth poleObtaining an angle of latitudeObtaining an angle of longitude equator latitude longitudeNorth prime meridian prime meridian Pole resulting (longitude 0)resultingparallel of meridianlatitudeLatitude Latitudeis a position on Earths Earthssurface north (N) or south (S) of thecenterEarths axisequator, the imaginary line around themiddle of Earth. angle of equator longitude Degrees of latitude are measured as (latitude 0)angles from the center of Earth. Aresultingdegree () of latitude is divided into 60 meridianSouth measured angleprime meridianminutes (). A minute is divided into 60 (longitude 0) Pole of latitudeseconds ("). A line joining locations with the samelatitude is called a parallel. Parallelsare so called because they run parallelto the equator and to one another. The equator is at latitude 0. TheDegrees of latitude Degrees of longitudeNorth and South poles lie at latitudes907590 N and S.6045Longitude 30north latitude Longitude is a position east (E) or15 (N)west (W) of the prime meridian, animaginary line on Earths surface,0 90 60 30 030 60 90passing through Greenwich, England,south 15and joining the North and Southlatitude30(S)poles. The prime meridian is at longitude 0.Meridians are measured up to 180 Eor W of it.westeastlongitude (W)longitude (E) Degrees of longitude are measured asangles from the center of Earth anddivided into minutes and seconds. Lines of longitude are 69 miles(111 km) apart at the equator, butKey latitudes Key longitudebecome closer together as their Arctic Circle66 30 Ndistance from it increases.tropic ofCancer23 27 Nequator 0tropic of Diagram Visual Information Ltd.Capricorn23 27 SAntarctic Circle66 30 S Greenwich (prime) meridian 0World time is calculated from the primemeridian (0).
13. 13. *01 Earth-space (8-25).qxd12/12/08 11:05 AM Page 13 13The solar system EARTH AND SPACEKey wordsPlanetary orbitsasteroidmoon PlutoUranus Saturn Jupiter Marscomet outer planetgas giant terrestrial NeptuneEarth Venus Mercuryinner planet Types of planets Theinner planets Mercury, Venus, Earth, and Mars have rocky surfaces. They are known as terrestrial or Earthlike planets. The outer planets Jupiter, Saturn, Uranus, and Neptune are gas giants. Pluto is a dwarf planet made of rock and ice. The distance of the planets from the Sun varies from 28.6 million miles (45.9 million km) for Mercury at its closest to 4,609 million miles (7,375 million km) for Pluto at its farthest. MercuryVenus Earth MarsJupiterSaturn Uranus Neptune Pluto Los NewAngelesYorkThis map of part of the United States demonstratesthe relative distances of the planets from the Sun ifit were located in Los Angeles, Californiaand Pluto at New York City.Planets mean distance from the Sun MilesKilometers Mercury 36,000,00057,900,000 Venus 67,200,000 108,100,000 Diagram Visual Information Ltd. Earth 93,000,000 149,700,000 Mars 141,600,000 227,900,000 Jupiter 483,800,000778,600,000 Saturn890,800,0001,436,600,000 Uranus1,784,800,0002,872,600,000 Neptune 2,793,100,0004,494,900,000 Pluto 3,647,200,0005,869,600,000
14. 14. *01 Earth-space (8-25).qxd12/12/0811:05 AMPage 14 14 EARTH AND SPACEStructure of the Sun Key words Structural view of the Sun chromospherephotosphere convectionSun core corona nuclear fusionsolar flareCore convective zone At the heart of the Sunnuclear fusionreactions convert radiative zonehydrogen intohelium. Temperaturesreach27,000,000F(15,000,000C).coreRadiativezone Energyproduced inthe core radiatestoward the surface ofthe Sun through thisregion. This energy prevents thephotosphereSun from collapsing underthe force of gravity. chromosphereConvective zonecorona Energy waves, weakened by their passage through the radiative zone, pass through this area via constantly churning convection currents.Photosphere Thephotoshere surface of the Sun is highly irregular. Temperatures vary from 7,80016,000F (4,3009,000C).Nuclear fusion at the Suns coreChromosphere loose hydrogen nuclei The chromosphere is a highly agitated zone of thin gases rising to about 6,000 miles (9,700 km) above the photosphere. This region is constantly disrupted by solar flares, prominences, hydrogen nuclei combined into helium atom and spiricules. Diagram Visual Information Ltd.Corona Extendingmillions of miles into spaceenergy released by fusion reactionthe corona is a very thinly dispersedball of gas. Atoms and molecules in this regionhave very high velocities andtemperatures up to 7,000,000F(4,000,000C).
15. 15. *01 Earth-space (8-25).qxd 12/12/08 11:05 AMPage 15 15The Suns energyEARTH AND SPACE Key wordsNuclear fusionRadiant energy nuclear 5Wavelengths fusion10(meters)1Nuclear fusion During nuclear fusion,2 hydrogen atoms fuse toproduce helium. The mass of heliumproduced is less than themass of the hydrogen3 radio wavesthat produced it. The mass that is lost isconverted to energy,given off by the Sun aslight, heat, and invisibleforms of radiation.4 Radiant energy The Sun radiates energythrough space atwavelengths in the5 more than electromagnetic90% ofspectrum from (veryinfraredthe Suns short wavelength) gammaradiantrays to the longestenergyvisible light longwave radio waves. Gamma rays, X-rays, andultraviolet rays areshortwave penetrativeultravioletforms of radiation that6 are potentially damagingENERGYto living tissue. Visible light comprisesalmost proton 10% ofwavelengths perceived asthe Suns colors ranging from violet X-rays radiant neutronthrough red.energygamma Infrared radiation israysperceived as radiant heat. positron Microwaves resembleneutrinothose used in microwaveovens. Radio waves from the Sun 1 Hydrogen nuclei (protons) collide. include waves shorter10-15 2 Collisions throw off two positrons and neutrinos,than those used for radio Diagram Visual Information Ltd. and form two deuterons (heavy hydrogen nuclei).broadcasts. 3 Each deuteron collides with a proton.Most of the Suns visible light can penetratethe whole of the atmosphere right down to 4 Collisions form light helium nuclei. Earths surface, except where cloud intervenes. 5 Fusion of light helium nuclei forms one stable However only some of the infrared radiationgets through: the rest is cut off, along with helium nucleus and frees two protons.the most harmful ultraviolet radiation, by 6 Fusion releases energy.atmospheric gases.
16. 16. *01 Earth-space (8-25).qxd 12/12/0811:05 AMPage 1616EARTH AND SPACEThe Moon Key wordsThe MoonEarth barycenter axisSunEarth barycenter Earth Moon orbitCommon center of mass Moon balance point (barycenter) Both the Moon and Earth travelaround a common center of massknown as a barycenter. As Earths mass is much greater thanthe Moons, their barycenter liesThe Moons path around Earth The Moons path aroundwithin Earths diameter.the SunThe Moons path TheMoon revolves aroundEarth every 27 days. Italso revolves on itsown axis once every27 days, so thesame side alwaysfaces Earth. As Earthrevolvesaround theSun, and theEarths orbitMoonaround Moons orbitEarth, theMoons patharound theSun resemblesa cogwheel.The Moons phases Diagram Visual Information Ltd. New Moon Waxing crescent Half Moon,Waxing gibbous Full MoonWaning gibbous Half Moon, Waning crescent Moon first quarter MoonMoon last quarterMoon
17. 17. *01 Earth-space (8-25).qxd 12/12/0811:05 AM Page 1717The Moon: surfaceEARTH AND SPACELunar seasMare Frigoris Sea of Cold Mare Imbrium Sea of Showers Mare Serenitatis Sea of SerenityMare Crisium Mare Vaporum Sea of CrisesOceanus ProcellarumSea of VaporsOcean of Storms Mare TranquillitatisSea of TranquilityMare Fecunditatis Sea of FertilityMare NubiumSea of Clouds Mare Nectaris Sea of Nectar Mare Humorum Sea of MoistureMajor lunar cratersPlatoCopernicus Comparative sizes of the Moon and EarthKeplerPtolemaeusGrimaldiLangrenus Diagram Visual Information Ltd.TychoTheophilusClavius
18. 18. *01 Earth-space (8-25).qxd12/12/08 11:05 AM Page 1818 EARTH AND SPACE The Moon: structure Key words asteroid mantle basalt regolith boulder core crust partially-moltenmetal zone 220 miles(350 km) thickThe Moons structure Like Earth, the Moon has a core,iron-rich coremantle, and crust.with a radius of Unlike Earths mantle and crust,190 miles (300 km)those of the Moon are rigid.Structure of a plainrigid mantle This block diagram shows features600 miles (1,000 km)typical of a basalt lunar plain. Much of it is covered by regolith: loosedebris from dust to boulders produced thick crustby old asteroid impacts.45 miles (70 km) thick fault scarp crater chain volcanoes impact crater Diagram Visual Information Ltd. regolith (surface debris) impact crater wrinkle ridge linear rille (shallow rift valley)
19. 19. *01 Earth-space (8-25).qxd 12/12/08 11:05 AM Page 1919Solar and lunar eclipsesEARTH AND SPACE Key words EarthSun eclipseumbraSolar eclipsesarea of partial eclipse: sunlight is partially blocked by the Moon MoonTotal eclipsearea of totality: sunlight is completely blocked by the Moonpenumbra planetEclipse Aneclipse occurs when oneSunEarthheavenly body blocks the lightshining from a second onto athird.Moon at perigee of orbitSolar eclipseAsolar eclipse happens whenPartial eclipse the Moon comes between theSun and Earth. This kind ofeclipse occurs on Earth at area of partial eclipseplaces crossed by the Moonsshadow.total eclipse shadow misses Earth Where the Moon completelySunEarthblots out the Sun, the umbra,the darkest part of the Moonsshadow, produces a totaleclipse. Here the sky becomesdark as if it were night. Moon Where the Moon concealsonly part of the Sun, its partialshadow or penumbraproduces a partial eclipse.Lunar eclipsesTotal eclipseMoon enters Earths total shadow Lunar eclipseA lunar eclipse happens when total shadow cast by EarthEarth passes between the Sunand the Moon. If Earth completely blots outthe Sun, Earths umbraSunEarthproduces a total eclipse ofthe Moon. If only Earths penumbra fallson the Moon, the latter ispartially eclipsed from theposition of an observer onEarth.Partial eclipse partial shadow cast by Earth During most lunar eclipses,the Moon remains visible fromtotal shadow cast by EarthEarth as it receives somesunlight bent by Earths Diagram Visual Information Ltd.atmosphere.SunEarth Moon enters Earths partial shadow
20. 20. *01 Earth-space (8-25).qxd 12/12/08 11:05 AM Page 2020EARTH AND SPACE Structure of Earth Key words Structure of Earth core rock During Earths formation, heavy elementsEarths outer core may be mainly iron crust moved toward the center, while lightand nickel with some silicon. Earth ones gathered at the surface. Part of the mantle is semimolten and element The hot, high-pressure core is mainly flows in sluggish currents. mantle solid iron and nickel. A crust of relatively light rocks rests on the mantle.Compositionsolid metal inner core with a radius of1,000 miles (1,600 km) molten outer core 1,140 miles (1,820 km) thicksemimolten rocky lower mantle1,430 miles (2,290 km) thick upper mantle 390 miles (640 km) thick crust 6.2525 miles (1040 km) thickEarth facts Earthis the only planet in thesolar system known to support life.Earths crust Earth takes 365.25 days to orbit the Earths crust is a shell of solid rock that floats on a sea of molten magma.Sun (that is, one year).continental crust Diagram Visual Information Ltd. It spins on its own axis every 23 hours56 minutes (one day).lithosphere The average temperature on the magmasurface is about 59F (15C). Earth is the only planet to have liquidwater on its surface. Earth has one natural satellite, oceanic crustthe Moon.
21. 21. *01 Earth-space (8-25).qxd12/12/0811:05 AM Page 21 21Earths magnetic field EARTH AND SPACEKey wordsEarths magnetic fieldcoremagnetic North Pole geographic North Pole EarthgeomagnetismEarths mantle Earths corelines of force Earth as a magnet Earthscrust and mantle rotate rather faster than its metallic core. This difference in speed produces a dynamo effect creating an immense magnetic field. This geomagnetic field consists of imaginary flux lines (lines of magneticlines of force force) that curve around Earth between its north and south magnetic poles. Compass needles point to thegeographic South Polemagnetic poles. magnetic South Pole The magnetic poles do not coincide with the geographic poles, and theirInside Earth inner core rotation positions shift through time.eddies in theouter core Regional variations Earths magnetic field varies in intensity from place to place across the planets surface. Its intensity is greatestrotation of mantle near the magnetic poles.The planet sectioned Local variations indicate differences inat the equator showsinternal differences subsurface rocks.of rotation producingthe magnetic field.Regional variationsVariations in strength of Earths magnetic field from 1 (high) to 11 (low) 34 3 4 5 6 7 8 9 89 10 6 Diagram Visual Information Ltd.11 5 4 3 2 1