TEXT-Earth'sImpendingMagneticFlip(Ac)IntegratedScienceA.Previewthetext:title/sub-title,source,date,hook;relatetoself;numbertheparagraphsB.CloselyRead,markingupasfollows:•Circleandthendefine/findsynonymsfornewvocabulary•Underlinesourcesofinformation:experts,affiliations,publications•Highlightclaimsmadeandevidenceand/orreasoningcited;paraphraseintheleftcolumn

Earth'smagneticnorthandsouthpoleshaveflip-floppedmanytimesinourplanet'shistory—mostrecently,around780,000yearsago.Geophysicistswhostudythemagneticfieldhavelongthoughtthatthepolesmaybegettingreadytoswitchagain,andbasedonnewdata,itmighthappenearlierthananyoneanticipated.TheEuropeanSpaceAgency'ssatellitearraydubbed“Swarm”revealedthatEarth'smagneticfieldisweakening10timesfasterthanpreviouslythought,decreasinginstrengthabout5percentadecaderatherthan5percentacentury.Aweakeningmagneticfieldmayindicateanimpendingreversal,whichscientistspredictcouldbegininlessthan2,000years.MagneticnorthitselfappearstobemovingtowardSiberia.Geophysicistsdonotyetfullyunderstandtheprocessofgeomagneticreversals,buttheyagreethatourplanet'sfieldislikeadipolemagnet.Earth'scenterconsistsofaninnercoreofsolidironandanoutercoreofliquidiron,astrongelectricalconductor.Theliquidironintheoutercoreisbuoyant,andasitheatsneartheinnercore,itrises,coolsoffandthensinks.Earth'srotationtwiststhismovingironliquidandgeneratesaself-perpetuatingmagneticfieldwithnorthandsouthpoles.Everysooftentheflowofliquidironisdisturbedlocallyandtwistspartofthefieldintheoppositedirection,weakeningit.Whattriggersthesedisturbancesisunknown.Itseemstheyareaninevitableconsequenceofanaturallychaoticsystem,andgeophysicistsobservethemfrequentlyincomputersimulations.“Similartoahurricane,youcan'tpredict[exactly]whenorwhereareversalwillstart,eventhoughyouunderstandthebasicphysics,”saysGaryA.Glatzmaier,ageophysicistattheUniversityofCalifornia,SantaCruz.Typicallythelocalreversalpetersoutafter1,000yearsorso,butsometimesthetwistingofthefieldcontinuestospreadandeventuallysucceedsinreversingthepolarityoftheentirefield.Theflippingtakesanaverageof5,000years;itcanhappenasquicklyas1,000yearsorasslowlyas20,000years.

ThereisagoodchancetheweakeningmagneticfieldthattheSwarmsatellitesobservedwillnotleadtoafullflip.Indeed,Glatzmaiernotesthattherehavebeenseveralfalsestartsovergeologichistory.TheintensityofEarth'smagneticfield,thoughwaning,nowequalsitsaveragestrengthovermillionsofyears.Thefieldwouldneedtoweakenatitscurrentrateforaround2,000yearsbeforethereversalprocessactuallybegins.Itishardtoknowhowageomagneticreversalwouldimpactourmodern-daycivilization,butitisunlikelytospelldisaster.Althoughthefieldprovidesessentialprotectionfromthesun'spowerfulradiation,fossilrecordsrevealnomassextinctionsorincreasedradiationdamageduringpastreversals.Aflipcouldpossiblyinterferewithpowergridsandcommunicationssystems—externalmagneticfielddisturbanceshaveburnedouttransformersandcausedblackoutsinthepast.ButGlatzmaierisnotworried.“Athousandyearsfromnowweprobablywon'thavepowerlines,”hesays.“We'llhaveadvancedsomuchthatwe'llalmostcertainlyhavethetechnologytocopewithamagnetic-fieldreversal.”

___________________________________________________________________________Snead,Annie."Earth'sImpendingMagneticFlip."ScientificAmerican.1Oct.2014.Web.02Feb.2016.

FollowUpQuestions:1.Whatistheoverallclaimthearticleismaking?(Whatisthemagneticflip?)2.Whatissomeevidenceprovidedtosupportthisclaim?