A Short History of Nearly Everything-第37章

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urprise：　the　mightiest　and　mostextensive　mountain　range　on　earth　was—mostly—underwater。　it　traced　a　continuous　pathalong　the　world’s　seabeds；　rather　like　the　stitching　on　a　baseball。　if　you　began　at　iceland；　youcould　follow　it　down　the　center　of　the　atlantic　ocean；　around　the　bottom　of　africa；　and　acrossthe　indian　and　southern　oceans；　below　australia；　there　it　angled　across　the　pacific　as　ifmaking　for　baja　california　before　shooting　up　the　west　coast　of　the　united　states　to　alaska。

occasionally　its　higher　peaks　poked　above　the　water　as　an　island　or　archipelago—the　azoresand　canaries　in　the　atlantic；　hawaii　in　the　pacific；　for　instance—but　mostly　it　was　buriedunder　thousands　of　fathoms　of　salty　sea；　unknown　and　unsuspected。　when　all　its　brancheswere　added　together；　the　network　extended　to　46；600　miles。

a　very　little　of　this　had　been　known　for　some　time。　people　laying　ocean…floor　cables　in　thenineteenth　century　had　realized　that　there　was　some　kind　of　mountainous　intrusion　in　the　mid…atlantic　from　the　way　the　cables　ran；　but　the　continuous　nature　and　overall　scale　of　the　chainwas　a　stunning　surprise。　moreover；　it　contained　physical　anomalies　that　couldn’t　be　explained。

down　the　middle　of　the　mid…atlantic　ridge　was　a　canyon—a　rift—up　to　a　dozen　miles　widefor　its　entire　12；000…mile　length。　this　seemed　to　suggest　that　the　earth　was　splitting　apart　atthe　seams；　like　a　nut　bursting　out　of　its　shell。　it　was　an　absurd　and　unnerving　notion；　but　theevidence　couldn’t　be　denied。

then　in　1960　core　samples　showed　that　the　ocean　floor　was　quite　young　at　the　mid…atlanticridge　but　grew　progressively　older　as　you　moved　away　from　it　to　the　east　or　west。　harry　hessconsidered　the　matter　and　realized　that　this　could　mean　only　one　thing：　new　ocean　crust　wasbeing　formed　on　either　side　of　the　central　rift；　then　being　pushed　away　from　it　as　new　crustcame　along　behind。　the　atlantic　floor　was　effectively　two　large　conveyor　belts；　one　carryingcrust　toward　north　america；　the　other　carrying　crust　toward　europe。　the　process　becameknown　as　seafloor　spreading。

when　the　crust　reached　the　end　of　its　journey　at　the　boundary　with　continents；　it　plungedback　into　the　earth　in　a　process　known　as　subduction。　that　explained　where　all　the　sedimentwent。　it　was　being　returned　to　the　bowels　of　the　earth。　it　also　explained　why　ocean　floorseverywhere　were　so　paratively　youthful。　none　had　ever　been　found　to　be　older　than　about175　million　years；　which　was　a　puzzle　because　continental　rocks　were　often　billions　of　yearsold。　now　hess　could　see　why。　ocean　rocks　lasted　only　as　long　as　it　took　them　to　travel　toshore。　it　was　a　beautiful　theory　that　explained　a　great　deal。　hess　elaborated　his　ideas　in　animportant　paper；　which　was　almost　universally　ignored。　sometimes　the　world　just　isn’t　readyfor　a　good　idea。

meanwhile；　two　researchers；　working　independently；　were　making　some　startling　findingsby　drawing　on　a　curious　fact　of　earth　history　that　had　been　discovered　several　decades　earlier。

in　1906；　a　french　physicist　named　bernard　brunhes　had　found　that　the　planet’s　magnetic　fieldreverses　itself　from　time　to　time；　and　that　the　record　of　these　reversals　is　permanently　fixed　incertain　rocks　at　the　time　of　their　birth。　specifically；　tiny　grains　of　iron　ore　within　the　rockspoint　to　wherever　the　magnetic　poles　happen　to　be　at　the　time　of　their　formation；　then　staypointing　in　that　direction　as　the　rocks　cool　and　harden。　in　effect　they　“remember”　where　themagnetic　poles　were　at　the　time　of　their　creation。　for　years　this　was　little　more　than　acuriosity；　but　in　the　1950s　patrick　blackett　of　the　university　of　london　and　s。　k。　runcorn　ofthe　university　of　newcastle　studied　the　ancient　magnetic　patterns　frozen　in　british　rocks　andwere　startled；　to　say　the　very　least；　to　find　them　indicating　that　at　some　time　in　the　distant　pastbritain　had　spun　on　its　axis　and　traveled　some　distance　to　the　north；　as　if　it　had　somehowe　loose　from　its　moorings。　moreover；　they　also　discovered　that　if　you　placed　a　map　ofeurope’s　magnetic　patterns　alongside　an　american　one　from　the　same　period；　they　fit　togetheras　neatly　as　two　halves　of　a　torn　letter。　it　was　uncanny。

their　findings　were　ignored　too。

it　finally　fell　to　two　men　from　cambridge　university；　a　geophysicist　named　drummondmatthews　and　a　graduate　student　of　his　named　fred　vine；　to　draw　all　the　strands　together。　in1963；　using　magnetic　studies　of　the　atlantic　ocean　floor；　they　demonstrated　conclusively　thatthe　seafloors　were　spreading　in　precisely　the　manner　hess　had　suggested　and　that　thecontinents　were　in　motion　too。　an　unlucky　canadian　geologist　named　lawrence　morley　cameup　with　the　same　conclusion　at　the　same　time；　but　couldn’t　find　anyone　to　publish　his　paper。

in　what　has　bee　a　famous　snub；　the　editor　of　the　journal　of　geophysical　research　toldhim：　“such　speculations　make　interesting　talk　at　cocktail　parties；　but　it　is　not　the　sort　of　thingthat　ought　to　be　published　under　serious　scientific　aegis。”　one　geologist　later　described　it　as“probably　the　most　significant　paper　in　the　earth　sciences　ever　to　be　denied　publication。”

at　all　events；　mobile　crust　was　an　idea　whose　time　had　finally　e。　a　symposium　ofmany　of　the　most　important　figures　in　the　field　was　convened　in　london　under　the　auspices　ofthe　royal　society　in　1964；　and　suddenly；　it　seemed；　everyone　was　a　convert。　the　earth；　themeeting　agreed；　was　a　mosaic　of　interconnected　segments　whose　various　stately　jostlingsaccounted　for　much　of　the　planet’s　surface　behavior。

the　name　“continental　drift”　was　fairly　swiftly　discarded　when　it　was　realized　that　thewhole　crust　was　in　motion　and　not　just　the　continents；　but　it　took　a　while　to　settle　on　a　namefor　the　individual　segments。　at　first　people　called　them　“crustal　blocks”　or　sometimes　“pavingstones。”　not　until　late　1968；　with　the　publication　of　an　article　by　three　americanseismologists　in　the　journal　of　geophysical　research　；　did　the　segments　receive　the　name　bywhich　they　have　since　been　known：　plates。　the　same　article　called　the　new　science　platetectonics。

old　ideas　die　hard；　and　not　everyone　rushed　to　embrace　the　exciting　new　theory。　well　intothe　1970s；　one　of　the　most　popular　and　influential　geological　textbooks；　the　earth　by　thevenerable　harold　jeffreys；　strenuously　insisted　that　plate　tectonics　was　a　physicalimpossibility；　just　as　it　had　in　the　first　edition　way　back　in　1924。　it　was　equally　dismissive　ofconvection　and　seafloor　spreading。　and　in　basin　and　range；　published　in　1980；　john　mcpheenoted　that　even　then　one　american　geologist　in　eight　still　didn’t　believe　in　plate　tectonics。

today　we　know　that　earth’s　surface　is　made　up　of　eight　to　twelve　big　plates　（depending　onhow　you　define　big）　and　twenty　or　so　smaller　ones；　and　they　all　move　in　different　directionsand　at　different　speeds。　some　plates　are　large　and　paratively　inactive；　others　small　butenergetic。　they　bear　only　an　incidental　relationship　to　the　landmasses　that　sit　upon　them。　thenorth　american　plate；　for　instance；　is　much　larger　than　the　continent　with　which　it　isassociated。　it　roughly　traces　the　outline　of　the　continent’s　western　coast　（which　is　why　thatarea　is　so　seismically　active；　because　of　the　bump　and　crush　of　the　plate　boundary）；　butignores　the　eastern　seaboard　altogether　and　instead　extends　halfway　across　the　atlantic　to　themid…ocean　ridge。　iceland　is　split　down　the　middle；　which　makes　it　tectonically　half　americanand　half　european。　new　zealand；　meanwhile；　is　part　of　the　immense　indian　ocean　plate　eventhough　it　is　nowhere　near　the　indian　ocean。　and　so　it　goes　for　most　plates。

the　connections　between　modern　landmasses　and　those　of　the　past　were　found　to　beinfinitely　more　plex　than　anyone　had　imagined。　kazakhstan；　it　turns　out；　was　onceattached　to　norway　and　new　england。　one　corner　of　staten　island；　but　only　a　corner；　iseuropean。　so　is　part　of　newfoundland。　pick　up　a　pebble　from　a　massachusetts　beach；　and　itsnearest　kin　will　now　be　in　africa。　the　scottish　highlands　and　much　of　scandinavia　aresubstantially　american。　some　of　the　shackleton　range　of　antarctica；　it　is　thought；　may　oncehave　belonged　to　the　appalachians　of　the　eastern　u。s。　rocks；　in　short；　get　around。

the　constant　turmoil　keeps　the　plates　from　fusing　into　a　single　immobile　plate。　assumingthings　continue　much　as　at　present；　the　atlantic　ocean　will　expand　until　eventually　it　is　muchbigger　than　the　pacific。　much　of　california　will　float　off　and　bee　a　kind　of　madagascar　ofthe　pacific。　africa　will　push　northward　into　europe；　squeezing　the　mediterranean　out　ofexistence　and　thrusting　up　a　chain　of　mountains　of　himalayan　majesty　running　from　paris　tocalcutta。　australia　will　colonize　the　islands　to　its　north　and　connect　by　some　isthmianumbilicus　to　asia。　these　are　future　outes；　but　not　future　events。　the　events　are　happeningnow。　as　we　sit　here；　continents　are　adrift；　like　leaves　on　a　pond。　thanks　to　global　positioningsystems　we　can　see　that　europe　and　north　america　are　parting　at　about　the　speed　a　fingernailgrows—roughly　two　yards　in　a　human　lifetime。　if　you　were　prepared　to　wait　long　enough；you　could　ride　from　los　angeles　all　the　way　up　to　san　francisco。　it　is　only　the　brevity　oflifetimes　that　keeps　us　from　appreciating　the　changes。　look　at　a　globe　and　what　you　areseeing　really