万物简史英文版_比尔·布莱森-第34章

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　none　of　this；　of　course；　was　supported　by　so　much　as　a　grainof　actual　evidence鈥攏othing　so　wrong　could　be鈥攜et　it　was　geological　orthodoxy　for　the　nexthalf　century。

even　land　bridges　couldn鈥檛　explain　some　things。　one　species　of　trilobite　that　was　wellknown　in　europe　was　also　found　to　have　lived　on　newfoundland鈥攂ut　only　on　one　side。　noone　could　persuasively　explain　how　it　had　managed　to　cross　two　thousand　miles　of　hostileocean　but　then　failed　to　find　its　way　around　the　corner　of　a　200…mile…wide　island。　even　moreawkwardly　anomalous　was　another　species　of　trilobite　found　in　europe　and　the　pacificnorthwest　but　nowhere　in　between；　which　would　have　required　not　so　much　a　land　bridge　as　aflyover。　yet　as　late　as　1964　when　the　encyclopaedia　britannica　discussed　the　rival　theories；　itwas　wegener鈥檚　that　was　held　to　be　full　of　鈥渘umerous　grave　theoretical　difficulties。鈥�

to　be　sure；　wegener　made　mistakes。　he　asserted　that　greenland　is　drifting　west　by　about　amile　a　year；　which　is　clearly　nonsense。　（it鈥檚　more　like　half　an　inch。）　above　all；　he　could　offerno　convincing　explanation　for　how　the　landmasses　moved　about。　to　believe　in　his　theory　youhad　to　accept　that　massive　continents　somehow　pushed　through　solid　crust；　like　a　plowthrough　soil；　without　leaving　any　furrow　in　their　wake。　nothing　then　known　could　plausiblyexplain　what　motored　these　massive　movements。

it　was　arthur　holmes；　the　english　geologist　who　did　so　much　to　determine　the　age　of　theearth；　who　suggested　a　possible　way。　holmes　was　the　first　scientist　to　understand　thatradioactive　warming　could　produce　convection　currents　within　the　earth。　in　theory　thesecould　be　powerful　enough　to　slide　continents　around　on　the　surface。　in　his　popular　andinfluential　textbook　principles　of　physical　geology　；　first　published　in　1944；　holmes　laid　outa　continental　drift　theory　that　was　in　its　fundamentals　the　theory　that　prevails　today。　it　wasstill　a　radical　proposition　for　the　time　and　widely　criticized；　particularly　in　the　united　states；where　resistance　to　drift　lasted　longer　than　elsewhere。　one　reviewer　there　fretted；　without　anyevident　sense　of　irony；　that　holmes　presented　his　arguments　so　clearly　and　pellingly　thatstudents　might　actually　e　to　believe　them。

elsewhere；　however；　the　new　theory　drew　steady　if　cautious　support。　in　1950；　a　vote　at　theannual　meeting　of　the　british　association　for　the　advancement　of　science　showed　that　abouthalf　of　those　present　now　embraced　the　idea　of　continental　drift。　（hapgood　soon　after　citedthis　figure　as　proof　of　how　tragically　misled　british　geologists　had　bee。）　curiously；holmes　himself　sometimes　wavered　in　his　conviction。　in　1953　he　confessed：　鈥渋　have　neversucceeded　in　freeing　myself　from　a　nagging　prejudice　against　continental　drift；　in　mygeological　bones；　so　to　speak；　i　feel　the　hypothesis　is　a　fantastic　one。鈥�

continental　drift　was　not　entirely　without　support　in　the　united　states。　reginald　daly　ofharvard　spoke　for　it；　but　he；　you　may　recall；　was　the　man　who　suggested　that　the　moon　hadbeen　formed　by　a　cosmic　impact；　and　his　ideas　tended　to　be　considered　interesting；　evenworthy；　but　a　touch　too　exuberant　for　serious　consideration。　and　so　most　american　academicsstuck　to　the　belief　that　the　continents　had　occupied　their　present　positions　forever　and　thattheir　surface　features　could　be　attributed　to　something　other　than　lateral　motions。

interestingly；　oil　pany　geologists　had　known　for　years　that　if　you　wanted　to　find　oil　youhad　to　allow　for　precisely　the　sort　of　surface　movements　that　were　implied　by　plate　tectonics。

but　oil　geologists　didn鈥檛　write　academic　papers；　they　just　found　oil。

there　was　one　other　major　problem　with　earth　theories　that　no　one　had　resolved；　or　evene　close　to　resolving。　that　was　the　question　of　where　all　the　sediments　went。　every　yearearth鈥檚　rivers　carried　massive　volumes　of　eroded　material鈥�500　million　tons　of　calcium；　forinstance鈥攖o　the　seas。　if　you　multiplied　the　rate　of　deposition　by　the　number　of　years　it　hadbeen　going　on；　it　produced　a　disturbing　figure：　there　should　be　about　twelve　miles　ofsediments　on　the　ocean　bottoms鈥攐r；　put　another　way；　the　ocean　bottoms　should　by　now　bewell　above　the　ocean　tops。　scientists　dealt　with　this　paradox　in　the　handiest　possible　way。

they　ignored　it。　but　eventually　there　came　a　point　when　they　could　ignore　it　no　longer。

in　the　second　world　war；　a　princeton　university　mineralogist　named　harry　hess　was　putin　charge　of　an　attack　transport　ship；　the　uss　cape　johnson。　aboard　this　vessel　was　a　fancynew　depth　sounder　called　a　fathometer；　which　was　designed　to　facilitate　inshore　maneuversduring　beach　landings；　but　hess　realized　that　it　could　equally　well　be　used　for　scientificpurposes　and　never　switched　it　off；　even　when　far　out　at　sea；　even　in　the　heat　of　battle。　whathe　found　was　entirely　unexpected。　if　the　ocean　floors　were　ancient；　as　everyone　assumed；　theyshould　be　thickly　blanketed　with　sediments；　like　the　mud　on　the　bottom　of　a　river　or　lake。　buthess鈥檚　readings　showed　that　the　ocean　floor　offered　anything　but　the　gooey　smoothness　ofancient　silts。　it　was　scored　everywhere　with　canyons；　trenches；　and　crevasses　and　dotted　withvolcanic　seamounts　that　he　called　guyots　after　an　earlier　princeton　geologist　named　arnoldguyot。　all　this　was　a　puzzle；　but　hess　had　a　war　to　take　part　in；　and　put　such　thoughts　to　theback　of　his　mind。

after　the　war；　hess　returned　to　princeton　and　the　preoccupations　of　teaching；　but　themysteries　of　the　seafloor　continued　to　occupy　a　space　in　his　thoughts。　meanwhile；　throughoutthe　1950s　oceanographers　were　undertaking　more　and　more　sophisticated　surveys　of　theocean　floors。　in　so　doing；　they　found　an　even　bigger　surprise：　the　mightiest　and　mostextensive　mountain　range　on　earth　was鈥攎ostly鈥攗nderwater。　it　traced　a　continuous　pathalong　the　world鈥檚　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鈥攖he　azoresand　canaries　in　the　atlantic；　hawaii　in　the　pacific；　for　instance鈥攂ut　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鈥檛　be　explained。

down　the　middle　of　the　mid…atlantic　ridge　was　a　canyon鈥攁　rift鈥攗p　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鈥檛　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鈥檛　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鈥檚　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　鈥渞emember鈥潯�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鈥檚　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鈥檛　find　anyone　to　publish　his　paper。

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

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鈥檚　surface　behavior。

the　name　鈥渃ontinental　drift鈥潯�was　fairly　swiftly　discarded　when　it　was　realized