A Short History of Nearly Everything-第38章

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lifetimes　that　keeps　us　from　appreciating　the　changes。　look　at　a　globe　and　what　you　areseeing　really　is　a　snapshot　of　the　continents　as　they　have　been　for　just　one…tenth　of　1　percentof　the　earth’s　history。

earth　is　alone　among　the　rocky　planets　in　having　tectonics；　and　why　this　should　be　is　a　bitof　a　mystery。　it　is　not　simply　a　matter　of　size　or　density—venus　is　nearly　a　twin　of　earth　inthese　respects　and　yet　has　no　tectonic　activity。　it　is　thought—though　it　is　really　nothing　morethan　a　thought—that　tectonics　is　an　important　part　of　the　planet’s　organic　well…being。　as　thephysicist　and　writer　james　trefil　has　put　it；　“it　would　be　hard　to　believe　that　the　continuousmovement　of　tectonic　plates　has　no　effect　on　the　development　of　life　on　earth。”　he　suggeststhat　the　challenges　induced　by　tectonics—changes　in　climate；　for　instance—were　animportant　spur　to　the　development　of　intelligence。　others　believe　the　driftings　of　thecontinents　may　have　produced　at　least　some　of　the　earth’s　various　extinction　events。　innovember　of　2002；　tony　dickson　of　cambridge　university　in　england　produced　a　report；published　in　the　journal　science；　strongly　suggesting　that　there　may　well　be　a　relationshipbetween　the　history　of　rocks　and　the　history　of　life。　what　dickson　established　was　that　thechemical　position　of　the　world’s　oceans　has　altered　abruptly　and　vigorously　throughoutthe　past　half　billion　years　and　that　these　changes　often　correlate　with　important　events　inbiological　history—the　huge　outburst　of　tiny　organisms　that　created　the　chalk　cliffs　ofengland’s　south　coast；　the　sudden　fashion　for　shells　among　marine　organisms　during　thecambrian　period；　and　so　on。　no　one　can　say　what　causes　the　oceans’　chemistry　to　change　sodramatically　from　time　to　time；　but　the　opening　and　shutting　of　ocean　ridges　would　be　anobvious　possible　culprit。

at　all　events；　plate　tectonics　not　only　explained　the　surface　dynamics　of　the　earth—how　anancient　hipparion　got　from　france　to　florida；　for　example—but　also　many　of　its　internalactions。　earthquakes；　the　formation　of　island　chains；　the　carbon　cycle；　the　locations　ofmountains；　the　ing　of　ice　ages；　the　origins　of　life　itself—there　was　hardly　a　matter　thatwasn’t　directly　influenced　by　this　remarkable　new　theory。　geologists；　as　mcphee　has　noted；found　themselves　in　the　giddying　position　that　“the　whole　earth　suddenly　made　sense。”

but　only　up　to　a　point。　the　distribution　of　continents　in　former　times　is　much　less　neatlyresolved　than　most　people　outside　geophysics　think。　although　textbooks　give　confident…looking　representations　of　ancient　landmasses　with　names　like　laurasia；　gondwana；　rodinia；and　pangaea；　these　are　sometimes　based　on　conclusions　that　don’t　altogether　hold　up。　asgeorge　gaylord　simpson　observes　in　fossils　and　the　history　of　life；　species　of　plants　andanimals　from　the　ancient　world　have　a　habit　of　appearing　inconveniently　where　they　shouldn’tand　failing　to　be　where　they　ought。

the　outline　of　gondwana；　a　once…mighty　continent　connecting　australia；　africa；antarctica；　and　south　america；　was　based　in　large　part　on　the　distribution　of　a　genus　ofancient　tongue　fern　called　glossopteris；　which　was　found　in　all　the　right　places。　however；much　later　glossopteris　was　also　discovered　in　parts　of　the　world　that　had　no　knownconnection　to　gondwana。　this　troubling　discrepancy　was—and　continues　to　be—mostlyignored。　similarly　a　triassic　reptile　called　lystrosaurus　has　been　found　from　antarctica　allthe　way　to　asia；　supporting　the　idea　of　a　former　connection　between　those　continents；　but　ithas　never　turned　up　in　south　america　or　australia；　which　are　believed　to　have　been　part　ofthe　same　continent　at　the　same　time。

there　are　also　many　surface　features　that　tectonics　can’t　explain。　take　denver。　it　is；　aseveryone　knows；　a　mile　high；　but　that　rise　is　paratively　recent。　when　dinosaurs　roamedthe　earth；　denver　was　part　of　an　ocean　bottom；　many　thousands　of　feet　lower。　yet　the　rockson　which　denver　sits　are　not　fractured　or　deformed　in　the　way　they　would　be　if　denver　hadbeen　pushed　up　by　colliding　plates；　and　anyway　denver　was　too　far　from　the　plate　edges　to　besusceptible　to　their　actions。　it　would　be　as　if　you　pushed　against　the　edge　of　a　rug　hoping　toraise　a　ruck　at　the　opposite　end。　mysteriously　and　over　millions　of　years；　it　appears　thatdenver　has　been　rising；　like　baking　bread。　so；　too；　has　much　of　southern　africa；　a　portion　ofit　a　thousand　miles　across　has　risen　nearly　a　mile　in　100　million　years　without　any　knownassociated　tectonic　activity。　australia；　meanwhile；　has　been　tilting　and　sinking。　over　the　past100　million　years　as　it　has　drifted　north　toward　asia；　its　leading　edge　has　sunk　by　some　sixhundred　feet。　it　appears　that　indonesia　is　very　slowly　drowning；　and　dragging　australia　downwith　it。　nothing　in　the　theories　of　tectonics　can　explain　any　of　this。

alfred　wegener　never　lived　to　see　his　ideas　vindicated。　on　an　expedition　to　greenland　in1930；　he　set　out　alone；　on　his　fiftieth　birthday；　to　check　out　a　supply　drop。　he　never　returned。

he　was　found　a　few　days　later；　frozen　to　death　on　the　ice。　he　was　buried　on　the　spot　and　liesthere　yet；　but　about　a　yard　closer　to　north　america　than　on　the　day　he　died。

einstein　also　failed　to　live　long　enough　to　see　that　he　had　backed　the　wrong　horse。　in　fact；he　died　at　princeton；　new　jersey；　in　1955　before　charles　hapgood’s　rubbishing　of　continentaldrift　theories　was　even　published。

the　other　principal　player　in　the　emergence　of　tectonics　theory；　harry　hess；　was　also　atprinceton　at　the　time；　and　would　spend　the　rest　of　his　career　there。　one　of　his　students　was　abright　young　fellow　named　walter　alvarez；　who　would　eventually　change　the　world　ofscience　in　a　quite　different　way。

as　for　geology　itself；　its　cataclysms　had　only　just　begun；　and　it　was　young　alvarez　whohelped　to　start　the　process。

part　iv　　dangerous　planetthe　history　of　any　one　part　of　theearth；　like　the　life　of　a　soldier；　consistsof　long　periods　of　boredom　andshort　periods　of　terror。

…british　geologist　derek　v。　ager

　。。



13BANG！

@小‘说〃网
people　knew　for　a　long　time　that　there　was　something　odd　about　the　earth　beneathmanson；　iowa。　in　1912；　a　man　drilling　a　well　for　the　town　water　supply　reported　bringing　up　alot　of　strangely　deformed　rock—“crystalline　clast　breccia　with　a　melt　matrix”　and　“overturnedejecta　flap；”　as　it　was　later　described　in　an　official　report。　the　water　was　odd　too。　it　wasalmost　as　soft　as　rainwater。　naturally　occurring　soft　water　had　never　been　found　in　iowabefore。

though　manson’s　strange　rocks　and　silken　waters　were　matters　of　curiosity；　forty…oneyears　would　pass　before　a　team　from　the　university　of　iowa　got　around　to　making　a　trip　to　themunity；　then　as　now　a　town　of　about　two　thousand　people　in　the　northwest　part　of　thestate。　in　1953；　after　sinking　a　series　of　experimental　bores；　university　geologists　agreed　thatthe　site　was　indeed　anomalous　and　attributed　the　deformed　rocks　to　some　ancient；　unspecifiedvolcanic　action。　this　was　in　keeping　with　the　wisdom　of　the　day；　but　it　was　also　about　aswrong　as　a　geological　conclusion　can　get。

the　trauma　to　manson’s　geology　had　e　not　from　within　the　earth；　but　from　at　least　100million　miles　beyond。　sometime　in　the　very　ancient　past；　when　manson　stood　on　the　edge　of　ashallow　sea；　a　rock　about　a　mile　and　a　half　across；　weighing　ten　billion　tons　and　traveling　atperhaps　two　hundred　times　the　speed　of　sound　ripped　through　the　atmosphere　and　punchedinto　the　earth　with　a　violence　and　suddenness　that　we　can　scarcely　imagine。　where　mansonnow　stands　became　in　an　instant　a　hole　three　miles　deep　and　more　than　twenty　miles　across。

the　limestone　that　elsewhere　gives　iowa　its　hard　mineralized　water　was　obliterated　andreplaced　by　the　shocked　basement　rocks　that　so　puzzled　the　water　driller　in　1912。

the　manson　impact　was　the　biggest　thing　that　has　ever　occurred　on　the　mainland　unitedstates。　of　any　type。　ever。　the　crater　it　left　behind　was　so　colossal　that　if　you　stood　on　oneedge　you　would　only　just　be　able　to　see　the　other　side　on　a　good　day。　it　would　make　the　grandcanyon　look　quaint　and　trifling。　unfortunately　for　lovers　of　spectacle；　2。5　million　years　ofpassing　ice　sheets　filled　the　manson　crater　right　to　the　top　with　rich　glacial　till；　then　graded　itsmooth；　so　that　today　the　landscape　at　manson；　and　for　miles　around；　is　as　flat　as　a　tabletop。

which　is　of　course　why　no　one　has　ever　heard　of　the　manson　crater。

at　the　library　in　manson　they　are　delighted　to　show　you　a　collection　of　newspaper　articlesand　a　box　of　core　samples　from　a　1991–92　drilling　program—indeed；　they　positively　bustle　toproduce　them—but　you　have　to　ask　to　see　them。　nothing　permanent　is　on　display；　andnowhere　in　the　town　is　there　any　historical　marker。

to　most　people　in　manson　the　biggest　thing　ever　to　happen　was　a　tornado　that　rolled　upmain　street　in　1979；　tearing　apart　the　business　district。　one　of　the　advantages　of　all　thatsurrounding　flatness　is　that　you　can　see　danger　from　a　long　way　off。　virtually　the　whole　townturned　out　at　one　end　of　main　street　and　watched　for　half　an　hour　as　the　tornado　came　towardthem；　hoping　it　would　veer　off；　then　prudently　scampered　when　it　did　not。　four　of　them；　alas；didn’t　move　quite　fast　enough　and　were　killed。