万物简史英文版_比尔·布莱森- 第39部分

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鈥檛　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鈥檛and　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鈥攁nd　continues　to　be鈥攎ostlyignored。　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鈥檛　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鈥檚　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

锛凤挤w。xi锛�os锛╱otxt。锛ｏ集锛�



13　　　　BANG！

灏忥紲璇达紲t锛渪t锛炲ぉ锛煛峰爞
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鈥斺�渃rystalline　clast　breccia　with　a　melt　matrix鈥潯�and　鈥渙verturnedejecta　flap；鈥潯�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鈥檚　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鈥檚　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鈥�92　drilling　program鈥攊ndeed；　they　positively　bustle　toproduce　them鈥攂ut　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鈥檛　move　quite　fast　enough　and　were　killed。　every　june　now　manson　has　a　weeklong　eventcalled　crater　days；　which　was　dreamed　up　as　a　way　of　helping　people　forget　that　unhappyanniversary。　it　doesn鈥檛　really　have　anything　to　do　with　the　crater。　nobody鈥檚　figured　out　a　wayto　capitalize　on　an　impact　site　that　isn鈥檛　visible。

鈥渧ery　occasionally　we　get　people　ing　in　and　asking　where　they　should　go　to　see　thecrater　and　we　have　to　tell　them　that　there　is　nothing　to　see；鈥潯�says　anna　schlapkohl；　the　town鈥檚friendly　librarian。　鈥渢hen　they　go　away　kind　of　disappointed。鈥潯�however；　most　people；including　most　iowans；　have　never　heard　of　the　manson　crater。　even　for　geologists　it　barelyrates　a　footnote。　but　for　one　brief　period　in　the　1980s；　manson　was　the　most　geologicallyexciting　place　on　earth。

the　story　begins　in　the　early　1950s　when　a　bright　young　geologist　named　eugeneshoemaker　paid　a　visit　to　meteor　crater　in　arizona。　today　meteor　crater　is　the　most　famousimpact　site　on　earth　and　a　popular　tourist　attraction。　in　those　days；　however；　it　didn鈥檛　receivemany　visitors　and　was　still　often　referred　to　as　barringer　crater；　after　a　wealthy　miningengineer　named　daniel　m。　barringer　who　had　staked　a　claim　on　it　in　1903。　barringer　believedthat　the　crater　had　been　formed　by　a　ten…million…ton　meteor；　heavily　freighted　with　iron　andnickel；　and　it　was　his　confident　expectation　that　he　would　make　a　fortune　digging　it　out。

unaware　that　the　meteor　and　everything　in　it　would　have　been　vaporized　on　impact；　hewasted　a　fortune；　and　the　next　twenty…six　years；　cutting　tunnels　that　yielded　nothing。

by　the　standards　of　today；　crater　research　in　the　early　1900s　was　a　trifle　unsophisticated；　tosay　the　least。　the　leading　early　investigator；　g。　k。　gilbert　of　columbia　university；　modeledthe　effects　of　impacts　by　flinging　marbles　into　pans　of　oatmeal。　（for　reasons　i　cannot　supply；gilbert　conducted　these　experiments　not　in　a　laboratory　at　columbia　but　in　a　hotel　room。）somehow　from　this　gilbert　concluded　that　the　moon鈥檚　craters　were　indeed　formed　byimpacts鈥攊n　itself　quite　a　radical　notion　for　the　time鈥攂ut　that　the　earth鈥檚　were　not。　mostscientists　refused　to　go　even　that　far。　to　them；　the　moon鈥檚　craters　were　evidence　of　ancientvolcanoes　and　nothing　more。　the　few　craters　that　remained　evident　on　earth　（most　had　beeneroded　away）　were　generally　attributed　to　other　causes　or　treated　as　fluky　rarities。

by　the　time　shoemaker　came　along；　a　mon　view　was　that　meteor　crater　had　beenformed　by　an　underground　steam　explosion。　shoemaker　knew　nothing　about　undergroundsteam　explosions鈥攈e　couldn鈥檛：　they　don鈥檛　exist鈥攂ut　he　did　know　all　about　blast　zones。　oneof　his　first　jobs　out　of　college　was　to　study　explosion　rings　at　the　yucca　flats　nuclear　test　sitein　nevada。　he　concluded；　as　barringer　had　before　him；　that　there　was　nothing　at　meteorcrater　to　suggest　volcanic　activity；　but　that　there　were　huge　distributions　of　other　stuff鈥攁nomalous　fine　silicas　and　magnetites　principally鈥攖hat　suggested　an　impact　from　space。

intrigued；　he　began　to　study　the　subject　in　his　spare　time。

working　first　with　his　colleague　eleanor　helin　and　later　with　his　wife；　carolyn；　andassociate　david　levy；　shoemaker　began　a　systematic　survey　of　the　inner　solar　system。　theyspent　one　week　each　month　at　the　palomar　observatory　in　california　looking　for　objects；asteroids　pr