自然地理学专业英语.docx

自然地理学专业英语.docx

《自然地理学专业英语.docx》由会员分享，可在线阅读，更多相关《自然地理学专业英语.docx（40页珍藏版）》请在冰豆网上搜索。

自然地理学专业英语

Lecture1

INTRODUCTIONTOEARTH

MajorConcept（I）

Theplanetsinoursolarsystem,includingEarth,begantoformoutofarotatingdiskofgasanddustabout4.6billionyearsago.

Relatedorsupportingconcepts:

Thepresentviewofthebeginningofthesolarsystemsuggeststhatacloudofgasanddustwasflattenedintoadiskbyrotation.Thedensityofthematterinthediskwasgreatestatitscenteranddecreasedtowardtheedges.

Thesunformedatthecenterofthediskwherethetemperaturewashighestandtheplanetsformedatgreaterdistancesawayfromthecenter.

Thecompositionsoftheplanetsdifferbecauseofanaturalsortingofelementsinthecloudwithdistancefromthecenter.

ThetemperatureoftheearlyEarthwasprobablyquitehighdueto:

a.thegravitationalcaptureofparticlesthatreleasedheatonimpact,

b.theincreasedpressureontheinterioroftheplanetasitcontinuedtogrow,and

c.thecaptureofradioactiveelementsthatgaveoffheatwhentheydecayed.

Duringthefirstfewhundredmillionyears,theinternaltemperaturerosehighenoughtomeltironandnickel.Theseheavymetalssanktoformthecoreoftheplanetanddisplacedlightermaterialthatrosetoformchemicallydifferentiatedshells.

MajorConcept（II）

Earth’soceansoriginatedearlyintheplanet’shistory.Therearetwoproposedsourcesofthewaterintheoceans.

Relatedorsupportingconcepts:

Theoldestsedimentaryrocksfoundthatrequiredwaterfortheirformationare3.9billionyearsold.ThissuggeststhattherearebeenoceansonEarthforroughly4billionyears.

TraditionallyscientistshavebelievedthatthewaterintheoceansandatmosphereoriginatedinEarth’smantleandwasbroughttothesurfacebyvolcanism.

Mostmagmascontainfrom1%to5%dissolvedgasbyweight,mostofwhichiswatervapor.

Ifweassumethatthecurrentrateofreleaseofwatervaporinvolcaniceruptionshasremainedessentiallyconstantforthepast4billionyears,thenthevolumeofwaterexpelled（putout）duringthattimewouldberoughly100timesthevolumeoftoday’soceans.

ArelativelynewproposalisthatasignificantamountofwaterisaddedtoEarthfromspacewhensmallicycomets（彗星）enterEarth’satmosphere.

Theearlyatmospheredidnothaveanyoxygen.Theoxygenreleasedfromtheinterioroftheplanetwouldhavecombinedwithmetalsatthesurfacetoproduceoxides.

Itwasn'tuntillargeamountsofoxygenwereproducedafterplantsformedthatitbegantoaccumulateintheatmosphere.

MajorConcept（III）

Thereiscompellingevidencethattheremaybeotheroceansinthesolarsystem.

Relatedorsupportingconcepts:

TwoofJupiter’smoons,EuropaandCallisto,mayhaveoceansbeneaththeiricysurfaces.

LiquidoceansonEuropamaybepossibledespiteextremelylowtemperaturesbecauseofheatgeneratedbyfrictionasitisdeformedbyJupiter’stide-producinggravitationalforce.

Bothmoonshaveinducedmagneticfieldsindicatingtheyconsistpartlyofstronglyconductingmaterial.Thismaybeliquidwaterwithelectrolyticsalts.

ThereisalsosomeindicationthatMarsoncehadanoceancoveringportionsofitsnorthernhemisphere.

MajorConcept（IV）

ThereareavarietyoflinesofindirectevidencethatallowustoestimateEarth’sageasbeingabout4.5to4.6billionyears.

Relatedorsupportingconcepts:

Earth’soriginalcrust,thatwouldhaveformedearlyinitshistory,hasbeendestroyedorcoveredbyactivevolcanismandtectonicprocesses.Thisisareflectionofthegeologicallyactivenatureoftheplanet.Consequently,theoldestsurfacerockswehavefound,roughly4billionyearsold,giveusaminimumageforEarthratherthananactualage.

IndirectevidenceofEarth’sageincludes:

a.thedatingofmoonrocksat4.2billionyears,

b.thedatingofmeteoritesat4.5to4.6billionyears,and

c.theoreticalcalculationsoftheageofthesunasbeingroughlythesameasthemeteorites.

Wecandeterminetheageofrocksthatcontainradioactiveisotopesofelementsthatdecayatconstant,knownrates.Thisiscalledradiometricdating.

Ifarockcontainsatomsofaspecificradioactiveisotope,halfofthemwilldecayintoanotherelement,calledthedaughterproduct,inaperiodoftimecalledthehalf-lifeoftheisotope.

AnexampleofthistypeofprocesswouldbeUranium235anditsdaughterproductLead207withahalf-lifeof704millionyears.Arockthatinitiallycontained100atomsofU235andnoPb207wouldhavethefollowingnumbersofthetwoelementsaftertheindicatedelapsedtimes:

Thereareseveraldifferent"parent-daughter"radioactivepairsthatoccurinrocks.Eachofthepairshasitsownspecifichalf-life,somequitelongandothersveryshort.Pairswithlonghalf-livesarebestfordatingveryoldrockswhilethosewithshorthalf-livesarebestforyoungerrocks.Ideally,anassigneddateforarockwillbebasedontheuseofmorethanoneradioactivepairsothatacheckcanbemadeonaccuracy.

MajorConcept（V）

Geologictimeisoftendifficulttograspbecauseofhowlongitiscomparedtoallofhumanhistory（tosaynothingoftheincrediblybrieftimespanofasinglehumanlife）.

Relatedorsupportingconcepts

Justaswedividetimeintosegmentslikeyears,months,anddaystoidentifybothdurationandsomesenseofposition,wedividegeologictimeaswell.Thelongestdivisioniscalledaneon.Eonsaredividedintoeras,erasaredividedintoperiods,andperiodsintoepochs.

Thegeologictimescaleandthehistoryofevolutionoflife-formsisgivenintable2.1.

Theeras,inorderofmostdistantpasttomostrecenttime,are:

a.Precambrian,

b.Paleozoic（ancientlife）,

c.Mesozoic（intermediatelife）,and

d.Cenozoic（recentlife）.

Thedivisionsofgeologictimewereoriginallydecidedupononthebasisoftheappearanceanddisappearanceofspecificfossils.

Thedevelopmentofradiometricdatingtechniquesallowedgeologiststoassignabsolutedatestothedifferenttimedivisions.

Becauseofthedifficultywetypicallyhaveincomprehendingtimespansasgreatasbillionsofyears,itisofteneasiertoimaginethattheearthismuchyounger,saytensofyearsold,andthenconsiderwhatmajoreventsoccurredinthatperiodoftime.Suppose,forexample,thatratherthantheearthbeing4.6billionyearsold,itisonly46yearsold.Thenwecanrecognizethefollowingimportantevents:

a.0yearsofage:

theearthformed

b.thefirstseveralyearsoftheplanet'shistoryhavenotbeenpreservedintherecord

c.6yearsofage:

theoldestdiscoveredrockswereformed

d.12yearsofage:

thefirstlivingcellsappeared

e.22–23yearsofage:

photosynthesisbeganproducingoxygen

f.31yearsofage:

therewassufficientoxygenintheatmospheretoallowthegrowthofcomplexcellsthatrequireoxygen

g.40yearsofage:

thefirsthard-shelledorganismsappeared,tobepreservedlaterasfossils

h.41yearsofage:

thefirstanimalswithbackbones,calledvertebrates,appeared

i.41yearsand8½months:

landplantsappearedandwereshortlyfollowedbyaperiodoftimewhenfishwerethedominantanimalform

j.43yearsofage:

theappearanceofreptiles

k.44yearsofage:

dinosaurswereabundant

l.45yearsofage:

thedinosaursdisappeared

m.aboutayearago:

flowersappeared

n.4monthsago:

mammals,birds,andinsectswerethedominantlifeforms

o.25daysago:

humanancestorsappeared

p.11daysago:

thefirstmemberofthegenusHomoappeared

q.30minutesago:

moderncivilizationbegan

r.1minuteago:

theindustrialrevolutionbegan

Majorconcept（VI）

Earthhasaroughlysphericalshape,bulgingslightlyattheequator,withasurfacethatisremarkablysmooth.

Relatedorsupportingconcepts

Theearthisnotaperfectlyrigidbody.Asaresult,itsrotationcausesittobulgeoutwardattheequatorandbeslightlyflattenedatthepoles.

Approximatevaluesforthefollowingfiguresare:

a.averageradius=6371kmor3956mi

b.equatorialradius=6378.4kmor3961mi

c.polarradius=6356.9kmor3947mi

d.（equatorial-polar）radius=21.5kmor15mi

Theunequaldistributionofcontinentsandoceanbasinsresultsinafurtherdeformationoftheplanetfromaperfectspheretoashapethatissimilartoapear.

Althoughitseemsasifthedifferenceinelevationfromthehighestpointonlandtothedeepestplaceontheseafloorisverylarge,itisreallyquitesmallcomparedtoEarth’ssize.Thedifferenceinsurfaceelevationislessthan20kmcomparedtoEarth'sradiusofover6000km.

IfEarthwasreducedtothesizeofabasketballoragrapefruit,itssurfacewouldbeaboutassmoothastheyare.

MajorConcept（VII）

ExactpositiononEarthisdeterminedbylatitudeandlongitude.

Relatedorsupportingconcepts:

AgridoflinescanbeplacedoverEarth’ssurfacetoserveasareferencesystemtodeterminelocation.Therearetwosetsoflinesthatintersectoneanothertodefinelatitudeandlongitude.

Linesoflatitudearedrawnascirclesparalleltotheequator.Thesecircleshavesteadilydecreasingdiametersastheygetclosertothepoles.Linesoflatitudearealsocalledparallelsbecauseallofthecirclesareinplanesthatareparalleltooneanother.

Latitudeis0°attheequatorandincreasesto90°atthepoles.FromthisitshouldbeclearthatlatitudeismeasuredasaninternalanglefromthecenteroftheEarthawayfromtheequator.

Byconvention,latitudessouthoftheequatorarenegativeandnorthoftheequatorarepositive.

Onedegreeoflatitudeisequalto60nauticalmiles.

Linesoflongitudearesometimescalled"greatcircles"becausetheyaredrawnbyconstructingcirclesperpendiculartotheequator,thatpassthroughbothpoles.