自然地理学专业英语.docx
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自然地理学专业英语.docx
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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.
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