英语.docx
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英语.docx
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英语
Lecture1
INTRODUCTIONTOEARTH
MajorConcept(I)
Theplanetsinoursolarsystem,includingEarth,begantoformoutofarotatingdisk(旋转的圆盘)ofgasanddustabout4.6billionyearsago.
Relatedorsupportingconcepts:
Thepresentviewofthebeginningofthesolarsystemsuggeststhatacloudofgasanddustwasflattened(变平)intoadiskbyrotation.Thedensityofthematterinthediskwasgreatestatitscenteranddecreasedtowardtheedges.
Thesunformedatthecenterofthediskwherethetemperaturewashighestandtheplanetsformedatgreaterdistancesawayfromthecenter.
Thecompositions(组织、组成)oftheplanetsdifferbecauseofanaturalsorting(分类)ofelementsinthecloudwithdistancefromthecenter.
ThetemperatureoftheearlyEarthwasprobablyquitehighdueto:
a.thegravitationalcaptureofparticlesthatreleasedheatonimpact,(那些在地球万有引力作用下捕获的颗粒因相互碰撞而释放热量)
b.theincreasedpressureontheinterioroftheplanetasitcontinuedtogrow,and(随着地球的不断发展增大,地球内部的压力不断加大)
c.thecaptureofradioactiveelementsthatgaveoffheatwhentheydecayed.
Duringthefirstfewhundredmillionyears,theinternaltemperaturerosehighenoughtomeltironandnickel.Theseheavymetalssanktoformthecoreoftheplanetanddisplacedlightermaterialthatrosetoformchemicallydifferentiated(化学分化)shells(壳层).
MajorConcept(II)
Earth’soceansoriginatedearlyintheplanet’shistory.Therearetwoproposedsourcesofthewaterintheoceans.
Relatedorsupportingconcepts:
Theoldestsedimentaryrocks(沉积岩)foundthatrequiredwaterfortheirformationare3.9billionyearsold.ThissuggeststhattherearebeenoceansonEarthforroughly4billionyears.
TraditionallyscientistshavebelievedthatthewaterintheoceansandatmosphereoriginatedinEarth’smantle(地幔)andwasbroughttothesurfacebyvolcanism.
Mostmagmas(岩浆)containfrom1%to5%dissolvedgasbyweight(包含1%到5%重量的溶解气体),mostofwhichiswatervapor.
Ifweassumethatthecurrentrateofreleaseofwatervaporinvolcaniceruptionshasremainedessentiallyconstantforthepast4billionyears(如果我们假设目前的火山爆发的水蒸气释放率在过去的4billion年里保持基本恒定),thenthevolumeofwaterexpelled(排出,putout)duringthattimewouldberoughly100timesthevolumeoftoday’soceans.
ArelativelynewproposalisthatasignificantamountofwaterisaddedtoEarthfromspacewhensmallicycomets(彗星)enterEarth’satmosphere.
Theearlyatmospheredidnothaveanyoxygen.Theoxygenreleasedfromtheinterioroftheplanetwouldhavecombinedwithmetalsatthesurfacetoproduceoxides.
Itwasn'tuntillargeamountsofoxygenwereproducedafterplantsformedthatitbegantoaccumulateintheatmosphere.(植物出现以后形成大量的氧气,但在此之前氧气已经开始在大气中积累)
MajorConcept(III)
Thereiscompellingevidencethattheremaybeotheroceansinthesolarsystem.
Relatedorsupportingconcepts:
TwoofJupiter’smoons,EuropaandCallisto,mayhaveoceansbeneaththeiricysurfaces.(在木星的两个卫星(木卫二和木卫四)的冰冷的表面下可能有海洋)
LiquidoceansonEuropamaybepossibledespiteextremelylowtemperaturesbecauseofheatgeneratedbyfriction(摩擦)asitisdeformed(相变)byJupiter’stide-producinggravitationalforce(潮汐引力).
Bothmoonshaveinducedmagneticfields(磁场感应)indicatingtheyconsistpartly(组成部分)ofstronglyconductingmaterial.Thismaybeliquidwaterwithelectrolyticsalts(电解盐).
ThereisalsosomeindicationthatMarsoncehadanoceancoveringportions(部分)ofitsnorthernhemisphere.
MajorConcept(IV)
ThereareavarietyoflinesofindirectevidencethatallowustoestimateEarth’sageasbeingabout4.5to4.6billionyears.
Relatedorsupportingconcepts:
Earth’soriginalcrust(地壳),thatwouldhaveformedearlyinitshistory,hasbeendestroyedorcoveredbyactivevolcanismandtectonic(构造)processes.Thisisareflectionofthegeologicallyactivenatureoftheplanet(这是地球的地质活动本质的反映).Consequently,theoldestsurfacerockswehavefound,roughly4billionyearsold,giveusaminimumageforEarthratherthananactualage.
IndirectevidenceofEarth’sageincludes:
a.thedatingofmoonrocksat4.2billionyears,
b.thedatingofmeteorites(陨星)at4.5to4.6billionyears,and
c.theoreticalcalculationsoftheageofthesunasbeingroughlythesameasthemeteorites.
Wecandetermine(确定)theageofrocksthatcontainradioactiveisotopes(同位素)ofelementsthatdecayatconstant,knownrates.Thisiscalledradiometricdating.
Ifarockcontainsatomsofaspecificradioactiveisotope,halfofthemwilldecayintoanotherelement,calledthedaughterproduct,inaperiodoftimecalledthehalf-lifeoftheisotope(同位素的半衰期).
AnexampleofthistypeofprocesswouldbeUranium235anditsdaughterproductLead207(铅)withahalf-lifeof704millionyears.Arockthatinitiallycontained100atomsofU235andnoPb207wouldhavethefollowingnumbersofthetwoelementsaftertheindicatedelapsedtimes:
Thereareseveraldifferent"parent-daughter"radioactivepairsthatoccurinrocks.Eachofthepairshasitsownspecifichalf-life,somequitelongandothersveryshort.Pairswithlonghalf-livesarebestfordatingveryoldrockswhilethosewithshorthalf-livesarebestforyoungerrocks.Ideally(理想情况下),anassigneddateforarockwillbebasedontheuseofmorethanoneradioactivepairsothatacheckcanbemadeonaccuracy.
MajorConcept(V)
Geologictimeisoftendifficulttograspbecauseofhowlongitiscomparedtoallofhumanhistory(tosaynothingoftheincrediblybrieftimespanofasinglehumanlife).
Relatedorsupportingconcepts
Justaswedividetimeintosegmentslikeyears,months,anddaystoidentifybothdurationandsomesenseofposition,wedividegeologictimeaswell.Thelongestdivisioniscalledaneon(宙).Eonsaredividedintoeras(代),erasaredividedintoperiods()纪,andperiodsintoepochs(世).
Thegeologictimescaleandthehistoryofevolutionoflife-formsisgivenintable2.1.
Theeras,inorderofmostdistantpasttomostrecenttime,are:
a.Precambrian,(前寒武纪)
b.Paleozoic(ancientlife),(古生代)
c.Mesozoic(intermediatelife),and(中生代)
d.Cenozoic(recentlife).(新生代)
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:
photosynthesis(光合作用)beganproducingoxygen
f.31yearsofage:
therewassufficientoxygenintheatmospheretoallowthegrowthofcomplexcellsthatrequireoxygen
g.40yearsofage:
thefirsthard-shelledorganismsappeared,tobepreservedlaterasfossils
h.41yearsofage:
thefirstanimalswithbackbones,calledvertebrates(脊椎动物),appeared
i.41yearsand8½months:
landplantsappearedandwereshortlyfollowedbyaperiodoftimewhenfishwerethedominantanimalform
j.43yearsofage:
theappearanceofreptiles(爬行动物)
k.44yearsofage:
dinosaurswereabundant
l.45yearsofage:
thedinosaursdisappeared
m.aboutayearago:
flowersappeared
n.4monthsago:
mammals,birds,andinsectswerethedominantlifeforms
o.25daysago:
humanancestorsappeared
p.11daysago:
thefirstmemberofthegenusHomo(智人属)appeared
q.30minutesago:
moderncivilizationbegan
r.1minuteago:
theindustrialrevolutionbegan
Majorconcept(VI)
Earthhasaroughlysphericalshape,bulgingslightlyattheequator,withasurfacethatisremarkablysmooth.(地球形状大致为球体,表面非常平滑,赤道略微突出。
)
Relatedorsupportingconcepts
Theearthisnotaperfectlyrigidbody.Asaresult,itsrotationcausesittobulgeoutwardattheequatorandbeslightlyflattenedatthepoles.(地球并不是一个严格的刚体,因此它在旋转时会使地球赤道向外凸起而两极略扁平)
Approximatevalues(近似值)forthefollowingfiguresare:
a.averageradius(平均半径)=6371kmor3956mi
b.equatorialradius(赤道半径)=6378.4kmor3961mi
c.polarradius(极半径)=6356.9kmor3947mi
d.(equatorial-polar)radius=21.5kmor15mi
Theunequaldistributionofcontinentsandoceanbasinsresultsinafurtherdeformation(变形)oftheplanetfromaperfectspheretoashapethatissimilartoapear.(由于陆地和海盆的不均匀分布使得地球形状由一个完美的球体变成梨形)
Althoughitseemsasifthedifferenceinelevationfromthehighestpointonlandtothedeepestplaceontheseafloorisverylarge,itisreallyquitesmallcomparedtoEarth’ssize.Thedifferenceinsurfaceelevationislessthan20kmcomparedtoEarth'sradiusofover6000km.
IfEarthwasreducedtothesizeofabasketballoragrapefruit,itssurfacewouldbeaboutassmoothastheyare.(虽然陆地上的最高点和海底最深处之间的高差看起来很大,但是相比地球的大小还是很小的。
地表的最大高差小于20km,而地球半径大于6000km。
如果地球被缩小到一个篮球或葡萄的大小,其表面会和他们一样光滑)
MajorConcept(VII)
ExactpositiononEarthisdeterminedbylatitudeandlongitude.
Relatedorsupportingconcepts:
AgridoflinescanbeplacedoverEarth’ssurfacetoserveasareferencesystemtodeterminelocation.Therearetwosetsoflinesthatintersectoneanothertodefinelatitudeandlongitude.
Linesoflatitudearedrawnascirclesparalleltotheequator.Thesecircleshavesteadilydecreasingdiametersastheygetclosertothepoles.Linesoflatitudearealsocalledparallelsbec
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