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ID:43530611
大小:2.08 MB
页数:14页
时间:2019-10-10
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1、——byEmilyTheoriginofLIFEthebigbangtheoryThestoryoflife'soriginsbeginswiththeformationoftheearth.Thesequenceofeventsthatgaverisetoourplanetbegan,inturn,withthecosmicexplosionphysicistscalltheBigBang.thesolarsystemThesunatthecenterofoursolarsystemcondensedfr
2、omacloudofprimordialmatterroughly5billionyearsago;theplanets,includingtheearth,condensedabout4.6billionyearsago.BasicphysicalfeaturesofEarththatmayhavemadetheemergenceoflifepossibleincludetheplanet'ssize,temperature,composition,anddistancefromthesun.Gas,pr
3、imitiveatmosphereColdwaterWater(ocean)CooledwaterContainingorganiccompoundsHeatsourceTovacuumpumpSamplingprobeMiller’ssimulatedexperimentelectrodeSamplingprobeTheprobablenextsteptowardlifewasthespontaneouslinkingofsuchmonomers(单体)intopolymers(聚合物)suchaspro
4、teinoids(类蛋白)andnucleiacids(核酸).Currentresearchsuggeststhatlikelysitesforthispolymerization(高分子聚合物)wereclayorrocksurfaces.EvidencesuggeststhatRNA,whichcanformspontaneouslyunderconditionsmimickingthoseoftheearlyearth,wasthefirstinformationalmolecule.Thefirs
5、tautotrophsproducedtheirownnutrientsandreleasedO2-ametabolicby-productthathadacrucialimpactonlaterlifeforms.Theresultingozonelayerintheearth'satmospherereducedthepenetrationofultravioletlight.最早的自养生物自己生产营养物质并释放氧气,这个新陈代谢副产物对后期生命的形成有一个深远的影响。地球上大气中臭氧层的出现减少了紫外
6、线的穿透力。Theoldestfossilsthatmayrepresentlivingcellsarefoundinrocksthatareabout3.5billionyearsold.Thecellswereprobablyanaerobicheterotrophs,withautotrophsarisingmuchlater.能说明活细胞存在的最古老的化石大约有35亿年了。最早出现的细胞可能是厌氧异养生物,自养生物很久后才出现。Asaresult,cellswouldsurviveinshallow
7、waterandonthelandsurface.Theincreasingquantityofatmosphericoxygenalsopermittedtheevolutionofaerobiccellsandcellularrespiration,whichinturnsignaledthebeginningoftheglobalcarboncycle.结果,细胞就能够在浅水区和陆地上生存了。大气中氧气含量的增加使得需氧细胞进化并产生细胞呼吸,这标志着全球碳循环的开始。Theevolutionalhi
8、storyoflife单细胞生物(鞭毛虫)Single-celledorganisms(Giardia)扁形动物(涡虫)Platyhelminth(Turbellarian)环节动物(水蛭)Annulata(Leech)肠腔动物(水螅)Enterocoely(Polyp)软体动物(蜗牛)Mollusc(Snail)节肢动物(昆虫)Arthropod(insect)棘皮动物(海星)echinodermata(Sea
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