免费theoriginoflife生命起源课件

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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