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Biological Sciences
BIOL 1202
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12610Chapter 25 History of Life on EarthHow did life beginA few centuries agooPeople thought that new living things appeared all of the time Maggots in garbage mold on bread etc1609 Spontaneous creation of lifeoSpontaneous generation was refuted by Louis Pasteur in the mid 1800s boiling the broth in the flask would kill the preexisting microorganisms As the broth cooled the condensing water collected sealing the mouth of the flaskPasteur broke the neck off of the flask and the outside air carried microorganisms into brothoConditions on early earth Atmosphere CO CH NH H N HCl HS and HO similar to Jupiter 2432222todayNo free oxygenFrequent storms with lots of lightningFrequent volcanic eruptionsFrequent meteor impactsUV light from the sunNo ozone layeroEarth Before Life AroseEarth is about 46 billion years oldRadiometric dating of meteorites and moon rocksLife arose about 38 billion years agoChemical traces in rocks 38 billion years oldFossil bacteria in rocks 35 billion years old prokaryotic cells existed first no skeletons only unicellular organisms existedNo spontaneous generation now but must have happened thenRate of Decay of 40K to 40ArPotassium 40 40K naturally decays to argon 40 40Ar half life of 13 billion yearsExperiment of Miller and Urey attempted to replicate earths early atmosphere but life was not formed spontaneously but they did find the organic molecules began to formLife appeared on earth 8 billion years after earth is formedHow to Assemble a living thingAccumulation of organic moleculesCatalyze reactionsReproduce from stored genetic infoSeparate the living thing from the outside environment phospholipid bilayerThe Chicken or the eggNow Dna to Rna to proteinoNeed proteins to synthesize more DNAHow did the earliest cells do itoRibozymes RNA molecule that can catalyze reactions exp Those involved in synthesis and processing of RNA itselfConclusion earliest cells used RNA to store infoRibozymes to catalyze reactionsMicropheres as ProtoCellsoJust add fat and protein to water then shake
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