SelfNotesBook - 14.1-14.29/13/2009 09:36:00 PM14.1...

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Unformatted text preview: 14.1-14.29/13/2009 09:36:00 PM14.1 FORMATION AND EARLY HISTORY OF EARTH evolution: DNA sequence change and the inheritance of that change, under selective pressure of a changing environmentBacteria+ Archaea-->eukaryaOrigin of Earthearth thought to have formed about 4.5 billion years agoplanets arose from materials making up a disc-shaped nebular cloud of dust and gases released from supernova of massive old starnew star compact and undergo nuclear fusion--> release large amounts of heat and lightmaterials left in nebular cloud began to clump and fuse b/c collisions and gravitational pullforms tiny accretionsgrew larger-->clumps-->planetsenergy released from this process+ energy from radioactive decay heated earthearth become hot magmaearth cooled-->mantle-->lower density surface crustwater formed via collisions with icy comets and asteroids and volcanic outgassng of interiorpresent as vaporsedimentary rocks formed under water foundoldest discovered 3.86 byaindicates that earth cooled sufficiently for water vapor to have condensed and formed the early oceanscrystals of zircontrapped impuritiesratio of O2 indicate earth cooled much more earlier than expectedliquid water implies that conditions might have been compatible with life after few hundred years of formationEvidence for Microbial Life on Early Earthfossilized remains of cells and carbon in rocks show evidence of early microbial lifestromatolites : microbial formationsfossialized microbial mats with layers of filamentous prokaryotesformed by filamentous photorophic bacterialrelatives of green nonsulfur bacterium chloroflexusoldest stromatolights, organisms were likely anoxygenic phototrophic bacterialnot O2-evolving cyanobacteria***Bacteria and Archaea evolved a morphological and metabolic diversity early in history14.2 ORIGIN OF CELLULAR LIFE Surface Origin Hypothesisfirst membrane enclosed, self-replicating cells arose out of primodial soup rich in organic and inorganic compounds-experimental evidence that organic precursors to living cells can form spontaneouslyunder certain conditionsBUT surface conditions of early Earth are to hostile to life and to inorganic and organic precursoroTemp. flux oMixing b.c meteor impact dust clouds, stormsohighly oxidizing atmosphereunlikely this is trueSubsurface Origin Hypothesislife originated at hydrothermal springs on ocean floorbelow earths surfaceconditions would have been less hostile and more stablesteady and abundant supply of energy reduced inorganic compoundsH2 and H2SWarm hydrothermal water flowed up thru crust and mixed with cooler acidic, iron-...
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This note was uploaded on 02/11/2011 for the course BIOMI 2900 at Cornell University (Engineering School).

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SelfNotesBook - 14.1-14.29/13/2009 09:36:00 PM14.1...

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