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SelfNotesBook - 14.114.2 09:36:00PM 14. evolution:,under...

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14.1-14.2 9/13/2009 09:36:00 PM 14.1 FORMATION AND EARLY HISTORY OF EARTH     evolution:  DNA sequence change and the inheritance of that change, under  selective pressure of a changing environment Bacteria+ Archaea-->eukarya Origin of Earth earth thought to have formed about 4.5 billion years ago planets arose from materials making up a disc-shaped nebular cloud of dust and  gases released from supernova of massive old star new star compact and undergo nuclear fusion--> release large amounts of heat  and light materials left in nebular cloud began to clump and fuse b/c collisions and  gravitational pull forms tiny accretions grew larger-->clumps-->planets energy released from this process+ energy from radioactive decay heated earth earth become hot magma earth cooled-->mantle-->lower density surface crust water formed via collisions with icy comets and asteroids and volcanic outgassng  of interior present as vapor sedimentary rocks formed under water found oldest discovered 3.86 bya indicates that earth cooled sufficiently for water vapor to have condensed and  formed the early oceans crystals of zircon trapped impurities ratio of O2 indicate earth cooled much more earlier than expected
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liquid water implies that conditions might have been compatible with life after few  hundred years of formation Evidence for Microbial Life on Early Earth fossilized remains of cells and carbon in rocks show evidence of early microbial  life stromatolites     :   microbial formations fossialized microbial mats with layers of filamentous prokaryotes formed by filamentous photorophic bacterial relatives of green nonsulfur bacterium  chloroflexus oldest stromatolights, organisms were likely anoxygenic phototrophic bacterial not O2-evolving cyanobacteria *** Bacteria  and  Archaea  evolved a morphological and metabolic diversity early in  history 14.2 ORIGIN OF CELLULAR LIFE     Surface Origin Hypothesis first 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  spontaneously under certain conditions BUT surface conditions of early Earth are to hostile to life and to inorganic  and organic precursor o Temp. flux  o Mixing b.c meteor impact dust clouds, storms o highly oxidizing atmosphere unlikely this is true Subsurface Origin Hypothesis
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life originated at hydrothermal springs on ocean floor below earth’s surface conditions would have been less hostile and more stable
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