Week Thirteen Notes-Geology G-104
Week Thirteen Notes-Geology G-104 GEOL-104 20584
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This 6 page Class Notes was uploaded by Ashley Hughes on Friday April 17, 2015. The Class Notes belongs to GEOL-104 20584 at Indiana University taught by Laura Wasylenki in Spring2015. Since its upload, it has received 80 views. For similar materials see Evolution of the Earth in Geology at Indiana University.
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Date Created: 04/17/15
41415 G104 0 What makes us think the Hadean Eon 4538 billion years ago was characterized by a magma ocean at the surface of the Earth 0 Rocks of Hadean age are all extrusive igneous rocks 0 Because there were more radiogenic atoms and because the earth had not yet lost much heat models of surface heat flux tell us the surface was too hot for magma to solidify o The earth was much closer to the sun in the Hadean Eon and as a result the surface was heated to the melting point 0 Actually we have direct evidence that there were water oceans on the surface during the Hadean Eon o Archean o Infer there were many small fast moving plates 0 Subduction zones 0 No oxygen in the atmosphere I Iron didn t turn to rust stayed in ocean o No life to consume Si like now 0 Stomatolites pile of photosynthetic bacteria 0 Evidence for life I Oldest definitive abundant life stromatolites at 35 billion years ago I Oldest definitive singleorganism fossil threadlike prokaryotes in rim of basalt at 35 billion years ago I Chemical evidence of photosynthesis at 37 billion years ago very light carbon isotope ratio in organic matter in shale I More chemical eVidence of methanogenisis at 35 billion years ago extremely light carbon isotopes Life 0 Some stuff separated by a boundary from its surroundings lipids fats o The stuff inside uses energy from the surroundings to maintain orderly internal chemical reactions 0 Replicates itself MillerUrey experiments 0 Produced amino acids 0 Amino also found in meteorites 0 Amino acids not proteins 0 Proteins not RNA or DNA How life works 0 Nucleotides DNA and RNA are the codes for useful proteins 0 They replicate 0 RNA is a sturdier molecule and not only codes but helps construct proteins Some of the earliest life forms liked it hot and most could not be around oxygen No idea Where life started but 0 Warm 0 Wet 0 With nutrients 0 Without UV 0 0 Without 02 Bottom of the ocean Black smokers Some were probably like modern cyanobacteria and purple sulfur bacteria Methanogens part of Archaea kingdom likely dominate form of life until 25 billion years ago Not much diversity in the Archean Proterozoic Eon the big part 25 billion years ago542 million years ago 0 O Earth s interior cooling down Convection not so vigorous Thicker larger pieces of land formed and survived for us to see Thick piles of elastic sediment accumulated Thicker continental crust deformed to make mountains Climate change and glaciation Tectonics first supercontinent I Reliable paleomagnetic data I Lots of folded and metamorphosed rocks of that age these were deformed and made into mountains at continental collision zones Breakup I Reliable paleomagnetic data I Rocks of that age are consistent with crystal thinning normal faulting volcanism and new shallow marine sediments The biggest ice age every toward end snowball earth 41615 0 Endosymbiosis 0 Two independent bacteria one engulfs the other both benefit the internal bacteria are passed on from generation to generation 0 Eukaryotic cells made 39 Cells With nuclei 0 May have happened many times but for sure happened at least twice I One instance made protoanimalfungus cells and the other protoplant cells 0 All multicellular life is derived from early eukaryotes o Mitochondria and chloroplasts have membranes similar to those of oxygen respiring bacteria and cyanobacteria respectively 0 Mitochondria and chloroplasts have their own ribosomal RNA machinery for protein building 0 Mitochondria and chloroplasts reduced the way bacteria do by dividing 0 Only eukaryotic cells make sterols Which get preserved as steranes o The earliest definitive steranes have been found in rocks in 21 billion years old but did not ourish until about 16 billion years ago 0 Until 24 billion years ago oxygen stayed low 0 Banded iron formations o Pyrite and uraninite in sediments o Cyanobacteria made 02 by photosynthesizing but I Fe and S in ocean reacted With 02 and removed it I Methano gens made methane which reacted with 02 I Decomposing organic matter also sucked up 02 o 2422 billion years ago Great Oxidation Event 0 O 0 Life became very productive including photosynthesizers So much organic matter was being deposited that it was buried before it could decompose less 02 destroyed by methane 02 started to build up in the atmosphere and ocean 0 02 presents a challenge for many prokaryotes including the cyanobacteria who made it 0 O 0 They evolved in a lowoxygen world Their DNA RNA and proteins are only inside one membrane and are readily destroyed by oxygen They evolved to use all the Fe in seawater as a nutrient and now the Fe is all rusting out on land Go extinct or learn to adapt 0 Some liked it this way 02 was helpful for some especially eukaryotes 0 Their internal membranebound DNA and RNA are safer More oxygen meant that nitrogen became nitrate N03 a very important nutrient for eukaryotes Efficient energy machinery made them compete will for other nutrients eg phosphorus Results I Eukaryotes got bigger diversified ourished after 16 billion years ago I Prokaryotes didn t die out but were forced to evolve 0 Many events didn t leave evidence 0 Most organisms don t fossilize o The ocean water of the past is gone 0 The atmosphere of the past is gone 0 Nobody recorded the weather 0 All we get are old rocks 0 Stable isotopes help us try to figure the past out
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