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ERS120 Planet Earth Notes.docx

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University of Toronto Mississauga
Earth Science

ERS120 Planet Earth Notes Lecture 2- Solar System and Earth Formation/ Jan 9 2013  Molecular clouds (star clouds) mainly hydrogen, helium, cold ices and dust, and lithium.  Six stages for ppd formation. First is h2 region (very hot region of ionized gas which come out and push on gas and dust around the h2 region, that eventually make dense cores.  stage 2 Turbulence causes the cloud to mix itself.  Stage 3 the ionization front of the h2 region passes through the dense core, which collapses the cloud.  stage 4 the core keeps getting blasted by uv radiation and photo evaporation dissipates and shapes the cloud and star forms in center because of gravitational collapse.  Last stage, the protoplanterary disk (ppd) and young stellar object (yso). Star heats the disk from the inside, and also heat is generated by the gas that is falling inwards thru the disk  Mineral condensation sequence: different mineral species will condense in a ppd as a function of T and distance from the central star  First minerals to condense are ca, al, oxides  Intermediate, ca, al, mg, silicates  Last to condense are more metal rich object like iron nickel metal and sodium calcium magnesium silicates  meteorites were the oldest and very first rocks to form in the universe  meteorites first to condense in our solar system, have calcium aluminum rich inclusions (cai’s (4567 Ma)) and chondrules (second oldest objects in our solar system)(4567- Ma)  meteorites came from planetesimals- colliding planetesimals, get hot, melt, and starts to form speherical shape and differentiates, iron starts forming the core and silicates surround the core  Formation of the earth-moon sytem Lecture 3- January 14, 2013 Geologic Time  Acasta Genesis oldest rock on earth  James hutton from 1726-1797 recognized that not all features form simultaneoulsly, so earth has a history  relative age- is just the event that event that happened in according to order but not exact date, ie world war 1, Vietnam war, ww2  numerical age- are events that are assigned a number ie. world war 1 was from 1814-1919, world war 2 was from 1930-1945 etc  relative age- principle of uniformitarianism which are physical processes that operare today that also operated in the past at roughly the same rates, and these processes formed the geologic features we see today  relative age determinism- principle of superposition – oldest layer at bottom, youngest at top  principle of inclusions- any piece of rock (inclusion or xenolith) included in another rock must be older than the rock in which it is incorporated  xenolith is a piece of rock that invaded another piece of rock  you decide if an inclusion is younger by checking what material it plucks off. ie if u hav sandstone then sill then sandstone and the sill layer has a bit of sandstone bits then that is younger then the top sandstone layer cuz it intruded and got chunks of sandstone  sedimanetry layers and lava flows are usually deposited horizontally  Principle of baked contacts- aan intrustion of igneous rock (pluton) cooks the invaded country rock. the baked rock must be be theier first (older)  principle of cross cutting relationships- any feature that cuts across other rocks or features must be younger  principle of fossil sucession- specific fossils, found cocuring in sedimentary sequences are only found in a limited and narrow time range  principle of unconformities- An unconformity is a rock interface which represents a GAP in the geologic record, like pages missing from a book.  different parts of world show rly different sedimentary layers  Numerical age – the ways used these days  radioactive decay- using isotopes that are used for dating  carbon is short half life but only dates organic  in decay, half the parents decay into different daughter compounds  works best for igneous rock but metamorphic rocks can work dependin on the minerals and the temperatures  not good for sedimentary rock  ca, al, inclusions (cai’s) oldest and first ss solids  chondrules are second oldest ss solids  carbon dating is much different from radio active decay  carbon dating is when solar radiation (neutrons) come into atmosphere and strike gases like Nitro 14 and then carbon 14 is produced and then forms co and co2.  c 14 dating can be done on tree stumps, fossils, old ashes, parchment papers, etc Lecture 4- January 16, 2013 Earth  Precambrian 4.6 Ga to 542ma, Paleozoic 542ma to 251ma,, ,Mesozoic 251ma to 65 ma, Cenozoic 65ma to present  geologic time scale broken into eon, era, period, and epoch  magma ocean surrounded the whole planet to a large depth around 4.54Ga (hadeon eon), no O2 at this point, atmosphere is CO2, H2O, CH4, SO2, NH3..  archean eon (4.2-3.8 Ga)- late heavy bombardment, this is when the inner solar system had a violent event where inner planetary bodies were bombarded by meteors= creation of large number of impact craters on the moon, as well as inner planets  archean eon- 80% of continental crust formed by the end of the archean  archean was also the time of first O2. very first chemical evidence of life was 3.5Ga  oldest bacteria cell fossil were about 3.2 Ga  miller urey experiment- done in 1960s- had a little inlet in a glass apparatus and bubbled in H20, CH4, N2, SO2 (and other gases found on early earth atmos) and put electric spark( supposed to represent lightning on earth) without any O2 and they found they can generate amino acids. this showed that the first biological molecules were formed due lightning heat and those atmospheric gases.  proterzoic eon: rodina (a supercontinent)- significant plate tectonic movement, supercontinent formed at approx. 1Ga- formed by continental collisions, rifted apart at aprox 700ma.  Next supercontinent was called pannotia when rodina turned inside out, formed aprox. 800-600ma, short lived  Wilson cycle- you have land mass, then lower mass breaks up cause of magma, then spreads, then eventually ocean forms cause of spreading, then crust on one side may subduct, so you get mountains, then mountain range gets drawn in until the mountain range crosses the ocean and collides with other side of the ocean  Proerozoic eon- oxygenation of the atmosphere  bif (banded iron formations)- when o2 was in atmosphere it started dissolving in sea water and started reacting with iron ions so you started getting iron deposits on sea floor called bif’s  last 500 myr of the proterozoic era there was an enormous increase in eukaryotic complexity because of O2 availibility, simple orgs transformed to complex ones  BUT then snowball earth happened- at least 4 major snowball events bet. 750-580ma, major mass extinction  snowball happened because after rodina broke up, you have large amount of small masses of continent near equator, which means closer to ocean moisture- moisture reduces levels of CO2 which is a natural greenhouse gas, global t falls, sea ice forms, then sea ice albedo reflects icoming heat energy from sun, t falls even more  earth plunged into an ICE HOUSE, T falls to -50 degrees ****Finish off the rest of this lecture from slides**** Lecture 6- January 22, 2013 Plate tectonic II  continental crust can not be destroyed  oceaninc can be destroyed at subduction zones  ocneanic crust also slides by at strike slip faults  divergent boundries- The Moho- 50-10 km (oceaninc crust) and 20- 90km (continental crust)  adiabatic decompression is the volume of magma that moves upwards and pushes up due to partial melting from the layers of the lithosphere and creates a mid atlantic ridge divergent coundries  initial rift forms but is not realy straight convergent boundries  Ocean ocean, ocean continent, continent continent,  an example is mt. everest, continent to continent  another example is the andes mts. ocean subductin’ under continent  another example is the Aleutians which is ocean to ocean  biggest most powerful quakes happen at convergent boundaries  san andreas fault (movin down) is slipping against the pacific plate (movin upwards)  triple junctions is where 3 plates meet at one point, ie india, African and Antarctic plate hotspots- mantle plumes  not linked to pl8 boundaries  orginate as deep as outer core  the north atlantic plate moves 1-2cm a year  the south atlantic moves 1.5-2.5cm a year  east pacific 3-8cm a year  pacific is movin around 18 cm a year what is the mechanism though that moves plates?  could be heat/convection but still unsure today  convection is one possible way, the mantle material moves up and is dragged in convection current in mantle  other idea is slab pull: convection drags material down and subducts the plate down and gravity pulls on it keeping it subducted  last idea is ridge push: where convection cells meet and they push up against each other and spread out Lecture 7- January 28, 2013 Earthquakes  An equake is just a vibration produced by the rapid release of energy. Caused by a movement along a fault  3 types of faults (different from plate boundries) divergent is a normal fault, convergent is a thrust fault transform is a strike slip fault.  3 main types of seismic waves- p waves, s, and L. p waves are compression waves, fastest waves goe into ground. s waves are shear waves, more up and down waving, much more damaging. L waves are surface waves that travel along the surface, most damaging.  tsunamis: part of plate boundry sticks. this causes deformation in the upper plate. a major equake releases stress and displac
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