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Earth Science

How did the earth become internally layerd? Term test review  Lecture 1 • The scientific method consists of a hypothesis, prediction, test, and then either acceptance or rejection of the hypothesis. Lecture 2 • Formation of the solar system: i) There are six stages of protoplanetary disk formation ii) Step one: a molecular cloud containing a dense core as well as a star with a HII ionization front; the advance shocks push gas and dust from the HII region iii) The second stage maintains a dense core due to pushes on advance shocks and induce motion iv) The third stage has a pre stellar core as well as a dense core . pre stellar cores are formed when the ionization front passes though the core, causing a lot of motion and further a collapse that is passed over with UV v) Fourth stage has the evaporating globules; UV continues to pass over causing evaporation and thereby shaping it and forming the star in the centre vi) The fifth stage leaves us with a dense core surrounding the start known as a proplyd which continues to be blasted with UV filling the star with isotopes vii) We are finally left with a protoplanetary disk with a young stellar object in the middle viii)The star heats the disk from the inside; gas falls towards the star and begins to mix and homogenize the chemical signature of the disc ix) 1 to condense: calcium aluminium oxides x) 2 to condense : calcium aluminium magnesium silicates xi) Last to condense: more metal rich and sodium calcium magnesium silicates • Earth formation: i) Dust and ice particles collide forming planetismals ii) Planetismals grow through continuous collision; a irregularly proto-earth is formed iii) Interior heats up and becomes soft How did the earth become internally layerd? iv) Ravity shapes earth into a sphere and core and mantle are formed (irons and metals sink towards the core) • Moon formation:  Mars sized objects collides with earth during the proto stage  Proto-earth breaks apart and forms a debris ring  The moon form from the debris ring • Gaseous planets: Saturn, Uranus, Jupiter, Neptune ; Rocky planets: Mercury, venus, earth, mars • Crust: is 10-70 km ( base of the crust known as the Moho) oceanic crust is 7-10 km thick composed of basalt and gabbro, continental crust is 35-40 km thick can be mafic or felsic in composition • Mantle 2880 km thick largest part in term of volume. Mantle is completely ultra mafic with a rock called peridotite; upper mantle is down till 660km and the lower mantle 660-2900km. the transition zone is between 400-660km deep. Almost the entire mantle is solid rock • Outer core 2260 km composed of a liquid iron alloy and generates our magnetic field • Inner core 1220 km thick of a solid iron alloy • Meteorites are the 1st objects to condense in the solar system • As of 2005 Pluto was no longer deemed a planet; it was unable to clear the neighbourhood of its orbit Lecture 3 • Relative time shows events in relation to one another with a a numerical denotation, whereas Absolute time applies a specific date to each event. • Cross cutting relationships: A feature that cuts across other rocks or features must be younger • Inclusions/Xenoliths: any piece of rock included in another must be older than the rock it is included in • Superposition: the oldest layers are present at the bottom of a rock formation • Unconformities: a rock interface which is a gap in the geological record ex. The Grand canyon separate the pre Cambrian from a later flat lying Paleozoic rocks How did the earth become internally layerd? • Original horizontality: sedimentary layers are deposited in a horizontals manner; if they are not now they have been deformed ( Kaibab, Coconino, Hermit) • Baked contacts: and intrustion of igneous rock (pluton) cooks the invaded country rock • Fossils can be used to assign relative age due to the principle of fossil succession since the occur in sedimentary sequences and only in a narrow time range, the occurrence in sedimentary sequences also allows for rock records to correlate around the world • The no. of daughter atoms decreases with each half life and the no. of parent atoms decreases • Radiometric dating works best with igneous rock because radioactive parent isotopes are separated by the previously formed daughter isotopes in the crystallization process. As the radioactive parents decay they and their daughters remain trapped in the crystal structure • The earth is 4.54 Ga and the solar system at 4.6 Ga. CALs are the oldest and fist ss solids followed by chrondules. Rock records for ex. The Acasta gneiss as the oldest rock on earth help geologists determine the absolute ages. Acasta Gniess was dated by isolating the Zircon in it Lecture 4 • The hadean Eon occurred around 4.54 Ga ago. There was no oxygen at this time, and a magma ocean a few hundred km deep. Atmosphere of water, methane, nitrate, nitrogen, hydrogen, sulphur dioxide and carbon dioxide • Archean eon occurred 4.1-3.8 Ga ago. This was a period of later heavy bombardment which created craters on the surface of the moon. The rocks on the moon are recrystallized formed by impact indicating late heavy bombardment. 80% of continental crust was formed during this eon at about 2.5 Ga, tectonic movements were quick and created the crust. 3.5 Ga shows first chemical evidence of life an 3.2 billion years stromatolites created oxygen (miller-Urey experiment). • Archean greenstone belt: early crust formed from mafic igneous rock that originally intruded or extruded at convergent plate boundaries. Once formed the rocks are too buoyant to be subducted so when arcs and plateaus collided the formed larger blocks at the surface. Represent suturing between proto continents • Proterozoic Eon: 2400 Myr • Wilson cycle: rift, spreading forms ocean, oceanic plates subducts making volcanic chain , accretion from sedimentary wedge welds material to continent, 2 continent collide forming an orogeny thickens crust mnts form, continent erodes thinning the crust How did the earth become internally layerd? • Rodinia, Pannotia, Pangaea • The great oxygenation even occurred when no other environments could absorb the oxygen from other organisms, and began to accumulate as a gas in air. The ocean became oxidizing environments • BIFs formed as a result of the oceans becoming an oxidizing environment. Huge amounts of iron settled out of the oceans to form colourful sedimentary beds • Radical climate shifts occurred at the end of the Proterozoic eon . accumulations of glacial sediments in Proterozoic stratigraphs indicate that the whole planet was cold enough for glaciers to form. • Snowball earth was created due to an icy sheath that prevented atmospheric CO from 2 dissolving in seawater. The breakup of supercontinent rodinia caused land locked areas to be closer to ocean moisture, the drop in moisture reduces carbon dioxide causing sea ice which reflects incoming heat causing tem drop. But volcanic activity continued to add CO 2,temp gradually increases melts ice and CO is re2bsorbed into the oceans. • Paleozoic: Laurentias eastern margin rammed into a volcanic island arc resulting in the Taconic orogeny and produced the eastern part of the Appalachians . Western margin continued to be passive until ceased with a collision forming the antler orogeny. Pangaea is formed a) Mesozoic: rifting occurred breaking apart Pangaea split NA from Europe and western margin of north America we see convergent margin tectonics subduction generate volcanic arcs and caused them along with microcontinents to collide with north America . NA grew by the accretion of crustal fragments pangae continued to break up opening the south atlantic ocean. Compressional stress along the western north American convergent activated large thrust faults east of the arc; produced a fold thrust belt.end of crestaceous period continued compression of convergent boundaries in NA causing faults to penetrate Precambrian rocksLAraminde orogeny formed current rockies b) Cenozoic era: final brakup of Pangaea break up of Greenland from NA and Australia from antartica forming the north sea. Atlantic ocean continues to grow due to sea floor spreading on mid
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