Popular in Physical Geology
Popular in Geology
This 7 page Class Notes was uploaded by samantha Flavell on Friday February 5, 2016. The Class Notes belongs to GEO 100 at State University of New York at Oswego taught by Rachel Lee (P) in Fall 2015. Since its upload, it has received 22 views. For similar materials see Physical Geology in Geology at State University of New York at Oswego.
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Date Created: 02/05/16
Geo 100-800 February 1, 2016 Prof. Nandini Kar Topography of Earth’s Surface *Bathymetry: The elevation variation of the ocean floor. **One side of the axis is nearly identical to the other. *In general Earth is flat without much variation. Layer Composition *End result of century of investigation We know much about nature of Earth’s interior This knowledge continues to evolve Earth’s layers consist of crust, upper, transitional and lower mantles and liquid outer and solid inner cores. Much complexity characterizes even these layers Crust *Outermost “skin of our planet” highly variable Thickest under mountain ranges: 70km: 40 miles Thinnest under mid ocean ridges 7km: 4 miles *Relatively as thick as membrane of a toy balloon *Mohorovicic discontinuity (Moho) is base Seismic velocity change between crust and upper mantle Crust is upper part of a tectonic plate There are two kinds of crust *Continental underlies continents Average density ~2.7g/cm3 Average thickness 3540 km Felsic (granitic) to intermediate in composition *Oceanic Crust ocean bases Average density of ~3.0g/cm3 Average thickness 710 km Mafic (basaltic and gabbraic) in composition *Crustal density controls surface position Continental crust *Less dense “floats higher” Oceanic Crust *More dense “floats lower” *Abyssal Plains: Broad and relatively flat regions of the ocean *Midocean ridges are elongated underwater mountain ranges with their peaks only about 22.5 km below sea level *trenches are the deepest points with depths of 812 km *Trenches are bordered by curing chains of active volcanoes (Volcanic arcs) *Seamounts are what were once active volcanoes but now have flat tops and are submerged *The ocean floor is compiled of fracture zones which are narrow bands of vertical cracks as well as broken rock Crustal Composition *98.5% of crust is comprised of 8 elements Oxygen is the most abundant element *This represents the importance of Silicate (SiO4) minerals *Oxygen is large. Occupies ~93% of crustal volume Mantle Composition *Solid rock 2,885 Km thick, 82% of earth’s volume *Entirely ultramafic rock peridotite *Convection aids tectonic plate motion *Upper, transitional and lower Core Composition *Iron rich sphere with a radius of 3,471 Km *Seismic waves segregate two radically different parts The outer core is liquid; inner core is solid *Solid Core: Liquid, ironnickelsulfur 2,255 Km thick Density is 1012 g/cm3 *Inner Core: Solid ironnickel alloy Radius of 1,220 Km Density is 13 g/cm3 *Outer core flow generates Earth’s magnetic flow Magnetic Field *Like a giant dipole bar magnet field has north and south ends grows weaker with distance Magnetic flux is directional Flows from South Pole to North Pole along bar magnet Flows from north to south along field lines outside bar. *The north pole of Bar is near Earth’s geographic south pole Compass needle aligns with field lines North compass arrow points to bar magnets south pole Opposites attract Magnetic field lines Extended into space Weaken with distance Form a shield around Earth (Magnetosphere) *Solar wind distorts the magnetosphere *Shaped like a teardrop *Deflects most of solar wind, protecting the Earth *The strong magnetic field of the VanAllen belts arrests deadly cosmic radiation *Magnetic field is revealed by spectacular aurorae Some charged particles make it past VanAllen belts These are channeled along magnetic field lines They cause atmospheric gases in Polar Regions to glow Northern lights: aurorae borealis Southern lights: aurorae australis *Interaction is close to earth *Polarities switch from north to south periodically *Pole reversal every 200,000300,000 years in last 20 Million years **Paleomagnetism is a record preserved in rock: Magnetic fields of ancient rocks can indicate what the orientation of the magnetic field was at the time of the rock. *Paleopole is the suspected position of the magnetic north pole of the Earth in the past. **Apparent polarwander path is the curing line that forms from the positions of dated paleopoles. *Magnetic Declination: is the angle which is between the direction a compass needle is pointing and the line of longitude of a specific location. *Magnetic Inclination: is the angle between a field line and Earth’s surface at a given point. Summarizing Earth’s Layers *Earth has layered interior *Crust Continental and oceanic *Mantle upper, transitional and lower *Core Outer: liquid, inner: solid *These layers are subdivided on the basis of seismic waves LithosphereAsthenosphere *We can also regard layering based on rock strength *Lithosphere: Outermost 100150 km of Earth Behaves rigidly as a nonflowing material Comprised of two components: Crust and upper mantle This is material that makes up tectonic plates *Asthenosphere: Upper mantle below lithosphere Shallow under oceanic lithosphere; deeper under continental Flows as a soft solid Continental Drift and Plate Tectonics *Robert Dietz named and described a process called Seafloor spreading which is a phenomena where new ocean floor forms between the drifting apart continents. **Old ocean floor ill sink down into the interior of the Earth in a process in called Subduction. *Theory of Plate Tectonics: From Greek work tekton (builder) because they plates move and build geologic features. *Leonardo da Vinci and Francis Bacon wondered about possibility of American and African continents having broken apart, based on their shapes. The thinking continued into the early 20 th Century to a meteorologist named Alfred Wegener. *Wegener revived early idea of continental drift contending that all of present day continents were connected side by side as long ago as the Carboniferous (~300Myr) *He called the super continental mass Pangea (Greek for ‘all lands’) *Wegener’s summary was based on a host of observations. Matching glacier, climatic belt, fossil, sedimentary rock, continental shield, rocks and structural relations. *Earth’s spreading rate is 2cm per year *Plate boundaries are the breaks which are found between the plates. **Active margins: Plate boundaries **Passive Margins: Not plate boundaries Global Evidence *Large ice masses tend to flow outward (generally downhill) from a central locality. Paleontological Evidence *Similarity of late Paleozoic Earl Mesozoic (310210 Ma) fossils on opposite sides of Atlantic Ocean. Plants and land dwelling animals No mechanism to transport across ocean *Even before geochronology relative framework of rock ages showed strong correlation across the Atlantic as did mountain ranges of similar age. Continental Drift *Proposed mechanism for drift *Less dense continental rocks plowed through denser ocean floor by Earth’s rotation *Experimental evidence at the time indicated that ocean crust was stronger than continental crust, so this would not work. *A divergent boundary is a boundary where two plates are moving away from each other. *Convergent boundaries are when two boundaries move toward each other so that one is forced to sink below the other. *Black Smokers are underwater chimneys which spew mineralized water from sea floor crack emitting a dark cloud of smoke. **WadatiDenioff Zone: Band of earthquakes in a down going plate. **Accretionary Prism: plates moving and being forced into a mass which is wedgeshaped. *Transform Boundary is the actively slipping sections of a fracture zone found in between two ridge sections. *Triple Junction: Places where there are three plate boundaries intersecting. *Hot spots are volcanic points not consequences of movements. Mantle plume is the heat source for hot spots and is a column of very hot rock rising through the mantle *Hot spot track is a chain of EXTINCT volcanoes where the plate has moved over a fixed plume *Rifting is the process of a continent splitting to form two continents *Collision is the process of a land mass moves into a subduction zone but is buoyant and therefore “jams” the system. *Continental rift is linear belts where continental lithosphere pulls apart (rifts). *A suture is a boundary of what was at one time two separate continents. *Ridgepull force is developed by the lithosphere of a midocean ridge lying at a higher elevation than an abyssal plain which lies adjacent. *Slabpull force is the downgoing, subduction applied to oceanic lithosphere at a convergent margin
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