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Chapter 13: Earth Structure, Earth Materials, & Plate Tectonics
Structure of earth (less dense near surface; more dense towards core)
Core Mantle Crust
o 1/3 of mass o Iron & nickel o Inner & Outer Core: link btw pressure, temp, mineral melting pt
- Inner = solid
- Outer = molten o 2/3 of mass; largest o Solid, rocky material o Behaves as plastic solid(deform & flow)
o 1% of mass; less dense
o Diff btw oceanic & continental crust (density)
- location, composition, thickness Layers: Oceanic Crust o Composition: -Basaltic (dark, fine-grained; extrusive) o Thickness:
- thinner (denser) Continental Crust o Composition:
- Granitic (light, coarse grained; intrusive) o Thickness:
- thicker (less dense) Lithosphere (crust & top part) o Elastic Solid: rigid & brittle, stand stress to brink then fracture Asthenosphere (lower part) o Plastic solid o Vertical & horizontal movement o Thermal currents o Heat Source: radioactive decay o Energy source Mohorovicic Discontinuity – boundary btw mantle & crust; change in density; varies in depth; fast change in speed of seismic waves b/c fast change in density Rocks – aggregation (collection) of minerals
Igneous Rocks Sedimentary Rocks Metamorphic Rocks
o Cooled & solidified molten rock material o Magma: subsurface o Lava: surface; only one we can see o Extrusive: surface (outside), lava, cools fast-smooth o Intrusive: beneath surface (inside), magma, cools slow-grainy o Formed from added sediments o Eroded, transported, deposited o Horizontal layers o Pressure from above-shrinks pore space & squeezes out water o Clastic: formed by fragments of pre-existing rocks o Organic: solid rock from remains of organisms(plants & animals) o Chemical: dissolved added & deposited on sea/lake bottom o Charged form
- by intense heat & pressure within crust
- stays in solid form(bonds btw atoms broken & rearrange into more stable form
- altered=harder & more compact
- weather resistant ROCK CYCLE (don’t go in perfect circle) o Form: cooled magma/lava o Can melt/reform into new o Can alter into met rocks o Can weather into fragments-eroded, transported, deposited to form sed rocks o Consist of particles from any o Can alter into met rocks o Sed or ig can be altered into met rocks o Can melt into magma & form ig rocks Early theories o Catastrophism – spontaneous formation o Uniformitarianism – inner & outer processes, still used today; operate at varying rates & magnitudes Continental Drift theory o Alfred Wegener (climatologist) early 1900s; landmasses/continents shifted position o Evidence: fit of coastlines, similarities in animal & plant fossils(once together), past glaciations o Weakness: no cause-needed energy source o Supporting: 1950s/60s; changing course of magnetic fields in basaltic rocks Paleomagnetism – iron rocks & minerals indicate magnetic field when they solidified; revealed- continents were grouped together 200 million yrs ago & polarity reversed Plate Tectonics – modern theory, movement of continents; litho broken into several plates=sit on plastic flowing aestheno o Evidence of plate tectonics found when studying sea floor: 1) similarity btw midoceanic ridges & continental coastlines 2) magnetic bands moving away from mido
3) young rocks on sea floor 4) oldest rocks near continents & get younger towards mido 5) hottest rocks found near mid & become cooler away from mido Seafloor Spreading – new crust created near mid & older crust being destroyed along other margins; powered by subcrustal convection cells o Warm mantle rises near mid, spreads out laterally, fractures seafloor where molten basalt wells up & cools = forming new ocean floor Tectonic Plate Movement – understanding ways plates move allow us to better understand = earthquakes, volcanoes, zones of crustal movement, major landform features Divergence Convergence Transform o 2 plates pull apart
- seafloor spreading/mido(ocean )
- Rift Valleys (land) o 2 plates push together o Subduction: denser plate forced under less dense plate - descend into aestheno-melted into molten=recycled - create friction=explains major earthquakes - explains spatial dist of mt ranges, volcanoes, ocean trenches o Lateral plates slide past one another in opposite directions o Transform Fault: divergent boundary occurs in crosshatched pattern-create transform movement - common along mido Hot Spots – stationary molten masses o Oceanic plate moves over hot spot - upper mantle & oceanic crust melt - causes volcanic eruptions & outpouring of basaltic material - creates volcanic island Accretion – most supported process for continental growth; adding large pieces of crust along border by plate tectonic collision Questions and things must know for Final:
- Oceanic & continental crust – which one is more dense? – oceanic crust
- Where is Moho located and what is it?
- 7 major plates slide: where are we most likely to see a trench/volcano/mt forming/rip valleys/etc.? a. Dotted lines are….. Lines are….. b. Letters on plates identify what?
- Must know all boundaries
- Less dense near surface/more dense towards core
- Focus on how rocks are formed