Summarized ers exam review.docx

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Earth Science
Lindsay Schoenbohm

Summarized ERS Exam Review Formation of universe, solar system and earth Formation of solar system: nebula forms from hydrogen, helium after big bang causing nebula to condense into swirling disc with central ball surrounded by rings. Centre ball = the sun, while rings – the dust particles collide and become planetesimals  which comes proto-earth. Gravity reshaped proto-earth into sphere and interior becomes core and mantle. Small planet later collides with it creating debris around earth  ring of debris = forms moon. Atmosphere develops volcanic gases – moisture condenses and rains create oceans • Rocky inner planet (e.g. earth) = closer to sun, relatively small, shell rock surrounding ball of metallic iron alloy • Gaseous outer planet – further from sun, large, consist of gas and ice Layers of earth(4.5 billion years old): Crust(10-70km): oceanic – basalt and gabbro, thin ; continental – mafic and felsic, oxygen – most abundant element Mantle(2880km): made of peridotite Outer Core (2260 km): liquid iron alloy Inner Core (1220 km): solid iron alloy Definition of planet: orbits sun, pull self into circle shape, has clear neighbourhood from its orbit Tectonics I Continental crust: low density, 35 km thick ; Oceanic Crust: 10 km, high density , Lithosphere(crust and upper mantle) : 100-250 km , hard, thin, cool, can be broken into large fragments called plated ; Asthenosphere(upper mantle) : 200 km , ductile (Easily deformed), hot, weak, plates “float” on asthenosphere Isostasy: plates “float” at elevation depending on thickness and density. Continental = low density yet thick. Oceanic = thinner yet high density Evidence of continental drift: fit of continents, matching rock units, matching mountain belts, fossils, matching paleo-climate belts, glaciations (age of glacial till deposits) Evidence of Sea-Floor Spreading: • Topography : mid ocean ridges - mirror image on other side, deep , deep ocean trenches – chains of active volcanoes, fracture zones – vertical cracks and broken rocks • Heat Flor: heat rising from earth’s interior up thru crust – magma rising into crust below mid ocean ridge • Volcanoes & Earthquakes • Formation of magnetic stripes on sea floor: magnetic reversals (reversed polarity), positive anomalies (same polarity as present magnetic field), negative anomalies (opposite to present field) Evolution of Sea Floor: near ridge (rocks = young, sediment = thin), away from ridge (rocks = older, sediment = thicker), youngest rocks, stripes of rocks parallel to crest alternate in magnetism Tectonics II Plate Boundaries • Divergent: moving away from each other (oceanic plate move apart by process of sea floor spreading, new lithosphere forms and takes place at mid ocean ridge) • Convergent: moving towards each other • Transform: move past each other Evolution of divergent boundaries Rifting causes continent to crack and break apart, mid ocean ridge forms and sea floor spreading begins. Continents pull apart  magma rises from mantle into magma chamber: Summarized ERS Exam Review magma along sides of chamber – cools to form gabbro, magma rises to fill verticle cracks above magma chamber: form dikes, dikes break in half and sea floor spreading continues, new magma rises and creates new dikes, magma makes it to surface: creates basalt pillows • Divergent ocean to ocean = common  b/c of mechanism of convection • Divergent Continent to continent  uncommon b/c wil become ocean to ocean after  not linear b/c as rifting progresses spreading ridges form perpendicular and transform faults form parallel to plate motion Features of Convergent Zones • Ocean to ocean : dense earthquake activity, thin volcanic activity • Ocean to continent: dense earthquake activity, thin volcanic activity • Continent to continent: elevation, sparsed earthquakes, low volcanic activity • Continental transform: no new plates form, young oceanic crust, high elevation Triple Junction: 3 plate boundaries come together Hot spots: volcanoes exist as isolated points are not consequences of movement at plate boundary. Heat source of hot spot – mantle plume : hot rock rising up thru mantle to base of lithosphere Mechanism of Plate Tectonics Mantle Convection: mantle rocks heated and become less dense than cooler upper mantle rocks – warmer rocks rise and cooler rocks since (creating verticle convection currents)  this movement creates pockets of circulation within mantle called convection cells  driving force of movement of tectonic plates Ridge push force: plates move away from crest of ocean ridge and into subduction zone Slab pull force: plate subducting at steep angle thru mantle – downward motion tends to pull other side of plate away from ridge crest Earthquakes Epicentre: point on earth directly above hypocentre Hypocentre: place within earth where rock ruptures and slips Faults along which earthquakes occur 1. Divergent: normal fault  hanging wall moves down 2. Convergent: thrust fault  hanging wall moves up ha 3. Transform: strike slip fault  no vertical displacement Divergent plate boundary: takes place at shallow depths Convergent plate boundary: intermediate and deep earthquakes Transform plate boundary: shallow focus, larger ones on land Types of Waves • P waves: compressional (fastest), S waves : shear (slower) , Surface Waves – cause more damage  L waves: ripple back and forth, R Waves: ripple up and down Earthquake predictions: examine landforms for evidence of recent faulting, seismic gaps – active fault hasn’t slipped for a long time – so stress building up, change in water level, crust distortion Tsunami Formation • Water recedes before wave arrives and rear of wave starts catching up w/ front due to friction of base of wave and sea floor – wave so wide – it plateaus • P waves: causes particles of material to parallel to direction in which wave itself moves • S waves: causes particles of material to move back and forth perpendicular to direction in which wave itself moves – DON’T TRAVEL THRU LIQUID Minerals I Atom: negatively charged electron + nucleus Summarized ERS Exam Review Element: grouping of same atoms that all have same # of protons and neutrons – pure substance Isotope: same atomic # but different number of neutrons Fundamental properties of mineral: naturally occurring, solid, crystalline structure, definable chemical composition, inorganic Crystal form: shape of crystal , Clevage: split along definite structural planes Properties of minerals: colour, luster, texture, hardness, cleavage, fracture, density, streak (rubbing against porcelain plate), special properties (magnetism, salty, reaction w/ acids) Minerals II Earth: iron, oxygen, magnesium Earth’s crust: oxygen, silicon, aluminum Rock Cycle Characteristics of Rock Naturally occurring, coherent, composed of multiple minerals Igeneous: cooling of molten Sedimentary(clastic, chemical, biochemical): deposition and cementation of particles Metamorphic: pre-existing rocks change thru pressure and temperature Intrusive (plutonic): formed from magma that cools and solidifies within crust  cool slower Extrusive (volcanic): formed at crust’s surface as result of partial melting  cool faster Fractional Crystallization: magma cools and cystallize out of magma Dike: curts across pre-existing layering (vertical intrusion) Sill: injects parallel to layers (horizontal intrusion) Pluton: irregular shaped intrusion Partial Melting: process by which only part of original rock melts to produce magma Geologic Time Relative time: earth’s geology based upon relative age relationships – subdivisions given names Relative age: specifying age of one feature w. respect to another Absolute time: numerical ages in millions of years – or some measurement Numerical Age: age of feature given in years Principles • cross cutting relationships: feature that cuts across rocks – feature must be younger than the feature that is cut • Inclusions/Xenoliths: pieces of one material incorporated in another (e.g. fragments in igneous body). Inclusion/xenolith included within another rock must be older than rock in which it is incorporated • Superposition: oldest layer @ bottom and youngest @ top • Unconformities: rock interface which represents GAP in geologic record • Original horizontality: sedimentary layers usually originally laid down horizontally but now may be deformed Fossil Succession: particular assemblage of fossil species can be found only in limited interval of strata and not above or below certain level Half Life : time it takes for half a group of parent isotopes to decay Isotopes – different version of element w/ same atomic # but different atomic weight have same protons but different neutrons Radioactive isotopes = unstable  undergo radioactive decay converting them into different element • Parent isotope : isotope that undergoes decay • Daughter isotope = decay product Summarized ERS Exam Review • Isotopic dating – calculating age of mineral by measuring ratio of parent to daughter isotopes in mineral • Isotopic clock – begins when crystal becomes cool enough for both parent and daughter isotopes to be locked into lattice – closure temperatures • Dating minerals in sedimentary rocks = determines only when minerals making up sedimentary rock first crystalized as part of igneous or metamorphic rock Groundwater Groundwater: subsurface water dampens soil and rock near surface, or sinks deeper to realm where it fills pores and crack, water in rocks or unconsolidated materials below earth’s surface Water table: boundary above which pore spaces contain mostly air and below which they contain water  above water table = unsaturated zone, below = saturated Cave system: caves originally form at or near water table – subsurface boundary b/w rock and sediment in which pores contain air and rock/sediment in which pores contain water Aquifer: high porosity and permeability – unconsolidated sands, gravels, sandstone, fractured rocks Aquitards: low permeability – mudstone or shale, unfractured igneous or metamorphic rocks Porosity: % of material that is made up of spaces Permeability: capacity of water/oil to flow thru rock – interconnectedness of pores Water table changes Hydraulic head: potential energy driving this flow • Inflow (recharge) – location where water enters ground and flows down • Outflow (discharge) – location where groundwater flows back up to surface Groundwater flowing to form springs 1. Ground surface intersects water table in discharge area – typically occur in valley floors where they may add water to lakes or streams 2. Flowing groundwater collides w/ steep, impermeable barrier, and pressure pushes it up to ground along barrier 3. Perched water table intersects surface of hill 4. Downward percolating water runs into relatively impermeable layer and migrates along top surface of layer to hillslope 5. Network of interconnected fractures channels groundwater to surface of hill 6. Artesian springs can form if ground surface intersects a natural fracture (joint) that taps a confined aquifer in which pressure is sufficient to drive water to surface Gaining Streams: gain water from an area w/ high water table Losing streams: flow over ground in dry areas and lose water into groundwater supply • Hydrolic cycle: water circulates thru reservoirs in earth , water evaporates from ocean and enters atmosphere o Atmospheric water gradually condenses  forming clouds to drop rain/snow on oceans/lands • Water on land can be held by glacial ice or in surface water (Surface-water reservoir) o Some flow back to the ocean, evaporates into the air, sink into the ground o Water sinking into the ground to remain temporarily on surface of soil grains o Some water sinks deeper to be trapped as groundwater • Groundwater fills holes/crack between grains of rock or sediment (Subsurface = water reservoir) o Some bubbled back to ground surface  lakes, rivers, streams (springs) o Some flow all the way back to the coast and reaches the sea • Some water becomes incorporated in organisms Summarized ERS Exam Review o Can return to the atmosphere via transpiration from plants + respiration from animals Lecture 19: Rivers Stream Gradient • A stream’s gradient = steeper near its headwaters (source) than near its mouth o Near its headwaters, an idealized stream flows down deep valleys or canyons o Near its mouth, it flows over nearly horizontal planes Waterfall Retreat • Forms where the gradient of a stream becomes so steep that the water free-falls down the stream bed • Energy of falling water may scour a depression (plunge pool) at the base of the waterfall • Waterfalls can eventually disappear as headward erosion slowly eats back the resistant ledge Materials Transported 1. Bed Load: Consists of larger particles bouncing &rolling across stream – sand, pebbles, cobbles • involves saltation = process during which grains on the channel floor get knocked into the water column momentarily, follow a curved trajectory downstream, and gradually sink into the bed again, where they strike other grains and knock them into the water column 2. Suspended Load: consists of tiny solid grains – silt or clay size; Swirls along with the water without settling to the floor of the channel 3. Dissolved Load: Running water dissolves soluble minerals from the sediment or rock of its substrate Higher Discharge Lower Discharge • More transportation and erosion • Lower transportation and erosion Braided Rivers • Fast-moving stream emerging from a mountain canyon  open plain at range front = spreads out over the surface o Water slows and drops its sedimentary load: alleuvial fan o Stream then divides into small channels that spread over the fan • During normal flow, sediment settles out and the channel becomes choked with sediment • As a result, the stream divides into numerous strands weaving back and forth between elongate mounds or bars of gravel and sand Meandering Rivers • A river channel that winds back and forth • Forms where running water travels over a broad floodplain underlain with a soft substrate, in a region where the river has a very gentle gradient • Development of meanders increases the volume of the stream by increasing its length o Natural variations in water depth cause fast-moving current to swing back and forth o Water erodes side of stream more effectively where it Summarized ERS Exam Review flows faster = begins to cut away faster on outer arc of the curve o Each curve begins to migrate sideways and grow more pronounced until it bec
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