Geology Midterm 2 Study Guide
Geology Midterm 2 Study Guide Geo 002
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This 7 page Study Guide was uploaded by H. Dawoody on Monday April 11, 2016. The Study Guide belongs to Geo 002 at University of California Riverside taught by Prof. Tim Lyons in Winter 2016. Since its upload, it has received 23 views. For similar materials see Earth's Climate Through Time in Geology at University of California Riverside.
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Date Created: 04/11/16
Geology Midterm #2 Study Guide OCEANIC CIRCULATION Water is a critical component because it cycles continuously among ocean, atmosphere and land, carrying with it energy, nutrients, gases and other matter.” Global Hydrological Cycle is in a steady state (transfer rates of 10 km per 3 year) Ocean loses water, as some evaporates, as it evaporates it condenses into clouds, precipitating and returning back to the ocean; some transfers to clouds above land trough advection and precipitates on land (vice versa- land water evaporates, condenses into clouds and transfers water to clouds above ocean, bringing water to ocean. Rivers bring back what is lost to the ocean giving it a steady state Global Water Distribution Oceans take up most volume on earth’s surface, making up 96.5 % of total water, but not as fresh water Ice caps/ Glaciers and permanent snow take up much less volume making 1.74% of total water, but giving s 68.7% of fresh water Groundwater makes up 1.7% of total water but gives of the rest (30.1%) of fresh water Water in the atmosphere Warm air holds more water vapor, air cools as it rises above the surface. Ocean Circulation (surface wind circulation and deep surface circulation; currents, temp., solidity) Ekman Transport drives sea surface circulation; which is a result of the Corolisis deflection; water moves 90 degrees to wind direction, giving surface water a spiral deflection moving downward until it disappears. Convergence- In a clockwise gyre (in northern hem.) effect of Ekman transport is to push water into center of the gyre. Convergence causes downwelling, and Divergence causes upwelling. Global Surface Ocean Currents (prevailing wind systems exert wind stress setting surface ocean water into motion) South and North east trade winds and westerlies Coastal Upwelling (Why CA coast water is cold) For the CA coast; Dominant surface current moves south towards equator, Ekman transport pushes water away from coast, as water moves away cold nutrient rich water is brought up to the surface, giving high productivity areas Gulf Stream Brings warm water to high latitudes, cold water to lower latitudes; latitudinal redistribution of energy. It also meanders; following a specific path, and rings Why is the Sea Salty? Salt in the sea is derived from breakdown of crustal rocks on land (physical and chemical weathering) Water flowing over or through rocks removes soluble materials (ions). Rivers carry the ions to the ocean (~4 billion tons per year). When ocean water evaporates it leaves behind the salt. Some of the evaporated water falls back on the land and eventually returns to the ocean with more ions, repeating the cycle. The salinity of the ocean does not increase on average, however, because many processes remove salts from seawater: (formation of evaporite deposits, biological processes, chemical reactions with the sea-floor). Input and removal are in a balance (a steady state). (salt has very long residence time) Salinity Variation in salinity caused by regional differences in evaporation ,precipitation, ice melting etc. Except for calcium, these elements are found in nearly constant proportion (conservative elements). Salt Content of earth’s oceans top 5: Chloride, Sodium, Sulfate, Mg, Calcium Vertical Structure of Oceans Surface Ocean is well mixed by wind moving across it and is in exchange with the atmosphere, giving very sharp differences and increases at the bottom of surface water (increase in density, salinity, and temperature) thermo, haline, pyno Stable density stratification insulates the deep ocean (80% of entire ocean volume) from seasonal changes in temperature and salinity. Bottom Water Densest and saltiest water in ocean produced at high latitudes near poles, where ocean water freezes, as it freezes sea ice is formed, but salt is excluded from the ice leaving behind salty unfrozen but cold water, combination of high salinity and low temp. makes very dense water which sinks to seafloor where it spreads to the equator The two major sites for bottom-water formation are the Weddell Sea off Antarctica (Antarctic Bottom Water, AABW) and the North Atlantic off Greenland (North Atlantic Deep Water, NADW). Thermohaline Conveyor Belt System that circulates water throughout the world's oceans based on density and salinity. Moves cold, salty deep-sea water from higher to lower latitudes; creates warm, less-salty shallow current and cold, salty deep-sea current. Transfers heat from the equator to Europe/North America, causing temperate climate Combined Effect of Atmospheric and Oceanic Circulation Pole ward heat transfer in northern hem. Is nearly 50:50 between ocean and atm. PLATE TECTONICS -Wegener the father of continental drift (1915) proposed continental drift using fossil evidence who were land based and couldn't have swam across the Atlantic Ocean (south am, and Africa) also based on the jigsaw puzzle like features of the continents and how they seemed to fit so well together, especially south am and Africa, mainly studied coastal areas of the continents similarities in rock types and structured on either side of the Atlantic Ocean like the Appalachians mountains and Scottish highlands Paleoclimatic evidence, basically that geographical climates have changed modern day deserts may have been colder regions in the past. Published on the origins of the continents and the oceans, stating 300 million yes ago during Carboniferous period earth formed one large supercontinent called pangea; meaning "all earth" This defeated the idea of lands bridges (older false theory of how fossils were the same, bc cont. we're connected by strips of land, which we couldn't see today, bc of rising sea levels. Wegeners theory was largely disapproved and not believed in as he couldn't provide an actual mechanism that could have possibly been responsible for drifting the continents apart over millions of years. It wasn't until decades later as a result of poster geophysics developed during the Cold War, that scientists discovered a mechanism and evidence that would verify Wegeners theory. PostWar Geophysics and Discoveries In 1930 Authur Holmes proposed that convection was occurring in earths mantle which could be the force during continents apart. (Mantle contained convection cells) convection transfer of heat by circulating motion of a liquid or flowing solid like the mantle heated from below. heat in earths interior largely comes from radioactive decay which then drives the mantle paleomagnetism iron bearing minerals act as fossil compasses pointing towards existing magnetic poles (after being cooled below a curie point) declination provides irection, as the offset between true and magnetic north inclination priced ns latitude as the angle and tilt of your location magnetic poles appeared to have moved dramatically over earths history, meaning either the continents or the magnetic poles themselves have moved over time apparent vs true polar wander path orientations of different rock minerals pointing different directions overtime (after cooling below a cutie point they are perm. set into place) curie point temp a t which magnetic mineral will cool and align with the magnetic field present at that time iron atoms behave tiny magnets aligning themselves in certain magnetic materials Earths Magnetic Dynamo /Geodynamo Magnetic Dynamo is a mechanism which transfers heat and energy from fluid motions into electric currents which create a magnetic field ( convection of earths outer core creates earths magnetic field which keeps our arm. From being swept away and protects us from harmful solar uv radiation). Looking at earths magnetic field indicate earths field lines vary from horizontal at the equator to vertical at the poles cont. Drift provides an explanation for polar wandering Harry Hess and Seafloor Spreading Harry Hess found with sonar technologies mapping the Seafloor on submarines he found that the ocean had topographic mountain ranges with chains of volcanos at mid ocean ridges where oceanic crust was being created and plates were spreading he found that cean ridges represent upwelling portion of convection cells in the mantle known as divergence which created more ocean basins and ocean trenches which are subduction zones represent downward limbs . Seafloor is relatively yound it is constantly being renewed and subduction ( oldest oceanic crust is 200 million yrs old relationship to carbon dioxide is the volcanos at mid ocean ridges and trench spew co2 into the atm. So without them there would be a co2 drawdown Seafloor spreading was verified by studies of magnetic properties of Seafloor (1963, recording of polarity reversals normal vs. reversed) reveals alternating stripes of normal and reversed polarity which parceled the ridges crest with a symmetrical pattern defined by the ridge new basalt added to oceanoor becomes magnetized according to e magnetic field existing at that time oldest ocean crust must be furthest away from ocean ridge magnetic reversals recorded in volcanic rock preserved on land for 75 mill. Yrs and when measuring orientation of mag. min. In the ocean crust the pattern is irregular. The Theory Continetial drift and Seafloor spreading were unified into the theory of plate tectonics in 1968 The lithosphere consists of about a dozen plates containing ocean floor, continent or a combination of both PLATE TECTONICS PART 2 The lithosphere which are earths plates consists of the earths crust, and upper most mantle the athenosphere which is included in the lithosphere is capable of flow as a flowing solid the mantle makes up the largest proportion of earths interior, underneath a liquid iron molten outer core, and then a solid iron inner core Oceanic crust is very thin (5 km, salty mafic min.) compared to Cont. crust which (35 km, felsic min.) plate boundaries are where interactions between different plates occur, these are locations of most earthquakes, and volcanism, mid ocean ridges and trenches Seafloor bathetrey measurement of the seafloor Ocean trenches are subduction zones where Seafloor is being recycled back into the mantle, these are areas of earthquakes Contocean subduction, as some crust begins to melt it rises creating volcano chains magmatic arcs on land, and island arcs at the sea (oceanocean subduction) Divergent boundaries are constructive ocean ridges produces new crustal materials, and clean basins convergent boundaries are destructive as crust is being subducted into the mantle betting off zone transform boundaries are conservative neither creating or dethroning material, instead two corn. Platsliding past one another, just earthquakes no volcanoes, as plates get stuck frictional,y sliding the slipping convergent boundaries in oceancont. ocean plate is subducted because it is more dense and magic in oceanocean older ocean plate sinks because it is colder and densser subduction zones, deep ocean trenches, volcanic magma and island arcs some magmatic arcs, are the Andes, and cascades contcont convergence neither plate is subducted leading to mountain building, as cont crust rises untains are uplifted. (Himalayas because of Indian and Eurasian plate converging, and the Appalachians which resulted from convergence of n.a and other plates millions of yrs ago.) passive continental margins have no plate boundaries (east coast, b/c its plate b. Is at mid ocean ridge) active continetial margins are locations of plate boundaries (west coast, ca) Pacific Ocean in South Am. Is active today, as Pacific Ocean plate is being subducted underneath the S.Am continetial plate mid ocean ridge also known as the east pacific rise is not a straight line as some portions are spreading faster, and is broken by transform faults Mantle And the Role of Convection mantle drag the lithosphere friction ally piggybacks on the connecting mantle) Ridge push gravitational as new oceanic crust is being pulled down by gravity at an angle and being pushed to the side Slab pull gravity at subduction zone is pulling crust into the mantle ridge isher tench is lower, hot material at ridge rises (more buoyant, less dense) then it cools becoming more dense an sinking, then is subducted back into the mantle. transform boundaries offset hotspot mantle plumes are stationary, while plate moves over, creating a chain of volcanic islands rising hot material causes volcanism (Hawaii, and Yellowstone) pacific plate moving over Hawaii hotspot has switched directions from moving southward, to eastward, seamounts come up from the seafloor but nt make it to the surface Supercontinents Pangea isn't the only supercontinent, Rodnia fromed 1 billion yrs ago, then drifted and formed agareating Pangea 300 mill. yrs ago) Cycles of Supercontinents which occur on million year time scales are called wilson cycles mark breakup and formation of Supercontinents and the opening and closing of ocean basins (Atlantic Ocean) Relationship Betwen Supercontinents, Seaflloor Spreading, and Carbon Dioxide Levels Co2 rises and falls with accordance to breakup and formation of Supercontinents chemical and physical weathering increases as many mountains are uplifted when a Supercontinent is formed exposing many rocks. activity of mide ocean ridges perish drawing down co2, as ridges thwart co2 into the atm. organic burial conversion to biomass enhanced in Supercontinents. Supercontinentshave higher sea levels APPARENT vs. TRUE POLAR WANDER Case 1 if magnetic poles move, that means that the polar wander paths of the continents are the same this is true polar wander Case 2if continents move (which they are) and magnetic pole stationary this means continents have two different polar wander paths, this is apparent polar wander path as it seems the magnetic pole is moving but it isn't, it's just the cont. moving. This evidence determines how cont. drift works
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