Geology 1010 FINAL STUDY GUIDE
Geology 1010 FINAL STUDY GUIDE 80176 - GEOL 1010 - 001
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80176 - GEOL 1010 - 001
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This 64 page Study Guide was uploaded by Ryan Jakszta on Saturday April 23, 2016. The Study Guide belongs to 80176 - GEOL 1010 - 001 at Clemson University taught by Alan B Coulson in Fall 2015. Since its upload, it has received 125 views. For similar materials see Physical Geology in Environmental Science at Clemson University.
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GEOL 1010 Dr. Coulson TEST 1 STUDY GUIDE Highlight = Important Principle Highligh= Key Term Lecture 1 ntro to Science and Earth’s Formation What is Science? Relies on using facts and principles Fact repeatedly demonstrated to be true Principl true ‘ides’ (unlike facts, which are true ‘statements’) Scientific Method: 1. Observation noticing things (physical features, colors, etc.) 2. Question asking how, why, where, etc. 3. Hypothesis an educated guess a. MUST be testable and predictive i. “Can I test it?” ii. “Am I able to predict the outcome?” b. Does it pass the “ifthen” statement test? i. Doesn’t HAVE to, but it is a safe and widely accepted format ii. ex:IF his happens,THEN this is true.” c. Can write a hypothesis for past and future events d. Can be an easy or difficult hypothesis: as long as it is testable and predictive, then it works! ***FOR TEST: Know how to identify a good/bad hypothesis!!!*** 4. Data Collection of numbers, facts, observations, etc. 5. Evaluation What does our data tell us? a. Was our hypothesis correct? i. More often than not, original hypothesis will be WRONG!! Theory a hypothesis that has stood up over time and tested to be true by other people Law a theory that has held up over time aalmost alwaysbeen proven true You MUST have scientific data to challenge scientific idea ex: You can’t use psychology or religion to disprove a scientific idea What is Geology? Catastrophism everything about earth is explained as a result of a catastrophe ex: Noah’s flood caused certain animals to be in certain places History of Geology: James Hutton (Scottish) wrot Theory of the Ear(1795) Principle of Uniformitari earth has behaved the same forever (“Present is the key to the past”) little changes can cause huge outcomes in the future exact opposite of “catastrophism” became cornerstone of Geology (replacing catastrophism) Actualism says that Uniformitarianism is truemost of the time, but everything happens at different speeds takes into account asteroids, ice ages, etc. meteors enter earth’s atmosphere at 40 km/s (90,000 mph) How did the Earth Form? 6 billion years ago (Ga), there was no solar system; just a nebula of Hydrogen atoms Nebula gas cloud in space Nebular Hypothesis best hypothesis to explain solar system formation Step 1) Gravity held clusters together and drew separate nebulas together Step 2) Solar Disk Model the massive clusters that were formed by gravity began to flatten out Step 3) Protostar prototype star forms in center and gains heat (6 Ga) Step 4) Fusion atoms surrounding protostar fuse with it, and it becomes a fullblown star (or sun) Planetary Accretion (4.5 Ga) formation of planets is explained by rocks, dust, dirt, etc. fusing together over time Planetary Accretion STILL HAPPENS TODAY Theia Impact Earth (in its earlier years) ran into another planTheia 1. Lunar formation the moon was finally formed 2. molten planet everything on earth turned to molten a. density measures capacity 3. Density Stratification separation of layers of earth (core, mantle, etc.) How old is Earth? 4.5 Ga (billion years ago) Lecture 2 Plate Tectonics **Geology in the News: Satellite data is giving geologists new info on why Greenland ice caps are melting Layers of the Earth 4 Chemical Layers each with different chemistry (aka “composition”) (know both names) 1. Crust lighter, lower density elements; lots of oxygen in this layer a. 845 km thick b. continental crust found under continents c. oceanic crust slightly more dense than continental crust; found under ocean 2. Mantle 452900 km thick; denser elements 3. Outer core high iron/nickel elements, but some other ones too 4. Inner core completely iron/nickel 5 Physical Layers (aka “mechanical”) 1. Lithosphere very brittle; thicker than the chemical layer “crust” 2. Athenosphere part of the mantle; malleable material (NOT the same as mantle) 3. Lower mantle or “ Mesosphere” brittle material 4. Outer core very malleable/fluid material 5. Inner core very brittle material Chemical/Compositional Layers Physical Layers **NOTE: Physical Layers and Chemical Layer are NOT the same thing!!** Basics of Tectonics Unifying theory of geology developed in the 1960s The Lithosphere (first of physical layers) is divided into pieces, or plates About a dozen major plates, none of which correspond to a specific continent Developing Plate Tectonic Theory Alfred Wegener’s Continental Drift Noticed that the continents fit together like a puzzle, and he began his research about the phenomenon Data supporting Continental Drift: Mountain chains Fossils Animal Species Very few people believe in this theory Wegener was unable to answer “how?” when people asked 1940s major research in oceans takes place Submarines used for investigating these depp, dark places Mid Ocean Ridge (MOR) new discoveries made Magnetic Reversals Positive/Negative magnetic readings were reversed in some areas Age Anomalies of Seafloor Rocks age of rocks would get older as moving away from the ridge Seafloor Spreading moving of seafloor away from the center to make room for new rock formation Explained magnetic and age anomalies Finally explained “how” continental drift worked How plates move all four of these ways work together and simultaneously 1. Convection material circulates between hot/cold and thus, new material is formed and pushes previous material away 2. Ridge Push Model Theory magma comes up through the crust and pushes material away 3. Slab Pull Model plates are pulled down into the earth 4. Slab Suction as plates are pulled down, others near it are sucked into the earth with it Plates move at about 3 in. per year on average Plate Boundaries* *NOTE: Subduction, Collision, Rift Valley, etc. are ALL types of boundaries 3 things can happen where two plates meet: 1. They can pull away from each other (divergent margins a. In Oceanic Areas (ex: Mid Ocean Ridge) i. Causes formation of volcanoes b. Continental Areas i. Causes Rift Valley formation; some volcanoes 2. They can run into each other convergent margins) a. Subduction oceancontinental collision i. Volcanic activity and earthquakes ii. Oceanic Plate always gets pushed downward b. Collision continentcontinent collision i. Mountain Range formation 3. They can slide past each other Transform Margin a. Lots of earthquakes **Important Plates to Know:azca, North American, South American, Eurasian, Pacific* * Lecture 3 inerals and the Rock Cycle **Geology in the News: Seismic activity in the Pacific Northwest linked to subduction of Juan de Fuca plate Materials and Rocks/Basic Chemistry minerals used for many things other than rocks in foods you eat, in products you use, etc. used in building/construction used to sell for lots of money (diamonds) Atoms contains nucleus (with neutrons and protons) and surrounding electrons Atomic Number tells us the number of protons in and atom tells us what element the atom belongs to you can change the number of electrons and neutrons, but NOT protons (without changing the entire element) Earth’s crust is made up of different elements, but not many almost 50% is oxygen, about 28% is silicon What is a Mineral? Must pass ALL 5 requirements: 1. Nonsynthetic must be formed in nature 2. inorganic not living and do not have lipids proteins, etc 3. crystalline molecules arranged in very organized, tight patterns a. opposite of crystalline is amorphous, meaning without a tight pattern 4. solid not liquid or gas 5. set chemical composition able to write a chemical formula a. some substitutions are ok, some substitutions have slightly different compositions Mineral Properties color although easy to identify, some minerals have different colors ex: a sample of Quartz could be blue while another sample of Quartz could be pink streak color of mineral when ground up sometimes the streak can be a different color than the actual mineral Hardness how difficult is it to scratch or damage Moh’s Scale scale of 110 (1=soft, 10=hard)(1=Talc, 10=diamond) Tools: fingernail (hardness of 2.5), pocket knife (hardness of 5), etc. There can be a range of hardness, as well as a range of tools Luster how shiny/bright the mineral is metallic very shiny/reflects light vitreous glassy; some light passes through silky,pearly, and more Effervescence the “Acid” Test will the sample fizz when acid is added? Crystal Formation how crystals form (some form in cubes, some with sharp edges, etc.) Most crystals are hard to identify unless in perfect condition Breakage Pattern how the mineral breaks Fracture no set pattern to the break Cleavage forms flat, smooth surfaces when broken pay attention to HOW it broke (in which direction, at what angle, number of faces) Many other mineral properties as well, including taste, magnetism, odor, etc Common Mineral Groups depends on what anion (negatively charge particle) the mineral has ***common test question: How do you classify a mineral? (answer: anions) Sulfides (S) sulfur atom as the anion (metal + anion) Oxides (O) oxygen atoms are anions (metal +anion) Sulfides and Oxides are very desirable due to cost effectiveness Sulfates (SO₄ ) sulfur bonded to oxygen used in construction (drywall), plasters (casts), etc. Phosphates (PO₄ ) not common, but important in fertilizers, bones, and teeth Carbonates (CO₃ ) found in invertebrates (corals, shells, etc.) strong effervescence feature Silicates (SiO₄ ) tetrahedron geometry Polymerization combing tetrahedron together (by the oxygen atoms) Types of Silicates: 1. island silicate no polarization 2. chain silicates form chains/strings of silicates a. single chain or double chain 3. sheet silicates expanding on 2D surface; layered structure a. weak bonding; easy to peel off of one another 4. Framework silicates encountered very often The Rock Cycle rocks DIFFERENT THAN MINERALS! minerals make up rocks only 3 types of rocks: differentiated by how they form (explained in Rock Cycle) 1. Igneous Rocks formed by cooling of magma (liquid, molten rock) a. weathering breaking down of rock b. erosion carrying of weathered rock to another location c. depositio placement of eroded sediments 2. Sedimentary Rock formed by Lithification (building up of previously broken up rocks) 3. Metamorphic Rock formed by Metamorphism (forming by replacing old minerals with new ones by high temperatures and high pressure) a. increasing temp may cause forming of magma which restarts the cycle **NOTE: There can be shortcuts in the cycle! Metamorphic Rock can be broken down into sedimentary rock, igneous rock can become metamorphic rock by increasing temp/pressure, and sedimentary rock can be broken down again to become more sedimentary rock Lecture 4 gneous Rocks and Processes **Geology in the News: 21,000 homes in Flint, Michigan have lead contamination in drinking water Magma Why do we care? some activity can be hazardous, so we want to know more about it igneous rocks are good for construction, as they are durable and easy to use magma liquid rock (low ground) lava same as magma but at high ground How to create magma: 1. Temperature rocks melting point is about 500/600 degrees a. rocks made up of different minerals, each with their own melting points b. partial melting melting of rocks occurs gradually and at a range of temps. (because of different minerals present) 2. wet melting presence of water causes lower melting point which leads to faster melting 3. Decompression Melting less pressure = lower melting point magma composition gases (small amounts, dissolved) important in volcanic eruptions SiO₂ (Silicon) 3 main types of magma: 1. Basaltic Magma most common magma on earth a. generated in mantle b. dry magma less water than other magmas c. 50% SiO₂ (pretty low percentage) d. over 1100 degrees C (relatively hot for magma) e. can find this magma almost everywhere 2. Andesitic Magma a. found only in/around Pacific i. Andesite Line and Ring of Fire b. more understood after plate tectonic theory i. subduction causes this odd magma ii. Andesitic Magma forms at subduction zones (continental and oceanic plates colliding) c. 60% SiO₂ d. 1000 degrees C (relatively lower temp for magma) e. relatively dry magma 3. Rhyolitic Magma a. cooler temp: 700800 degree C b. 70% SiO₂ c. wet magma (higher water content) **STUDY TIP: Don’t try to memorize all 3 types and each detail; know HOW each one relates to each other (ex: higher SiO₂ content, low/wet magma, etc.) crystallization freezing of magma to form igneous rock partial freezing freezes at a range of temps due to multiple minerals equilibrium crystallization everything in magma is frozen into the rock; identical chemical composition from liquid⟶solid fractional crystallizatio something is removed during freezing process; different chemical compositions from liquid⟶solid as the minerals freeze, they form in a specific sequence Bowens Reaction Series diagram that shows how this works Discontinuous Branch goes from forming one kind of mineral to forming another (lefthand branch) Continuous Branch plagioclase is calcium or sodiumrich, based on temp (righthanded branch) **Know order of minerals on the branches, and know the lefthanded margin (temp bar) Igneous Rocks how to identify igneous rocks Texture how large mineral crystals are Composition what makes up to rock 2 broad types: 1. Plutonic (aka Intrusive) formed in low surface (not lava; only magma) pluton any large body of plutonic rock dikes and sills long/narrow dikes oriented vertically sills relatively parallel to ground Laccolith domeshaped frozen magma Batholith large plutons with no particular shape main characteristic: Large size Mt. Rushmore is carved in Batholith **Know how these look: common test Q is to identify pictures Textures Pegmatite (negmatite) many relatively large crystals Phaneritic smaller crystals but still visible Composition could identify each mineral individually color index color can tell you composition (works most of time) Felsic lighter color (white, pink, red) intermediate equal mix of light/dark; grayish color mafic dark colors (black/brown) ultramafic green/yellow minerals 2. Volcanic (aka Extrusive) formed above surface of earth use textures/composition to determine Texture: porphyritic some small some large crystals forms due to rapid freezing process of this type of rock Aphanitic can’t see many crystals without magnification glassy looks and feels like glassy example of how color index can fail you vesicular many holes and openings in the rock holes form because of lastminute gas bubbles popping while rock is freezing **Geology in the News : volcanic glass ‘egg’ found after Kilauea eruption last week (never seen before) Volcanoes the US does NOT have to worry about volcanoes Japan and Indonesia are the only countries with more volcanoes than the US Active US volcanoes Hawaii: 7 Alaska: 41 Other 48 states: 20 Case Study: Krakatoa Indonesia island volcano Aug. 23, 1883 200 million tons TNT (13,000x amount of Hiroshima atomic bond) air pressure waves circled the globe in 5 days (all the way to the English Channel) over 30,000 languages extinct as a result ⅔ of island destroyed; new volcano built since then Volcano Explosivity Index (VEI) measures intensity of volcano/eruption many smaller eruptions Types of eruptions : 1. explosive large explosion 2. nonexplosive steady lava flow Viscosity measures thickness/ability to flow (low=flows fluidly)(high=flows slowly) controlled by 2 things 1. Temperature increases in temp = lower viscosity 2. Silica content increases in Silica = higher viscosity controls gas content higher viscosity lets less gas to flow through it; this causes pressure build up and leads to explosive eruptions more gas retained = bigger explosion nonexplosive features: 1. Pahoehoe first stage of cooling soft look cooling on top but still hot and in motion underneath 2. Aa next stage of cooling lava looks more brittle, uneven, and broken there can still be some small bits of gas in them (vesicles) speed of flow: “faster” lava about 16km/hr (10mph) explosive features: more hazards beyond lava Lahar mudslide of volcano eruptions faster than lava flow, so more dangerous Pyroclasts solid objects being ejected divided by size Bombs : >64mm Lapill: 2mm64mm Ash: <2mm Very dangerous: can fall in high amounts can build up and weigh down roofs can be sucked up into engines can be inhaled and destroy lungs not something that has been burned up: just like bombs and lapilli, ash is made up of solids Pyroclastic Flow gas overflow that flows down sides of volcanoes not easy to escape from Types of Volcanoes: 1. Shield Volcano gentle slope, shield shape (hence the name) a. very common b. Basaltic magma (explains shape of volcano) 2. ephra (Cinder) Cone steeper slope smaller size more solid debris (pyroclasts) 3 Stratocones aka composite volcano, stratovolcano more explosive eruptions high viscosity steeper landscape; stereotypical shape Supervolcanic Eruptions large enough to change climate on global scale Tambora (1815) 100km^3 ejecta in Indonesia changed climate patterns over a year later in England, US, Ireland, etc caused drastically cooler temps Yellowstone Huckleberry Ridge 2 million years ago, 2500 km^3 ejecta covered almost half of the US not even the largest eruption in history Hot Spots typically where two plates meet The Hawaiin Problem Hawaii and all of its volcanoes are in the center of the Pacific Plate “Hot Spot” is where there is magma that is coming up from underneath Hawaiin Problem explained moving of the plate caused formation of new volcanoes which, as the plate continued, became dormant and able to live on GEOL 1010 Dr. Coulson TEST 2 STUDY GUIDE Highlight= Important Principle Highligh= Key Term Lecture 5: S edimentary Rocks and Processes Forming Sedimentary Rocks sedimentary rocks are the most common on on earth’s surface used in construction, in energy resources, where fossils are found Parent roc original rock/preexisting rock Formation 1. Weatherin breaking down rock a. physical weatheri physically breaking down rock i. ex: plant roots breaking up rock ii. frost wedgi water between cracks of rocks freezes in low temps and breaks apart rocks potholes can be a result of this b. chemical weatheri chemical reaction breaks down the rock i. more common in nature ii. ex: Feldspar + O + HCO₃ ➡Kaolinite + dissolved ions iii. ex: Saprolite formation 2. Erosio carrying of sediments (transport process) a. requires energy b. 4 ways of transportation i. water (very common) ii. gravity (rocks rolling down a hill) iii. wind (sand blowing at a beach) iv. glacier ice (less obvious, but still common) 3. Depositio depositing sediments in new place a. basi any place you can deposit sediment b. accommodation space volume of space for sediment to be deposited c. subsidenc sinking of land into a basin d. Layers (strata, beds) 4. Lithificatio getting sediments and compacting them into one rock a. cementation solidifying fusion of sediments by compacting the rocks together i. water gets pushed out and deposits wet minerals, which act as the cement to bind the rocks and minerals together Classification 3 main categories of sedimentary rocks 1. Detrital (aka clastic) sediment mainly physical weathering a. ‘how big are the sediments?’ b. sorting ‘how uniform is the sediment size’ (wellsorted, moderate, poorlysorted?) i. improves as time progresses c. rounding roundness of minerals within rock i. improves as time progresses 2. Chemical Sediment form via chemical reactions a. dissolution and reprecipitation b. saltwater evaporation c. usually comprised of one major mineral type i. ex: halite = rock salt, quartz=chert d. economically viable 3. Biogenic Sediments used to be parts of plants/animals a. ex: shells (large or microscopic), coral, etc b. ex: chalk, limestone, coal Mass Wasting (Landslides) important due to danger of occurrence angle of repose max angle where a slope is stable typically 35°, but always check! slope destabilization lack of moisture (only dry sediment leads to difficult in compactness) too much moisture lack of vegetation plant roots are good at holding things in place, so lack of them leads to lack of holding things in place excessive vegetation roots can also form natural pathways for water to run down, and plants are heavy and could fall/slide types of mass wasting (based on material, type of movement, and speed) ex: Rockslide rocks sliding down at a moderate speed creep slope is unstable, and rocks are sliding very slowly *NOTE: unstable slope does not automatically mean landslide* Causes of Mass wasting lightning, earthquakes, deforestation, etc. are all causes Risk Assessment Map assessment of an area that shows dangerous spots adjustments are constantly made: landslide patterns change constantly Prevention: Drainage Control decrease slope grades building codes retaining walls rock bolts COST: although all of these prevention measures could be costly, the amount of money in damage would cost much more Case Study: Thistle, UT 1983 slide cost $200 million in damage deemed preventable if $0.5 million had been spent on drainage system Lecture 6: Metamorphism and Structural Geology Why do we care? many minerals used for technology metamorphic rocks help discover history of an area very slow process (could take a million years to start) Temperature increase is needed for process Geothermal gradient how hot it gets and how fast beneath the earth at different depths average geo. gradient = 30°C/km typical range = 2060°C/km can still be higher or lower in special cases high gradient = hotter temp per km Metamorphism vs. Heat contact metamorphism rock coming into contact with hot magma ex: Plutons projectile driven by temp localized/small scale Pressure vs. Heat 1 bar = 1 atm (atmospheric pressure) Pressure gradient is about 300 bar/km confining pressure pressure on all sides of object, even distribution ex: swimming under water directed pressure (differentia) pressure coming from mostly one direction most metamorphic rocks form at 1030 km (midlower crust) = 6.25 18.75 miles How metamorphic rocks get to surface as layers get pushed up through plate movements/faults, they soon get weathered/ eroded and make it to the surface regional metamorphism opposite of contact metamorphism at convergent plate boundaries pressure driven large scale fault metamorphism faults occur and form metamorphic rocks small scale, pressure driven Metamorphism vs. Fluid metasomatism hot groundwater interacts with rock water carries things in it and could deposit some things into rocks forms ores seafloor metamorphism close to MidOcean Ridge like metasomatism, but in specific area (MOR) Metamorphic Rocks and Environments Parent rock is the key to figuring out which metamorphic rock forms Metamorphic grade how much did the rock change lowgrade = low change, high grade= high change not very specific; there is a lot of variation in each field index minerals gives range of temps/pressures for rocks smaller range the better metamorphic facies group of index minerals that form under similar conditions ex: blueschist facies include minerals epidote, lawsonite, and glaucophane major facies : a. zeolite lowest temp/pressure b. Hornfels high temp increase but low pressure increase c. Blueschist high pressure but low temp increase (subduction zones) low temp due to coldness of oceanic plate submerging d. Eclogite very high pressure e. Granulite starting to melt again *NOTE: diogenesis = before facies start (NOT metamorphic rock)* Length of Metamorphism large range Prograde portion of history when rock had increase in temp/pressure retrograde temp/pressure of rock began decreasing changes within minerals Types of Metamorphic rocks 1. Foliated Metamorphic rocks sheets/layered appearance a. ex: slate, schist, gneiss (gneiss has felsic/mafic separation) i. not obvious: can come from different parent rocks, crystals can cover up sheets, etc. 2. NonFoliated Rocks opposite of Foliated a. difference from foliated is from type of pressure (confining is nonfoliated, directed is foliated) i. ex: Hornfels, Quartzite, Marble **know examples of Hornfels, blueschist, nonfoliated, and foliated** **Geology in the News: ‘Sudden’ volcanic eruptions found to trigger from gas bubbles in magma Structural Geology/Tectonic Forces Structural geology study of how rocks are deformed after they are formed Topographic features on surface of earth (on maps); landscape Tectonic forces (how rocks are formed) 1. Tensional stretching object (pulling in different directions) a. ex: divergent boundaries 2. Compressional squeezing in form multiple sides a. ex: convergent boundaries 3. Shearing sliding in 2 different directions a. ex: transform boundaries Responses: 1. Brittle strong/ resistant rocks shatter into random pieces 2. Ductile rock can bend and is malleable Responses vary based on: rock type temp/pressure speed of deformation quicker applying of deformation means more likely to have brittle reaction, while slower = ductile Types of Structures 1. Folds ductile response to compressional force happens on low/high scales typically happens in groups limb sections of fold with pretty straight portions hinge where rocks pivot/turn into curvy edges in a fold classifying folds (3) 1. shape crosssectional view (aka ‘roadcut’, ‘cliffface’) a. antiform rainbow shape b. synform ushape c. overturned : i. overturned antiform ii. overturned synform iii. overturned overturned antiform overturned overturned synform 2. Age of layers relative to each other acticline oldest layers is in between layers (center) syncline oldest layer on outside part of fold *NOTE : sometimes tectonic forces can cause an entire stack of layers to be turned upside down 3. Geometry how force was applied must be seen from above and second crosssectional views horizontal force applied from two sides above view horizontal stripes side view folds/layers plunging force applied from two sides and force applied to cause tipping up or down more common in world visible in above view, NOT in crosssectional 2. Joints brittle response and no other forces lots of cracks (called ‘joints’) most common geological structure 3. Faults brittle response with movement along cracks motion is relative varies in sizes (1 inch to 1000s of miles) classified by slip direction 1. DipSlip faults vertical motion inclined fault plane: one side clearly moves upward foot wall plane that has acute angle hanging wall plane that has obtuse angle Normal dipslip hanging moved down and foot moved up reverse dipslip hanging moved up and foot moved down Thrust fault handing goes up and foot goes down only difference between thrust and reverse: thrust is almost horizontal important in subduction zones **STUDY TIP: Don’t just memorize the pictures! You MUST identify hanging vs. foot walls to determine if it is normal or reverse 2. StrikeSlip fault horizontal movement no hanging/foot faults leftlater relative to each other, each block has moved to the left rightlatera relative to each other, each block has moved to the right **make sure that you know the orientation (birdseye view, crosssectional, etc)** **notice that different fault types form based on forces applied* Lecture 7: Earthquakes **Geology in the News: 6.4 magnitude earthquake in Taiwan caused the cancellation of Chinese New Year Why do we care? Can cause a lot of damage and loss of lives we can try to prevent What is an earthquake? when two plates move past each other, energy builds up Time 1: Stress<Friction Plates Stationary Time 2: Stress~Friction Elastic Deformation Time 3: Stress>Friction Plates move energy builds and process repeats itself small quakes are very common 1 million magnitude 2 quakes per year category 9 energy = annual energy used in USA Point of Movement focus where movement originates (many are 220 km deep) epicenter point directly above the focus on the surface Movements before and after foreshocks small movements prior to the earthquake in an attempt to relieve energy aftershocks small but bigger than foreshocks not all energy has been released in main quake Seismic Waves waves moving away from focus (3 types) 1. P (Primary) compressional motion through earth’s surface a. alternating compression/expansion b. 20 times faster than speed of sound c. can move through solid/liquid 2. S (Shear) a. added vertical range of motion b. cannot move through liquids c. half the speed of Pwaves d. forms shadow zone through earth 3. L (Long, Surface) move along the surface a. slowest b. moves in vertical/horizontal range Measurement and Detection seismometer aka seismograph (outdated) Myths: 1. You only need one machine a. you need 3: one for each axis 2. Old fashioned a. data is almost all digital today 3. Swinging needles for amplitude a. needle is on a pendulum and machine shakes (outdated) data xaxis travel time in minutes yaxis amplitude for all axes of movements p waves come first, then s, then a long period of L key to finding focus is different that different waves travel at different speeds distance = difference between p and s times draw circles with radius of this distance to triangulate focus How big was the earthquake? 1. Mercalli Index lower Roman numerals/little damage a. based on damage to environment b. not commonly used with scientists c. for the same quake, the index will be different per location 2. Richter Scale measures amount of shaking at various seismometer stations a. designed by Charles Richter in 1935 b. logarithmic scale i. ex: a magnitude 3 is 10x a magnitude 2 c. moving between numbers is a big deal 3. Movement magnitude measures amount of slip on the fault a. easiest to calculate from field measurements/seismometer data b. scientists prefer Earthquake Locations much deeper foci occur along subduction zones Blueschist facies has very brittle behavior, creating huge earthquakes in these zones Risk assessment maps made to indicate change of quakes Predicting quakes is nearly impossible Damage control land use policies ex: California Law (1972) ‘do not build on faults’ building codes Not building skyscrapers near fault zones myth: Earth cracks open and swallows things These are actually the best locations to build Site selection: building on strong foundation like bedrock is the best Gravels, sands and muds are worst choices liquificatio liquid inside unstable foundations lead to sinking and tipping buildings Lecture 8: Geologic Time **Geology in the News: Tin cans collapsed between walls from Taiwan earthquake Why do we care? we want to know when certain things occurred 2 approaches 1. Relative sequence of events; qualitative a. not hard numbers; more like ‘this before this but after this’ 2. Absolute not comparative; gives exact numbers a. can be very expensive to pay for Research, while relative is nearly free b. can need highly qualified researchers/lab equipment c. not always necessary Relative Dating Fossils any evidence of past life on earth (skeleton, shells, footprints, etc) only really found in sedimentary rocks led tostratigraphy study of strata people wanted to know about fossils and the rocks they were found in unconformities strata is rarely in continuous line (gaps/breaks in strata timeline) why are there gaps? 1. run out of sediments 2. run out of accommodation space (basin) 3. start eroding sediment faster than deposition types of unconformities: classified by strata above/below gap 1. disconformity different kinds on top and bottom (both sedimentary 2. nonconformity sedimentary on one side and not sedimentary on other 3. angular rocks below are tilted at angle while on top is horizontal a. complicated formation problems with unconformities identification can be difficult to classify duration how much time was lost? Stratigraphic Principles 1. principle of original horizontally strata is originally horizontal 2. principle of superposition oldest layer on bottom, youngest on top 3. principle of crosscutting two things intersect/cut through each other a. whatever did the cutting is the youngest formation 4. principle of faunal succession fossils found in specific order a. older fossils are on bottom, younger on top b. correlation comparing strata in two areas by age i. not all fossils are good for correlation ii. want to identify short spans of time iii. index fossils aka guide fossils good for correlation 1. very numerous 2. widespread 3. went extinct quickly 4. easy to identify iv. other correlation tools 1. lithostratigraphy correlate layers by rock type a. good for generalizing, but has a lot of exceptions and errors 2. sequence stratigraphy correlation based on patterns of unconformities a. works well in coastal areas 3. chemostratigraphy correlation based on chemical properties a. ex: Iridium anomaly at CretaceousTertiary 4. magnetostratigraphy looks at magnetic current Geologic time scale originally built via stratigraphy fossils were key to defining boundaries eons largest units on scale (only 34 recognized) 1. Hadean when earth formed a. 4.54 Ga b. almost no material left on earth to study this 2. Archean 42.5 Ga a. when different parts of continent formed b. atmosphere had no oxygen 3. Proterozoic oxygen begins forming a. 2 Ga 4. Phanerozoic most fossils found here a. 3 eras i. Paleozoic (550 Ma 200 Ma) vertebrates 1. Cambrian Explosion large diversity change (much more) ii. Mesozoic reptiles 1. 200 Ma 65 Ma iii. Cenozoic mammals 1. 65 Ma now **Geology in the News: new info on why earthquakes occur deep in subduction zones water released from a mineral called lawsonite enables to fault to move despite high pressure Absolute Ages Quantitative Approach 1. NonRadiometric Approach a. varves sediment deposit alternating dark/light layers in lakes i. need top layer to freeze to become a varve ii. each band represents different seasons dark colors = winter light colors = spring/summer 1 light band + 1 dark band = 1 year iii. used to find/measure times and to discover climates iv. only gives climate data for specific location v. can’t have mixing layers (caused by living organisms) b. dendrochronology counting rings in a tree i. used on local scale ii. can only go so far back in time with one tree iii. can use overlapping to get further back in time iv. must know what kind of tree some trees don’t form annual rings v. rings may not show due to climate issues 2. Radiometric use of radiometric data for dating specimens isotopes atoms of same element but with different numbers of neutrons labeled by atomic weight (protons+neutrons) some isotopes are unstable Radioactive Decay emitting particles of energy to become stable Radiation the given off energy parent atom starting atom daughter atom atom given off decay series/chain multiple radioactive daughters decay series ends with a stable daughter atom how to measure radioactive decay: misconception watching atoms ‘pop’ no way to know when an atom will decay ex: bag of popcorn popping halflif time it takes half of parent atom to decay decay/halflife is NOT linear; it is exponential (hence ‘exponential decay’) daughter and parent atoms are equal, and add up to original amount of parent atoms every radioactive isotope has its own halflife
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