Final Exam Review questions - 2014.doc

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Earth Science
Lindsay Schoenbohm

LECTURE 13: METAMORPHIC ROCKS ‐*Describe the importance of each of the five factors, which control the features of metamorphic rocks: pressure, temperature, deformation, composition and time. A: Understand the rock cycle. Metamorphic rocks depend on: • Pressure  >5km deep within earthquake • Temperature (approx. 280 to 850) below the needed temp the rocks aren’t hot enough to change, aboeeded temp – melts and becomes igneous rock • Deformation  compression or shear • Composition  dictates what you start and finish w/ • time ‐Explain the difference between recrystalization (mineral and elements stay the same but minerals grow bigger), phase change (elements stay the same but are rearranged to form new minerals) and neocrystalization (elements rearrange to form new minerals). o Recystalization: same mineral but different size and shape o You start off with mineral A and end off with mineral A (same mineral but different appearance) o *Not changing the mineral, only the size o Solid state = no melting  Atoms migrating one at a time, result to change in shape over time o Neocrystalization: changing combination entirely = new minerals all around o Any atom can combine with any atom (new atom) o New composition and new minerals ‐Under pressure, atoms will want to rotate to try to get the least amount of pressure Perpendicular to direction they’re being squeezed Explain why during metamorphism tabular (flat) minerals are reoriented or grow perpendicular to the stress. A: During metamorphism tabular (flat) minerals are reoriented or grow perpendicular to stress because ‐Define protolith. A: Protolith is the rock before metamorphism takes place ‐*Define the important compositional characteristics and give an example of a protolith and a metamorphic rock for each category of composition: aluminous, quartzo-feldspathic, calcareous and mafic. A: o Aluminous: rich in Al (aluminum) o Quartzo-feldspathic: rich in quartz and feldspar o Calcareous: rich in calcite o Mafic: rich in mafic minerals ‐*Know the protolith for a number of common metamorphic rocks, including marble, quartzite, metaconglomerate, slate, phyllite, schist and gneiss. A: Protolith for metamorphic rocks: o Marble – limestone (calcareous) o Quartzite – sandstone (quartzo-feldspathic) o Metaconglomerate – conglomerate (quartzo-feldspathic) o Slate – crystallizes and grows new minerals o Phyllite – micas are small, sheen have a mirror like reflection o Schist – visible layers of muscovite + biotite o Gneiss – common metamorphic rock, micas crystalize new minerals + strong foliation ‐Describe the appearance of migmatite and explain why it straddles the boundary between metamorphic and igneous rocks. A: • Migmatite : half melted rock (half metamorphic and half magma) • Mudstone (aluminous) composed of siligen and oxygen and aluminum • Metamorphose it by neocrystalization and creates new mineral micas (muscovite and biotite) • When apply more heat and pressure making it more visible through growth (see schist) • Increase temperature and pressure more, produce rock gneiss (micas recrystallize to new minerals) – strong foliation (layer) • Increase more heat and pressure you melt the rock and is not considered metamorphic rock anymore (transition from metamorphic rock to igneous is migmatite) ‐*Name and describe the rocks, in terms of foliation and minerals composition, which form from increasing metamorphism of mudstone/shale (slate, phyllite, schist, gneiss, migmatite). A: ‐Name and describe three types of metamorphism (mountain belt, subduction zone, contact) and compare them in terms of heat and pressure conditions. A: Three types of metamorphism and comparison in terms of heat and pressure conditions: 1. Mountain belt a. Increasing temperature and pressure from edges to center b. Roots of mountains increasing pressure and temperature c. Interior have increasing grains d. Center is hot and starts to melt e. Produces metamorphic rocks and nested zones from lowest to highest grades 2. Subduction zone a. Increasing pressure, lower temp b. Where one oceanic plate dives underneath the other c. Plate diving down is cold (contact with seawater or surface of earth for long time) d. Carrying cold temperature down into earth’s interior (high pressure, low temperature) e. Get Blueschist 3. Contact a. b. High temperature, low pressures c. Mineralization is associated with contact/thermal metamorphism d. Produces a rock called Hornfels which varies widely depending on the protolithic composition e. Mineralization is common ‐Name a metamorphic rock commonly found in subduction zone settings. A: Metamorphic rock commonly found in subduction zone settings is Blueschist *Types of Metamorphism ‐*Name the metamorphic rock associated with contact/thermal metamorphism. A: Metamorphic rock associated with contact/thermal metamorphism is hornfels ‐Describe the process of dynamic metamorphism and name the metamorphic rock that it produces. A: Process of dynamic metamorphism is pulverizing (reduce to fine particles) rocks and producing stretched out looking fabric which the metamorphic rock produces mylonite. A consequence of shearing is rocks move past each other and shear things out. ‐*Sketch foliation and lineation and describe the conditions under which each form. A: The conditions under which each form LECTURE 14: DEFORMATION ‐Describe the difference between brittle and ductile deformation in terms of the temperatures and pressures at which they occur, and the deformation rate and compositions associated with each. A: Difference between brittle and ductile deformation in terms of the temperature and pressure at which they occur and deformation rate and compositions associated with each: o Brittle Deformation: easy to break o Temperature = low o Pressure = low o Time (deformation rate) = fast o Composition = strong o Ductile Deformation: deform (change shape) but won’t break o Temperature = high o Pressure = high o Time (deformation rate) = slow o Composition = weak ‐Name which features (fractures, faults, folds, foliation) are associated most with brittle deformation, which with ductile deformation, and which are associated with both. A: Associated with: Most brittle deformation: • Fractures (joints) • Faults • Folds Ductile deformation: • Faults • Folds • Foliation (cleavage) Both: • Faults • Folds – layers of different rocks ‐Explain the difference between a fault and a fracture. A: Faults are • Fracture like • Perceptible movement across the plain Fractures are • Folded rocks that are squeezed together and deformed not shattered • Open up fractures to allow fluids to move into it and fill up fractures • Fold is more or less intact ‐Recognize thrust faults from drawings or field photos, explain the associated features (repeated section, older on younger rocks), and identify the type of associated deformation (compression) and plate boundary type (convergent). A: • Thrust faults are something that is thrusted up the back of the lower part rocks • Marker bed and dip slip fault is movement o Shortening, compression o Older rocks on top of younger rocks – repeated section • Compression: when you squeeze body of rock and it becomes shorter o Occurs at convergent plate boundaries o Strain: shortening, thickening, contraction ‐Recognize normal faults from drawings or field photos, explain the associated features (missing section, younger on older rocks), and identify the type of associated deformation (tension, lengthening) and plate boundary type (divergent). A: • Normal faults are something that dip-slip faults (move straight up or down) o Extension, lengthening, tension o Younger rocks on older rocks o Missing section • Tension o Occurs at divergent plate boundaries o Strain: extension, lengthening, thinning, stretching, elongation ‐Recognize strike-slip faults from drawings or field photos and identify the type of associated deformation (shearing) and plate boundary type (transform). A: • Strike-slip faults are movements sliding left or right o Shearing • Shear o Occurs at transform plate boundaries o Strain: shear ‐Draw, recognize and describe anticlinal and synclinal folds. A: Anticline • Shaped like an anthill • Youngest rocks on top before folds • Oldest rock in the core Syncline • Shaped like a sink ‐Describe the differences in terms of geometry and deformation mechanism between flexural slip and passive flow folds and relate each to brittle or ductile deformation. A: Flexural-slip folds are brittle because they don’t deform individual beds • Don’t make any thicker or thinner layers which cause them to slip past each other • Beds inside gets squeezed out (hand in hand example) • Stay uniform in thickness Passive-flow folds are ductile because the layer of thickness changes • Get thin in the limps and thicker in hinges of the fold • Deformed in flow (some places are faster and others slower) • More ductile = gluey and softer ‐Explain how the alignment of platy/flat minerals forms foliation. • Ductile results to compression • Metamorphism forms a cleavage which is how the rocks break ‐Know the names applied to different types of foliation in slate, phyllite, schist and gneiss. - bedding - cleavage - foliation - ‐Given a map of folds, draw on the axial trace (including an arrow indicating which way the fold is plunging down) and interpret whether folds are anticlines or synclines. ‐*Know and apply the formula for calculating the percent lengthening in a faulted region. LECTURE 15: MOUNTAIN BUILDING ‐Describe the features that form at divergent plate boundaries and give two real world examples of different types of such boundaries. A: Features that form at divergent plate boundaries are • Tectonic movements cause mountains • Divergent continental-continental crust stretch out • Upper crust is brittle (break and form faults) • Faults form in tilted blocks, almost like dominoes fall over • Planks (edges of rift) get high mountains • End up with lots of small mountain ranges spread out and lined up with each other Examples: 1. Easy African Rift a. Part of Africa slowly ripping apart b. Keeps going and will rip continent and create new oceanic spreading ridge (crust) c. Edges have really large mountain ranges 2. Basin and Range province a. Extension divergent boundaries b. Mountain ranges bound by normal faults c. Sediment accumulates d. Stretch landscape and mountain ranges stretch perpendicular to direction it moves ‐Explain the idea of terrane accretion (*what is accreting to what?). A: Terrane Accretion: when exotic material is added to edge of continent (dock was one piece but split in transform boundary) • Exotic terrane: little islands out in ocean (ocean subduct under continent) • Continental crust doesn’t like to subduct so when terrane slides into subduction zone it’ll cause a clog since it’s too buoyant ‐Draw the basic anatomy of a mountain range, with metamorphic rock in the core, fold-thrust belts on the edges and undeformed rock on either side. A: • Continental collision: when continent subduct under another continent • Suture: original boundary between tectonic plate before collision ‐Give two real world examples of fold-thrust belts and *describe their basic characteristics. • Analogy: snowplows push snow in front, grows in the wedge of snow in same geometry • 2 real world examples of fold-thrust belts: o The Appalachians o Canadian Rockies ‐Describe the criteria for identifying continental plateaus and name the three largest on Earth today. A: Identifying continental plateaus: after colliding two continents and get giant mountain ranges • Significant aerial extent • High elevation (3000-5000+m) • Low relief • Thick crust (50-70km) 3 largest on Earth today: 1. Collision of India with Asia a. India trying to subduct at continental crust (very difficult to do) b. Major collision c. Not going far but shows lower part of plate peeling off and sinking away into the mantle 2. Tibet and the Indian Monsoon a. During summer Tibet is high region (due to hot air rising) and acts as reverse plunger b. Air is sucked in on the side c. Adjacent region is Indian monsoon containing moist air d. Runs into the Himalayas and tries to make it over mountain range (water it carries doesn’t reach other and it starts to cool down and comes out of the range e. Cooling rings air out of water and it starts to rain 3. Mount Everest a. Mountain topography b. Mountain ranges spread out through the Himalayas ‐Describe the basic geography/geology/history of the Tibetan plateau (which plates are colliding? Where are the Himalayan Mountains? How high is the Tibetan Plateau?) ‐Explain the relationship between the monsoon and the Tibetan Plateau. During summer months Tibet is a high region that gets heated up from the sun and air rises. And acts as a reverse plunger. As it rises up something has to fill the void thus air comes in to fill the gap ‐Explain the concept of Isostacy and how it explains why regions with thicker crust have higher elevation. A: Concept of Isostacy and why regions with thicker crust have higher elevation • High mountains = thick crust • Isostacy: balance point in material of floating liquid (adjust height of stuff above it that’s floating) o I.e. ice burg because tall ice burgs sticking up means it has deep root to support it • Normal continental crust hardly sticks above sea level • Oceanic crust which is thicker is below sea level • Something of lower density and lower thickness will float higher ‐Define craton and platform and know their approximate location in North America. A: craton: old and stable part of the continental lithosphere Platform: continental area covered by relatively flat or gently tilted mainly sedimentary strata which overlie a basement of consolidated igneous or metamorphic rocks of an earlier deformation LECTURE 16: EARTHQUAKES ‐Define the epicenter and hypocenter of an earthquake. A: Epicenter earthquake is where you feel location of the earthquake. Hypocenter is where the actual location of the earthquake happens. ‐Describe the relationship between plate tectonics and Earthquakes. Where do most occur with respect to plate boundaries? Where are they shallow? Where are they deep? Where do the biggest earthquakes occur? A: • Relationship between plate tectonics and Earthquakes is o Vibration produced by rapid release of energy caused by breaking rocks o Caused by movement along a fault which is displacement of rocks in interior (putting rocks under strain with little elasticity and bends too far = stick breaks) • Most occur with respect to plate boundaries o Most earthquakes happen on faults • *Where they are shallow • *Where they are deep • Where biggest earthquakes occur o Biggest earthquakes happen at convergent boundaries ‐*Compare and contrast P, S, L and R waves. Be able to recognize a drawing of the type of motion associated with each. Know which travel fastest and which have the largest amplitude at the surface. A: P-waves: pushing motion in same direction wave is travelling S-waves: “doing the wave” motion perpendicular direction of travel L-waves: most damaging in earthquake because they’re very strong R-waves: only matter on surface of earth, same as ocean waves because they die out when you go deeper, but - don’t crest and break like they do at the beach ‐Explain how a seismograph works to record an earthquake. A: Seismograph works to record an earthquake by putting it all together. How to measure: mostly buried within the earth. Frame bolted to earth therefore when the earth moves = the frame moves. • Weight on spring, box moves up and down and the weight remain in the same place • Fixed reference frames • First wave to arrive is P wave, then S wave, then surface waves (small-big) • Its all done electronically, machine buried in earth and has the highest altitude to the earth – so if earthquake happensit will feel it • So weight is suspended on a spring and it moves up and down  if earthquake happens the weight doesn’t move ‐Recognize the arrival of P, S surface and aftershocks on a seismogram and explain why their arrival is staggered. ‐Explain how P and S arrival times can be used to calculate the epicenter of an earthquake using the P-S interval from three seismic stations. p waves trael faster vs s waves travel later the farther away from the epicenter the distance between the p and s waves increase ‐Describe and name the advantages and disadvantages of the Mercalli, Richter and Moment Magnitude scales. Mercalli intensity scale : based on what ppl feel on the surface of the earth (qualitiative)  varies on how far you are from the epicenter Richter magnitude: looks at how large s waves are when they arrive Problem: tell us epicenter rather than hypocenter Moment magnitude: complicated, used today, not a linear scale ‐Explain how a tsunami forms. • Part of plate boundary “sticks” • Deformation in upper plate • Major earthquake release stress and displace sea water • Bulge of water collapses and spreads outwards ‐Compare a tsunami to a normal ocean wave in terms of wave speed, period and length. A: Ocean waves • speed : 8 – 100 kph • wave period:5-20 seconds • wave length: 100 – 200 m Tsunami wave • speed: 800-1000kph • wave period: 10 minutes – 2 hours • wave length: 100-500 km ‐Describe our ability to make long and short-term earthquake predictions. A: Long-term earthquake predictions • Identify hazardous areas and probability of major quake Short-term earthquake predictions • Based on precursor phenomena but mostly unsuccessful o Micro earthquakes that happen before major one o Folk tales: animals acting weird o Tsunamis give you more time (10-15 minutes heads up) ‐*Draw a typical earthquake cycle with time on the x-axis and stress on the y-axis. LECTURE 17: GEOLOGIC TIME ‐Explain the difference between relative and absolute time. A: Relative Dating is human history of events • Putting it in order – useful to see lineages • No actual dates • Most valuable information is putting things in order • Not evenly spaced, clustered Absolute Chronology • Precise dating • More difficult then relative and more expensive • Hasn’t been around for long, developed more recently ‐*Determine the relative geologic history of a region from a diagram showing the different rocks units. A: Relative chronology • First approach: most recent event and peel they’re way back • Second approach: start from the beginning and see what’s next event o Geologic Scenario: Figure out what is the story? o Most recent thing that happened is erosion – geomorphic process (“v” shape) o Next most recent thing that happened is Basalt I – cuts across everything else o Next most recent event is Basalt II (sill) – see pieces (chunks) of conglomerate  Shoot in along bedding plane which rips off rocks above and below o Next most recent event is conglomerate  Looking at youngest sedimentary layer o Next most recent event is Breccia – peeling off layers  Angular difference – some kind of erosion and period of time where no rocks are being deposited  Missing time – aka unconformity o Next most recent event is Erosion and tilting o Gneiss  Next is Limestone  Next is Shale  Next is sandstone • Down to basis of igneous and metamorphic rocks ‐Explain and apply the principles of (1) cross cutting relationships; (2) inclusions/xenoliths; (3) superposition; (4) unconformities; and (5) original horizontality. A: (1) Cross Cutting Relationships • Any feature that cuts across other rocks or features must be younger • Whatever does the cutting is younger, whatever cuts is older • Superposition (2) Inclusion/xenoliths • Any piece of rock (inclusion or xenolith) included within another rock must be older than the rock in which it’s incorporated • Example of still ripping off pieces above and below it • Whatever contains pieces is younger and whatever generates pieces is older (3) Superposition • The oldest layer is at the bottom and the youngest layer is at the top • Stuff on the bottom is oldest • Pour stuff on top = younger (4) Unconformities • An unconformity is a rock interface which represents a GAP in the geologic record, like pages missing from a book • Unconformity represents huge amount of earth history missing • About 900mya of earth’s history missing (time missing): after this time rocks just started depositing (5) Original horizontally • Sedimentary layers (and lava flow) are USUALLY originally laid down horizontally • If they’re not now horizontal they have been deformed • Sedimentary rocks are deposited more or less horizontally – minor variations • Deformational event causes tilting ‐*Describe how fossils can be used to assign relative age and to correlate rock records around the world. ‐*Describe how the amount of parent and daughter atoms changes with each half-life. Draw or interpret a diagram showing this change. Radiometric Dating ‐*Explain how the half-life relates to what kind of materials is dated (e.g. age of earth from U-238, archeology from C-14). A: How do we know the age of rocks/crystals Radioactive element • Decay over time – radiation emitted, decreased in mass over time • Becomes daughter product • Way we measure reaction: half life – how long it takes to decay to led • Random – can say statistically half of parent decay daughter… ‐*Explain why radiometric dating works best for igneous rocks (cooling through the blocking temperature). A: Radiometric dating works best for igneous rocks. But metamorphic rocks can work too, depending on the minerals and the temperatures. Radiometric Dating Works best for Igneous Rocks But metamorphic rocks can work too, depending on the minerals and the temperatures… ‐*Explain how dates of igneous rocks can be used to bracket the age of sedimentary rocks. ‐*Memorize the ages of the major boundaries of the geologic timescale, between the Precambrian, Paleozoic, Mesozoic and Cenozoic times. Radiometric Dating LECTURE 18: EARTH HISTORY ‐Know when the Hadean Eon occurred and describe the structure and the conditions on the surface of the earth at that time. A: The Hadean Eon occurred 4.6 billion years ago. The structure and conditions of the surface of the earth during that time was o Dense and toxic atmosphere o Acidic atmosphere (probably not suitable for many life forms during this time) o Probably had small areas of surface water shown o Too early on Earth o Process of raining, then water settles, evaporates into the air and cycle begins again o After the collision the ocean was filled with magma aka magma ocean o The earth was much closer to the moon therefore the moon appeared to look bigger o Increase in tidal energy o There were comets and asteroids crashing into earth Hadean Eon 4600-4000ya • Dense, toxic atmosphere • Surface water? • Comets and Asteroids • Magma Ocean • Closer moon • Atmosphere could be acidic • Could be some rain and water that evaporated before it settle out into oceans • No continental crust ‐*Know when the Archean Eon occurred and describe major events that occurred in this time, including the beginning of formation of continental crust and the development of single-celled life and stromatolites. A: The Archean Eon occurred 3.9 billion years ago. o Where things settled down a bit and was a transitional period o Had the surface of water on Earth and the beginnings of life Beginning of Formation of continental crust: o Melting of mantle underneath Earth = oceanic crust o Over time built up what looks like continental crust – formed core of continent *Development of single-celled life and stromatolites: o Probably liquid water (with dissolved carbon dioxide) on surface o Atmosphere a lot more hospitable (still didn’t contain oxygen) o Stromatalites – little bacterial organism (fungus like) – clear evidence of life o Stromatalites are cyanobacteria mats ~ liquid water and dissolved CO 2 Archean Eon 4000-2500ya • Beginning of life • Beginning of formation of continental crust; 80% of continental crust- growing • Continental crust bits- accumulate and cool down: core • Oceanic crust looked different- thicker and more buoyant • Subduction, formation of volcanic chain of island, former arc (ripped apart- new volcanic rock that fills space), become more felsic, partial melting • Liquid water and dissolved CO2 • Ocean absorb CO2 form atmosphere • Stromatalites- cyanobacteria mats o Life- but not complex Formation of Continental Crust **Describe the composition and structure of greenstone belts, and the plate tectonics which formed them** ‐*Describe the composition and structure of greenstone belts, and the plate tectonics, which formed them. The composition and structure of greenstone belts is: Plate tectonics that formed them: ‐Know when the Proterozoic Eon occurred. A: The Proterozoic Eon occurred 2,500 million years ago. When things started to look like they do presently. • Oxygenation of the atmosphere driven by respiration of cyanobacteria: • Oxygen- very low level to absent • Cyanobacteria: when evolved was a waste product- produce oxygen • Eventually, rate of reaction went down and production of oxygen increased • Banded Iron Formation (BIF) o Bands of silver and red o Silver- Hematite, red- chert -ironic rich- INC O2 o When oxygen low, lots of free iron floating in ocean o When O2 available, start to react, form oxygen o Seasonal ‐Explain and sketch the six steps of the Wilson Cycle. • A: Rift continent apart, creates oceanic crust, oceanic crust gets old, it becomes dense, so it subducts (not stable), and recycle back down to the mantle, forms little chain of volcanoes, the subduction causes oceanic crust to be destroyed, continental crusts become closer together. o Wilson cycle: building continents and then breaking them apart (natural consequence of plate tectonics) o Pulling apart continent (stretch it and create divergent then snap it creating convergent) o Proceeds for period of time o Eventually oceanic crust gets old o Becomes so dense it wants to subduct o One point – (compress so ocean it much larger) it will subduct and form chain of islands o Brings 2 continental pieces close again starting all over again ‐Name and know the order in which four major supercontinents formed. A: 1. Pangea formed 300 million years ago 2. Rodinia formed 1300 million years ago 3. Nena formed 1800 million years ago 4. Arctica formed 2500 million years ago ‐Recognize the parts of North America that correspond to the formation of the supercontinents Arctica, Nena, Rodinia and Pangea and the breakup of Pangea. A: o The original North American continent Arctica, which started to form about 2.5 billion years ago from smaller continents was completed about 1.9 billion years ago when old Archean cratons were welded together by Trans-Hudson Orogen and others o Added to the North American continent during the formation of Nena about 1.8 billion years ago after the Penokean Orogeny o Added during the formation of Rodinia about 1.3 billion years ago during Grenville Orogeny o Added during the formation of Pangea about 600 million – 300 million years ago o Added after Pangea broke up about 250 million years ago ‐Understand the timing and cause of the increase in oxygen in the atmosphere during the Proterozoic. A: The timing and cause of the increase in oxygen in the atmosphere during the Proterozoic is: o Proterozoic: Oxygenation of the atmosphere o Driven by the respiration of cyanobacteria o Low levels of oxygen or absence o Cyanobacteria: single-celled organisms as waste product produced oxygen (small trace) o As reactions happened from oxygen – over time (unsteady way) level of oxygen increased o Overall levels are extremely low – start to climb up near the end of Proterozoic o Created banded iron formation Proterozoic: The Snowball Earth • Runaway Icehouse Effect • Up to 4 major snowball events between 750 and 580 Ma • Widespread Glaciation (glacial deposits found in all continents) • Sea ice 1km all over • Oceans didn't freeze completely ‐Explain the formation of “banded iron formation” and why it is found only in Proterozoic rocks. A: Formation of “banded iron formation” is: • Silvery colored: streak left blood red streak behind (hematite) • Alternating band from the oxygen in atmosphere • When oxygen level low: lots of free ions in the ocean • When oxygen available: started to react and formed hematite • Once that formed: there was solids (falling/settle down into the ocean) Prologue: Before the Snowball (About 770 Ma) • Breakup of supercontinent Rodinia = small continents near the equator. • Formerly landlocked areas are closer to ocean moisture = more erosion. • Erosion reduces levels of CO2, a natural green house gas. • Global temperatures fall, sea ice forms. • Sea ice reflects incoming heat energy from the sun, temps fall even more => RUNAWAY COOLING • Ice bergs • Glaciations move, picks up rocks and goes to edge of ocean and breaks into ice bergs • As ice berg melting, all debris and melts get dropped out • Happened at breakup of Rodinia Remove CO2- falling temperature- form more glaciers and sea ice, sea ice reflect heat ‐Describe the evidence for global glaciation in the late Proterozoic. A: Runaway Icehouse Effect: Up to 4 major snowball events between 750 – 580 million years ago • Late Proterozoic where earth completely froze over (all ocean covered in sea ice) • Ocean didn’t freeze completely • Giant snowball • Runaway icehouse: up to four events ‐*Explain how the hypothesized cause of the snowball earth, including CO2 depletion by weathering and reflection of incoming solar energy from growing ice during the runaway cooling phase, and CO2 increase from volcanic emissions and the absorption of solar energy in emerging seawater during the runaway greenhouse phase. A: Proterozoic: The Snowball Earth ~ 750 – 580 million years ago widespread glaciation o Glacial deposits found on all continents • Blue regions show regions for evidence of major glaciations • Continents in different positions then today • Still distribution of ice all over the globe • Ice sheets at equator ‐*Describe the Phanerozoic (Paleozoic, Mesozoic and Cenozoic) evolution of North America in terms of the east coast (from passive margin to subduction and accretion to continental collision to rifting and back to passive margin) and the west coast (passive margin to subduction and accretion). A: Early Cambrian (~510 million years ago) • What North America would look like during Paleozoic • No plate boundary just shallow sea (left side) • Passive margins, warm and shallow seas Middle Ordovician (~475 million years ago) • Right side – still have shallow seas • Passive margin on the West coast • Subduction on the East coast • Warm and shallow seas Devonian (~400 million years ago) • See Appalachian mountains – bigger pieces colliding • Subduction on the West coast • Beginning of major collision on East coast • Caledonian Orogen • Acadian Orogen (Appalachians) • Warm and shallow seas Latest Permian (~250 million years ago) • Major collision of Appalachian – partially flooded in the South • Lots of shallow seas depositing rocks at that time • Pangaea! Late Cretaceous (~65 million years ago) • Now countries rift • West coast get subduction zone • High sea levels • Subduction on West coast • Passive margin on the East coast The Present • Today: still mountain building on West coast • Alpine-Himalayan Orogen – mostly continent–continent collision • Cordilleran and Andean Orogen – mostly subduction ‐Describe and place on a map the location of major Active Mountain ranges on Earth today. LECTURE 19: FOSSILS AND HISTORY OF LIFE ‐Describe the difference between fossil types: frozen/dried, amber, replaced bones or shells, molds and casts, and trace fossils. A: History of life comes from fossils but most creatures that have lived and died were not preserved/no records. Fossil record is biased towards the ocean because it is easier to preserve creatures in the ocean than on land. Difference between fossil types: • Frozen/dried body fossils: mummified remains often in dry of cold regions and are relatively young o Happens in cold, dry regions (i.e. Canadian Arctic's) – last 10,000 – 20,000 years o Freeze dried (naturally mummified) o All skin and internal organs were preserved o Wholly mammoth o Able to fully analyze body • Amber: preserved whole organisms in sap or tap which can preserve DNA (i.e. Jurassic Park) o Idea of insects feeding on tree o Sap landing on tree o Traps insects, hardens and dries o Now preserved • Replaced bones or shells: most fossils are these ~ original material is replaced by more durable minerals o As process of turning sediment into sedimentary rock o Most of bone materials will be replaced with other materials o Actual material (calcium etc.) will be replaced with other things (i.e. silica) o Shells (in marines) are same kinds of things • Molds and casts: impression of a shall… or a soft-bodied organism o Get soft bodied organism through imprint o Jelly-fish like o Hard to really preserve something like that o We get impressions of their body o Shelly organisms didn’t develop until after Cambridge era o See fossils that predate explosion • Trace fossils: footprints of worm burrows… not organism itself but trace of their existence o Like impressions o Footprints of dinosaurs o Places of human footprints in volcanic ashes in Africa o Marine trace fossils that leave trace behind o Tell us about locomotion of organism o By numbers can determine a family unit or herd o Don’t actually have the organism (difficult to determine info) ‐List and explain the conditions necessary for preserving fossils. A: Conditions necessary for preserving fossils:
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