Earth science exam 2 university of iowa – Flashcards
131 test answers
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3 types of changes due to metamorphism?
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size shape arrangement of mineral grains
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Foiliated
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Preferential alignment of minerals or structural features along a plane. Often shiny
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Why does foliation occur?
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different types of stress fields, minerals that preferientally align
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Schistosity vs slaty/phyllitic texture
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Schistosity is shiny and contains accessory minerals
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Why are there bands of felsic and mafic materials in gneiss?
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Bands of light and dark stripes from because ions are more stable near other, similar ions
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Why is magmatite special? What happened to the felsic material?
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The light bands are an igneous melt while the dark bands are metamorphic. It is a mix between meta and ign. Ign has melted but meta has stayed the same
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What does marble form from? how does it form?
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Limestone or dolostone calcite of the protolith recrystallize
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12. How can we use index minerals to learn about the conditions of metamorphism
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index materials tell us what conditions metamorphic rocks experienced during formation
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What happens to crystal size and folitation with increasing metamorphic grade?
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Higher metamorphic grade= bigger crystals foliation becomes more compact increasing coarseness of foliation
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What are the 2 different ways we classify outer layers in the earth?
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Chemical-what its made out of Physical- how solid it is
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What layers of the earth can we easily sample?
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Crust and lithosphere
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How much of the earth is made up of the crust by volume?
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.6%
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What are the two types of crust?
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Oceanic (more dense sinks) Continental (less dense floats)
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What type of plate boundary do most mountain belts form at?
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Continent-continent
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How do continents grow?
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accretion of terranes-small crustal fragments collide and merge with continental margins
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What is a terrane?
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Crustal fragements with geologic histories distinctive from that of adjoining terranes
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What is an orogenic process? Where do they occur?
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1. Mountain forming crust 2. occur at convergent continental
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Where does contact or thermal metamorphism occur?
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Convergent boundaries
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Hydrothermal metamorphism
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chemical alteration as hot, iron-rich fluids circulate through fissures and cracks in rocks (mid ocean ridges)
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Impact metamorphism
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Meteorites hit at high velocity
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Regional metamorphism
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Occurs when rocks are squeezed between 2 plates as they create mountains (greatest quantities of meta rocks)
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Where does ecoglite form from and where might we find it on earth surface?
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1. Forms from a mafic metamorphic rock 2.Found in the mantle in a subduction zone
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Are older or younger mountains likely to be taller? why?
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Younger, they have experienced less weather and deformation. Also plate boundary is no longer active
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3 parts of continents
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1. Shields- oldest parts of continents (exposed craton) 2. cratons- stable part of continents. Continental crust that hasn't been deformed 3. Stable platforms- cover in horizontal sedimentary rocks (part of craton that lies over the shield)
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Strike-trend
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compass direction of line produced by intersection of inclined rock, layer or fault with horizontal plane
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dip-inclination
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angle of the surface of a rock unit or fault measure from horizontal plane
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What controls how high mountains can get?
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The foundation they are built on. Weight of mountain overwhelms the foundation and it starts to settle downward.
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What is deformation?
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General term for all changes in original form or size of a rock
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What kinds of deformation do we usually see?
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Folding or faulting
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Stress? Compressive stress tensional/ extenional shear forces
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1. Stress- force applied to a certain area 2. squeezing until fold or break 3. pulling so rock thins 4. masses of rock to slip
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Brittle deformation
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breaks quickly, like dropping a plate on the ground (rapid)
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Ductile deformation
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deforms platically like dough. (slow)
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What effects deformation style? 4 things
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1. Temp 2. Confining pressure 3.rock minerals 4. Time(fast or slow)
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Joint
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No appreciable movement across crack (very common)
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Fault
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Relative movement of rocks on either side of the fracture
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Strain
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changes in the shape and size due to stress.
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Elastic deformation
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Rock returns to nearly its original size and shape when stress is removed
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What happens when a rocks elasticity limit is reached?
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1. Flows ( ductile deformation) 2. Fractures (brittle deformation )
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4 types of faults (first 2 dip slip second 2 strike slip)
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1. Dip slip- hanging wall on right 2. reverse fault-hanging wall on left 3. left lateral- standing on fault, left moves towards you right moves away (vertically) 4. Opposite of 3.
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Anticline
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Folded into an arch upward(oldest rock in center)
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syncline
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downfold into a trough(youngest rock in center)
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Relative dating
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Order of events. Comparing older and younger without numerical dates
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Absolute dating
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actual age is given in years
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What is an isotope?
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element with a different number of neutrons
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Why do isotopes decay?
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Unstable isotopes=radioactive isotopes and change spontaneously to become stable
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3 types of decay
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1.Alpha decay- new element created containing 2 fewer protons and neutrons 2. Beta- nuetron changes to proton, eliminating and electron 3. electron capture- proton to neutron
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Half life
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How long it takes for half of the parent atoms to turn into daughter atoms
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What limits radiometric dating?
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Not enough parent material left to date. Too much daughter material after certain amount of time.
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What happened in Chelyabinsk, Russia?
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Meteor shower
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What big assumption are made when radiometric dating?
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1. no daughter material initially 2. closed system
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What is the best material for radiometric dating and why?
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Igneous rocks due to good closure temperature
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How have we estimated the age of the earth?
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1. Age of meteorites 2. Age of moon rocks
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Uniformatarianism ( the present is the key to the past)
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Theory that changes in the earths crust during geological history have resulted from the action of continuous and uniform processes.
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Nicholaus Steno
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Father of stratigraphy
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2 examples, one for relative dating and one for absolute dating
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relative - im older than my dog absolute- my dog is 14 years old
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What is stratigraphy?
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Order of strata and their relationship to geologic time scale
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Superposition
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Stacking of strata takes place according to age.
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Inclusions
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If something is included in another rock bed or layer, it must be older than what it is in
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lateral continuity
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Dumping sediment into a basin or flat plane, sediment will spread until flat or full.
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Original horizontality-
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sediment when deposited will form horizontal layers
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Cross-cutting relationship
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if something cuts across something else it must be younger than that which it cuts
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Do steno''s laws allow us to relative or absolute dating?
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Relative
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Unconformities
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Tell you that you are missing time (from erosional surface or a surface of non-deposition)
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disconformity
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wrong ages. Happens when sea level drops
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nonconformity
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wrong kinds. pluton intrudes
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angular conformity
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Wrong angles. occurs from folds
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James hutton
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Founder of uniformitarianism
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What is the principle of faunal succession?
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Species are born, have a life span and then they go extinct.
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6 characteristics of good index fossile
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1. easy to identify 2. common 3. easy to preserve 4. global distribution 5. facies independent 6. short ranging
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common index fossils (5 young to old)
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1. Cenozoic 2.Mesozoic 3. Late paleozoic 4. Ordovician devonian 5. Cambrian Ordovician
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3 eons of earth history and dates of their boundaries?
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1. Hadean era- 4.4 billion years ago 2. Archean era- Cartons appear, 3 billion YA 3. Proterozoic era- 2 billion years ago
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Major events of Hadean era
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1. earth and solar system found, formation of protocontinents and moon. 2. Possible origin of life
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Major events of Archean era
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1. protocontinents make micro continents 2. Earths really hot 3. First cratons appeared
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What is a body fossil and how old are the oldest ever found?
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1. Body fossil- reamins of actual parts of an ancient organism 2. olders is 3.5 billion YA
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What is oldest potential evidence for life on earth and how old?
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1.Isua Formation 2. 3.7-3.8 BYA
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names of 3 major supercontinents? When were they formed?
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1. Nuna- 1.8 BYA 2. Rodina- 900 MYa 3. Pannotia- 625 MYa
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When did complex life evolve?
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Cambrian explosion
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Major events of Cambrian, ordovician, and devonian
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1. Cambrian explosion 2. millipedes and first fossil of complete plant 3. age of fish and forests
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When did plants arrive on land?
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Early middle ordovician
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Big five mass extinctions
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1. End Ordovician 2. late Devonian 3. end Permian 4. late Triassic 5. end cretaceous
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When did dinos originate?
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Late triassic
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When did our lineage split from chimps?
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7 MYA
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What is a fossil?
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Remnants or traces of ancient living organisms that were preserved from burial
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What is taphonomy?
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study of fossilization process
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Robert Hooke
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Introduced idea of extinction 2. described and cataloged specimens
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William smith
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1. canal surveyor 2. Recognized that fossils could be used to tell age of rocks
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Mary anning
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1. Princess of palentology 2. collected fossils and recognized extinction
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3 main types of fossils (in order from most to least common)
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1.Chemical 2. Trace 3. Body
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Chemical fossil
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signs of life, carbon is realeased when orangism dies. realates to photoysnthesis
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Trace fossils
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A fossil of any sign of life (footprints, poop...)
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Body fossils
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Bodies of an organism (skull, shells)
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What maximizes fossilization? (bad places to live=good places to die)
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1. Quick burial 2. Abundance 3. anoxic (lacking oxygen) 4. Robust and mineralized
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What percent of marine organisms have mineralized hard parts?
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1/3 or 33%
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5 modes of preservation
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1. Unaltered remains- tar or amber 2. Permineralization- all open spaces fill with minerals 3. Recrystallization- Mods and casts a shape, but no real fossil 4. Replacement- Hard parts replaced with new minerals 5. Carbonization- Thin film of carbon left behind from decay
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What is Lagerstatten?
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German for mother lode. Preservation of soft body parts and soft bodied organisms.
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What is mass wasting?
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Downward movement of material under influence of gravity
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What drives mass wasting?
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Gravity
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Which can hold a steeper slope? Consolidated or unconsolidated material?
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Consolidated
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3 factors that increase likelihood of slope failure
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1. increase load 2. increase slope 3. decrease strength
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Build a highway into anticline or syncline?
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Anticline
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How does angle of repose change with addition of water?
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Water decreases angle and compromises stability
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3 factors to classify mass wasting event
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1. How material moves (falls-free falling, flows-behaves as fluid, creeps-freeze/thaw and slides-slides along plane) 2. type of material 3. Rate of movement
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How do we predict slope failure?
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Past failures steep slopes changes in slopes
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5 ways to prevent slope failure
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1. hazard mapping 2. revegetation 3. regarding-stabilize slopes 4. reinforcement 5. improved drainage
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How much water is in earths hydrosphere?
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3.6x10 to the 18th gallons
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How much of earths water is freshwater? where is it mostly stored?
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2.8%, mostly in glaciers
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5 processes of hydrologic cycle
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1. evaporation 2. transpiration 3. precipitation 4. infilatration 5. runoff
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What is infiltration capacity?
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Maximum amount of water that the soil can absorb
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What factors affect infiltration?
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1.Intensity and duration of precip 2. soil saturation and level prior 3. soil texture 4. slope of land
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What factors increase runoff?
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1.High velocity 2. steep slope 3. saturated regolith 4. impermeable ground
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Laminar flow vs Turbulent flow
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Laminar- water moves i a straight line path downstream Turbulent- erratic water flow, white water rafting
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What factors determine stream velocity?
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1. Gradient of channel 2. Shape, size and roughness of channel
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Streamflow discharge equation ?
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Channel width x channel depth x velocity
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What is a drainage basin?
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Area where runoff drains downhill into a waterway or body of water
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How does the Continental divide relate to drainage basin?
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Mountainous line that forms border between two watersheds, water has to choose which side to flow to.
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What is base level?
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lowest point where a stream can erode
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What does raising and lowering base level do?
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Raising- causes deposition Lowering- erosion
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Stream competence
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largest particle a stream can move
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What are the 4 different types of floods?
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1. regional-large areas 2. flash floods-small 3. ice-jam floods 4. dam failures
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What is groundwater?
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Water that has infiltrated the lands surface through pore spaces and cracks
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What do we use groundwater for?
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Drinking Irrigation industry
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How does groundwater enter the ground, and where is it most commonly stored?
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Infiltration, Majority is stored in pore spaces between sols and sediment as well as narrow fractures in rock beds
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Porosity vs permeability
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percentage of total volume of rock or sediment that consist of pore spaces (how much water can be stored) VS ability of a rock or fluid to transmit fluid(connection of pores to allow water to flow through it).
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Porosity factors
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size and shape of sediments/fractures. How tightly grains are packed, grain sizes well/poorly sorted
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What is specific yield?
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part of groundwater that is retained as a film on practice and rock surfaces and in minute spaces
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aquitards vs. aquicludes.
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-Aquitard: an impermeable layer of rock or sediment that hinders or prevents water movement (ex: clay). -Aquifer: permeable rock or sediment that transmits groundwater freely (such as sand and gravel)
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How can streams interact with groundwater?
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streams lose water to the ground water, and gain water from the inflow of the ground water
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