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55 Cards in this Set
- Front
- Back
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What rock formed the first crust ever of the earth and what was its composition?
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Komatiite
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What unique texture does komatiite possess?
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spinifix texture
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In what specific chemical element are "ultra mafics" very high in
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magnesium
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under what circumstance do pillow lavas form?
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pillow lavas form only underwater
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along what kind of plate boundary does the ocean floor (oceanic crust) form?
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divergent plate boundaries < >
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from what part of the mantle does magma come that forms the ocean floor?
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the asthenosphere
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what causes this part of the mantle to melt
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decompression caused by the separation of two diverging plates above
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what is a rift zone
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the gap that opens up when 2 adjacent plates move into opposite directions away from eachother
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what two theories accound for how the earth acquired its water
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1. the earths orbital path crossed that cof a comet, which are made of ice. The melting of the ice due to fractional impact formed water.
2. early arriving meteorites each carried in the molecules of water contained in crystals of salt |
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what is outgassing
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outgassing is the release of gasses the earth's interior via volcanic eruption
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why does a mid-ocean ridge form along an oceanic divergent zone
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heat carried up with the ascending magma raises the overlying ocean floor
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does the age of the ocean floor become younger or older with increasing distance from the oceanic rift zone
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it becomes older
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what determines which of the tqo oceanic plates will be subducted along an O-O convergent zone
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density. the densest of the two plates always subducts. the plate that has traveled the greatest distance since it formed will have had more time to cool and contract, thus becoming the densest of the two plates
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what deep feature of the ocean floor is formed by the subduction process?
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a deep ocean trench or a deep-sea trench (same thing)
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what does water do to the melting temperature of a rock
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it lowers it
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why do intermediate minerals (hornblende, Na-spar, biotite) crystallize from magma that formed from the melting of the MAFIC ocean floor
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due to the presence of water, the mafic ocean floor melts by 2500 degrees. Since mafic minerals can only crystallize at temperatures of >2500 degrees, they cannot form from the ascending magma as it cools. The next minerals in line to crystalize are those of intermediate composition
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what unique igneous rock forms only at subduction zones
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andesite
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why does felsic rock eventually crystallize from ascending intermediate magma at a subduction zone?
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as a volcanic island arc increases in height and size it becomes increasingly more difficult for magma to reach the surface. Once magma cna no longer reach the surface, it remains beneath the surface where it eventually cools to temps that forces the "stuck" intermediate magma to become felsic
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why is there no subduction when two continents collide
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continental crust, which is felsic in composition, is too light to ever subduct. Two colliding continents simply pile up into a towering mountain range.
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why is the composition of the rock that forms the "weld" at a suture zone felsic?
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because the converging continents are mad eof granite (felsic). When they melt alonga C-C convergent zone, the composition of the resulting magma is felsic
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why are teh continents of the earth so much older than the modern ocean floor?
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once formed, continents can't subduct and be destroyed. Oceanic crust, however, continuously subducts and is destroyed at subducted zones
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what percentage of geologic time is included in the Precambrian Era?
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87%
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in what way were the "first oceans" of the earth morst different CHEMICALLY from the way they are today?
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they were nearly saturated with dissolved iron
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what color would the "first oceans" have been
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murky, lime green
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in terms of solubility, what is the difference between ferrous and ferric iron
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ferrous iron (Fe+2) is extremely soluble in water. Ferric iron (Fe+3) is insoluble.
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what supplied the oxygen that changed the oceans ferrous iron to ferric iron
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blue-green algae (cyanobacteria)
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what 2 minerals make up unaltered banded iron formations (BIF)?
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hematite and chert
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what causes hematite to change to magnetite
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when hematite is heated to >600 degrees in the ABSENCE of oxygen it converts to magnetite
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what is not possible for banded iron formations to ever form again
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the oxygen in the air today changes ferrous iron to ferric iron on land before it has a change to dissolve in water. Because ferric iron is insoluble, it cannot dissolve. Only dissolved iron can precipitate to form a BIF
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what is a stromatolite and what is its claim to fame
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a stromatolite is a mound shaped pile of sediment built by blue-green algae on tidal flats. Stromatolites are believed to be earths oldest macroscopic fossil
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what is rodinia and what is its claim to fame
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rodinia was earths first supercontinent
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what is tillite and waht specific kind of rock are most tillites
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tillite is lithified till. Tillite is typically a SPARSE boulder congolomerate or breccia
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what is meant by the shield of a continent
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a shield is a large vast region of exposed PRECAMBRIAN rock
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WHAT IS MIGMATITE AND HOW DOES IT FORM
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migmatite is a mixture of igneous and metamorphic rock. It forms when only teh low-temperature minerals in gneiss melt and then recrystallize to produce a rock with alternating bands of foliated metamorphic rock and non-foliated igneous rock
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What is a depositional environment?
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a depositional environment is a natrual setting on the earths surface where sediment commonly accumulates. To put it another way, depositional environments are the specific places on teh surfae of the earth where sedimentary rocks are formed
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what substance imparts the color black to sedimentary rocks
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carbon
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which depositional environments most favor the formation of black sedimentary rocks
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swamp & marsh, and deep lacustrine
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which particle sizes most often become black? why
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silt and clay, because they are the only sediment sizes that get carried far out into the calm quiet bodies of water
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what substance imparts the color red to sedimentary rocks
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hemetite
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which depositional environments most favor the formation of red sedimentary rocks
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talus, alluvial an, eolian, floodplain, tidal flats, and beach (all of which are exposed directly to air so that oxygen can make contact with iron)
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which particle sizes most often turn red and why
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sand, because it is most easily blown aroudn by the wind, causing iron-bearing sand to become easily oxidized
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in which one depositional environment would EXCLUSIVELY boulder/cobble breccia formed
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talus
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which one depositional environment would and UNSORTED boulder\cobble breccia form
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glacial (till)
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which one depositional environment would a MODERATLEY SORTED boulder cobble conglomerate form
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alluvial fan
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what one depositional environment would pebble or gravel conglomerate/breccia form
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fluvial
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which 3 dep environments would sandstone most likely form
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eolian, beach, delta
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which 5 dep environ would shale most likely form
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lucustrine, swamp/marsh, tidal flats, floodplain, inner continental shelf
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which 2 dep environ would graywacke most likely form
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deep marine, floodplain
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where does argillite form
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proglacial lake
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where does coal form
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swamp n marsh
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where does limestone n dolostone form
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outer continental shelf
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where does rock gypsum n rock salt form
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inland sea
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what is a cast
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a cast is the lithified sediment or precipitated mineral that fills in a depression that occurs in sediment or sedimentary rock
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what is top and bottom indicator (geopetal structure)
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a feature in a rock used to distinguish the top of the rock from it's bottom
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what is paleodirection indicator
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a feature in sediment or a rock used to determine the direction the sediment was moving just prior to deposition
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