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Geography 120 > earths crust dynamics > Flashcards

earths crust dynamics Flashcards

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1
Q

earth is thought to have condensed from a nebula of dust, gas, and icy comets about _____ years ago

A

4.6 billion

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2
Q

______ and _________ are two dominant materials

A

silica;iron

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3
Q

during the early stages of formation, earths temperature was so high that silica and iron were all in a ________ state

A

molten

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4
Q

as temperature decreased, earth solidified and gravity sorted materials by density, iron settled to for, the _______; silica rose upwards to form the __________

A

core; crust

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5
Q

_______________________ encompasses internal processes (plate tectonics, earthquakes, and volcanism) that produce flows of heat and material from deep below earths crust, radioactive decay is the main energy source

A

endogenic system

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6
Q

____________________________- involves extrernal processes that set into motion air water and ice (win, rivers, glaciers), all powered by solar energy

A

exogenic

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7
Q

our knowledge of earths inner structure is baed on studying how ___________ _______ associated with earthquakes travel through the earth

A

seismic waves

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8
Q

earths core =

A

inner core+outer core

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9
Q

inner core is solid: iron Fe and nickel Ni

A

3200-5200° C well above the melting temperature for iron but remains solid due to immense pressure

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10
Q

outercore is molten; capable of flowing

A

flow generates much of earths magnetic field

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11
Q

two parts of earths mantle

A

lower mantle and upper mantle

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12
Q

mantle=1300°C and ______ pressures

A

high

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13
Q

the ___________consists of silicate minerals rich in iron and magnesium average of 4500kg/m3

A

mantle

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14
Q

rocks in upper mantle are ______; able to flow slowly

A

molten

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15
Q

boundary between the uppermost mantle and the crust above is called the

A

mohorovicic discontinuity, or MOHO

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16
Q

the uppermost mantle is a layer called the ______________; molten rock capable of flowing

A

asthenosphere

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17
Q

the ____________ lies at a depth of 40-250km

A

asthenosphere

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18
Q

flow of materials here initiates the movement of

A

lithospheric plates

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19
Q

overlying the asthenosphere, is the rigid ___________________ and ___________ movement of materials causes rocks to or break

A

uppermost mantle and crust:

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20
Q

_______________ consists of the crust and the uppermost mantle

A

lithosphere

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21
Q

continental crust

A

30km thick beneath continents, 50-60km thick beneath mountains
average density is 2700 kg/m3
rich in silica, aluminum, potassium, sodium, calcium; sial
composed mainly of granite (an intrusive igneous rock) and gneiss (a metamorphic rock)

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22
Q

oceanic crust

A

5km thick beneath ocean basins
average density is 3000kg/m3
rich in silica, magnesium, iron;sima
composed mainly of basalt (an extrusive igneous igneous rock) and gabbro (an intrusive igneous rock)

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23
Q

buoyancy: something less dense (wood, ice) floats in something more dense (water)
earths crust floats on the denser layers of the underlying __________

A

mantle

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24
Q

where the load of the crust is greater (beneath Glaciers, sediment, or mountains) the crust tends to ______ or ride lower in the asthenosphere

A

sink

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25
Q

without the load the crust rides higher; uplift known as

A

rebound

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26
Q

entire crust is in a constant state of compensating adjustment, or ___________

A

isostacy

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27
Q

kola superdeep borehole

A

12,262 meters deep, 9 inches in diameter,
took almost 20 years of to reach only half the distance or less to the mantle
abandoned in 1992 because of the higher than expected temperatures
discoveries - microscopic plankton fossils - 6km
water and change in granite due to metamorphism - 7km

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28
Q

our knowledge of earths inner structure is based on studying how seismic waves associated with ____________ travel through the earth

A

earthquakes

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29
Q

structure of the earth

A

crust - outermost, solid shell of the earth, density - continental 2.7g/cm3 or 2700kg/m3
- oceanic 3g/cm3 or 3000kg/m3
mantle, a rock layer beneath the crust
density - 4.5g/cm3 or 4500kg/m3
moho - boundary between crust and mantle, based on change in velocity of seismic waves
lithosphere, brittle outer chell of the earth, breaks, crust plus upper mantle, gradual change to asthenosphere
asthenosphere, semiplastic or soft. part of mantle, below melting point (T=1400°C)
deforms under great pressure, underlain by less easily deformed rock

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30
Q

a ____________ is an inorganic natural compound having a specific chemical formula and possessing a crystalline structure

A

mineral

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31
Q

a _____ is an assemblage of minerals bound together, or a mass of a single mineral, or undifferentiated material, or even solid organic material such as coal

A

rock

32
Q

three basic rock types

A

igneous(fire formed, molten) sedimentary (from settling out), metamorphic (altered)

33
Q

silicon and oxygen form silicate minerals make up ____% of earths crust, and form primary minerals during the cooling of magma

A

90

34
Q

igneous rocks

A

derived from molten rock
magma emerges on earths surface as lava associated with volcanic eruptions
magma intrudes and cools within crustal rocks; intrusive igneous rocks (granite)
slow cooling produces coarse-grained rocks
magma is erupted as lava and cools on earths surface; extrusive igneous rocks (basalt)
rapid cooling produces fine-grained or glassy rocks

35
Q

mineral composition of igneous rocks; based on the relative contribution of SiO2

A

felsic rocks: high %SiO2 - quartz, feldspar - light colored minerals; dominate continental crust
aluminosilicate minerals
mafic rocls low SiO2 - mica amphibole, pyroxene- darker coloured minerals; dominate oceanic crust
ferromagnesian minerals

36
Q

sedimentary rocks

A

begin as the products of rock weathering (clastic sediments) , accumulations of calcareous materials (chemical sediments),accumulations of organic matter (organic sediments)
erosion, transport and deposition of sediments
lithification - compaction, cementation
both clastic and chemical sedimentary rocks are deposited in layers - strata - that record the enviromental history of a region

37
Q

clastic sedimentary rocks

A

classified according to clast size
gravel, cobbles, boulders - conglomerate
sand - sandstone
silt - mudstone
clay - shale

38
Q

chemically precipitated sedimentary rocks

A

formed of thick deposits of mineral compounds that accumulate in marine enviroments or evaporate from solutions
- limestone forms as calcium carbonate from either marine organisms or carbonate precipitation, cements into thick deposits
- dolomite is a carbonate rock that contains abundant magnesium
- evaporites form in continental locations when minerals evaporate from concentrated solutions

39
Q

organic sedimentary rocks

A

Consist of carbon-based materials that accumulate in thick deposits at the surface and then get buried by other sediments
- coal results when the carbon deposits are very slowly compacted, removing water and oxygen, and lithified
- petroleum results when organic deposits are heated so much that they liquefy
- natural gas comes from the remains of microscopic plants that lived in the ocean
* when they died they sank to the bottom of the ocean to decompose, forming gas

40
Q

metamorphic rocks

A

igneous and sedimentary rocks are transformed by heating and great pressure to form metamorphic rocks
* rocks become harder and more resistant to erosion
* metamorphism may involve creation of new minerals and/or
changes in mineral arrangement
* distinguish between foliated (e.g., gneiss) and non-
foliated rocks (e.g., quartzite, marble)

41
Q

relative time and superposition

A

earth scientists assign ages to rocks or landscapes based on the geological time scale
relative age vs numerical age
principle of superposition: rock and sediment are always arranged with the youngest materials superposed toward the top of the rock formation and the oldest materials at the base, if they have not been distrubed; relative age

42
Q

how old is our earth?

A

the oldest rock on earth is about 4 billion years old, and the oldest fossil on earth is about 3.5 billion years old,
radiometric dating determines numerical age of the rock
- based on unstable isotope ratios in rock minerals and organic materials

43
Q

plate tectonics - earths crust consists of individual lithospheric plates that move indivdually and collectively
explain the geographic distibution of mountain chains and why earthquakes and volcanoes occur mostly along lithospheric plate boundaries
emerged from obsevations of similar rocks and fossils on different continents in the southern hemisphere

A
44
Q

continental drift

A

in 1912 german geophysicist alfred wegener presented an idea that challenged long held assumptions in geology and three years later published his book origin of the continents and oceans
wegener concluded that all landmasses migrate, and that approximentaly 225my they formed one supercontinent that he named pangaea meaning “all earth”
today scientists regard wegener as the father of plate techtonics, which he first called continental drift

45
Q

continental drift was proposed as

A

the process that broke up the super continent, pangaea and created the current configuration of lithospheric plates

46
Q

_________________________ is the theory that the lithosphere is divided into a number of plates that float independently over the mantle and along whose boundaries occur the formation of new crust, the building of mountains, and the seismic activity that causes earth quakes

A

plate tectonics

47
Q

plate tectonic theory describes the motion of earths

A

lithospheric plates

48
Q

plate movement - passive margins

A

where continental crust and bordering oceanic crust are actually on the same tectonic plate and do not move relative to each other, not geologically active - seismic activity but no active volcanism

49
Q

_________________ ________________ occur in areas of seafloor spreading, where upwelling material from the mantle forms new seafloor and lithospheric plates spread apart in a contructional process

A

divergent boundaries

50
Q

an example of a divergent boundary is

A

the divergent boundary along the east pacific rise, which gices birth to the nazca plate
(moving eastward) and the pacific plate (moving northwestward)

51
Q

most divergent boundaries occur at mid-ocean reidgrs, a few occur within continents themselves

A

an example is the great rift valley of east africa, where continental crust is rifting apart

52
Q

convergent boundaries occur in areas of crustal collision and __________ where areas of continental and oceanic lithosphere meet, crust is compressed and then lost in a destructional process as it moves downward into the mantle

A

subduction

53
Q

convergent boundaries form _________________ zones, such as off the west coast of south and central america, along the aleutian island trenches, and along the east coast of japan

A

subduction

54
Q

convergent boundaries also occur where two plates of continental crust collide, such as the collision zone between ______ and _______ and where oceanic plates, such as along the deep trenches in the western pacific ocean

A

india, asia

55
Q

____________ ______________ occur where plates slide past one another horizontally, as plates move past eachother horizontally , they form a type of fault, or fracture, in earths crust, called a transform fault

A

transform boundaries

56
Q

volcanoes

A

a mountain or a large hill containing a conduit that extends down into the upper mantle, through which magma and gases are periodically ejected onto earths surface or into the atmosphere
- magma errupted onto the surface is lava

57
Q

most volcanoes are inactive for sometime and only erupt when

A

the pressure of the rising mantle material becomes excessive

58
Q

explosive volcanoes: composite volcanoes

A

build up and grow over several eruptions; eruptions are violent
magma is rich in silica and viscous, trapping gases ad building up pressure
sends volcanic ash and pyroclastic material into the air
volcanoes composed of lava and pyroclastic sediments
characterized by steep slopes and small surface area

59
Q

effusive volcanoes:shield volcanoes

A

volcanoes with very fluid eruptions
magma has far less silica and has a low viscosity
lava associated with such eruptions flows as rivers of molten rock

60
Q

shield volcanoes have ________ sloping sides

A

gently; they develop with succesive eruptions that gradually build up over a broad area

61
Q

______________________ are chains of volcanoes that occur at converging , or subduction plate boundaries

A

volcanic island arcs

62
Q

an area of volcanic or geothermal activity associated with a stationary zone of an upwelling mantle plume from the asthenosphere is

A

hot spot volcanism

63
Q

hot spot volcanism occurs randomly under both continental and oceanic crust, lithospheric plates move over stationary hotspots,
plate movement can be traced by the evidence of volcanic or geothermal activity

A
64
Q

oceanic hotspot with fluid eruptions that have built a variety of shield volcanoes making up

A

the hawaiian island chain

65
Q

A string of islands and submerged volcanoes left behind after being previously positioned over the hotspot, is called a __________________

A

seamount chain

66
Q

compare and contrast the physical properties of oceanic and continental crust

A

differnce in density? come back to me (66)

67
Q

compare and contrast the physical properties of intrusive and extrusive igneous. what is the difference between a mafic rock and felsic rock

A

67

68
Q

indentify the various kinds of sedimentary rocks. list the order of processes that contirbute to the formation of sedimentary rocks

A

68

69
Q

identitfy 2 ways that rocks become metamorphic rocks

A

69

70
Q

describe the transformation of rocks that occurs within the rock cycle

A

70

71
Q

how is relative age different from numerical age with regards to geological time

A

71

72
Q

using the terms of epoch era time period and eon arrange them in the hierarchy of geological time

A

72

73
Q

what is the differnce between a converging and a diverging plate boundary?

A

73

74
Q

how does a contitnent-continent collision cause mountains to grow

A

74

75
Q

discuss why earthquakes happen, the nature of seismic waves, and how the epicentre is located after an earthquake has occured

A

75

76
Q

compare and contrast normal, reverse, overthrust, and strike slip faults

A
77
Q

what are the differeneces berween composite and shield

A

Geography 120 (4 decks)

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