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Geography > Hazardous Earth SG6 > Flashcards

Hazardous Earth SG6 Flashcards

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1
Q

How long ago were the continents a single land mass called Pangaea?

A

200 million years ago

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2
Q

How long ago did Pangaea split into two continents - Laurasia and Gondwanaland?

A

120 million years ago

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3
Q

What is Alfred Wegener’s theory called?

A

Continental Drift

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4
Q

When did Alfred Wegener publish his theory?

A

1915

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5
Q

What four pieces of evidence did Alfred Wegener use for his theory?

A

Jigsaw fit of continents, Geological sequences (matching mountain belts), Glacial deposits, Fossil evidence

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6
Q

What were the two fossils Wegener used as evidence?

A

Mesosaurus and Glossopteris

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7
Q

Why were Alfred Wegener’s ideas dismissed?

A

Couldn’t understand how the continents could travel through the solid sea floor

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8
Q

Define Echo Sounding

A

Send pulses of sound which travel to the sea floor and bounce back up again, The time it takes to come back up is how deep the sea floor is in that location

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9
Q

What did Bruce Heezen and Marie Tharp discover from the echo sounding data?

A

Vast mountain chain running down the bottom of the ocean

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10
Q

How long was the mountain chain found by Tharp and Heezen?

A

60,000km

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11
Q

What did Tharp and Heezen notice about the crest of the mountain chain?

A

There was a cleft - a mid ocean ridge

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12
Q

How did the mid ocean ridge found by Tharp support Wegener’s theory?

A

The ridge would be formed naturally if the continents were pulled apart

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13
Q

Define Continental Drift

A

The theory that the continents are mobile and have moved across Earth’s surface through geological time

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14
Q

Define Seismic Profiling

A

Dropping explosives off a ship and recording how long it takes for sound waves to return

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15
Q

What was Harry Hess’ theory for continental drift?

A

Seafloor spreading

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16
Q

Define Seafloor Spreading

A

Lateral movement of new oceanic crust away from a mid ocean ridge

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17
Q

What evidence did Hess use for his idea of sea floor spreading?

A

The age of ocean floor basalt

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18
Q

What data from the ocean floor did Vine use?

A

Magnetic reversals of polarity on the sea floor

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19
Q

Define Core

A

The metallic centre of the earth, composed of mainly iron and nickel

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20
Q

What state is the inner core?

A

Solid state (despite being more than 3,000 degrees)

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21
Q

What state is the outre core?

A

Liquid state

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22
Q

How thick is the mantle?

A

2,900km

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23
Q

What is the mineral composition of the mantle?

A

Iron and magnesium rich

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24
Q

What is the main rock type of the mantle?

A

Peridotite

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25
Q

Define Crust

A

The outer layer of the earth which varies in characteristic depending on whether it is continental or oceanic

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26
Q

What is the thickness of continental crust?

A

35km

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27
Q

What is the thickness of oceanic crust?

A

5-70km

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28
Q

What is the density of the mantle?

A

3.3g/cm3

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29
Q

What is the composition of continental crust?

A

Granite

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30
Q

What is the composition of the oceanic crust?

A

Basalt

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31
Q

What is the density of the continental crust?

A

2.7g/cm3

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32
Q

What is the density of the oceanic crust?

A

2.9g/cm3

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33
Q

Define Asthenosphere

A

The semi-molten or viscous layer that extends from 100km to 300km deep

34
Q

Define Lithosphere

A

The rigid layer comprising of crust and the upper mantle above the asthenosphere

35
Q

Define Mohorovicic Discontinuity (Moho)

A

The boundary between the crust and the mantle

36
Q

How old is continental crust?

A

Up to 3.8 billion years old

37
Q

How old is oceanic crust?

A

Up to 220 million years old

38
Q

Define 1300 Degree Isotherm

A

The boundary between the lithosphere and asthenosphere

39
Q

Who developed the convection current theory?

A

Arthur Holmes

40
Q

What are the two sources of internal heat to generate convection currents in the mantle?

A

Heat remains from the formation of the Earth, Decay of radioactive elements - U, Th, K

41
Q

Define Ridge Push

A

Upwelling of magma at the mid ocean ridges creates new ocean crust causing the plates to push apart

42
Q

Define Plate Drag

A

Convection currents in the asthenosphere drag the overlying plate with it

43
Q

Define Trench Pull

A

The weight of the dense, cold oceanic crust subducting into the asthenosphere at an oceanic trench pulls down the rest of the plate with it

44
Q

Define Basaltic Magma

A

A type of magma which is low in silica and flows easily

45
Q

Define Decompressional Melting

A

A reduction in overlying pressure enables the peridotite to melt, leading to magma formation

46
Q

Define Fault

A

Cracks in rock due to stresses in the earth’s crust

47
Q

What four features are associated with divergent plate boundaries?

A

Mid Ocean Ridges, Rift Valleys, Pillow Lavas, Black Smokers (Hydrothermal Vent)

48
Q

Define Mid Ocean Ridge

A

The boundary between two diverging plates consisting of two parallel chains of submarine mountains separated by a rift valley

49
Q

How are MORs formed?

A

As magma rises to the surface, the overlying rock thermally expands and is forces upwards into a dome

50
Q

What is the total length of a MOR?

A

60,000km

51
Q

What is the approximate height of a MOR?

A

300m

52
Q

What is the approximate width of a MOR?

A

1,000km

53
Q

What is the spreading rate of the Mid Atlantic Ridge?

A

2-3cm/year

54
Q

What is the spreading rate of the East Pacific Rise?

A

16.5cm/year

55
Q

What faults occur at MORs?

A

Transform faults

56
Q

Define Transform Fault

A

Large-scale faults in the crust at right angles to a mid ocean ridge, Earthquakes occur along their lengths as they slip

57
Q

Define Seamount

A

Submarine volcano

58
Q

Define Pillow Lava

A

Rounded mounds of lava erupted along mid-ocean ridges which cool rapidly on contact with sea water

59
Q

Define Black Smoker

A

Hydrothermal vent on the ocean floor, The water carries high amounts of metal sulphides

60
Q

Define Rift Valley

A

A valley formed by down faulting between parallel faults on MORs and at a divergent boundary on land

61
Q

What faulting occurs at rift valleys?

A

Normal faulting

62
Q

Define Normal Fault

A

A fault in which blocks of rocks slip straight down due to tension in the lithosphere

63
Q

Define Graben

A

The downfaulting section of a rift valley

64
Q

Where do grabens occur?

A

Rift valleys

65
Q

What % of the world’s active volcanoes occur at convergent plate boundaries?

A

80%

66
Q

Define Andesitic and Rhyolitic Magma

A

Two types of magma which are high in silica and viscous (slow moving)

67
Q

What faulting occurs at convergent plate boundaries?

A

Reverse faults

68
Q

Define Reverse Faults

A

A fault in which one block of rock slides over another due to compression in the lithosphere

69
Q

What four features are associated with O/C convergent plate boundaries?

A

Earthquakes, Ocean Trenches, Fold Mountains, Volcanoes

70
Q

Define Ocean Trench

A

A narrow, deep depression on the ocean floor adjacent to a subduction zone

71
Q

How deep do ocean trenches go?

A

6,000 - 11,000m

72
Q

What are the dimensions of the Peru-Chile trench?

A

5900km long, 8km deep, 64km wide

73
Q

Define Benioff Zone

A

Boundary between a subducting ocean plate and the over-riding continental plate at a destructive boundary where earthquakes take place, Has an angle of 45 degrees

74
Q

Define Fold Mountains

A

A mountain built up by the crumpling (folding) of crustal rocks, Associated with convergent boundaries

75
Q

What four features are associated with O/O convergent plate boundaries?

A

Ocean Trench, Island Arc, Earthquakes, Volcanoes

76
Q

Define Island Arc

A

Chain of volcanic islands formed along a subduction zone

77
Q

What two features are associated with C/C convergent plate boundaries?

A

Fold Mountains, Earthquakes

78
Q

Define Tectonic Plate

A

A large slab of the Earth’s lithosphere and crust

79
Q

Define Subduction

A

The tectonic process found at destructive plate margins where an oceanic plate descends into the Earth’s mantle and is destroyed

80
Q

Define Divergent Boundary

A

Two tectonic plates move away from each other

81
Q

Define Conservative Boundary

A

Two tectonic plates slide past each other

82
Q

Define Convergent Boundary

A

Two tectonic plates move towards each other

Geography (40 decks)

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