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Science > Chapter 9- Plate Tectonics > Flashcards

Chapter 9- Plate Tectonics Flashcards

1
Q

What was the name of the massive continent?

A

Pangea

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2
Q

What did Wegener base his observations of ‘continental drift’ on?

A
  1. That all the continents seemed to fit together

2. That fossils of the same species were found on different continents

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3
Q

What two continents look like the fit together like a jigsaw puzzle?

A

Africa and South America

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4
Q

What did scientists discover on the ocean floor?

A

A mountain ridge in the Atlantic Ocean

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5
Q

What is are all the ridges in the oceans called?

A

The ‘Great Global Rift’ system

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6
Q

What did Harry Hess propose in 1962?

A

That new rocky crest was being formed at ridges and spreading outwards

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7
Q

What is ‘sea floor spreading’?

A

New rocky crust being formed at the mid-ocean ridges and spreading outwards

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8
Q

What is subduction?

A

That the crust was sinking down into the Earth, creating ocean trenches

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9
Q

What are ridges and trenches?

A
  1. Ridges are rises in the sea floor

2. Trenches are dips in the sea floor

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10
Q

What were the three pieces of evidence to support the ‘sea floor spreading theory’?

A
  1. Magnetic Striping
  2. Age of the sea floor
  3. Sediment thickness
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11
Q

How does magnetic striping work?

A

Earth’s magnetic field changes every few million years which creates striped of rock pointing to North or South

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12
Q

How did this provide evidence to Hess’s theory?

A

That new sea floor was being added equally to each side

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13
Q

How did the age of sea floor theory work?

A

The further the rocks of the sea floor were from the ridges the older they were which is what you’d expect if new rocks formed at the mid-ocean ridge and moved outwards.

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14
Q

Was the sea floor younger than the continent?

A

Yes

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15
Q

How did the sediment thickness evidence work?

A

When rock layers on the floor were studied it was found that the layers became thicker as you moved away which showed that sediment had been falling for longer on the rocks further away from the ridges

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16
Q

What is the crust?

A

It consists of many huge, cracked plates or tectonic plates

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17
Q

What is the asthenosphere?

A

A layer of ‘semi-liquid’ rock in the upper mantle

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18
Q

What are the two theories as to how the plates move through the asthenosphere?

A
  1. Convection currents

2. Gravity

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19
Q

How does the convection current theory work?

A

Plates are dragged along the hot magma which causes convection currents and as the liquid flows, the friction may cause the plates to move

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20
Q

Who claimed that the continents were once all connected to each other?

A

German Scientist, Alfred Wegener

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21
Q

What are the two ways gravity could be involved in moving plates?

A
  1. Slab Pull

2. Ridge Push

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22
Q

How does the slab pull theory work?

A

Plates at subduction zones are denser than those at Mid-Ocean ridges so gravity pulls the dense plates down and the plates are pulled apart

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23
Q

How does the ridge push theory work?

A

Gravity pulls the newer crust down and pushes the older crust below and this may be enough to move the plates

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24
Q

What is rifting?

A

The theory that the crust cracked and subsided, allowing in water from the ocean e.g the Red Sea and as the new crust formed the continents moved along with the ocean floor

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25
Q

What are the three types of plate boundaries?

A

Diverging, converging and transform boundaries

26
Q

How do diverging boundaries work?

A

The plates are moving apart from each other and when they separate they leave a rift and magma rises up and solidifies, forming new crust which is why they are called ‘constructing boundaries’

27
Q

How do converging boundaries work?

A

They occur when two plates collide head on. Rock is destroyed so they are known as ‘destructive boundaries’

28
Q

What happens when oceanic crust collides with continental crust?

A

The denser oceanic plate sinks underneath and subducts, forming a trench. The continental plate becomes distorted and forms mountains

29
Q

What happens when two continental plates collide?

A

Both are pushed upwards and they form very high mountain systems e.g the himalayas

30
Q

What happens when two oceanic plates collide?

A

The faster-moving plate subducts and forms a deep trench which melts and a chain of volcanic islands forms e.g lesser Sunda Islands in Indonesia

31
Q

How do transform boundaries work?

A

When two plates are sliding parallel to each other but in opposite directions.

32
Q

What happens at transform boundaries?

A

The plates usually move slowly but when one slips it causes an earthquake.

33
Q

How do GPS technology prove the continental drift theory?

A

There is are gps ground stations around the earth. A group of 24 satellites orbit the earth and sends signals to the ground stations. The ground stations work out where they are and by comparing all the data we can work out how far each ground station has moved.

34
Q

What material erupts at a volcano?

A

Gases, ash, lava and lumps of volcanic rock

35
Q

When do volcanoes form?

A

When magma from under the earth accumulates below a weak spot in the crust

36
Q

Why are most volcanoes found at plate boundaries?

A

Because the movement of the plates creates weak spots in the crust

37
Q

How do diverging boundaries create weakness?

A

Separating plates thin the crust which lowers the pressure in the asthenosphere

38
Q

How do converging plates create weakness?

A

Where subduction occurs, weak spots are created and if at the sea, volcanic islands are formed

39
Q

How do hot spot volcanoes work?

A

Hot spots are isolated weak spots where a lot of hot magma is being created

40
Q

How was Hawaii formed?

A

A weak spot in the crust created a volcanic island and then when the plate moved, the weak spot formed another volcano etc. So in every chain of islands there is one Island with an active volcano and the rest have dormant ones

41
Q

What is an earthquake?

A

The rapid movement of ground in a back and forth and up and down wave motion

42
Q

How do earthquakes happen?

A

When the force between two plates is great enough, the friction can no longer hold and so it slips. The sudden movement sends out waves of energy that shake rocks and water as they pass

43
Q

How are earthquakes measured?

A

By using a seismometer which detects seismic waves

44
Q

What are the three types of seismic waves?

A

Primary, Secondary and Surface

45
Q

What are primary waves?

A

Longitudinal waves that travel quickly THROUGH the earth

46
Q

What are secondary waves?

A

Transverse waves that travel slight slower than p-waves THROUGH the earth

47
Q

What are surface waves?

A

The slowest waves that travel through the surface of the earth and cause the most damage. There are two types- Love and Rayleigh waves

48
Q

Where do earthquakes occur?

A

At the edges of tectonic plates and the strongest earthquakes occur near converging boundaries

49
Q

What is the place where an earthquake happens called?

A

The focus

50
Q

What is the epicentre of the earthquake?

A

The point on the earths surface, directly above the focus where the most damage occurs

51
Q

How are the severity of earthquakes measured?

A

Using the Ritcher Scale where each successive number is ten times greater than the previous one e.g 5.0 is ten times greater than 4.0

52
Q

What are some effects of earthquakes?

A

Damage to buildings, landslides, tsunamis, casualties

53
Q

What are tsunamis?

A

When earthquakes happen under the sea they can cause tsunamis which are waves that can be 100m high

54
Q

How are faults formed?

A

When the strata is out under immense pressure all though the plate, not just at the boundaries

55
Q

What are the three types of pressure caused by this force?

A

Tension
Compression
Shear

56
Q

What does compression result in?

A

Folds

57
Q

What are the two types of folds?

A

Syncline folds which go down and anticline folds which go up

58
Q

What are normal faults?

A

When the strata of a rock breaks along a line, it’s a fault, normals faults are caused by tension

59
Q

What are reverse faults?

A

Faults caused by compression

60
Q

What are multiple normal faults called?

A

Graben

61
Q

What are multiple reverse faults called?

A

Horst

62
Q

What do shear forces result in?

A

Strike Slip faults

Science (12 decks)

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