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Tectonics Flashcards

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1
Q

What are the difference in the Earth’s different layers?

A

They have different chemical compositions and/or physical properties such as temperature and viscosity.

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2
Q

What are the two layers in the core?

A

Inner and Outer

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3
Q

What is the core made up of, and what is the difference between the two?

A

Both layers are made up of iron and nickel, but while the inner core is solid due to immense pressure, the outer core is liquid

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4
Q

What are the temperatures of the inner and outer core?

A

The inner core is around 6650 degrees celsius and the outer core is around 4700 degrees celsius

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5
Q

What is heat in the core thought to be generated by?

A

The decay of radioactive isotopes

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6
Q

What is the densest layer of the Earth?

A

The inner core

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7
Q

What does the heat of the core generate and allow to happen?

A

It generates convection currents on the mantle and drives plate tectonics

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8
Q

What generates Earth’s magnetic field?

A

The flowing iron and nickel in the Earth’s outer core

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9
Q

What is the mantle composed of?

A

Dense, rocky material -> mostly silicates

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10
Q

What is the texture (?) of the mantle

A

It is more solid towards the core but more squidgy towards the crust

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11
Q

What is the upper part of the mantle called?

A

The asthenosphere

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12
Q

Why are the parts of the mantle different textures?

A

Due to temperature and pressure, but they are said to have the same composition

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13
Q

What is the difference in the asthenosphere and the mantle

A

The asthenosphere is weaker and more flexible than deeper parts of the mantle

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14
Q

What is the lithosphere?

A

Outermost layer of the earth, makes up the top 100km of the Earth

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15
Q

What does the lithosphere include?

A

Upper mantle and crust

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16
Q

What is the crust made up of?

A

Not a solid layer, but curved tectonic plates -> either continental or oceanic crust

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17
Q

How many plates are the crust made up of?

A

7-16 major plates, 60 smaller plates

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18
Q

Relative thickness and density of oceanic and continental crust

A

Continental crust is thicker but less dense, oceanic crust is thinner but denser

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19
Q

What is a theory?

A

An explanation for observations of the natural world through a scientific method, bringing together facts and hypotheses

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20
Q

What happens to a theory if new facts come about?

A

The facts are tested against the theory, and if it does not match, the theory is either refined or rejected

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21
Q

Difference between scientific law and theory>

A

Law describes WHAT happens, theory describes WHY or HOW something happen

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22
Q

Outline Alfred Wegener’s theory of continental drift

A

The theory that all the continents were once joined to form a supercontinent called Pangea, and slowly drifted apart over millions of years.

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23
Q

How did Wegener use the shape of continents as evidence to support his theory

A

He noted that the continents seemed to fit together like jigsaw puzzle, such as South America and Africa, suggesting they were once joined

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24
Q

How did Wegener use fossils as evidence to support his theory

A

The fossils of the same prehistoric species were on continents separated by oceans. He found no way for the fossils to cross the oceans and instead concluded that the fossils moved apart with the continents as they drifted

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25
Outline Hess' theory of sea floor spreading
The theory that new crust was being formed at ocean ridges and spreading outwards, causing the sea floor to spread and continents to move apart
26
How does magnetic stripping work?
Many rocks contain magnetite, which has a north and south seeking pole. As molten rock solidifies, the magnetite particles line up with Earth's magnetic field to point in the same direction, showing the direction of the magnetic field at that time on Earth.
27
How does magnetic stripping support Hess' theory?
There was a pattern of alternating strips of rock, and were symmetrical on either side of mid-ocean ridges, showing how new seafloor is being added on each side.
28
Why does the magnetite point in different directions at different points of time?
The Earth's magnetic field changes polarity over millions of years, which is why magnetic stripping shows how new seafloor is being added over millions of years
29
How does the age of the sea floor support Hess' theory?
The rock further away from the mid-ocean ridges were found to be older than the rock closer, which is what you would expect if new crust is being formed there.
30
How old is the seafloor compared to the continents?
The oldest sea floor was found to be around 200 million yrs old, while continental rock was thousands of millions of yrs old, showing how the seafloor is relatively young compared to the continents
31
How does the sediment thickness support Hess' theory?
The seafloor closer to the mid-ocean ridges have had less time to collect sediments, and therefore are thinner compared to seafloor further away from mid-ocean ridges
32
What is the theory of Plate Tectonics?
The theory that the lithosphere is divided into tectonic plates which move around on the asthenosphere below them relative to each other
33
What is the evidence to support Plate Tectonics?
Radiometric dating, magnetic stripping, age of rocks, fossil evidence, sediment thickness, etc
34
What is the evidence to support Hess' theory?
Age of rocks, magnetic stripping, sediment thickness
35
What is the evidence to support Wegener's theory?
The shape of continents, fossil locations
36
What is radiometric dating?
A method that accurately measures the age of geologic materials by measuring the presence of short-life radioactive elements
37
What is the rock in the asthenosphere like?
Very hot and is referred to as plastic - can change shape very slowly and move
38
How does radiometric dating support the theory of Plate Tectonics?
Rocks closer to mid-ocean ridges are younger, continental crust is much older than oceanic crust, showing how oceanic crust is constantly created and destroyed, moving around tectonic plates, and showing that there is no singular age of the Earth's surface
39
How does the actions of convergent, divergent, and transform plate act as evidence for the theory of Plate Tectonics?
The Earth's surface must be made of different plates, as they are all moving in different directions. If it was all one piece, it would move in one direction collectively. But as they are plates, they move in different directions
40
How do convection currents cause tectonic plates to move?
The heat from the core travels to the mantle, creating convection currents in the mantle that acts as a conveyor belt (the friction between the liquid rock and the tectonic plates) and drags tectonic plates along, either converging, diverging, or transform.
41
What are the types of gravitational forces that cause tectonic plates to move?
Slab Pull and Ridge Push
42
Where does slab pull occur?
Subduction zones
43
What is slab pull?
Slab pull is when part of an oceanic crust is subducted, and it causes the rest of the plate to move towards the subduction zone at a faster rate, like a chain due to gravity.
44
What is the difference between a very dense and a not so dense slab when it comes to slab pull?
A denser slab will move at a faster rate due to gravitational pull (it will exert a greater force on the plate attached to the subducting part)
45
Where does ridge push occur?
Mid-ocean ridges, where magma rises and forms new crust
46
What is ridge push
When the magma is formed, it is elevated compared to older floor, and gravity causes it to slide away from the ridge, pushing the rest of the plate along, adding to speed
47
Is a ridge push convergent or divergent?
Divergent
48
Is a slab pull convergent or divergent?
Convergent
49
What kind of crust is affected by ridge push?
New, just created, elevated crust
50
What kind of crust is affected by slab pull?
Oceanic crust, old, dense crust
51
How is the plate tectonic system finely balanced?
The amount of new crust is equal to the amount of crust destroyed, so the earth neither shrinks nor grows
52
What direction does a divergent boundary move in?
Away from each other
53
What happens at divergent boundaries?
New magma rises from the asthenosphere to fill the gap, forming new crust. Constructive
54
Where do divergent boundaries occur?
They occur at mid-ocean ridges (ocean floor). There are also some on land, such as the mid-Atlantic ridge, which runs right through Iceland.
55
What direction do convergent boundaries move in?
Towards each other
56
What happens at convergent boundaries?
Land features are formed depending on the type of crust that collides
57
What is formed if oceanic collides with continental?
Due to subduction (oceanic subducts), forms ocean trenches and volcanic mountain ranges on the continent
58
Example of land feature formed when oceanic and continental plate collides
Where Nazca and South America Plate collided, formed the Andes (volcanic mountain range)
59
What is formed if two continental plates collide?
Neither subducts as they have the same density, driving both plates upwards and forming high mountain ranges
60
Example of land feature formed when two continental plates collide
When Indian and Eurasian plate collided, formed the Himalayas
61
What is formed if two oceanic plates collide?
Deep trenches, volcanic islands
62
Example of land feature formed when two oceanic plates collide
Pacific and Mariana plate collided, formed the Mariana Trench
63
What direction do Transform boundaries move in?
They slide past each other in opposite directions
64
What happens at Transform boundaries?
They usually slide past each other very slowly, but occasionally slip, creating earthquakes
65
What feature is usually at transform boundaries?
Fold Mountains, with fault lines parallel to each other
66
Example of transform boundary
Where Indo-Australian and Pacific Plate slid past, they created the mountains of New Zealand's South Island
67
How do convergent boundaries create volcanoes?
Subduction melts sinking plate -> magma rises -> volcano forms Japan Islands -> Pacific and Eurasian Plate
68
How do convergent boundaries create earthquakes?
Plate collision creates stress -> sudden release -> earthquake Example is the Sumatra Earthquake (Indian Plate subducted under the Burma Plate)
69
How do divergent boundaries create volcanoes?
Magma forms volcanoes and fissures along the ridge Example is the Mid-atlantic Ridge
70
Can divergent boundaries create mountains?
Yes, mid-ocean ridges such as Iceland
71
When you describe subduction, how should you phrase it?
The denser oceanic crust subducts under the less dense continental crust
72
Where are island chains formed?
In the middle of a plate, due to a hotspot
73
Where are island arcs formed?
On a plate boundary, due to subduction of an oceanic plate under another
74
Example of Island chain
Hawaiian Islands
75
Example of Island Arc
Aleutian Islands, Alaska
76
What causes an earth quake?
The rapid release of energy as tectonic plates move. When the force is great enough, the plates suddenly move as friction can no longer hold them, sending out waves of energy
77
Define Focus
The focus is the place in the Earth where the volcano originates
78
Define Epicentre
The place on the Earth's surface directly above the focus
79
If the focus of the earthquake is deeper underground...
it is usually less destructive
80
What instrument is used to measure earthquakes?
A seismometer
81
What are the types of seismic waves?
Primary waves, secondary waves, surface waves
82
Features of Primary waves
Longitudinal, shake the earth up and down, the fastest.
83
How do primary and secondary waves travel?
They travel deep underground and then bend upwards to reach the surface of the crust
84
Features of Secondary waves
They are transverse waves, travel slower than primary waves, shake the earth side to side
85
How do surface waves travel?
They travel along the crust near the surface
86
Features of surface waves
They are the slowest but can cause the most damage
87
What substances can primary waves travel through?
Solids, liquids, gases
88
What substances can secondary waves travel through?
Only solids
89
What does the Richter scale measure?
The magnitude of an earthquake -> the energy released by the earthquake
90
What kind of scale is the Richter scale?
It is a logarithmic scale
91
How can the arrival times of P and S waves indicate the distance from the earthquake?
By calculating the difference in their arrival times and using that to find the distance
92
How fast do P waves travel through upper crust
About 6 km per second
93
How fast do S waves travel through upper crust
About 4 km per second
94
What happens to the speed of P and S waves as they travel deeper into the mantle
It increases
95
What type of volcanoes are formed at hotspots?
Shield volcanoes with gentle slopes
96
What type of volcanoes are formed at divergent boundaries?
Shield volcanoes
97
How does a volcano form?
Magma rises through weaknesses in the crust, pressure releases, lava erupts and cools to form new crust, the rock builds up and a volcano forms
98
What type of volcanoes are found at convergent boundaries?
Composite volcanoes
99
Characteristics of shield volcanoes
Eruptions are frequent but gentle, formed by eruptions of thin, runny lava
100
Characteristics of composite volcanoes
Erupts in explosive way, violently, made up of layers of lava and ash, pyroclastic flow
101
Example of shield volcano
Mauna Loa in Hawaii
102
Example of Composite Volcano
Mount St Helens in Washington, USA
103
How do earthquakes cause tsunamis
An earthquake under the ocean can cause a tsunami. The earthquake displaces the seafloor, pushing water and generating tsunami waves
104
What happens as tsunami waves approach the shore?
They slow down but they appear higher as their energy is compressed into a smaller volume of water. Before they rush onto the land, they may pull back far, exposing the seabed.
105
What type of wave is a surface wave?
Longitudinal
106
What are the types of surface waves?
Love waves and Rayleigh Waves
107
Characteristics of Love waves
Faster than Rayleigh waves, closer to surface, horizontal shaking
108
Characteristics of Rayleigh waves
Slowest wave, deeper underground, moves up and down and back and forth, like ocean waves -> appears to roll
109
What are body waves?
P waves and S waves
110
What can surface waves travel through?
Only solids
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